PROCEEDINGS O F THE

WESLEYAN UNIVERSITY CONFERENCE

O N

LECTURE DEMONSTRATIONS

Middletown, Connecticut

22 - 24 June 1959

EDITORIAL COMMITTEE V. E. Eaton, Wesleyan University C. J. Overbeck, Northwestern University R. P . Winch, Williams College

Executive Secretary Miss Constance Carpentiere, Wesleyan University

PLANNING COMMITTEE V . E. Eaton, Wesleyan University H. C. Jensen, Lake Forest College W. C. Kelly, American Institute of Physics P . Kirkpatrick, Stanford University

SPONSORED B YTHE AMERICAN ASSOCIATION O F PHTSICS TEACHERS

UNDER A GRANT FROMTHE NATIONAL SCIENCE FOUNDATION

INTRODUCTION

With the increased emphasis on physics in American education i t is important that physicists consider carefully the content of our physics courses, the goals we hope to reach and the methods we use to accomplish our purpose. The American Association of Physics Teachers is aware of the problems. Various committees of AAPTare work-ing on certain aspects of this problem and two conferences have been held to study and attempt to answer particular questions.

The first of these AAPT conferences was held at CarletonCollege, 5-8 September 1956. The principal concern at this conference was the content of general physics courses at the college level. The second conference was held at the University of Connecticut, 17-19 June 1957. At this conference the aims and methods of laboratory instruc-tion in general physics were considered. Reports of both of these conferences were published in the October 1957 issue of the American Journal of Physics.

At a meeting of the Educational Advisory Committee of the American Institute of Physics in December 1958, it was suggested that the time had come for a conference on lecture demonstrations. It was recommended that the conference be .held at Wesleyan University under the sponsorship of AAPT. V. E. Eaton agreed to serve as direc-tor of the conference and prepared the following proposal which was submitted to the National Science Foundation.

PROPOSAL

That a small working conference be held on the campus of Wesleyan University in Middletown, Connecticut, in June 1959. The three-day period, June 22 to 24, seems the most appropriate time. To secure maximum results the conference should be limited to approximately thirty participants and to teachers who have established a repu-tation as demonstrators.

Some of the topics which should be studied are: (a) why demonstrations are important, (b) the art of demon-strating, (c) making demonstrations visible, particularly to large classes, (d) demonstrations on television, both closed circuit and broadcast, (e) films as substitutes for live demonstrations, (f) low cost demonstration apparatus from the local store, (g) models, (h) schematic apparatus.

A committee will be appointed to draw up the conclusions of the Conference. These conclusions will be widely distributed to physics departments and printed in the American Journal of Physics.

It is proposed that the invitedparticipants be reimbursed for travel expenses to and from the conference and that housing and meals be provided. while they are in Middletown. We are therefore asking the National ScienceFoundation to provide the necessary financial support for this Conference and are proposing the following budget. This proposal is based upon our experience with similar conferences.

Travel, 3 0 participants at conference plus 5 panel members to earlier planning conference, first class air fare only

Rooms and meals at Wesleyan University, 3 days and 3 or 4 nights

Secretarial and drafting service Materials, supplies, incidentals Publication of Proceedings

Total direct cost

Indirect costs (15% of direct cost) Grand Total

$4,000.00

800.00500.00200.00

2,000.00

$7500 .001,125.00

$8,625.00

Conference rooms and facilities of Wesleyan University are offered to the Conference without cost. Rooms and meals are priced essentially at cost.

Original signed by

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C . J. Overbeck President of AAPT

V. E. Eaton Director of Conference

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With assurance from NSF that our request for financial support probably would be granted, a planning committee was appointed and this committee met in Middletown on March 30-31. At the planning conference the list of those to be invited to the conference was prepared and a tentative program agreed upon. With slight modification this tentative program b e c a m e the program of the meeting. The members of the Planning Committee were Paul Kirk-patrick, William C. Kelly, Harald C. Jensen and Vernet E. Eaton.

The following persons accepted our invitation and participated in the Conference.

ANDERSON, Harry E.

ANDREWS, C. Luther

BOCKSTAHLER Lester I.

B O L L M A N Vernon L.

B O T T O M Virgil E.

CRAM, S . Winston

EATON, Vernet E.

EINHORN, Marvin

HAYNSWORTH, J. H.

HECHT, K.

HOYT, Rosalie C.

JENSEN, Harald C.

KELLY, William C.

KENWORTHY, Ray W.

KIRKPATRICK, Paul

MAJOR, John K.

MARCLEY, Robert

MANNING, Thurston E.

O'CONNOR, R. T.

OLSEN, Leonard O.

OVERBECK, Clarence J.

PALMER, R. Ronald

PICARD, R. G.

POHL, Robert O.

POHL< Robert W.

RESNICK, Robert

RIPPEN, Robert

ROBINSON, Howard A.

ROGERS, Eric M.

SCHILLING, Harold K.

SEEGER, Raymond

SUTTON, Richard M.

SWIGART, John I.

TAYLOR, Edwin F.

VAN DYKE, Karl S .

WAAGE, Harold

WALERSTEIN, I.

Massachusetts Institute of Technology

New York State College for Teachers (Albany)

Northwestern University

Occidental College

McMurry College (Texas)

Kansas State Teachers College (Emporia)

Wesleyan University

National Broadcasting Company

Welch Scientific Company

E. Leybolds Nachfolger

Bryn Mawr College

Lake Forest College

American Institute of Physics

University of Washington

Stanford University

Western Reserve University

American Institute of Physics

OberlinCollege

Welch ScientificCompany

Case Institute of Technology

Northwestern University

B e l o i t College

Central Scientific Company

Cornell University

University of Gottingen

Rensselaer Polytechnic Institute

National Broadcasting Company

Adelphi College

Princeton University

Pennsylvania State University

National Science Foundation

California Institute of Technology

University of U tah

Wesleyan University

Wesleyan University

Princeton University

Purdue University

WALL, C. N.

WINCH, Ralph P .

WISSLER, Benjamin F.

VON ZAN THIER, Miss G.

WOODCOCK Karl S.

ZEMANSKY, Mark W.

University of Minnesota

Williams College

Middlebury College

J. Klinger

Bates College

City College of New York

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PROGRAM

Page

Session

I. VALUE O F DEMONSTRATION LECTURES

Presiding: W. C. Kelly ........ . 1

Panel Discussion ............... . 3

The Role and Purposes of Lecture Demonstrations in the Teaching of Physics, V. L. Bollman ......................................... . 3

Real Experiments Show Real Nature, E. M. Rogers 5

O n the Rationale of Lecture Demonstrations, H. K. Schilling 7

The Value of Demonstration Lectures, R. M. Sutton 9

Evaluating Results, P . Kirkpatrick .......... . 10

II. INVITED DEMONSTRATIONS

Presiding: C. J. Overbeck 13

The Surprise Element in Demonstrations, R. M. Sutton 15

Open-Air Alpha Counter, H. M. Waage ... 17

Demonstration Model of Magnetic Domains, V. E. Bottom 18

Corridor Demonstrations, H. C. Jensen .. 19

Surface Tension and Stokes Law, E. M. Rogers ..... 19

The Fundamentals of Transients in Electrical Circuits, J. I. Swigart .............. . 21

Microwave Equipment and Demonstrations, L. C. Andrews ....... . 23

Images with a Calcite Lens, I. Walerstein .................. . 24

Optical Effects with Water Ripples, V. E. Eaton .................... . 25

III. DEMONSTRATION TECHNIQUES

Presiding: B. F. Wissler ......... . 29

Large Scale Lecture Demonstration Apparatus, R. W. Kenworthy ... 31

Meters and Read-Out Devices, C. N. Wall .................. . 35

Optical Projection of Demonstration Experiments, R. W. P oh l ..... 38

The Demonstration Lecture as an Art, V. E. Eaton . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

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viii

Session

IV. TELEVISION

Presiding: M. W. Zemansky ..... .

TV Camera for Magnification, R. Hoyt .

Multiple Classes-Closed Circuit TV, I. Walerstein; K. S. Woodcock ...

Broadcasting, R. Rippen; M. Einhorn . . . . . . . . . .

V. SPACE AND EQUIPMENT

Presiding: J. K. Major

Lecture Room and Its Facilities, R. R. Palmer .......................... .

The Shop in a Physics Demonstration Lecture Program, L. I. Bockstahler ........ .

New Demonstration Apparatus Manufacturers Should Provide, H. A. Robinson ........ .

VI. INEXPENSIVE AND SIMPLE APPARATUS

Presiding: R. R. Palmer ......... .

Each member of the Conference showed a piece of apparatus that cost less than a dollar and could be demonstrated in less than two minutes.

VII. DEVELOPING SKILLED DEMONSTRATORS

Presiding: R. J. Seeger ...

Training Junior Staff Members, L. O. Olsen .

Literature and Training for the Demonstrator, H. C. Jensen

Summer Institutes and the Preparation of Demonstrators, H. K. Schilling ....... .

VIII. PROBLEMSO F CURATORAND ASSISTANTS

Presiding: C. N. Wall ............. .

Problems and Solutions at M.I. T., H. E. Anderson .

Some of Princeton's Solutions, H. M. Waage .....

IX. SUMMARYAND RESOLUTIONS

Presiding: P . Kirkpatrick ......... .

Page

45

47

48

51

53

55

57

59

65

67

69

70

72

77

79

79

81

Resolutions Committee, V. E. Bollman; T. E. Manning; M. W. Zemansky . . . . . . . . . . . . . . . . 83

APPENDIX. List of Apparatus Exhibited at the Conference ........•.........

Central Scientific Company . . .

J. Klinger Scientific Apparatus (E. Leybold's Nachfolger) ....................................... .

W. M. Welch Manufacturing Company ................................. .

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9091

SessionI. VALUE O F DEMONSTRATION LECTURES

Presiding: W. C. Kelly

INTRODUCTORY REMARKS BY THE PRESIDING OFFICER

W. C. Kelly, American Institute of Physics

As we proceed with the Conference, we shall be con-cerned increasingly with the technical details of lecture demonstrations. It seemed appropriate to the Planning Committee, however, that we begin the Conference with a review of what our educational objectivesare and at-tempt to answer the question, Why do we give lecture demonstrations? We are concerned in this session with an appraisal of the lecture demonstration as a means of teaching physics. It seems clear that as our educational responsibilities become greater we will have to be more and more critical of our methods to be sure that we are using our resources of manpower, time, and money as wisely as possible. Some of the critical questions we might well ask ourselves about lecture demonstrations are these: What do we hope to accomplish by lecture demonstrations and do we in fact accomplish it? Could these objectives be reached with greater effectiveness by other means -by more frequent meetings of quiz or recitation sections, for example, or by the laboratory work? What effects will increasing enrollments and a persisting shortage of competent lecturers have on the arguments we present during our meetings here? Will we see the lecture demonstration in a different light when college enrollments have doubled? Are college and university administrators sufficiently informed about the strength and weaknesses of the lecture demon-

stration system? Are decisions about class size and other things being made with full knowledge of the strength and weaknesses of the demonstration system?

Here to discuss these topics in the first part of our session are four men who are extremely well qualified to do so. Dr. Vernon Bollman is Dean of the Faculty at Occidental College and Professor of Physics. Pro-fessor Eric Rogers is Professor of Physics at Princeton University. Dr. Harold Schilling is Dean of the Graduate School at Pennsylvania State University and Professor of Physics. Dr. Richard Sutton is Professor of Physics at the California Institute of Technology. O u r speakers have not been given detailed instructions as to what they should talk about. The Planning Committee believes our panel members are properly qualified to select the themes they think important in this broad subject-the Value of Lecture Demonstrations. These men are out-standing physics demonstrators as you well know. They are also either administrators or are wise in the way of administrators. I suggest that we give each panel member fifteen minutes to present his views. After the four panelists have spoken we will have discussion from the floor and perhaps further discussion among the panelists. I shall call on Dr. Bollman first.

THE R o l e AND PURPOSES O F LECTURE DEMONSTRATIONS IN THE TEACHING O F PHYSICS

V . L. Bollman, Occidental College

Physics is an experimental subject. In the study of physics, no matter whether the student is looking toward specialization in experimental or theoretical physics, it is essential that he have the widest possible experience in the observation of physical phenomena. With all the demands made upon the student, it is obvious that a limited amount of time is available within his program for individual laboratory work in the observation of a large number of basic physical laws and concepts. This is true for the student majoring in physics and the other physical sciences and particularly so for the non-science student who takes physics as a part of his general edu-cational requirement. The tremendous growth in modern physics during the last half century along with the de-velopment of the modern mathematical treatment of ab-stract atomic and subatomic phenomena makes i t more and more imperative that methods be employed in the teaching of physics which will bring to the student an understanding of the increasing number of basic con-cepts in modern physics as well as the fundamental

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concepts in classical physics. Without reference, at the moment, to the pedagogical advantages of lecture demonstrations in the teaching of physics, it seems im-perative that this most useful technique be employed in order to meet the needs of the students.

A tremendous increase in the body of knowledge con-tained within the field of physics resulting from the rapid advances in the last few decades has placed great pressures upon both teacher and student. The abstract nature of the mathematical description of physical phe-nomena has changed our thinking and our approach to the description of physical laws through the employment of mechanical analogies and visual observation. The extreme specialization necessary for research in theo-retical physics has tended to develop a dichotomy be-tween theoretical and experimental physics to the detri-ment of both areas. There has also developed the atti-tude in the minds of many students of the notion of an elite in the field of theoretical physics with a tendency towards a disregard of matters experimental. The use

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of large research teams in various university and in-dustrial laboratories has also had an effect upon the attitude and capabilities of young physicists. All of these factors contribute to the chances that within the faculties of our colleges and universities there will be less likelihood of finding those who will have an interest in, and a capability for, effective lecture demonstration in physics and in laboratory experimentation. This is a very serious matter. There seems to be a tendency to move away from the demands of the lecture demonstra-tion technique and to resort to the textbook method in a strictly analytical approach to the study of physics. The latter approach, although apparently covering greater ground, meeting what seems to be the needs in terms of the total range of material covered, leaves very much to be desired in the way of understanding of basic physi-cal phenomena on the part of the student.

It is the tendency for one to assume that students with an interest in physics and a desire to qualify in the profession are not in need of motivation and that they need no special consideration in terms of the stimula-t i on which can be afforded through excellent lecture demonstrations and carefully developed laboratory pro-cedures. There is also a trend toward less coverage within the experimental laboratory. This trend to allow students to come face to face with more realistic situa-tions of limited scope is a desirable trend in terms of real values obtained from laboratory work, but where these programs are instituted it is understood that a considerable degree of routine coverage of basic physi-cal phenomena will be omitted. If this is done, then such a procedure makes i t more imperative that the student gain insights into experimental phenomena through techniques other than individual laboratory con-tact. The lecture demonstration can serve this need.

There is a great need for the teaching of physics to non-science students in a manner which is of the highest quality, and in a manner which employs the best in tech-niques to stimulate the student and to excite his curi-osity about the physical world. O n e cannot assume that these students have an understanding of even the sim-plest of physical principles, and it is therefore neces-sary in such a presentation to develop carefully a se-quence of demonstrations which illustrate basic physical concepts. For this group there is no substitute for a demonstration of a basic physical law.

It is thus evident that there is greater and greater need for the use of lecture-demonstration techniques in the teaching of physics, both for the physics major and the non-science student. I t is the only hope for obtain-ing the coverage of essential concepts in the discipline.

The lecture demonstration makes great demands upon the teacher. He must be a skillful mechanic, a skillful manipulator, and an artist. Admittedly, he must also be an actor of first quality who combines, with skillful timing, words and actions to the best advantage.

A good lecture demonstration possesses certaines-sential features:

1. The demonstration selected should be carefully planned and tested beforehand.

2. The demonstration should be simple and clear. Either the number of demonstrations in a given lecture

should be kept to a basic minimum, and/or provision should be made to focus the attention of the class upon the demonstration under consideration. Black boxes should be kept to a minimum.

3. Every possible means should be employed to make the demonstration equipment to a large scale so as to be visible to the entire class.

4. There is a tendency to introduce demonstra-tions which are not fundamental to the understanding of physics. Some of these are satisfactory if these more spectacular or practical forms of demonstrations do not take the place of less colorful ones illustrating basic concepts. The main thread of the course should not be side-tracked in order to accommodate a favorite but perhaps not an essential demonstration.

5. The lecture should make full use of all the range of possibilities of the demonstration. I t may be used to introduce a new concept without previous prepa-ration, or it may be used to verify a theoretical develop-ment, or it may be used to test the student's ability to analyze new problems.

6. Attention should be given to the appearance of apparatus and its neat arrangement before the audience. The distraction produced by haywire and makeshift arrangements should be avoided.

Carefully planned and developed lecture demonstra-tions used by a competent teacher will result in many dividends.

1. The development of demonstrations and their effective use will greatly improve the understanding of both the instructor and the student.

2. Demonstrations properly employed can save considerable time in the introduction of a basic concept.

3. Interest can be maintained in the subject and motivation can be at its highest.

4. The proper use of lecture demonstrations re-lated to the laboratory work associated with the course will result in much wider coverage of essential experi-mental material.

5. A student can learn a great deal by observation of the expert technique of the lecturer.

6. Good lecture demonstrations will hold the at-tention of the class and stimulate greater participation. This is particularly true in classes with non-science majors, although I think i t is true also for science majors.

7. A properly arranged sequence of demonstra-tions can be a helpful guide to :the teacher in maintain-ing the continuity of his lecture presentations.

8. First-rate performance in lecture demonstra-tions is a source of great enjoyment to both the teacher and the student.

The lecture-demonstration method has an important place in the total educational procedure at all levels of instruction. Every possible effort should be made to increase the use of the method under proper circum-stances. It is of great value both to the student and to the teacher.

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REAL EXPERIMENTS SHOW REAL NATURE

E. M. Rogers, Princeton University

An old saying sets the stage for what I want to say about demonstration lectures: "Art, Music, Labour, Love; these make men's lives." These are our ancient allies. I shall begin my discussion of good teaching on this happy note of high ideals. I shall end it on a doubt-ful note, facing a new mechanism which has yet to show whether it is friend or foe: Television.

O n e day recently on a college campus, neither my own nor yours, I met a pleasant man in a neat felt hat. We started talking and he asked, "Why do you give lecture demonstrations?" I was truthful and said, "Because I like it." He gave me an odd look and said, "Any other reason?" So I added, "Because they like it." He said, "But does that teach people the Laws of Physics?" And I started operating on him as a student and asked, "What is a Law of Physics?" He didn't say very much; so I took a dime and a quarter and raised them high up and let them go, and I said, "That's worth seeing, for real delight, even if you lose the money. Real experiments show real nature." Now that was an unfortunate begin-ning, as I then discovered, he was a Dean and he was busy evaluating this affair. My demonstration carried him right on to money. He said, "Are lecture demon-strations cheaper than labs where students can do things themselves-and I know you like labs?" I said, "Much cheaper, three or four times cheaper than good labs anyway. But good labs run slowly and students need to do some learning fast, with lectures." The Dean said, "Yes, but are lecture-demonstration lectures the same price as ordinary lectures?" "No, they are much more expensive," I said. "What do you gain? Why do you give lecture demonstrations? Never mind whether you like it. Never mind whether they like it. I'm the Dean and I tell them to study." Instead of continuing the argu-ment , we took a tour around the campus and talked to various people. The first person we met was someone in the Humanities, lecturing on poetry. And we got on very well until I asked him whether he got poets to read poetry at his lectures. He said, " O f course." I said, "Bu t that's expensive, in time, fees, good amplifiers; above all, in time." We went to the Music Department, and asked about the big box in the corner of their lecture room. The man there said, "Why that's for records. We have to play a lot of music." In the Art Department someone said, " W e are glad you have come; please help us mend our projection lantern." Then to the History Department, where we found the old tables of dates piled in a closet, replaced by new blackboards, maps, tables and chairs for much discussion. Wherever we went, in that excellent university, there was good machinery: blackboards, lots of books, lanterns, apparatus--to fit the needs of teacher and students in each field. And then in one room we found a lecturer who wrote clearly, capably, and oh so dully, on a small blackboard while students scribbled notes: on and on and on. As we left I said, "Nobodywill really come out very much alive from his lecture. He's missing something." The Dean thought so too.

Then the Dean and I sat down to talk and he stopped evaluating and started thinking. He talked about the business of teaching, the business of communicating knowledge. And I think we came to the conclusion that everybody who is doing good teaching communicates knowledge somehow. It is not the same for different teachers. Something in the personality of the lecturer; something in the style of his impedance-match with young minds; something that belongs to the subject matter of his course-all these help to define the best manner of communication in each case. For some of us who are teaching science, demonstration lectures are our own best form of intimate communication: The transmission of our field of knowledge to younger minds. It is our form of the teaching art. Demonstrations should not be "monkey on a pole" business to amuse students and waste time and money. O u r real demon-strations are to communicate knowledge of physics, to show physics and physicists at work, come alive. We can argue and discuss as we show the experiment; we must, for that is what makes much of the difference be-tween mere fun and good science.

Thus I see lecture demonstrations playing an essen-tial part in giving a feeling for physics as living knowl-edge. They are also valuable in preventing physics being treated as a purely deductive science. It is not deductive, but primarily inductive in the early stages. It belongs with Nature rather than solely with men's logic. I try to show physics as part of our acquaintance with Nature by lecture demonstrations. Students get even closer contact with Nature in laboratory work; but there I am sure we must not talk to them, we must let them get on with their work and experience the joys and sorrows of experimenting themselves. So if we want to comment, expound and argue about the experimental side of science we had better do that in lecture. And, in the early years, the way we talk with students should be illuminated with experiments. The delights of neat de-ductive treatment will come later, all the richer for an experimental background. As time goes on, demonstra-tion lectures enable us to convey an understanding of the growth of science: information-rules-theory-theory reacting with experiment--then further growth. All this is unconvincing to a student just lectured at; told the structure. With real experiments shown, and arguments developed around them, learning is far easier and the understanding is likely to last.

Who then should give demonstration lectures? All who like communicating that way, including those who can be persuaded to try and like it. I notice that theo-retical physicists often give the best demonstrations once they are persuaded to try. They have an air of sharing the miracle of the experiment's success with the students.

In Bernard Shaw's "Saint Joan," the Archbishop, cornered with a demand for a definition, says, " Amiracle, my friend, is an event which creates faith." In a minor way, some demonstration experiments are

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miracles; they are something that creates faith in the genuineness of science. (In that way, demonstration lectures are a special art, within the general art of teaching. Could we save time by agreeing once and for all that they are an art, for the rest of this discussion?) If a demonstration lecture is an art, if it is part of mak-ing a miracle to give people faith in physics, I think we should give very simple demonstrations. The compli-cated gadgets which are our private delight have only one good purpose: To give a sense of participation. When we have spent anxious hours to balance the gyro-scope bearings, or to coax amplifier and discriminator into cooperating audibly, we are still nervous about what will happen, and this gives the lecture a zip that the au-dience will share. It is the Art of Art, Music, Labor, Love that makes the lecture worth while to the audience. But most of our experiments should be simple, as our conference guest, Professor Pohl , has set us an ex-ample: Big experiments that all can see, and chiefly simple ones at that.

Experiments big enough for the back row to see: That is an old rule, such obvious good manners towards students in the back row that we often preach it; yet we break it again and again. The lecturer who weighs a bullet on an invisible balance should not bother to fire it. The professor who putters with a small thermometer, announces the temperature rise is 1.6 degrees and cal-culates the mechanical equivalent of heat, might just as well announce the result for J, ready made.

As our audiences grow in size, the back row suffers more and more from things that are too small. Supposewe have a lecture-bench clock with a dial 12 inches in diameter. To a student 50 feet away, at the back of a fairly big lecture room, that will look the size of a quarter-inch dial held one foot from his eyes. Try mak-ing measurements with the seconds hand on the small circle on your wrist watch! If we make the lecture room still longer, this grows worse; if we make it wider, the lecturer's vision is asked to make an uncomfortably wide sweep, and some students will see things too ob-liquely. (I suggest this criterion: If the lecturer stands behind his table, facing the center of the audience, sight-lines at 45 degrees each way from his normal view en-close the maximum comfortable width for audience.) Yet demonstrations can be made visible to all, as Pro-fessor Poh l and a few others have shown. But audiences bigger than 200 make serious demands both of costly apparatus specially made and of special preparation by the lecturer. As I look towards the future of larger en-rollments I see little hope of a proportionate increase in lecturers; until in some future age teachers are paid as much as physicians. (I can conceive of a highly civi-lized world coming to the conclusion that teachers must be paid as much as physicians; in a sense they are our intellectual physicians.) Even today, we might find a large state university collecting teachers from a great area around to meet growing needs; we may even fear that non-state colleges and universities will be starved, within twenty years. Looking fifty years ahead I see a hopeless problem except for one line of solution: movies and television.

Many of us who have tried giving television lectures or making films with demonstrations, have been shocked

by unexpected difficulties; so badly shocked that we are not yet sure whether the new media can really succeed, at least for a generation or two. The obvious difficul-ties-the impersonal atmosphere, communication with the audience only one way, discomforts of poor projec-tors and darkened rooms-are offset by advantages of specially skillful lecturers, close shots with cameras, quick changes of time and distance scales that give students the advantage of a front row seat or even of standing beside a master scientist. But the surprising difficulties are quite different: They are the interfer-ence of amateurs who do not understand our work of teaching science, who do not know the physics we are teaching, who gaily substitute for the help of an academic colleague their insistence on entertainment and amateur scientific commentary. That can wreck serious teach-ing. It may sound a silly, unnecessary difficulty, but many who have tried using the new media have met i t .In a good TV studio several cameras watch the lecturer and his experiments. An expert in the control room decides from moment to moment which of the camera pictures is shown to the audience. Again and again his training in the entertainment world makes him choose the wrong one for good teaching-the lecturer's face for "human interest value" just when a close-up camera is offering to show the heart of the experiment. So far as I can see there is no hope of retraining the present con-trol-room experts; they have been selected for interest and skill that are foreign to our serious teaching. This may not spoil an isolated TV talk on science for the general public, although it gives science a poor name as a whizz-bang affair, but it will wreck the serious use of such lectures for teaching a course.

Films seem safer, and they are if those of us pro-ducing films are strict in our requirement that both the physics and the teaching of it should be in the hands of physicists who know the material to be treated, know the kind of students aimed at, and know the stage of the course already reached. This may require us to impose still more stern discipline on ourselves in refusing the warmhearted aid of experts. And finally even with the best of filming, directed under the full control of physi-cists, the way the film is cut and pieced together to make the final version can affect its teaching value tremendously; the cutting too must be done with the physicist in charge. The time will come when it is recognized that it is important to have a spare physicist watching a physics film being made, watching at every stage, as to have a spare surgeon at a major operation.

So I look forward to a good physics teaching going on i n fifty years from now, but mostly by films and TV, from sheer demand of numbers. Meanwhile, we can do great things for those future films by keeping our own art and trade alive. And when the future comes, even with the best of f i l m s with TV teaching that is clear, inspiring and thorough: I hope there will be demonstra-tion lectures here and there as sources of inspiration to maintain standards in the new media and, as real con-certs do for music, to add a human element that is part of showing science. Let us hope that if our grandchildren are brought up on the most wonderful pictures of camels, elephants and so on, there will still remain for them an occasional visit to the Zoo.

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ON THE RATIONALE O F LECTURE DEMONSTRATIONS

Harold K. Schilling, Pennsylvania S ta te University

My thesis is that lecture demonstrations are indis-pensable to adequate teaching and learning in physics, and that the reason for this is that their contribution is unique, and virtually unattainable by any other means. The argument rests on my conception of certain aspects of the nature of physics, and of the learning process by which the student attains understanding of it. This is an extensive subject. I shall try to develop only four ideas. There are, of course, many others that are pertinent.

I

Physics, as I see it, involves two kinds or aspects of scientific knowledge and experience. Therefore, the learning of physics requires at least two different ap-proaches. First, it means becoming deeply interested in certain particular areas or facets of nature, and ac-quiring direct, experiential acquaintance with them. Second, it means becoming interested in and conversant with the conceptual and symbolic structures physicists have erected as they have studied nature. The former involves direct observation of phenomena, while the latter involves experience in theorizing about them.

In view of this dual nature of physics, I urge that the study of physics must be dual also, and must provide well-balanced opportunities for intimate and extensive contact with both the concrete realities of nature and the abstract theories related to nature. The reason for in-sisting on the absolute necessity of both is that altogether too much teaching of physics has in practice emphasized the one at the expense of the other. It is an undeniable fact, I submit, that the study of physics has become more and more a matter of simply reading textbooks, listening to teachers talk, and of engaging with fellow students in so-called "discussion," and less and less of doing physics or experiencing it directly. Tragically few students have observed for themselves any signifi-cant number of even the most important phenomena they have read about in textbooks. This is true for a very large majority of high school students, as well as of many, many college students. Indeed I believe that most graduate students of physics are in the same situation. While I have no statistics to support these assertions, I make them on the basis of rather extensive observations.

The public, and even many of our own colleagues, seem not to realize that physics is in many respects like music and the other arts. I would say that no matter how many books about music a person may have studied, no matter how much he may have read about the opera, the s y m p h o n y , or the string quartet, if he has not him-self heard operas, symphonies, and quartets, he simply does not know music. SimilarlyI would say that, no matter how well one knows a textbook, or scores of text-books and other treatises of physics, no matter how much one may know from reading about electro-mag-netism, about the phenomena of reflection, refraction, dispersion, diffraction, and polarization of waves, about the gas laws, or about gyroscopic motion, if one has not

himself seen these fascinating phenomena one simply does not know physics. Music deals with sounds that must be experienced. Physics deals with certain aspects of nature that must be experienced.

Now even if this be granted, it may be argued that this proves nothing about the necessity of lecture demon-strations. All it might imply is the need for laboratory work. In reply I suggest that there are two ways of ex-periencing music directly: first, by playing music one-self as a performer, and second, by hearing it as a spectator. Doubtless both ways are important and in-dispensable. Indeed, adequate knowledge of music in all its dimensions is possible only if ones experience includes that of the performer and that of the spectator-not to speak of that of the composer. As performer one experiences music in depth, so to speak, learning di-rectly what it means to play music, becoming intimately acquainted with a few musical instruments, and a limited repertoire; whereas as spectator one experiences music in breadth, hearing many instruments and works one could not have time to master oneself, and becoming aware of interpretations and nuances of performance one might never encounter otherwise. While analogies are, of course, never altogether appropriate or con-vincing, I suggest that the analogy here between music and physics is very close. In empirical physics, too, there is the role of the performer and the spectator, and to learn physics in all its fullness requires both types of experience, along with others. In the laboratory the student is performer, learning physics in depth: Actually doing physics, becoming intimately acquainted with a few instruments and techniques, and a limited repertoire, i.e., investigating a small number of phe-nomena. In the demonstration lecture room he experi-ences physics in breadth, becoming acquainted, as spec-tator, with many instruments, methods, phenomena and nuances of physical interpretation that he might never encounter otherwise. O f course, in both music and physics the study of books is very valuable and still further enlarges ones horizon. But no amount of book work can provide what can be learned through the per-former and the spectator experiences.

Another comment may be in order concerning labora-tory work. It provides two kinds of experience inten-sively, namely, experimentation under precise control of conditions, and measurement requiring relatively complex techniques and instruments. These are, of course, absolutely prerequisite to adequate understand-ing of physics. They demand so much time, however, that no student can make many such experiments or measurements in any one physics course. Therefore, the amount of time available in the laboratory for the far-ranging spectator experience that is needed in learning physics is virtually nil.

The first point I have tried to make is, then, that lecture demonstrations are necessary in order that the student may be confronted by nature itself, i.e., to enable the student to observe basic phenomena themselves.

8

Laboratory experience cannot in general provide such opportunity over a wide enough front. My basic argu-ment has been that physics is the study of certain as-pects of nature, and that, therefore, learning must be more than learning from books and from blackboard-and-chalk lectures.

II

In developing my second point I want to recognize more explicitly that physics is also to a large extent a process of conceptualizing, hypothesizing, and of deduc-tive reasoning. I suggest that in physics these theoreti-cal processes lean heavily (though not exclusively) upon what I would like to call "physical reasoning" or "physi-cal thinking," in contrast to the corresponding processes of pure mathematics, that depend upon what might be called "mathematical thinking" or "conventialistic think-ing." By physical reasoning I mean thinking that is al-ways related to physical objects, phenomena or rela-tionships, that deals with physical categories and that takes i t s cues for imaginative hypothesizing from the physical situation. To a large extent, I feel, the student's ability to learn physics depends upon his doing p h y s i c a lthinking-whether he realizes it or not. Before a new concept or a theoretical development can have maximum meaning for him, he must be aware of what there is about concrete actuality that calls them into being. Moreover, I never cease being impressed by how much easier it is for students to think about what they have seen or heard for themselves, than about something they have only read about. Haven't all of us at times en-countered apparently insurmountable mental blocks in trying to think through something or other, and then been surprised at how quickly our difficulties disappeared after seeing a good demonstration of the effect in ques-tion? Ove r and over again I have observed utter dis-belief stemming from faulty reasoning give way to ut-terly satisfying understanding after a demonstration. Somehowseeing something often releases the imagina-tion. O n e can th inkbetter thereafter. This happens, I think, much more often to students than many teachers realize.

My second point is, then, that theoretical and concep-tual thinking is facilitated by physical thinking, and that this in turn is greatly facilitated by the spectator ex-perience provided by lecture demonstrations.

III

Next I suggest that lecture demonstrations provide unexcelled opportunities for students to watch physicists in action, to see how they think and operate (a) when they attempt to isolate particular phenomena for study, (b) when they try to identify causes, effects and func-tional relationships, (c) when, confronted by puzzling situations, they make guesses, follow hunches and con-struct various hypotheses, and (d) when they have to choose among alternative theoretical possibilities.

If physics be thought of not only as a body of knowl-edge, but as an aggregate of methods of knowing and of ways of doing things, then learning physics means also learning how physicists do things. As I see it, the

methods of physics are to a large extent simply the ad hoc methods that physicists use. Therefore, I be-lieve that i t is largely futile to try to teach the method-ology of physics by precept, and that for the most part i tmust be learned by example or by contagion. Now about the only opportunity most students can ever have of observing a physicist's methods is when he is at work empirically in the demonstration lecture room. At least that much of this kind of apprentice experience of learn-ing from the master we should insist upon as an irredu-cible minimum for our students.

My third point is, then, that lecture demonstrations enable students to observe how a physicist thinks and proceeds in a physical problem.

IV

Finally, I suggest that since physics has a history, an important component of "knowing physics" is to know something about its history. To know its history means, among other things, to be able to follow in retrospect the sequence of pivotal or decisive observations, dis-coveries and experiments that represented breakthroughs into new orders of reality and the disclosing or creation of new realms of thought. If the student is to have an historical perspective of physics, if he is to have a feel-ing for i t as an ongoing, evolving enterprise with roots in the past, or if he is to appreciate its particular, unique contributions to intellectual history, and to under-stand how present ideas have evolved from earlier ones, he simply must know something about the decisive mo-ments or turning points of the past. I count the repeti-tion of historically-important experiments or discoveries to be one of the most valuable and unique contributions the demonstration lecturer can make to the teaching of physics. I refer to this as a unique contribution because almost never is there sufficient equipment or time to enable large numbers of students to repeat such classi-cal experiments in the laboratory, and because book descriptions of such experiments are frustratingly dis-appointing and for most students rather uninteresting.

v Summary: Among the important, unique contributions

lecture demonstrations can make to the effective teach-ing of physics are the following:

1. They confront the student with nature itself. Students need both the performer and the spectator ex-perience.

2. They facilitate physical thinking. It is easier to think about a phenomenon after one has observed it directly.

3. For most students they provide unexcelled op-portunities for observing, and thinking with, a physicist in action in a concrete problem situation. The best way to teach method is not by precept, but by example and contagion.

4. They contribute to historical perspective and understanding, especially through the re-enactment of classical observations or experiments, representing momentous discoveries that turned out to be decisive turning points in the history of ideas.

9

THE VALUE O F DEMONSTRATION LECTURES

Richard M. Sutton, California Institute of Technology

I would like to remark further about the historic as-pect of the demonstration experiment to which Harold Schilling has alluded. This often plays an important part in our every -other -week large lectures to Freshmen and Sophomores at Cal Tech. For example, I started off this year with a Freshman lecture on Archimedes, and Professor Earnest Watson followed with lectures on Galileo and Newton. I always like to show in all their simplicity the crucial experiments of Oersted and Fara-day. There is much value in seeing "great ideas at work in the nascent state." Moreover, I often bring extra experiments into my own section of 20 boys just because I cannot refrain from showing them some of the simple graphic experiments that they should observe. I want my students to realize that physics is the work of men, that they made mistakes along the way, that they were human and sometimes slow to see what is now "obvious," and yet they often performed simple but cru-cial experiments. However, rather than just repeat the experiments as they were originally performed, we can also bring our ingenuity to bear, and we can give new twists to old experiments which make them modern, make them different, make them unexpected. In my lec-ture on Archimedes I gave three or four experiments which I would like to think Archimedes himself would have enjoyed seeing, because they took what he had started and in a delightful manner went a step further.

In recent years when talking about demonstration experiments, I have often used the simple title "T ryIt and Think." To my mind, the advantage of the experi-ment is to stop the student and make him think about nature performing in ways which he might have read about but which he hadn't personally seen. Those of you who know some of the experiments that I like to show, know that i t is more fun to show something with a twist to it, making some simple piece of equipment do unex-pected things. I tis fun to outguess the student. I don't say you outguess nature although you may appear to do so. You will have succeeded i f you can make the student leave the lecture room with a question in his mind and with the desire to try an experiment for himself.

At Cal Tech we now have what we call the free labo-ratory in which we encourage Freshmen to perform ex-periments of their own designing. As I talk with stu-dents, I am aware of the tremendous amount they haven't seen and aren't likely to see unless opportunity is of-fered them. Sometimes, in connection with our free laboratory the student feels at a loss to know what he may do. I recently took our textbook and began to enu-merate: I found that there wasn't a single section of that book that couldn't be made the basis of either a good demonstration experiment or a good laboratory experiment, and in many cases several experiments. Problems, too, often suggest suitable experiments, and vice versa.

A number of years ago, Michelson talking in Cali-fornia about his experiments on the velocity of light (and he had been doing them for more than forty years

at that time) said, "peopleask me why I do them and I have to say 'Because it's so much fun.'". Certainly, as it has already been said, we ought to get some fun out of physics. We should, however, be sure that the fun we get out of our own little private experiments on the lecture table is also shared by those who are far away in the lecture room. All through this year I have sat back and watched our Freshman and Sophomore lectures with a critical eye. When you're off at the far end of the room you have a different view from that of the lec-turer. This is the place where television has a real contribution to make. As I watched Continental Class-room this year, I realized that there, three thousand miles away from the lecturers, I could see things better than i f I had been sitting in the third row of the ordinary lecture room. Let us not discard this new medium as an impossible thing just because the present art is har-rassed by the director, as Eric Rogers has pointed out.

In the first year of my teaching, Professor Culler at Miami University said to me, "Whatever happens in an experiment is just what ought to happen. It may not be what you expect to happen." That point of view has oftentimes saved me from what might otherwise have been failures. It is good to take advantage of the un-expected events which may occur in an experiment. This is where the student sees the physicist at work creatively, especially i f he has the facility to turn an accident to good advantage. But sometimes the unex-pected gets the better of you. One time I was completely stopped; I don't think I was ever quite so nonplussed. I twas in performing the innocent ball-and-ring experi-ment where you heat the ball to show its expansion. I heated the ball with a Bunsen burner as usual and tried i t in the ring. It went plop right through! I heated it some more but with the same result. Finally, with further heating, steam started coming out of the ball! Now for ten years I had assumed that the ball was solid, so when steam emerged from it I was dumbfounded. I found out later that my colleague, Tom Benham, had been performing an experiment on buoyancy a few weeks before. Unknownto me, he had dunked the ball in water and the water had remained there unt i l I got hold of i t .Now you see I didn't start o f fto say anything about the heat capacity of water and change of state! I was out-smarted by nature and by my tacit assumption of the solidity of the ball and the students knew it.

On one occasion, I was luckier than I had any right to be. It was at Columbia University five years ago. I was nearing the end of a lecture on heat engines, adiaba-tic compression and the work-heat relations in gases. I was rushing along too fast, trying hurriedly to show this and that, a bad habit, I'm sure. At one end of the table there was a coffee can with a half-inch hole in top and bottom. It was filled wi th illuminating gas, and a flame burned quietly at the top. Eventually I knew that the flame would duck down through the hole, explode the gas and blow the lid and the weights that were resting on it three or four feet in the air. But time was pressing

10 and the bell was about to ring, so I dashed to the other end of the table, grabbed hold of the handle of the fire-syringe and plunged it downward. At that instant the can went BOOM If you have ever watched a dynamiter at work you can imagine the evident appearance of Cause and Effect. Here were two events utterly unconnected which by accident I had connected. The students roared! I stopped my lecture and said "Ladies and Gentlemen, on. the stage, that is what is known as Timing!"

A year ago, at the University of Colorado, I had one of the greatest surprises of my life. You have doubtless tried freeing a loop of chain 6 inches in diameter from a rapidly rotating disk and have had it dash across the table and bounce and do various spectacular things. You know full well that it sometimes jumps off backwards and skids like a comic strip star trying to make a quick get-away. This time it not only jumped off backwards but it fell to the floor. As was my custom, I just waited for it to grind itself out on the floor before picking it up to start it again. To my amazement, one second later, the chain reappeared on the table, ran the full length of the top and dropped down on the other side. S o m b o d yin the back row called out "Do i t again!" But I didn't: I knew when I was ahead and I stopped at that point. However, I still would like to discover just how that lively chain climbed from the floor back onto the table. If I could repeat that experiment at will, I should have one of the phenomena that ought to go onto television.

I like paradoxes. I like those things which prompt a student to see further into new principles. Also, I like

to catch the conclusion jumper off base. Another im-portant thing is simplicity. We need to keep our experi-ments simple and yet with a nugget of good physics and of something to excite the imagination. Onc e in awhile it is a good thing to show an experiment and not explain why things work as they do, letting the students argue about it. Professor Frederick Palmer of Haverford College had the great art of leaving us frequently at the end of an hour with an unsolved question.

Watch others demonstrate, learn from their mistakes, and see how you can improve on their experiments. Ac-tive imagination can develop ordinary ideas into better ones. Do not let new ideas escape from you. My own habit when a new idea strikes is to jot down on a card the date and the occasion which sparked it. If it's a live idea maybe half a dozen cards will develop in the next two or three days as the idea grows. Good ideas rarely develop full blown the first time.

The demonstration experiment can be a valuable lubricant in the teaching of physics. It can help to keep the interest high, it can keep up a certain excitement that we are dealing directly with nature and that unex-pected things can be found even in simple observations. When the student tries to diagnose an experiment that doesn't do just what he expected it to do, when he thinks the demonstrator has put one over on him and has got him out on the end of a limb only to cut the limb off, at that point Thought may hopefully begin. Let us take advantage of our opportunities which are great because the number of available experiments is great.

EVALUATING RESULTS

Paul Kirkpatrick, StanfordUniversity

If a general physics course were analyzed as a busi-ness proposition, some of the components which have been retained through decades because of inertia, lack of imagination, or academic folly, might not secure the approval of the cost accountants. Professors are prob-ably protected from any such analysis by the general distrust of educational measurements. Even a precise measurement of the knowledge imparted to students, or acquired by students under the teacher's catalysis, would not be a full assessment of the product output of Physics 1, 3, 5; the course, like any college course, is supposed to do more than inform. It is supposed to open the channels to future information for as long as the en-rollee remains educable, and to do something immeas-urable about his conscious orientation in his world and perhaps provide a positive or negative occupational appeal.

So the first thing to be said about evaluating results is that we can't hope to do it with either the reliability or the precision that as scientists we could deem re-spectable. But you knew that already. Of all the peda-gogical devices it is my opinion that the wise cost ac-countant would esteem the textbook as the most produc-tive of educational profit per invested dollar. The spoken words of the teacher would come next, and in

competition, ranked somewhat lower, would be the labo-ratory apparatus and the demonstration equipment. Now there has been some little attention paid to evaluation of the effect of laboratories and to the relative benefits of differing laboratory procedures, but I have not found any comparable attempt to measure the effects of demon-strations as they are used to illustrate a lecture. We ought to try to evaluate these demonstrations with re-spect to two scales. The first is with regard to their dollar cost because administrators think in these terms and have in some cases controlled the acquisition of demonstration apparatus using no evident criterion ex-cept the minimization of the total budget. It is a dis-tasteful business, but when teachers have to say buy this and defer that, they should be able to say which choice will buy the most education.

The second kind of evaluation is just internal com-parison of one teaching activity with another. Here I have a couple of hundred ignorant sophomores before me at the beginning of the year and they are willing to put in perhaps twelve hours a week of their valuable time learning physics. I t is up to me and my associates to decide how they should split up this time, and up to now we have no real rational basis for the distribution of these hours. I think I get them to spend i tabout as

follows: reading a textbook, rereading it and thinking about i t , 22 per cent; solving and writing up assigned problems, 15 per cent; reviewing their notes and cram-ming for tests, 12 per cent; laboratory activities, in and out of class, 27 per cent; lectures, 24 per cent. Break-ing down the last entry I should estimate the demonstra-tion content at about 1 0 per cent. Other teachers do it differently, of course, but the evaluation of results is a task pertaining to the whole course and not just an iso-lated component. The question is, how should we slice the pie? I think teachers have not addressed themselves to it very seriously, but I noticed some recognition of it in comments here this morning. If in our enthusiasm we resolve to do more demonstrations, what are we going to do less of?

The demonstrations are really in time competition only with other things that can be done in the predeter-mined lecture hour, and I believe the visual nature of the demonstrations assure them a justified place in competition with merely audible instruction. In a com-petition of the senses, the eye appeal wins out; if a late coming student enters during your most eloquent lecture, all eyes switch over to the door.

Certainly the results of the demonstration may be valuable or a waste of time, depending upon how i t is conducted and utilized. It may serve many functions. If you merely hang up a pendulum for students to look at, it is better than a picture of a pendulum in a book. At least i t is three-dimensional and the right size and color. If you swing the pendulum, the students are see-ing a phenomenon and not just a thing. If they time it (by their own watches or the wall clock), they have an opportunity to see a mathematical formula come to life. They get exercise in careful observation and the meas-urement of time. Next come rational recording, formula

11

juggling, drill in the handling of units, slide rule prac-tice, and finally the determination of a physical constant of some interest. The student must learn to bring his best brains with him to the demonstration and not merely stare at it as at a TV commercial.

If anyone undertakes a serious evaluation of the re-sults of lecture demonstrations I shall read his reports eagerly but not gullibly. I am not certain that it is pos-sible to make measurements that would serve any useful purpose beyond the procurement of a master's degree in educational measurements; such are the difficulties in the way of precise specification of what is being measured, control of the measuring process without disruption of educational procedures, and collecting valid numerical measures of the results. Parallel, equivalent, and statistically numerous student sections must be arranged, with the control section being in some way instructed in the subject material covered by the demonstrations. Full attendance should be maintained. Parallel sections should be handled by the same teacher. Tests specifically covering the subject matter of the demonstrations should be applied. These things can hardly be done without having students realize that they are being experimented upon, and probably those de-prived of demonstration entertainment will develop a slightly disturbing sense of discrimination. Finally, if one relies upon prompt tests there can be no considera-tion of the long-term educational effects I cited in the first paragraph. The decay constants of a physics course vary widely among the several course components. My own belief, based upon unsystematic observations over several years, is that the visual experiences decay more slowly than the book learning, but perhaps this is based upon testimony concerning a few spectaculars in the demonstration repertory.

DISCUSSION

Eaton called attention to the fact that at the Middle-town meeting of AAPT, one session (held nine years ago yesterday) was devoted entirely to the demonstration lecture and at this time tribute was paid to some of the giants in this field. Bockstahler told us about Foley's lectures at Indiana. Caspari, 1 a biology professor at Wesleyan, who had been one of Pohl's students at GBtt-ingen, told us of Pohl's famous lectures. Unfortunately Caspari could not attend the present conference but we have done better this time by bringing the master him-self from Germany.

At the 1950 meeting, J. C. Blankenagell of the Wes-leyan German Department gave us a very vivid picture of Benjamin W. Snow as teacher and person. The fact that he remembered so much of what went on in this class at the University of Wisconsin forty-six years be-fore supports the contention that demonstrations are a powerful aid to memory. Professor Blankenagel, now retired, was in the audience and was asked for com-ments.

1. Am. J. Phys. 19, 60-63 (1951).

He recalled that at his one and only appearance be-fore professional physicists he had remarked that each time Bennie Snow entered the lecture room he was given an ovation and they often wondered what would happen if the students did not applaud. When he sat down the man behind him tapped him on the shoulder and told him that years later this happened. One day, as a result of a student conspiracy, there was no applause. Snow was so taken aback that he could not say a word. He re-turned to his office and on the second appearance re-ceived the accustomed ovation. The class then pro-ceeded with the usual vigor and brilliance. Blankenagel also remarked that he had just heard that in keeping with the policy of naming the new men's dormitories at Wisconsin after distinguished professors, one of them is to be named for Professor Snow.

Professor Pohl said, "Theories come and go like the generations of men, but the facts remain," and students have first-hand knowledge of the facts if they have seen them demonstrated. He stated that physics lectures in

12 Gottingen are now using closed-circuit television as a means of magnification and amplification so all students, of the 500 watching at one time, will see the important parts and the results of an essentially small-scale demonstration. He illustrated his point with a descrip-tion which showed how an experiment on superconduc-tivity in a lead plate at liquid helium temperature was made visible to an audience of this size through the use of closed-circuit television. He emphasized, however, that whenever possible the student should see the physi-cal phenomenon itself, not an image on a screen.

Reviewing a thought brought out by Professor Boll-man, Professor Overbeck emphasized the necessity and importance of careful selection of material to be shown in lecture demonstrations. Many physical principles and instruments are best illustrated and studied in labo-ratory, and the lecture demonstrations should not waste time either duplicating or preempting such material. As examples he cited the Wheatstone bridge, much of composition and resolution of forces, and the beginning work on image formation and the laws of lenses and mirrors.

Professor Schilling agreed and urged that in the lec-ture room we teach by demonstration only that which the lecture demonstration teaches best. The lecturer should time his presentation so the student sees some-thing at just the moment in his learning process when

he most needs to see that thing. Our examinations often seem to indicate that students learn as well without either laboratory or lecture demonstrations as with them, but "this is always because the examinations we give are of such a nature that they are not directed at those specific things which the laboratory or the lecture demonstration can give." He urged that we find those places where lecture demonstrations make a unique contribution and use it vigorously there and not else-where. The important thing is to get the teaching job done in the best way for the students.

Professor Rogers urged that demonstration experi-ments relating to Newton's laws of motion must be shown in lecture demonstrations in any event. They belong to that class of phenomena which must not be relegated solely to the laboratory. He also urged that some experiments be set up in the corridor where stu-dents can do them individually and really see what happens.

Dr. Seeger suggested that much more should be done to present lecture demonstrations to high school stu-dents. This should be done both in the high school and by means of demonstration lectures to which high school students are invited. He cited the example in England where the Royal Institute shows lecture demonstrations by noted scientists to as many as eight thousand school children per year.

Session II. INVITED DEMONSTRATIONS

Presiding: C. J. Overbeck

THE SURPRISE ELEMENT IN DEMONSTRATIONS

Richard M. Sutton, California Institute of Technology

(1) "Quantum Mechanical Pendulum." An innocent-looking styrofoam ball swings in a plane as a simple pendulum on the end of a thread 1 m long. Beneath its gravitational rest position, with a clearance of about 1 em, is placed a book on elementary physics. Soon thereafter, the swinging ball begins to move in an er-ratic and unpredictable way, far from the staid motion of a simple pendulum. The demonstrator picks up the book and leafs through its pages, to the mystification of his audience who naturally suspect magnetic influences at work. The pendular motion exhibits the "tunneling effect" of a particle which probes potential barriers and may finally break through them as in the quantum me-chanical view of radioactive emission of particles from a nucleus. The secret lies in four thin ceramic magnets (see Fig. 1) which are inserted in rectangular holes cut in the first 80 pages of the book, and a fifth circular

SUPPORT

Fig. 1. Quantum Mechanical Pendulum. All four rectangular magnets with N-faces upward. Eight-pole magnet at center.

magnet symmetrically situated at the center. The pen-dulum bob encloses a 5 em bar alnico magnet with axis along the vertical line of support. Four possible rest positions for the bob are presented, and the bob demon-strates almost complete uncertainty as to which it will choose as its final resting place.

(2) "Dynamic Use of the Force Table." Suppose that an object D rests at the center of a horizontal force table in equilibrium under the action of three concurrent forces supplied by three weights A, B and C suspended

15

from threads passing over pulleys. Two of these forces due to A and B act at right angles. Now, which of the three threads should be burned so as to produce the greatest initial acceleration of the object at the center? And what is the initial magnitude and direction of this acceleration? As an example, let the central object D have mass 50 gm and let the three objects A, B and C suspended from the cords have masses 100 gm, 20 gm, and ,11002 + 202 = 102 gm. The thread supporting C is at tan-1 1/5 with the thread to A, or 11°40'.

It is fairly intuitive that the thread supporting object C should be burned. However, the initial acceleration of the central object is not that due to a pull of 102 x 980 dynes opposite in direction to the burnt thread. It is necessary to proceed with caution. Initially, a force of 100 X 980 dynes accelerates 150 gm along direction A giving D an acceleration 2/3 g; and a second independent force of 20 x 980 dynes accelerates 70 gm along direc-tion B, giving D an acceleration 2/7 g. The resultant acceleration of D is g v' (2/3)2 + (2/7)2 = 0. 726 g along a direction DD' making tan-1 3/7 with A, or 23°15'.

To convince those who answer the question too glibly, a projection force table (see Fig. 2) is demonstrated consisting of a lucite disk with three movable pulley supports set on a vertical projector. The weights which all descend when the thread to C is burnt are promptly arrested after each falls only 0. 5 or 1. 0 em, thus allow-ing the central object after the initial impulse to con-tinue sliding without further forces other than friction acting on it. It comes to rest within the field of view, clearly showing by a trace left in chalk dust that it went in direction DD', not DC'. One may, if desired, com-pute the initial acceleration by measuring the distance traversed against friction after the initial, measurable impulse.

(3) "Jumping Ball Experiment." A 2. 5-cm diameter iron ball (see Fig. 3) rests in a shallow concave cup be-neath a large (20 em) carriage bolt or iron nail whose tip is about 1 em above the ball. The bolt is held firmly in a vertical position by a laboratory clamp stand. Shadow projection shows the ball, bolt and intervening gap. Suddenly, the ball jumps up and clings to the nail. It may be caused to drop off and jump up again at will. No wires or magnets are in evidence.

Beneath the lecture table, with its broad pole face (6 or 8 em diam.) pressed as close to the table top as possible, is placed a strong electromagnet which may be controlled by (a relay and) a footswitch. The ball in its cup rests directly over the center of this pole piece. When the lecturer energizes the magnet, the bolt and lab stand become part of a magnetic circuit having a strong inhomogeneous field in the gap between the ball and vertical bolt. The tractive force on the ball is greater than its weight and the ball jumps up against

16

c

D PROJECTION LENS

A. SIDE VIEW

D' / / ,. C'

,/

B. TOP VIEW

Fig. 2. Force Table.

A

gravity. It is best to use a U-shaped electromagnet with two poles, placing the lab stand over one pole and the ball over the other.

(4) "Mechanical Firecracker." This is a provocative self-starting vertical pendulum which might be called "Operation Bootstrap." A cardboard mailing (see Fig. 4) tube 50 em long, 5 em diameter is covered with red shelf-paper. Its lower end is firmly closed with a large cork stopper. The tube is suspended vertically from a very flexible spring, and it is shown that, when displaced from equilibrium position it oscillates up and down. Now, while it is at rest, a "fuse" is ignited at the top of the tube and after 5 or 10 seconds of suspense, the "firecracker" suddenly jumps up about 20 em and thereafter proceeds to execute a vertical oscillation

SPIKE IRON STAND

"\!'-"" __ h MAGNET UNDER -!-""- TABLE

ij.--

b....

- C1 POWER FOOT SWITCH

Fig. 3. Jumping Ball.

with no other assistance from the demonstrator who has retired to a "safe" distance.

The secret lies in suspending a brass weight (about 150 gm) by a loop of thread from the yoke at the top of the tube. The tube weighs about 75 gm. The fuse is simply a match which, on being ignited by another match, slowly burns until it destroys the loop of thread holding the weight. For a brief interval of time, the brass weight descends with acceleration g and the tube ascends with (initial) acceleration 2g, since the initial force stretching the spring was 225 gm. f. The equality of impulses imparted to weight and tube is demonstrated by the equally sudden stopping of the vertical rise of the tube when weight and tube come together again.

An informative variant of this experiment is to sup-port the "firecracker," (without the spring) ready for action, on a carefully balanced Atwood's machine. The balance is momentarily destroyed when the weight is released by burning the thread loop, the firecracker

MATCH FUSE

TALL STAND

FLEXIBLE SPRING

LOOP OF THREAD

I 50 GM. WEIGHT

75 GM. TUBE

Fig. 4. "Operation Bootstrap."

takes a sudden jump upward as the counter balancing weight descends, but the whole system stops dead as suddenly as it started.

17

The use of this simple system for quantitative ex-periments, problems, and deeper insight into impulsive forces and momentum exchanges is evident.

(5) "Oscillation of a Hydrometer." If a hydrometer floats in a tall graduate full of water, it will oscillate vertically if depressed and released, albeit the oscilla-tion is highly damped. If the same hydrometer were supported by a rubber band from the hand and the hand were moved up and down rhythmically, the hydrometer would oscillate relative to the hand. But if the graduate full of water in which the hydrometer floats is oscillated vertically, the hydrometer does not move relative to the hand.

This simple observation, easily performed, is "for the space age" since it shows that buoyancy depends upon the gravitational field and that acceleration and gravity (if in the same direction) are indistinguishable from one another, as pointed out so firmly by Einstein. In this case, the "weight of the hydrometer" is m(g ±a) where +a is for acceleration upward, -a downward. But the buoyancy of the liquid likewise depends upon the weight of the liquid displaced, and this is also always m(g ±a). "You can't win" unless you jerk the graduate downward with acceleration greater than g, thus leaving liquid and hydrometer behind!

(6) "Vibration of a Teacup." This is a simple con-tribution to physics of the dinner table, showing as it does something about the modes of vibration of a teacup.

If the rim of any teacup is struck a gentle blow at a point opposite its handle, it gives a more or less musi-cal note. But if it is struck at a point 450 from the first spot, the pitch of the note is higher. The explanation is not far to seek: In the first instance, the handle is situ-ated at a loop of vibration, and the inertia of the vibrat-ing system is greater than in the second case, where the handle is situated at a node and does not partake in the motion.

As many had not seen it in operation, the author showed the conference his apparatus for demonstrating the equality of action and reaction and the conservation of angular momentum, as described in A. J. P. 26, 580, 1958. -

OPEN -AIR ALPHA COUNTER

Harold M. Waage, Princeton University

Mr. Waage demonstrated the open-air alpha particle counter which won third prize at the January 1959 AAPT Apparatus Competition.l

Because of its simple construction and the fact that the alpha particles are both audibly and visually appar-ent to a large audience, this equipment is of value to the demonstration lecture.

The following is a brief description of the apparatus. The counter, Fig. 1, consists of a ten kilovolt rf voltage supply, a coaxial cable, a fine wire grid and back plate housed in a lucite frame and optical bench parts for mounting both the lucite frame and the holder carrying an alpha particle source. The lucite frame is packed with a small piece of masonite protecting the wire grid.

1. Held in New York at the joint meeting of the AAPT and APS, January 29-31.

18

Fig. 1. Open-Air Alpha Counter.

A weak alpha source is on a small piece of wire in a small glass rod which passes through a cork in the en-closed bottle. A clip clamp on a 3/8 in. rod is mounted on one of the riders and serves to hold the alpha source in a horizontal position toward the wire grid. The knob on the rf voltage supply is advanced slowly until the meter shows about 4500 volts. Beyond this voltage sparking will occur spontaneously. The operating point is just below that voltage. The source is kept at a dis-tance well within the range for alpha particles in air (which is of the order of 3 or 4 em).

DEMONSTRATION MODEL OF MAGNETIC DOMAINS

Virgil E. Bottom, McMurry College

Our present understanding of ferromagnetism is based upon the theory of magnetic domains. A domain is a region in a ferromagnetic material in which the magnetic moments of the atoms are substantially paral-lel. In an unmagnetized specimen the domains are ar-ranged so that the net magnetic moment of the specimen is zero.

When a magnetic field is applied to the unmagnetized ferromagnetic material, two processes take place. (1) Some domains grow at the expense of their neighbors, i.e., domain boundaries move, and (2) The magnetic moments within a domain rotate into more favorable directions with respect to the applied magnetic field.

Both of these processes are illustrated by the follow-ing demonstration: Four or five small sintered magnets of the type commonly used with iron bulletin boards are finely powdered by crushing in a vise or with a hammer and anvil. The particles should be about the size of fine sand. Although perfectly dry, these finely ground parti-cles adhere together as if they were wet because of the tendency of each particle to minimize its potential en-ergy relative to its neighbors. The net magnetic mo-ment of the mass is zero as may be seen by holding a compass needle near by.

A thin layer of the particles is sprinkled onto a glass or plastic plate using an ordinary salt shaker. The par-ticles arrange themselves into small islands as they fall, each island having negligible magnetic moments as indicated by lack of attraction for others.

The plate with the magnetic powder is so arranged that its image may be projected on the ceiling or a screen. A compass needle in a transparent plastic case

brought near the plate indicates no magnetic moment. A uniform magnetic field supplied by a large electro-

magnet or by a radar magnet with wide pole pieces is arranged so that the direction of the field is in the plane of the plate. As the field is slowly increased some islands grow at the expense of others. As the field is further increased whole islands break away and rotate with respect to the field illustrating the Barkhausen effect.

If the field is uniform, little or no translation of the powder occurs, but if the field is non-uniform, as is more likely, some migration of particles will occur.

After the magnetic field has been removed, the pow-der retains a strong permanent magnetic moment as shown by the compass needle, thus demonstrating per-manent magnetization.

The slight elongation of the area covered by the pow-der in the direction of the field is suggestive of the magnetostriction effect although the change of dimension in the direction of the field is often negative, hence the name magnetostriction.

Reversal of the field direction causes 180° rotation of many of the "domains." The frictional forces in-volved simulate the energy losses due to hysteresis.

In answer to questions, Dr. Bottom stated that the magnets do not appear to be seriously demagnetized by the "grinding" process. He places a magnet on an anvil and pounds it to pieces with a hammer. There is no tendency to splatter all over the room because the frag-ments cling to the anvil and hammer.

19 CORRIDOR DEMONSTRATIONS

Harald C. Jensen, Lake Forest College

The physics museum is not a new technique for arousing interest in physics and providing information and instruction related to physics. The museums at the University of Chicago, the University of Wisconsin and the Museum of Science and Industry in Chicago are some rather famous examples. They are, however, rather formal, semi-permanent and, in general, represent rather large expenditures of money.

The corridor demonstrations described on the sheets to be passed out to youl constitute a slightly different approach to the museum idea and, as a result, serve somewhat different functions. While they d.o supplement the Classroom and laboratory instruction in physics in an informal manner, their principal purpose is to catch the attention of the casual passer-by and to promote in-terest in physics. We have used these corridor demon-strations at Lake Forest College for several years and know that they continue to attract favorable attention. It is hard to show whether or not they induce any perma-nent interest, but one can always hope. They do tend to show that the physics department itself is alive and in-terested in physics.

At Lake Forest College the demonstrations are pre-sented on a shelf 14 inches wide and 30 inches long mounted on a wall in the corridor at waist height. It is located near the foot of the main flight of stairs and in the vicinity of the water fountain. The location is such that anyone using the building finds it difficult to avoid the shelf and the displays mounted on it.

An electrical outlet, compressed air jet and gas jet are available near the shelf. If water is needed, it can be secured at the fountain. A small bulletin board is attached to the same wall at eye level just over the shelf so that instructions for operating the apparatus are near at hand.

It must be emphasized that the shelf is entirely in the open. No exhibit or museum case is used. Several years' experience have shown that one is not necessary at our school. No item has ever been taken from the shelf nor has any damage beyond that involving ordinary

wear been inflicted on the apparatus placed on the shelf. The openness of the exhibits has proved to be one of the most important interest-attracting characteristics of this endeavor. The persons attracted to the shelf are not only allowed to manipulate the apparatus but are ac-tively encouraged to do so by the operating instructions. The various displays and demonstrations have been selected and planned so that the observer becomes the demonstrator. In fact, the title of the entire project is "Play With This." Our experience indicates that stu-dents appreciate this opportunity.

It must be noted that the displays are changed every week. It is fairly apparent, I believe, that change is necessary if a continuing interest on the part of the ob-servers is to be maintained. We have been successful in developing enough displays so that, at the rate of one per week, no repetition is necessary over a two year period. That is to say, we have at present a library of about fifty displays. New displays are constantly sought and ones used previously are being modified to eliminate the aspects shown by experience to be undesirable.

The present form of the project is a result of trying to use the museum idea in the most inexpensive and convenient manner possible. As it has turned out, how-ever, the factors contributing to low cost and conven-ience-that is: relative simplicity and ease of opera-tion-have been those which have contributed in large measure to its success.

Before concluding and putting the descriptions! of the individual displays used at Lake Forest into your hands, I must disclaim any attempt at originality. Most of the demonstrations are well known. Several of you will notice that your contributions to the demonstration art are being used by us. Professor Sutton's book has been the mainstay for our efforts. Any modification has been only in the direction of attempts to make the apparatus tamper-proof so that the untrained observer is able to operate the displays without endangering either himself or the apparatus.

SURF ACE TENSION AND STOKES' LAW

Eric M. Rogers, Princeton University

I. SURFACE TENSION; "RAIN ON FIBERS OF WATERPROOF FABRIC"

Texts give diagrams to show how water is held back by fibers of fabric with which it makes a large angle of

contact. Instead of sketching "what should happen," I find it quicker to show what does happen, by projecting a model (see Fig. 1) with real water. Waterproof fibers are represented by rods of black bakelite about 3/8" diameter coated with a thin layer of paraffin wax. Half

1. Many of these descriptions were taken directly from: Demonstration Experiments in Physics, R. M. Sutton (McGraw-Hill Book Company, Inc., New York, 1938). M-292, S-17, S-37, S-42, H-9, E-120, E-136, E-156, E-256 and L-94 were included. The complete set of descriptions may be secured by writing to the Physics Department, Lake Forest College, Lake Forest, lllinois.

20 a dozen rods are pushed through holes in the face of a thin lucite tank that fits in a projection lantern (see Fig. la). The rods are seen end-on as black discs spaced about 1-1/2 diameters apart along a shallow curve (see Fig. lb). Water (tinted to make it visible) is allowed to flow into the tank from a reservoir. When

Fig. la.

Fig. lb.

it rises to the rods, the flow is slowed so that the audi-ence can watch the stages of water creeping through the "barrier" of waterproof rods. Since it is projected, the water appears to descend from above, and I explain that the black discs represent sections through fibers of my umbrella, on a greatly magnified scale. The water /air surface makes a large angle of contact with the rods, and as the rain descends the water bulges through be-tween the rods clearly restrained by surface tension.

The water ·is removed, and treated with a little wetting agent (e.g., a few drops of 10% Aerosol 0. T.) so that the angle of contact is small. Then when the water reaches the rods it clings to them, and quickly runs through.

With careful washing the rods become waterproof again; but it is better to re-proof them by dipping them in molten wax.

II. STOKES' LAW DEMONSTRATION: FREE HELP FROM THE DRUG-STORE

We can demonstrate terminal velocity by dropping small steel balls in viscous liquid, but we cannot show directly that the friction-drag varies directly as veloci-ty, because when we change to a ball of different weight we also change its size. However, we can now make uniform streamlined objects by using medicine capsules

loaded with small steel balls. The capsules are made of gelatin, intended to dissolve when the patient swallows them. Glycerin will soften them in a few hours, but mineral oil does not affect them.

Several capsules are opened, immersed in oil to re-move bubbles and then reassembled under oil. (One half slides on to the other but I find I must push hard for sometime-the clearance is close and mineral oil is viscous).

One capsule is loaded with a single steel ball inside (e.g., 1/16" diam.); another with 2 balls, another with 3, etc. The loaded capsules are allowed to fall in a tall transparent tank of (the same) oil. With no loading, a capsule with oil inside and outside is practically "weightless," buoyancy and gravity nearly balancing. The loads of 1, 2, 3, ... steel balls provide gravity pulls in proportions 1:2:3: .... If Stokes' law holds, the capsules should fall with terminal velocities in propor-tions 1:2:3 .... They do.

By holding the tank in a projection lantern we can show the loading of the capsules clearly. (Better still, we can have students do the experiment themselves.)

Fig. 2.

The best tank is a large rectangular box of lucite. With a backing of translucent screen illuminated from behind, the capsules are clearly visible. The tank must be wide enough to keep the falling capsules far from the walls (and from each other) or the motion is modified.

The capsules are not expensive and are now so widely used that a drug store will usually give a dozen to a physicist, free.

III. MODEL TO ILLUSTRATE PRECESSION OF EQUINOXES

Many gyroscope experiments show precession beauti-fully; but in discussing precession of the equinoxes some students find it difficult to see the connection between the model's behavior and the case of the earth. The only

21

virtue of the following model, is that students seem to find it clearer as an illustration of the earth's motion.

A small demonstration gyroscope has its outermost frame removed, so that it has two free axles: the spin axle of the wheel and the axle of the remaining frame that carries the wheel (see Fig. 2, pg. 20). A piece of stout wire is bent to form a loop with hooks to carry that outer axle. The wire is hung on a long string so that the outer axle is horizontal and free to turn around the ver-tical by twisting the string. The wheel is then made to spin fast (by an electric motor) and set with its axis pointing in some tilted direction. It remains pointing in that direction. Then a rubber band is suddenly installed, pulling one end of the outer axle towards the center of the wire loop, thus trying to rock the wheel about the outer axle. Instead, the wheel precesses. If the rubber band is removed the precession stops.

THE FUNDAMENTALS OF TRANSIENTS IN ELECTRICAL CIRCUITS

J. Irvin Swigart, University of Utah

Nearly all university physics texts discuss transient currents in circuits containing combinations of any two or all three of the elements of resistance, inductance, and capacitance. The derivations given usually express the current, i, as a function of the applied potential dif-ference, V; the resistance, R; the inductance, L; the capacitance, C; and the time, t. Calculations of the transient potential differences between the terminals of any component in the circuit as a function of time may then be derived from fundamental definitions; e.g., the potential difference between the terminals of a resistor is -iR, the potential difference between the terminals of

di an inductor is -L dt, and that between the terminals of

a capacitor is - ~ J idt.

Visualization of these principles seems to be im-proved by the use of circuit boards which have been con-structed for the purpose of demonstrating to large classes some of the basic transient phenomena in elec-trical circuitry.

Large scale circuit diagrams are drawn on boards that are 14" X 22" mounted on a base that stands on the lecture table, with the upper edge of the board tilted back 30° from the normal to the surface of the lecture table. The circuit elements, or components, of each board are mounted on the back of the board; and their manual controls extend through to the front, which faces the class. Their height allows the demonstrator to stand back of the lecture table and reach over the tops of the boards to adjust the controls and to point out de-tails while demonstrating the circuits.

The three basic circuits demonstrated at the Wes-leyan Conference on Lecture Demonstrations are:

1. The R-L circuit (circuit containing resistance and inductance), Fig. 1 (b), consists of:

V 3 v flashlight battery Ro 0 Q to 25,000 Q , 2 watt variable resistor R1 0 Q to 10,000 Q , 2 watt variable resistor R2 Ro + Rl L 2 (4-henry), low resistance, filter chokes with

S P D T switch

(a) (b) Fig. 1

2. The R-C circuit (circuit containing resistance and capacitance), Fig. 2 (b), consists of:

V 3 v flashlight battery R1 R2 0 Q to 10,000 Q , 2 watt variable resistor

C .005 JJ.f to 1.0 JJ.f capacitors varied by a multipoint rotary selector switch

22

(a) (b) Fig. 2

3. The R-L-C circuit (circuit containing resistance, inductance, and capacitance), Fig. 3 (b), consists of:

V 3 v flashlight battery C .0005 J.J.f to . 5 J.J.f capacitors varied by a multi-

point rotary selector switch R 0 Q to lO,OOOQ , 2 watt variable resistor L 2 (4-henry), low resistance, filter chokes with

S P D T switch

(a) (b) Fig. 3

The switch used to open and close the various cir-cuits is a high pressure mercury -wetted contact relay. The particular one used here is a Western Electric Re-lay, type 275C. Its entire mechanism is mounted in a standard octal base, metal tube. This relay tube is mounted in an upright position on the wooden base at the rear of the board. The octal base is connected as shown in the schematic diagram, Figs. 1 (a), 2 (a), and

3 (a). The coils of the relay (terminals 5, 6, 7, and 8) are connected, as indicated in Fig. 1 (a), in series with a germanium diode rectifier, D; a 60 cps, 120 v line; and a 6,000 ohms to 10,000 ohms, 2 watt regulator re-sistor, R. The coils of the relay are thereby energized by the output of a half-wave rectifier operating at 60 cps. During the conducting half of the cycle, the S P D T switch is closed in one direction; and during the non-conducting half of the cycle, the switch is closed in the opposite direction. Thus, the S P D T switch is oper-ated at a frequency of 60 cps.

Binding posts are placed at various points in the cir-cuit diagrams on the fronts of the boards and connected to the corresponding points of the circuit elements on the rear sides. The transient potential differences be-tween various points of interest in the circuits are dis-played on the screen of a cathode ray oscilloscope, whose vertical input is connected to the binding posts on the fronts of the demonstration boards, and whose sweep is synchronized on the a. c. line frequency.

Several different transient potential differences can be displayed on the oscilloscope from each of the three circuit boards. Figs. 1, 2, and 3 show a single demon-stration from each of the three circuits as they were presented in the Conference on Lecture Demonstrations at Wesleyan University. The lower left of each figure shows the switching circuit which has been described.

Figure 1 (b) shows the R-L circuit board described in a preceding paragraph. The chart just above the board sets forth the equations of the transient currents during the cycle of operation and of one of the transient potential differences. The values calculated from these equations are plotted in the graph at the lower right of Fig. 1 (b) and are experimentally displayed on the oscil-loscope at the top of Fig. 1 (a).

Figure 2 (b) shows the R-C circuit board described formerly. The chart above this circuit board presents the equations of the transient potential differences be-tween the terminals of the capacitor during a cycle of operation. The values calculated from these equations are graphically represented at the lower right of Fig. 2 (b) and are experimentally demonstrated on the oscil-loscope in the upper part of Fig. 2 (a).

Figure 3 (b) shows the R-L-C circuit board previous-ly described. The chart above establishes the mathe-matical relationship of the transient currents in the circuit during a cycle of operation to the potential dif-ferences due to the back electromotive force of self-induction in the inductor. This is interpreted geometri-cally in the lower right of Fig. 3 (b) and indicated ex-perimentally on the oscilloscope in the upper left of Fig. 3 (a).

The close agreement between the graphs of the theo-retical equations plotted in the lower right of each figure, and the experimental display on the oscilloscope observed at the upper left of each figure, give confidence to the student and satisfaction to the lecturer.

23

MICROWAVE EQUIPMENT AND DEMONSTRATIONS

C. L. Andrews, State University of New York, College for Teachers, Albany

The purpose of this paper was to call attention to new microwave oscillators and detectors, to discuss a micro-wave demonstration that has not been presented to the American Association of Physics Teachers before, and to treat an old demonstration about which the question has been asked, "Does it really work?"

OSCILLATOR

For some years the author has tried to make a quarter-wave mode cavity-oscillator to replace the three-quarter wave ones used with the 2C40 disk-seal triodes at 2450 megacycles/sec, but the brass fingers made by slotting the cylinders with a milling machine were necessarily too short and stiff. Collapsed toroidal springs were found to make superior microwave cavity contactors.1 Figure 1 shows a collapsed toroidal con-tactor held on a tube about to be inserted in the cavity.

Fig. 1. Collapsed toroidal spring contactor on disk-seal triode tube being inserted into oscillator cavity.

These collapsed springs made three sets of forty posi-tive contacts with the grid ring, forty butt contacts with the cathode shell and forty sliding contacts with the cy-lindrical wall of the cavity. In all previous oscillators which the author has designed for educational use, the user was requested to twist the tube in the cavity to the position of maximum output. As we turned the tube in the cavity with the toroidal spring contactors, the output power remained constant. The shorter quarter-wave-length cavity permitted putting the oscillator2 in a small metal cabinet which shielded in the microwave power

1. C. L. Andrews, Jour. Appl. Physics 26, 777 (1955). 2. No. 80422, Central Scientific Company, Chicago. 3. Crystal Diode 1N82A, Sylvania Electric, Boston.

that was previously radiated from the base of the light-house tube.

DETECTOR

Heretofore the only sensitive microwave crystal de-tectors were the silicon crystals in capsules with mas-sive brass ends designed to fit into waveguide measuring equipment. Crystal detectors with wire leads were less sensitive by a factor of 50. Recently silicon crystals in glass capsules with wire leads and sensitive for the microwave region have been made available3 at a frac-tion of the cost of previous microwave detectors. These crystals were fastened across the backs of microam-meters to make intensity meters and mounted at the ends of wooden dowels to serve as both antennas and de-tectors. A twisted line indicated in Fig. 2 was soldered close to the glass capsule and extended to a microam-meter, oscilloscope or audio amplifier.

GLASS CAPSULE

Fig. 2. Microwave probe.

DOPPLER EFFECT

A demonstration which the author has used for fifteen years but has not been shown at the meetings of physics teachers is the microwave Doppler effect. The trans-mitter and receiver were set side by side as in Fig. 3. In this case some power is transmitted directly to the receiver. If mirror M was moved toward or from the source, the moving image source transmitted a Doppler frequency which was beat with the frequency of the pri-mary source. The beat frequency was observed to be proportional to the speed of the mirror toward or away from the source.

24

MICROWAVE MIRROR

""~ Fig. 3. Arrangement for demonstrating Doppler

effect with microwaves.

THIN FILMS

The author has received recent requests about thin film demonstrations with microwaves, "Did they really work?" If the index of refraction of the film and the corresponding surface reflection were sufficiently high, the interference pattern of the transmitted light showed high contrast either for light or microwaves. Glass and Transite with indices of refraction of about 2.5 gave high contrast. Polystyrene and Plexiglas with indices of refraction of about 1.5 were not satisfactory for thin film demonstrations.

Figure 4 was an arrangement for measuring trans-mission by stacks of sheets of window glass which served as thin films. The thickness of the glass "film"

I METAL SHIELD

DIELECTRIC ~SITY METER

OSCILLATOR

Fig. 4. Arrangement for demonstrating interfer-ence of microwaves in thin films.

was increased in steps of 1/8 inch and the transmitted intensity plotted. Glass sheets of finite width, 5 inches by 8 inches, gave a diffraction pattern. To keep the dif-fraction effect constant, the sheet of metal with a 4-inch aperture was mounted as a support for the first sheet of glass. As the number of sheets was increased to five, the transmitted intensity decreased to a minimum. In-creasing the thickness by another five sheets restored the transmission to nearly 100 per cent. Another five sheets gave a second minimum of transmitted intensity.

We may note an application of the quarter-wave filter in the new oscillator. To reduce the leakage of micro-wave power by way of the plate lead, a brass cylinder as part of the plate lead was covered with a dielectric "spaghetti" which was a quarter wavelength long for the wave in the dielectric. This in turn was slipped inside the brass tube which may be seen protruding from the side of the oscillator cavity in Fig. 1. This reduction of leakage increased the power through the antenna.

It is hoped that this paper will encourage exchange of ideas that will convert satisfactory microwave demon-strations into outstanding demonstrations.

IMAGES WITH A CALCITE LENS

I. Walerstein, Purdue University

The ordinary demonstration of the double images seen through calcite is usually followed by an explana-tion involving the two indices of refraction for this and other uniaxial crystals. To convince students that this is not merely a bit of sophistry but is physically real, other experimental demonstrations should be adduced. One of these can be the observation that a crystal which has been polished with two faces parallel to the optic axis will show two apparent depths. This experiment is best done by observing through a microscope and does not lend itself easily to a demonstration for a large class, since the two images are only slightly separated. If one has already gone to the trouble of polishing a face of a calcite crystal parallel to the optic axis, it then be-comes more profitable not to polish another plane face parallel to the first but to make the second face a spheri-cal surface. We then have a plano-convex lens of cal-cite. Such a lens can be used to give a convincing dem-onstration experiment proving that calcite has two dif-ferent indices of refraction. It is also possible to get the values of n0 and ne.

Demonstration. A diaphram with a cross cut in it has been found to serve well as the object for this lens. The cross is illuminated by a projection lamp and the calcite lens of about twelve inch focal length is placed in front of it. As the lens is moved away from the ob-ject, a position is found where a sharp enlarged image appears on the screen. Object and image distances can be measured, the focal length deduced, and knowing the curvature of the spherical surface, the value of n can be calculated. If now the lens is moved still further from the object, a second sharp enlarged image will appear on the screen. Measurements similar to those taken previously will now yield a second value of n.

If a polaroid is inserted between the object and the lens, it can be shown then that for one orientation of the polaroid, one of the images is effaced and for the 90° position of the polaroid the other image disappears. It is well at this point to replace the calcite lens by one of glass and of approximately the same focal length to show that there is only one position for sharp imaging of the object and no effect on the part of the polaroid.

It should be observed that when the calcite lens is in a position to give a sharp outline of one of the images, a blurred appearance of the other image may appear superimposed. It will, of course, not be eliminated when the polaroid blocks out the sharp image.

Even if the radius of curvature of the calcite lens is

25

not known, the ratio of (ne - 1) / (n0 - 1) can be com-puted. If the lens is tilted with respect to the incident light, two images (neither of them very sharp) will appear.

This demonstration is convincing proof of the exist-ence of two indices of refraction for calcite.

OPTICAL EFFECTS WITH WATER RIPPLES

V. E. Eaton, Wesleyan University

One of the standard exercises in the general physics laboratory is the measurement of surface tension but it .is generally assumed that accurate results are not to be expected. Believing that poor results are not necessary I assigned to a superior freshman a few years ago the special project of measuring the surface tension of water in all possible ways to determine which gave consistent and dependable results. Since, as I learned later, there are almost a hundred ways of measuring surface tension this was of course a naive assignment. However, this project led to the conclusion that the best results came from measuring the velocity of capillary waves.

Using this method, our students obtained excellent results and later improvements converted it into a re-search piece giving at least four and perhaps five sig-nificant figures. It has also given excellent results in the study of mono-molecular layers and the determina-tion of the cross-sectional area of certain fatty-acid molecules. Our task at this conference is not, however, the improvement of laboratory procedures or the de-velopment of research apparatus. I shall explain, there-fore, how we use this ripple tank to demonstrate certain wave phenomena in the large lecture class in general physics.

A schematic diagram of the apparatus is shown in Fig. 1. The wave generator V is constructed from a telephone harmonic ringer. This ringer has a natural frequency of 66-2/3 cycles per second, but when the vi-brator is properly loaded it will resonate on the 60-cycle power supply. Sheet rubber couples this vibrator to a strip of metal which dips into the tank of water. For best results this metal strip should be bent to form a cylindrical boss on the front surface.

Each wave acts as a cylindrical lens and forms a line image of the point-source of light L on the screen above. These images move rapidly across the screen but with stroboscopic illumination may be made to stand still or move slowly. The stroboscope consists of a motor M equipped with a disk D having a pair of slits on opposite ends of a diameter. For lecture demonstra-tions M is a variable speed motor. For quantitative work a synchronous motor is used and the waves may be recorded photographically by using a large sheet of photographic paper for the screen. Figure 2 was made this way on a 16" x 20" sheet of F-4 Kodabromide paper.

The images may be brought into sharp focus by ad-justing the amplitude of the waves. The amplitude is controlled with the auto-transformer T, Fig. 1. When the crest of a wave has the proper curvature for a sharp image a fine line is formed. For a curvature less than this, the line is somewhat diffused. If the curvature at

rY~ I<

Fig. 1. Schematic Diagram of the Stroboscopic Ripple Tank.

Fig. 2. Waves Generated by a Straight-Line Source.

26

the crest is too large, there will be two places on the wave, one on each side of the crest having the proper curvature and two images will be formed by each wave. Examples of these effects are found on all of the figures 2 through 7.

In Fig. 2, for which a straight line source was used, it is clear that the images are sharp and the wave length can be measured with considerable accuracy. To deter-mine the wave-length the scale K, Fig. 1 is placed in the tank and the ratio )l /S determined by measuring the shadow of scale K on the screen. Although it is not serious it is obvious that there is some attenuation of these waves.

In Fig. 3 the source is curved and the waves are brought to a focus at the center of curvature of the

Fig. 3. Using a curved source the waves are fo-cussed at the center of the curvature.

dasher. It can be seen that the amplitude of the wave is greater at the focus than at the source. If the curva-ture of the source is properly chosen the increase in amplitude due to focusing may just balance the decrease in amplitude due to attenuation. This is particularly important when studying mono-molecular layers on the surfac~ of water.

The apparatus may be used to show various inter-ference effects. In Fig. 4 the waves come from two point sources vibrating in phase. A couple of escutcheon pins soldered to the vibrator, the heads dipping into the water, serve as a source.

Using ten point sources the interference pattern shown in Fig. 5 is produced. A similar pattern is

Fig. 4. Interference Pattern with Two Point Sources.

Fig. 5. Interference Pattern with Ten Point Sources.

shown in Fig. 6 but it is produced by a diffraction grat-ing. In this case "plane" waves enter from the top and after passing through the slotted barrier interfer as predicted by Huygens' principle. The interference "fringes" between the "plane" waves is significant in both figures five and six.

In Fig. 7 a very interesting diffraction pattern pro-duced by a single slit is shown. It can be seen that waves radiate in all directions from the slit with a strong band directly ahead and weaker bands on each side.

It has been my experience that demonstrations of this sort are more convincing where the students can see the wave fronts than are the experiments where the students see simply the fringes which represent the integrated effect of the various waves. In other words physical optics has a certain advantage over geometri-cal optics in visualizing interference patterns.

27

' '''!'

Fig. 6. Diffraction Grating. Fig. 7. Diffraction by a Single Sli t .

SessionIII. DEMONSTRATIONTECHNIQUES

Presiding: B. F. Wissler

LARGE SCALE LECTUREDEMONSTRATIONAPPARATUS

R. W. Kenworthy, Universityof Washington

There are certain types of demonstrations which re-quire apparatus of large size if the progress of the demonstration is to be visible to members of a large class. Over a period of years we have developed a num-ber of pieces of large scale apparatus which we have found highly satisfactory. In the descriptions that fol-low, no claim of originality is made, and nearly all pieces can be duplicated by any apparatus technician. The accompanying illustrations indicate the types of some of the equipment.

Figure 1 illustrates a large force board for the reso-lution or composition of forces. It is made of a piece of

Fig. 1.

plywood four feet square mounted in a vertical position so that it may be clamped flush with the edge of the lec-ture table. A small removable peg in the center of the board prevents large displacements while adjustment of weights or their positions are being made. The combi-nation of forces that may be used is limited only by the ingenuity and patience of the demonstrator.

Figure 2 illustrates a metal incline about twelve feet long which is used for two purposes; viz.: (a) to illus-trate the laws of uniformly accelerated motion, and (b) to show that the velocity at the foot of the incline is proportional to the square root of the difference in the heights of the two ends. For the first purpose the angle of the incline is adjusted so that a steel ball rolls down the incline with a linear acceleration of 16 cm/sec^2. A number of small lamps have been mounted along the in-cline at distances of 8 em, 32 em, 72 em, 128 em, etc. from the point of release of the ball. The lamps are flashed at one second intervals by a synchronous motor-driven timer. Students observe that the ball is at the

31

Fig. 2.

position of each lamp when that lamp flashes. The data serves to illustrate clearly the relations between dis-tance, velocity, time and acceleration in the equations of uniformly accelerated motion.

For the second purpose, the time of descent of the ball is measured with a hundredth second timer which is started at the instant the ball is released, and stopped when the ball strikes a micro-switch near the bottom of the incline.

The buoyant force on a body immersed in a liquid can be very clearly seen with the apparatus shown in Fig. 3. The scales are of the type used in produce markets, they are about fourteen inches in diameter

Fig. 3.

and have a weight limit of 3 0 pounds. When the object (metal cylinder) is immersed in the jar of water on the lower scale, i t is clearly evident to the student that the

32

decrease in reading of the upper scale is exactly equal to the increase in reading of the lower scale.

There are several va r i e t i e sof apparatus to demon-strate projectile motion. The one illustrated in Fig. 4a consists of a spring gun which fires a small wooden ball

Fig. 4a.

a maximum distance of about 20 feet. It is used to show two important characteristics of projectile motion, (a) the variation of range with angle of elevation, and (b) that a ball dropped from a point along the line of sight at the instant of firing will collide with the fired ball.

Some details of the spring gun may be seen in Fig. 4b. A coil spring is mounted on a hollow tube for accuracy in sighting, and is held in a compressed position by a simple notched trigger mechanism. The fired ball knocks a fine wire from the semi-circular mounting,

Fig. 4b.

which opens the circuit to the electromagnet so that the second ball is released. Collision occurs between the two balls in a large percentage of the firings.

The thread screen shown in Fig. 5 for demonstrations in optics is certainly not a new device, but its effective-

Fig. 5.

ness seems not to have been recognized. It consists of a series of fine vertical threads of white silk or cotton, spaced 2 or 3 mm apart on a rectangular wooden frame. A size of 80 or 100 em square is very convenient. Lenses or sections thereof may be inserted between the threads, and mirrors can be mounted on the framework. A distinct advantage of the screen is that both instructor and student can see directly through the screen while the demonstration is in progress.

The use of the screen to show the focusing effect of a concave mirror is shown in Fig. 6.

Fig. 6.

Figure 7 illustrates the formation of a real image in space by a large (14 inch aperture) concave mirror in such a manner that it may be seen by at least one-third

Fig. 7.

of a large class. A lighted candle placed at the center of curvature seems to be burning at both ends. The mirror is mounted on a small table with casters so that it may be rotated in front of the class. (The mirror was obtained from a military surplus searchlight.)

Interference effects in a thin film may be shown on a large scale by two pieces of plate glass about 6 by 60inches, mounted at 4 5 with the vertical on a black back-ground. When illuminated in a darkened room by sodium light diffused vertically downward through a ground glass plate, interference fringes irregularly spaced from a millimeter to several centimeters apart may readily be seen by the entire class. Such a system is illustrated in Fig. 8.

Fig. 8.

The shallowing effect of refraction can be strikingly shown with a large block of glass having a high index of refraction. The one illustrated in Fig. 9 is about 3. 5 by 12 by 15 inches, and is a special lead glass whose index of refraction in approximately 2.

A demonstration of the time delay for the current to reach its maximum value in a circuit wi th a large self-

33

Fig. 9.

inductance can be very effectively done wi th the equip-ment shown in Fig. 10 . It consists of a 3 volt battery, a milli-ammeter and a coil wi th an extremely large self-inductance. The t ime for the current to reach a maximum value of about 23 milli-amperes is approxi-mately 25 seconds. Under these conditions the calcu-lated coefficient of self-inductance is 700 henrys! The coil was obtained from military surplus and is labelled "Retard Coil"; apparently i twas designed to be part of a high-voltage filter circuit.

A number of other types of large scale apparatus are used which are not illustrated, of which a few are:

(a) A Foucault pendulum about 24 feet long. Dur-ing the lecture period it has an apparent change of di-rec t ion of about 100, which is indicated by the movement of its shadow along the wall.

(b) A 21 inch oscilloscope, which may be built ac-cording to the published circuits, or a "slave scope" operated by a much smaller oscilloscope.

Fig. 10 .

34

(c) A free-fall apparatus with a hundredth second timer, micro-switch and electrical release.

(d) A Van de Graaff generator with long narrow strips of paper fastened around the circumference to illustrate a radial electric field about the sphere of the generator.

Some pieces of large scale equipment must be per-manently mounted on tables with casters; this requires storage space which may not be readily available. This should be a point for consideration in planning for new construction.

Our lecture halls are so designed that no student sits farther than sixty feet from the lecture table; most of them are within fifty feet. With normal vision they should be able to resolve objects which have a separa-tion of 0.2 to 0.3 inches, and be able to see all details in the apparatus which has been described.

There is a distinct psychological advantage to the student to be able to actually observe the progress and details of a demonstration experiment. We feel that this is a compelling reason for the use of as much large scale apparatus as is feasible.

DISCUSSIONfollowing Dr. Kenworthy's paper

Q. What must be the scale of this large apparatus to be clearlyvisible to all students in large demonstration lecture rooms? The apparatus manufacturers as well as the physics departments building equipment need this information.

A. According to the llluminating Engineering SocietyHandbook, persons with normal vision can distinguish details of black objects on whitebackground which sub-tend at l eas tone minute of arc at the eye. At forty feet, detail below about 1/4 inch in size is not detected and letters or numerals should be approximately 1-1/2 inch in height for good visibilityat this distance. At eighty feet, and we have lecture rooms of this dimension, the size of these features should be doubled.

Comment: Many lecturers s t i l luse miniature apparatus and the students, other than those in the front seats, can only s i tand guess what is going on at the demonstration table.

Comment: Before the apparatus manufacturers can proceed, they need to know whether to build for 50 feet or 100 feet rooms. The trouble is if they build for 100feet rooms, nobody would have space to store the ap-paratus.

Q. I'd like to ask Dr. Kenworthy about storage. I know you are generously supplied (3,000feet2}. How much storage space is needed?

A. Storage is a problem, but much of our large scale apparatus is permanently mounted, that is, set up at all times.

Q . Don't you save money that way?

A. I think we do. We also save time. Now that we are involvedwith problems of one class following right after the other, the demonstrator sometimes has only ten minutes in which to clear the previous lecture apparatus and set up a new demonstration. Most of the new appa-ratus is put on movable tables to hurry the process. This also requires additional demonstration preparation room space.

Comment: The word "large" lecture room is not a very definite picture of the problem. It seems to me that one must know something about the angle of vision, that is, the width as well as the depth of the room.

A. Yes, you cannot spread out a lecture room wider tli.an a certain angle because of the angle of skew. The people on the outlying edges cannot see well because the angle is too oblique. A room for 300 people re-quires a depth of at least fifty feet.

Comment: There is another angle we must consider. That is the angle of elevation of the seats. In many cases, a rather large elevation angle is good. Many demonstration pieces can be better arranged and made more visible when the students look down on the lecture table rather than sit approximately horizontally with it. I have come to like a room which has seating elevation of nearly 30°. (The room has been referred to as the Grand Canyon.) At any rate, when demonstration appa-ratus is built, it must be designed differently for these two types of seating plans.

Comment: Anyone who has watched a lecture at Penn State and noted the effect of the colors which Schilling puts on the apparatus knows what color does for visi-bility and impression. It has all the color of the Grand Canyon. I put in a plug for bright colors and plenty of splash. It is a relatively inexpensive way to improve visibility and it gives an element of life to the lecture table.

Comment: Color does have an effect. If one has con-trasting colors one can get away with smaller size ap-paratus. For example, if one takes an ordinary meter stick and paints alternate centimeters yellow and red, an audience of 350 people can clearly see measurements. The same thing is true for other apparatus. You can get away with half the size of larger equipment if it's painted that way to show contrast.

Comment: For twenty years, I have painted meter sticks in alternating decimeters of different colors; black and white, red and white. I've lent them to many people, but I haven't found a single apparatus manufacturer

that sells them in this country, so we have to import from Europe or paint them ourselves. Something is wrong with our missionary department.

Comment: I don't want to take away from the fun of this afternoon but an awful lot has been said on building problems and of storage problem of large scale appa-ratus. These apparatus problems can be readily solved by closed circuit television. Just focus the camera on the little apparatus, say a five-inch meter scale, and everybody can see the pointer reading on the large scope. Apparatus is then small stuff which you can buy in the market and there is also no storage problem.

Comment: Some of our small scale problems can be solved by forethought. A balanced balsam wood pointer can be attached to the small pointer of a meter and the readings on an enlarged scale are visible all over the room.

Q. What are our reasons for wanting large scale equip-ment? We know these demonstrations can be made visi-ble by projection methods. Do we want this big appa-ratus because physicists like to work with things in the flesh? Is there something psychologically important about showing the demonstration directly rather than projecting the operation using a small model?

35

A. It is the difference between a stage play and a movie. Also in large scale you can go on staring at the thing and brooding about it. You see the real thing, and not a momentary projection.

A. I'd like to say that regardless of what you can do with electronic gadgetry, it does not take the place of seeing real wheels that turn. There is a reality in see-ing the real thing.

Comment: I'd like to mention one other scheme which we have been using more and more. A projection transparency can be made quickly with a Polaroid Camera. For example, you can get data on free fall by dropping a small neon flash tube, photographing the event with a Polaroid and a few minutes later, you can project this transparency and the students can take data from the projected image.

Suggestion: Would it not be a good idea for AAPT to study the problems of size, color, view angle, etc. of suitable demonstration apparatus and make recommen-dations based on such study? It is not a simple job but a big and very important undertaking which should be done right away.

METERS AND READ-OUT DEVICES

C. N. Wall, University of Minnesota

Demonstration lectures play an important role in the instructional pattern of the general physics courses at the University of Minnesota. These lectures, along with frequent written quizzes and a two-hour laboratory pe-riod each week, constitute the bulk of the course work.

The lectures are given in any one of four well-equipped lecture rooms each connecting directly with a central demonstration apparatus room in charge of two experienced apparatus men. These men are responsible for setting up demonstration experiments and for main-taining and improving demonstration apparatus.

This system enables us to handle enrollments of about 2000 students in our general physics courses. At times the system resembles a four-ring circus, but on the whole it seems to work reasonably well.

The success or failure of the system depends very much on the success or failure of our lecture demon-strations. Without effective demonstrations in the lec-ture, our physics courses would quickly degenerate into an authoritarian presentation of textbook material deal-ing exclusively with words and equations· instead of with

real objects and real processes. It is a never-ending struggle to keep this from happening, and hence, to keep students from misapprehending the true nature of physics.

We often have to assign to large lecture sections, new staff members who have had little or no experience in givinllecture demonstrations. For such members Sutton's book on Demonstration Experiments in Physics and Pohl' s2 books on Physical Principles are invaluable reference aids. In addition each lecturer is given a copy of our "Handbook of Lecture Demonstrations." This Handbook produced by George Freier, a member of our physics staff who has had a long and intimate experience with lecture demonstrations, lists some 350 demonstration experiments in physics for which appa-ratus is available. The experiments are classified ac-cording to subject material and consist primarily of a good free-hand sketch of the equipment and the process used in each of the experiments. We have found this Handbook to be extremely useful for all lecture demon-stration purposes. Although it was originally designed

1. R. M. Sutton, Demonstration Experiments in Physics (McGraw-Hill, 1938). 2. R. W. Pohl (tr. W. M. Deans),

a. Physical Principles of Mechanics and Acoustics (Blackie 1932). b. Physical Principles of Electricity and Magnetism (Blackie 1930).

Unfortunately, these books are now out of print. German editions are still available.

36

and produced for the use of our own staff at the Univer-sity of Minnesota, it would undoubtedly be highly useful as a reference wherever lecture demonstrations in physics are given. Hence we are trying to find a pub-lisher for it. A typical page of this Handbook is shown in Fig. 1.

5. DISPLACEMENT

6. SIMULTANEOUS FALL

7. MONKEY AND CANNON

Fig. 1.

T I

4' \ \ l_sz_

I tl' I

~

As is well known, demonstrations in physics before large groups of students present formidable difficulties. Ordinary laboratory equipment is not generally suitable for demonstration purposes because of its small size. One way of surmounting these difficulties is by use of large size apparatus. Professor Kenworthy has just described some such equipment used at the University of Washington. Another way of achieving the same end is by use of projection methods. Professor Pohl will describe some of these methods in the next paper.

In the remainder of this paper, I wish to describe briefly a few pieces of large scale apparatus which have proved to be quite successful in lecture demonstrations at the University of Minnesota.

The first is a large vacuum tube voltmeter. It was built eight years ago by F. E. Christensen, now Pro-fessor of Physics at St. Olaf College. This voltmeter consists essentially of the working movement of a Weston Station Meter (milliammeter). It is encased in

a glass housing in which is placed the electronic equip-ment needed to convert the milliammeter into a multi-range vacuum tube voltmeter. The external power source needed is 110 v A.C. The instrument measures either D.C. or A.C. voltages in the ranges 3, 15, 150, and 750 volts. Its impedance is about 1 megohm. The meter has a uniform fan-shaped lucite scale about 24 inches long. Its readings are clearly visible to all stu-dents in a lecture section of 200. It may be shadow projected for larger audiences. Figure 2 shows a front view photograph of this instrument.

Fig. 2.

The second is a 21 inch oscilloscope. This apparatus was built in our electronics shop about four years ago. It consists of a 21" T.V. tube converted into a usable oscilloscope. An electronic switch is incorporated in the instrument. Its frequency response is good in the range from 400 c.p.s. to 5000 c.p.s. Unfortunately, it is not a very rugged instrument and demands frequent visits to the electronics shop for repairs. For this reason I would not recommend its being built in any physics department without a good electronics shop. In this respect we have much better luck with a smaller 16" oscilloscope with a usable frequency range from 40 c.p.s. to 500 c.p.s. Wiring diagrams for both of these instruments can be obtained from Joseph A. Carr, our apparatus supervisor. Figure 3 shows a front view photograph of the 21" oscilloscope.

The third and last device which I wish to describe is an automatic chart plotter designed and built about ten years ago by A. 0. Nier and R. B. Thorness of the University of Minnesota. A complete description of this device may be found in the October 1951 issue of the American Journal of Physics.3 Hence it will be sufficient to give only a bare outline of the operation of this remarkable piece of demonstration apparatus.

The device is primarily a recording millivoltmeter

3. A. 0. Nier and R. B. Thorness, Am. J. Phys., ~' 416-417, 1951.

F.ig. 3.

which gives a record sufficiently large and distinct so that the record, in the form of an x-y plot, can be seen by a large lecture audience. The chart paper is about 3 feet long and 2-1/2 feet high. A vertical aluminum bar is driven across the chart at a constant speed (the speed may be varied). A pen carriage mounted on the bar moves up and down in response to an input signal (0-10 mv). The pen, in response to the signal, traces a heavy black line on the chart paper. Thus a permanent and large record of any physical event can be obtained by this device provided the output can be transformed into an electrical signal. For example, Professor Nier used this device with great success in a lecture on mass spectroscopy in which the chart plotter, connected to an operating mass spectrometer in the basement of the physics building, drew the mass spectrum graph of the isotopes of neon. The entire process took only

about five minutes. Figure 4 shows the chart plotter being used in one of our physics lecture sections.

Fig. 4.

37

Although this automatic chart plotter works beauti-fully in the hands of a skillful operator and has great potentialities, I must admit that we have not exploited these potentialities in our general physics courses. There are several reasons for this. It is not a piece of apparatus which can easily be moved from one lec-ture room to another. It requires the use of auxiliary apparatus which is expensive and not readily available. And finally, considerable time and skill are required to put it into satisfactory operation. None-the-less it is a read-out device of great merit and deserves more use than we have given it. Perhaps as a result of this Conference we will do something more with the auto-matic chart recorder at the University of Minnesota. We hope that others will be encouraged to do likewise.

DISCUSSION following Dr. Wall's paper

Comment: A small x- y plotter has been developed at R. P. I. for use with an overhead projector. We haven't exploited it fully but find it extremely effective in the classroom for the demonstration of various types of oscillatory motion.

Q. In addition to chart recorders, oscilloscopes, and large galvanometers, already discussed, are there other devices that permit students to take readings di-rectly from the lecture table instrument?

A. Thermoelectric devices can be used in place of small therometers, the micromax recorder potentio-meter can well be used to chart, for example, the super cooling of water. Manometers can be readily made of readable size.

A. The Weston bi-metal thermometer can be adapted for

projection by substituting a transparent scale and using a special diagonal mirror. An image several yards in diameter is then possible.

A. We use thermistors to read temperatures, and as many other things as we can display by electric cur-rents, on projection meters. We take meter movements out of their boxes and make our own calibration scales for projection.

Comment: Our experiences in trying to make scopes out of television receivers has been disappointing. The manufactured product is superior, but you may find the cost of such devices prohibitive.

Comment: One should be able to use a small scope screen and project it by means of an overhead projector.

38

INTRODUCTION OF DR. POHL

Projection Methods will be the next topic treated. Several years ago a group of visiting scientists had dinner together at our institution. In the discussion of lecture demonstrations and demonstrators, we agreed that Dr. Pohl is the outstanding man in this field. We are fortunate in having him with us today. He will speak to us on Projection Methods and will, I am sure, give us something very worthwhile.

OPTICAL PROJECTION OF DEMONSTRATION EXPERIMENTS

Robert Wichard Pohl, Goettingen University, Germany

There are, I think, three reasons which make optical projection, including shadow projection, methods useful for lectures.

1. The size of the apparatus to be shown can be rather small, which in turn means that the apparatus is not very expensive and it is easy to handle.

2. The second reason for applying the optical pro-jection method is the fact that you have to restrict your-self in the setup to the important things in order to get a clear silhouette.

3. And third, optical projection reduces the num-ber of experiments which can be observed by only a small number of observers. But we should never forget that optical projection is only an experimental method. The choice of the experi-ments is more important for the success of a lecture. A well chosen experiment has to show not just a sur-prising phenomenon, but it must give some insight into facts which can be used in different fields of Physics. Another important feature of a good experiment is that it is enjoyable not only for the audience but for the lec-turer as well.

After these general remarks let me now give you three examples which I believe are more instructive than many words. Two of the experiments are old and probably known by most of you. The third is new and not published yet.

The first experiment is particularly adaptable to shadow projection. The experiment demonstrates the behavior of an electrically charged particle in an in-homogeneous electric field. A carbon arc is used as a light source. To produce the field and the charge of the particle we use a very old and simple method. We rub a piece of amber and use this to charge a feathered thistle seed. (For the remainder of this experiment, Professor Pohl used a 6-ampere carbon arc to cast shadows on a large screen on the far side of the lecture room. His shadow and those of the thistle seed, the amber rod, and his son, who was his assistant, were visible in detail to everyone in the lecture room. His comments below describe the experiment as it pro-gressed. Ed.)

Now the experiment. The seed is allowed to float in air. We see the constant velocity of the seed and there-fore the influence of the friction of the air. We can

move this "big ion" by approaching or removing the charged rod thus changing the field. We see the velocity increasing with increasing field, in other words, the mobility of the carrier in air. All this is an example of electric conduction in matter. It finally gives the prin-ciple of the experiment which is used to determine the elementary electric charge. It is a simple experiment but shows some very important facts.

The second experiment demonstrates something which has become very important in the more recent past, namely the mean life time. Normally this is shown with radioactive materials, using Geiger counters and elec-tronics. But again a simple experiment shows the basic features.

A shallow watch glass contains a small amount of glycerin in alcohol. Mercury in a thin stream is poured into the liquid to form, initially, a great number of little drops, each of them approximately 1 mm in diameter (see Fig. 1). The total surface of the mercury is now very big. But one by one the drops combine with each other, forming a bigger drop. By this process the life time of the drops may be determined. After approxi-mately one minute only a single big mercury drop re-mains. Under the influence of the surface tension the surface of the mercury has contracted to the minimum possible value under these conditions. This is a par-ticularly instructive experiment.

(For this experiment, Professor Pohl had the appa-ratus in the focal plane of a horizontal platform projec-tor with a mirror and the image of the apparatus was cast on the large screen referred to above. Thus the audience watched the "smaller ones being devoured by the bigger ones." Ed.)

The drops are "physical individuals." It is not pos-sible by means of physical methods to make any predic-tions about the immediate future of any of the drops. One cannot tell which of the drops is going to disappear next. Nevertheless there is a law governing the group: Their number reduces according to an exponential law with a certain "mean life time" T. In other words, one can make very precise predictions of behavior for a sufficiently large number of individuals even though this is impossible for the single individual. It is well known that this fact plays an important role in atomic physics, for example in radioactive decay.

0 sec 205 lndividuen

~100%

10sec 78 Individuen ~38%oe 1/e

20sec 29 lndividuen ~1'1'/ooe 1je2

JOsec

'lOsee

50 sec

60sec

Fig. 1. Unification of Hg drops in alcohol with a small added amount of glycerin. A good example for a statistic process: For a sufficient number of drops (as in the three pictures at the top) it is possible to deter-mine a mean life time T = 10 sec, e.g., within every 10 seconds the total number of drops goes down to 1/e z 37%. Photo-graphic pictures: exposure time 4 x 10-3 sec. The bigger drops are par-tially distorted due to vibrations after unification with other drops.

So far the two old experiments. Let me now talk about the new experiment. This deals with the modula-tion of vibrations in amplitude, phase, and frequency.

In the case of transmission of information by elec-trical means, one originally used direct current as the carrier. The direct current was modulated by switches, for instance a telegraph key or microphone. Later the frequency range of the human voice produced a chopped direct or alternating current. Nowadays one mostly uses modulated radio frequency waves as the carrier. They are produced by resonating electric circuits.

These modulations can be shown with simple me-chanical devices. You know the method of producing a sinusoidal motion. One looks at a circular motion from the side. A rod rotates in front of a slit, and the picture of the slit is projected over a rotating polygon mirror on the screen (shadow projection). Figure 2 shows this in a slightly modified form. Here two sinusoidal mo-tions of different frequencies and amplitudes are com-bined. We see the rod and the slit in the top of Fig. 2. On either side the ends of the rod are held by the cir-cular disks I and II. These disks are rotated by an electric motor. The toothed wheels produce a fixed integer frequency ratio and in addition any phase dif-ference wanted between the two vibrations.

For a phase change the upper right toothed wheel can be rotated against the lower toothed wheel. It can slide on its shaft and is held in place by the spring F.

3

305"

Fig. 2. Demonstration apparatus for the super-position of two sinusoidal motions. The two shafts 1 and 2 are driven by an elec-tric motor attached to shaft 3.

39

The slit can be moved horizontally within the window. By this the ratio of the amplitudes of the two vibrations can be adjusted to the value desired.

Figure 3 shows the pictures of the two vibrations S1 and S2 with the amplitude ratio A1:A2 z 3:2. Their superposition yields curve Sr. The three curves a:re symmetric to the time axis.

Zeif t --Abb. 311.

Fig. 3. Superposition of two vibrations S1 and S2 with different amplitudes, frequencies, and an initial phase difference. Direct photographic picture obtained by using the apparatus shown in Fig. 2.

Now the modifications in order to obtain the modula-tions. First, the amplitude modulation. The left end of the rod rotates as usual, the right end goes through a hole in a lever which can be moved in the direction of the arrows, Fig. 4. It can be seen without further ex-planation how the amplitude can be modulated by simply moving the lever. The results are shown in Fig. 5.

To get the modulation of frequency or phase, we use a mechanical phase shifter, as shown in the lower left side of Fig. 4. The upper toothed wheel can rotate on

40

A

Fig. 4. Apparatus for the demonstration of ampli-tude and phase modulation.

Fig. 5. Photographic picture of amplitude modu-lation. It shows the three periods T 0 , T 11 and T2 • Accordingly one has to distinguish between three circular frequencies, namely w 0 for the vibration which is modulated (carrier frequency), w 1 for the modulation, and w 2 for the result, the modulated vibration.

the shaft A. By moving this shaft A perpendicular to the plane of drawing we can change the phase and frequency periodically. The results are shown in Fig. 6.

For the electrical transmission of information as well as in Optics (phase contrast microscope) the trans-formation of a phase modulated sinusoidal motion into

~V0MNvV Fig. 6. Photographic picture of a phase modu-

lated wave.

an amplitude modulated one is important. In order to do this one has to superpose two sinusoidal motions with equal frequency and amplitude, but a phase differ-ence of goo. The resulting sinusoidal motion reacts on a change in phase of the one component with a change in amplitude.

The demonstration apparatus is shown in Fig. 7. It is developed out of the one shown in Fig. 2 and does not

Fig. 7. Demonstration apparatus for the trans-formation of a phase modulation into an amplitude modulation.

require any further explanation, except the remark that this time all the four toothed wheels are of the same size. Now the experiments:

1. The two phase shifters remain in a fixed posi-tion. The ends I and II of the rod rotate with the same circular frequency w 0 , the two vibrations are super-posed to one resulting sinusoidal motion. Its amplitude Ar depends on the phase difference ¢. To show this, one has to change the phase difference slowly with the right phase shifter. At¢= goo, b..Ar/t:.. ¢ reaches a maximum. For an illustration of this behavior, see Fig. 8.

2. With the motor shut off, a phase difference of goo is established by turning the handle of the right

Fig. 8.

Spall

If there exists between the two ends I and II of the rod a phase difference of¢= goo, then a small change in the phase differ-ence results in a change of the amplitude Ar of the vibrating part of the rod which can be seen through the slit.

phase shifter. After the motor is turned on again the left phase shifter is moved periodically in the direction perpendicular to the plane of drawing. Without the second vibration this results in a phase modulated vi-bration as in Fig. 6, with the second vibration one now obtains instead of that an amplitude modulated vibration as in Fig. 5. By slowly moving the right phase shifter one can change between the two kinds of modulation.

(Dr. Pohl's fourth demonstration was his well-known [see, for example, p. 840 of "University Physics" by

41

Sears and Zemansky, second edition, Addison-Wesley Publishing Company) interference fringe pattern using the reflection of the light of a small intense mercury arc source from the front and back surfaces of a thin mica sheet. Fringes covering a large section of the wall of the room were visible to everyone. Ed.)

I hope that these examples may have given you an impression of what seems to me of importance in choosing demonstration experiments and showing them in optical projection.

DISCUSSION

following Dr. Pohl's paper

Q. What type lamp did you use for the interference pat-tern obtained by reflection from the mica sheet?

A. It is a General Electric H-100 A4 Mercury arc lamp with the outer glass wall removed. (Such lamps are available from Welch or Cenco.)

Comment: It is advisable to shield the back side of the lamp to reduce the room illumination and to protect the students' eyes from ultraviolet light since the inner tube of this lamp is quartz.

Comment: I am surprised that so little shadow projec-tion is used in this country. It is a technique much used in Europe. We should develop it as an effective way of getting around some of the problems of large scale ap-paratus.

Comment: One must really see the great variety of ap-paratus now available for shadow projection to appreci-ate its possibilities. Some universities have a large collection, Michigan State for example. I understand that there will be a display of such apparatus, both U. S. and foreign, after this meeting. (The Conference had a display of all types of apparatus which was demonstrated by the manufacturers.)

Comment: May I say that this fine demonstration by Dr. Pohl shows us the importance of having a good as-sistant. It is an accepted plan to have lecture assistants

in European Universities. We lack this type of needed help.

Comment: Good shadow projection lamps are made by Western Union and come in sizes from 2 to 300 watts. The latter is very suitable for shadow projection but the cost/hour of lamp life is rather steep.

Comment: One of the disturbing features of shadow projection is the continuous shifting of sight from screen to see what happens then to the operator to see what he does to make it happen. It's like watching a tennis match. In many cases both can be put on the screen, or in the line of sight of the student, and when this is possible, it is important to do so. Keep the mo-tion and the image close together. Sometimes this re-quires mirrors or special platforms to stand on.

Comment: May I show you a piece of Pohl's equipment? (A cart built with four bicycle wheels supporting a plat-form elevated only a few inches from the floor was brought out.) When one is on this cart, he is isolated from his surroundings for motions back and forth. In that direction there is no way he can change his center of gravity. He moves one way, the cart moves the other way. When he stops, the cart stops. Of course if he runs off the end, the cart continues to go in the opposite direction. If he runs and moves over the cart without changing his momentum, the cart stands still. If you want a real reaction, turn and run off in the same direction.

TilE DEMONSTRATION LECTURE AS AN ART

V. E. Eaton, Wesleyan University

First let me make clear that I shall not describe new demonstration experiments or new apparatus. Good ap-paratus is important but unless the demonstrator is skilled in the art of using it much of the effectiveness is lost. The successful demonstrator is a good show-man, but a showman in the very best sense of the word. He is not a show-off. He is an actor aware of and skilled in the use of the acting techniques used by the best dramatic performers.

A showman must be expert in the matter of timing. In many demonstrations the equipment should operate as the explanation unfolds, the two marching along to-gether. In this case the lecturer is using the apparatus simply to illustrate physical principles. Many experi-ments in rotary motion fall into this category. In other experiments the theory is developed first and then demonstrated. For example, the demonstration in which the falling monkey is shot in mid-air is more

42

convincing if the explanation and description of the ex-perimental set-up comes first with the comment that if the switch fails to open at the proper time by as much as one-hundredth of a second the monkey escapes. But you must be sure that he never escapes. To make the results convincing my monkey is a cow-bell with the clapper removed. There are other experiments where something happens unexpectedly and the students are eager for an explanation. This is an ideal situation for students to be in; make the most of it. There are many examples of this approach such as force applied to the axle of a rotating wheel, series resonance in ac circuits, and the Thomson coil with jumping ring.

A good showman must be able to get across the foot-lights. The audience must feel drawn into and become a part of the act. May I remind you of the little blond in the musical comedy; she was perhaps the second girl from the right in the front row. Remember how when she smiled, she smiled directly at you, and when she sang, the song was for you alone. You refused to be-lieve that every other male in the audience felt the same way. Obviously she had learned to get across the foot-lights. How does the demonstration lecturer draw in the audience, make each student feel that he is a part of the act and feel that it is all being done for him? If the stu-dents can be made to anticipate what is going to happen, particularly if what he expects to happen does not hap-pen, you have captured him. Take, for example, the well-known cord and spool experiment, Fig. 1. If the student guesses the spool will roll to the right it goes

Fig. 1.

left, if he guesses left it rolls to the right, but if he is only sure it will roll one way or the other he also loses for the spool is pulled along without rolling. This ex-ample may be used to explain why a judicious selection of the axis around which moments are taken is impor-tant. Another interesting experiment to surprise the conclusion jumper is based on the model apothecaries balance, Fig. 2. If the weights A and B are at the outer ends, the inner ends or accurately in the middle of the horizontal rods the system is, of course, in equilibrium. If A and B are both moved to the right-hand ends of their respective rods the students mistakenly expect B to go down. A third experiment of this kind may be performed using simply a meter stick. Rest the meter stick on the hands with one hand at the 5 em mark, say, and the other at the 70 em mark. Tell the students that the hands are going to be brought together slowly and ask them to determine where on the meter stick they will meet and which way the stick will fall.

Fig. 2.

Now a showman uses props but he does not talk about his props. He does not say, "Look at my cane. It is a gold-headed cane. Watch me swing my cane." Likewise the demonstrator usually should not talk about his apparatus. He is using the apparatus for making gestures--very effective gestures-as if he had a twelve-foot arm. One should remember that we are demon-strating not performing experiments.

The demonstrator is not only the principal actor, he is his own stage manager, lighting expert and electri-cian. It is his responsibility to see that the stage is properly lighted and visible to all. For example if this barometer is lighted from the front the mercury column can hardly be seen. If, however, it is,backed with a translucent screen and this screen is illuminated from behind the mercury stands out in bold relief. The back-ground is very important. Some apparatus requires a dark background while others require a light background. Even such a simple thing as the kind of cord used for support is important. A white cord can be seen against a dark background and a black cord against a light back-ground. However, by twisting a black cord and a white cord together we have a cord that can be seen against any background.

The ordinary Hartl disk, the kind commercially available, can be seen by very few people at a time and is, therefore, very unsatisfactory for demonstrations. The apparatus shown in Figs. 3 and 4 is much more effective. The cylindrical lenses are made of one-inch thick Lucite and the screen of plastic tracing sheet.

Fig. 3.

Fig. 4.

The screen measures 3 feet by 4 feet and each lens has an "aperture" of approximately one foot. With the con-verging lens, both spherical and chromatic aberration can be observed. For the "rays," parallel slots are cut in a 2 in. X 2 in. brass sheet and this sheet is mounted in a projection lantern. Since the lenses, Fig. 3, and the Dove prism, Fig. 4, are mounted back of the screen there is nothing to obstruct the view.

For most lecture rooms the apparatus should be in a vertical plane and for this purpose I find what might be called schematic apparatus very helpful. In Fig. 5 is shown parallel resonance. Similar boards may be

Fig. 5.

used to show series resonance, a Wheatstone bridge, a potentiometer and many other electric circuits.

Models can be very helpful, particularly where three dimensions are involved. In Fig. 6 is shown small wooden blocks supported by springs. Note that the ver-tical springs are stiffer than the horizontal ones. This is used to introduce students to the concept of double refraction. The model in Fig. 7 is used to explain the

43

Fig. 6.

Fig. 7.

rainbow. Since the apparatus may be rotated around an axis parallel to the incident rays and around an axis perpendicular to the plane of the paper, it can be used to show why a bow is produced and why the size of this bow depends upon the time of day. For cases where vectors in three directions are required, particularly with gyroscopes, vectors made from dowel rod and supported at a common point with heavy copper wires can simplify matters very much.

A good showman enjoys his own show. He does not merely recite lines but lives the part assigned to him by the casting director and care must be taken that the role fits him. The same is true of a demonstrator. If he is naturally informal and attempts to be formal he will succeed only in being stiff. When a naturally

44 formal person tries to be informal he usually looks a bit silly.

The two adjacent rooms on my left are full of equip-ment developed and made here at Wesleyan. Feel free to browse through these rooms at your leisure.

Schilling: I'd like to ask Eaton if he ever used the elastic model to show the passage of acoustic waves.

Eaton: No, I haven't. Schilling: It looks like a natural. Pohl: I have learned some very useful things and I

thank you. Eaton: Earlier I said that the highest compliment I

had ever received was from a student who said that I seemed to enjoy my own lectures. Now this student's remark has become the second best compliment.

Session IV

TELEVISION

Presiding: M. W. Zemansky

This session as you know is devoted to Television. This has become almost a dirty word but when physicists learned that it would not put them out of their jobs they were more tolerant. It raises many problems but perhaps it has a real place in our teaching.

The first talk will be by Rosalie Hoyt of Bryn Mawr who will discuss the TV camera for producing magnification.

TV CAMERA FOR MAGNIFICATION

Rosalie C. Hoyt, Bryn Mawr College

I have here an RCA TV Eye Camera and its control box, and have it connected to a portable 17-inch home receiver. We ordinarily use a 21-inch home receiver which, of course, gives a bigger picture, necessary for a large class.

In order to d@monstrate what can be done with the TV camera, I have brought with me several items that are among the more difficult things to focus on. Fo-cussing the camera onto this ordinary mercury-in-glass thermometer, you can easily see on the TV screen the position of the mercury column. Again, with this small compass only a half inch in diameter, the needle is clearly visible. The direction of the magnetic field about current carrying wires can easily be shown to a large class with this half-inch compass.

Both these items present difficulties due to the glass covering. Care has to be taken with the lighting to avoid glare, but, as you can see, these difficulties are not in-superable. Where possible, it is, of course, best to re-move glass covers. For example, this two-inch panel meter has had its glass cover removed and then with the camera focussed onto it you can easily see on the screen both the pointer and the scale. T:,J.king the meter out of its metal case, the camera now shows up some of the details of the construction of the meter; the horseshoe magnet and part of the coil are visible on the screen.

One of the advantages of using the TV camera and TV screen for demonstrations is that one can use com-mon, ordinary, small scale laboratory pieces of equip-ment such as thermometers, panel meters, etc., and blow them up so that a large class can see them. This leads to a saving in time and money, obviating the need of constructing much large scale demonstration equip-ment, useful only for demonstrations. For our depart-ment, where we have little technical assistance, this time saving aspect is extremely valuable.

For example, here is an obvious way of converting a five-inch scope into a 21-inch scope. Focussing the camera onto the face of the five-inch scope, the scope pattern shows up very clearly on the TV receiver, and is clearly visible to a large audience.

As another example, for demonstrations in radio-activity, we use an ordinary commercial scaler, focus the TV camera onto the decade scaling units (as I am doing here with a scaler loaned by Wesleyan), or onto the output meter of a Rate Meter (this one borrowed from Dr. Eaton), and an entire class can see what hap-pens when a source is brought near or moved away from the Geiger or scintillation counter.

As you can see, the equipment is easy to set up, very little fussing is necessary with the controls to get a clear picture, and with a little practice the tricks of lighting, etc. are easy to work out. We are using it more and more in our Freshman course as we gain

47

more experience with what it can and cannot do. In addition to demonstration use, other laboratory uses such as monitoring are, of course, obvious.

There is one danger with an outfit like this TV camera. One tends to get over enthusiastic and use it for demonstrations in cases where other methods are really better, or where the only real solution is still for students to get their own close up views in small groups or individually. For example, shadow graph techniques often do a better job than the TV camera. However, here there is often a legitimate and advanta-geous use of the TV camera as a supplement. The camera can be focussed behind the screen, so that in addition to what the shadow shows the student can also look, at the TV screen and see what the demonstrator is doing.

Among the other uses to which we have tried to put the TV camera is that of projecting the tracks in a dif-fusion cloud chamber. As yet, we have not been able to get the lighting to the point of providing sharp enough contrast to be of much use. We can get vague lines on the TV screen, but the picture is not clear enough for the students to get much out of it. This is one thing that the student must look at himself.

We have tried, just to see if it works, using the TV camera with a good high-powered microscope. This does work very well. So far we have not put this to use in demonstrations, but we are thinking of using it for demonstration of Brownian motion. We think it should be feasible. Another similar demonstration we want to try out is the Millikan Oil Drop; again, we think this should be feasible.

I have had a number of requests for information as to the cost of such an outfit. It is an RCA TV Eye Camera #MI-36250 with Control Unit #MI-36251. At the time we bought it, about three years ago, the two units sold for about $1100. We obtained these from RCA as reconditioned units, the cost to us being $750. (This does not include the cost of the receiver which is an ordinary 21-inch home receiver.) The camera came with an F /4.5 lens, but we soon decided that we could do a lot more with this outfit if we had a faster lens. So we bought, at an additional cost of $104, this F /1.5 Cine Raptor Wollensack lens with portrait attachment that I have been using here today, and it has made all the difference.

Using a 21-inch screen, the maximum magnification with this lens is 4x without the portrait attachment and 8x with it. Zemansky:

How does this work with interference of light and diffraction? Have you tried any of that? Hoyt:

We have tried, but this is one of those cases where I

48

think other demonstration techniques are better. With a diffraction grating, for example, one can see vague lines in the first order mercury spectrum, but it does not give the students as good a picture as projection tech-niques, nor as good as they can see for themselves when you pass out individual pieces of the grating material that has recently come on the market.

Kelly: How about e/m?

Hoyt: We have focussed this camera onto the Cenco e/m

tube. It does show up the curved beam, and one can focus onto the rings on the plates. But it in no way com-pares with the actual close up view by the student.

MULTIPLE CLASSES-CLOSED CIRCUIT TV

I. Walerstein, Purdue University

K. S. Woodcock, Bates College

Zemansky: The job of teaching many classes at the same time

with the aid of closed-circuit TV is something that is particularly interesting and we are very fortunate in having Professor Walerstein to talk to us about it. Walerstein:

I'll be very brief because my presence on the pro-gram is a mistake. A couple of years ago, Professor Lefler and I conducted multiple classes over TV for recitation purposes. We had never attempted multiple classes of demonstration experiments and the results of the work with recitation classes as near as could be de-termined by the person who carried out the statistical study was that it was no worse than the usual recitation class. We had expected it to be not as good and in some respects it showed up a shade better. I imagine that that may be due to the fact that special preparations were made by the people who appeared before the TV camera. Inasmuch as you have no audience in front of you, you do not see any raised hands, you do not hear any questions and you have to decide before hand what are the most likely queries in the minds of the students. That takes a little more preparation. While I'm on my feet, I would advance the usual arguments I think you have against multiple classes for demonstrations on closed-circuit TV. I do not see any gain and I see a number of dis-advantages. In the first place, Professor Rogers al-ready has raised the question about the directors. Even these people who are in educational institutions probably have been trained for commercial work and they do try to put the pressure on you and as a consequence you are not quite a free agent. Secondly, I think the time for preparation would be enormous and therefore the advan-tages that would be gained by saving an instructor would be no advantage at all since the financial element would be multiplied by certain factors rather than divided. There is one more argument I would like to make against multiple-class demonstration on TV and that is that the basic idea is that you run several classes at the same time, therefore, you use one setup and one lecture. I think that is wrong because of the many reasons that have been put forth by several speakers before, mainly you are not training new people to take over some of this work and contribute new ideas and new suggestions. If the demonstration lecture can be passed around among staff members there is the advantage that you build up a

larger group of people interested in the problem and get many more suggestions. I think this factor should weigh exceedingly important in considering whether any at-tempt at multiple TV classes in demonstration lectures should be attempted. I must say that some of my mis-givings may not be quite valid. I had very strong mis-givings about the recitation class and as I said, it turned out it was no worse than classroom contact and perhaps a shade better, so there may be possibilities for TV. But I do think the matter of developing a larger group of demonstration lecturers is important. Zeman sky:

Just what is it you did? I don't understand. Walerstein:

What we did was not the lecture in physics with demonstration experime'nts but the regular recitation class. We had four classes scheduled for a particular hour. We ran two of those classes in the regular recita-tion form and two classes on TV. Then at the end of the half semester we interchanged the groups. So each of these classes was conducted in regular recitations for half of the semester and by TV for the other half. Zemansky:

Was there another instructor in the class watching the TV set at the same time? Walerstein:

There was one instructor in the two adjoining rooms watching the TV at the same time and answering the questions of the students at the end of the period. The end of the period happened to be ten minutes to twelve. This was unfortunate.

The problem arose because of the fact that it is diffi-cult to get enough experienced recitation instructors to take over the work during the recitation classes and this was intended to meet the situation. We were not enthusi-astic about the results and we are looking for other ways to answer that same question. Seeger:

In Washington they have had a religion course in one of the universities and it seems to me that what they did there was something like this. The instructor lectured about a half hour to a studio class. He had the class there and they asked questions. It seems to me that if you were doing this before a class it would be much more alive. This is a possible way of doing it.

Walerstein: I think there are a number of factors. I didn't want

to discuss them because it is a demonstration lecture problem. However, we wanted to be able to see the two rooms that we were talking to. We want to be able to see the hands go up and see that person talk into a microphone and talk back. It's so totally impersonal and as Professor Eaton pointed out you do want to talk to somebody. Sutton:

Yesterday, I think, Dr. Olsen mentioned the work that is going on at Case in this area. And some of the disadvantages you speak of were not present there. I attended on several occasions. The lecturer was talking to twenty people. He was lecturing and showing how to draw and design a machine screw. I learned more about this in one hour than I ever expected to know and more than I know now. I went around then to the other classes. The lecturer had in front of him three or four groups. He had monitor scopes for each of these rooms. If they wanted to raise a question they could. There was two-way communication. If they wanted to ask a question they could go to a microphone and ask it. I was im-pressed with the amount of detail which he could get over in the way of using slides. One technique he used would be useful for any of us whether for TV or not. He put up some of the things he wanted to work on and then when he wanted to modify them he had sheets of cello-phane and could work on the drawing without destroying it, and if he wanted to repeat the lecture, that much of it was not affected. I feel there was more two-way com-munication than what you have indicated and that more two-way communication is both needed and desirable if it is to be a success. Andrews:

We have been conducting a closed-circuit television experiment at the State College for Teachers at Albany. There we had three classrooms with three screens in front of them. This is two-way both for sound and video. But it did turn out that very few of the instructors learned to use these screens well. It seems quite a technique to keep an eye on three screens and see a hand when it goes up on any one of the three screens. It takes a -very unusual teacher and the teacher has to like it. If he doesn't, all the students hate it. Robinson:

A year ago I spent a few days at the University of New Mexico and in that particular state, the university has a very highly developed system of television for high school teaching and for extension courses which seem to me to be unusually successful. I actually watched some experiments in biology and saw the re-sults on the screen. I could see the man lecturing and I could see the screen at the same time. Now listening to those lectures were students in 150 different scattered communities throughout the state, each one of whom had its own teacher. Each teacher was provided with a script so that he could study before the lecture was given. So this was a lecture demonstration given to 150 separate bodies over some 300 or 400 miles and the question period was conducted by the individual teacher in the audience who was prepared. Now they've done

49

this for a number of years and developed the art very highly, and I thought it was one of the most successful programs for extension work that I have ever seen. Now the problem was presented to us at our college recently in another framework and, fortunately, I had observed the situation at New Mexico. On Long Island we find that schools in the elementary grades are having more and more science brought into them. Many of the elementary teachers are poorly trained in science, so they asked us to take some of the fifth-grade students from the local schools. They brought them to the college and they sat in different rooms. I lectured but the teacher was with them and we had prepared the teacher for what we were going to say and the teacher asked questions. We broke it up so that questions could be asked during the lecture. The students actually asked the questions and I answered them on a two-way circuit. This worked out very well. Now I am fairly sure that this was successful. The level of the students which I had in that group was unbelievely sophisticated and these couldn't possibly have been drawn out by the usual methods because the teachers themselves were very poorly prepared. Now we did run into a number of prob-lems. Of course, the problem that Dr. Rogers talked about, being in the hands of the director, is certainly a terrific one. I took the part of the director myself. The other thing was the enormous amount of preparation that was necessary. You must try these things out first because very simple things which you can do here you can't possibly do on television. On the other hand there are a number of things you can do on the television screen that you cannot possibly do here. Olsen:

I think we should probably summarize the Case ex-periment. The final conclusion reached on multiple recitations was that it was not particularly good. Why shouldn't you just as well put those two hundred students in a big room and do the same thing with TV and let them raise their hands and answer questions? It certainly is no longer a recitation situation when two hundred people are permitted to raise hands and ask questions. Zemansky:

We will devote the remaining part of this session to a very important point. We have learned during the last few sessions various tricks and important features of lecture demonstrations. We have learned how to make things big, we have learned how to keep them deliberately small and magnify them through various means, such as shadow projection and television. And we have learned certainly that physics had to be taught through various means, one of which is television. We shall call on Dr. Woodcock to talk on the experiment that was made at the U. S. Naval Academy with regard to teaching by television but in a different manner from that which has been con-templated up to now. We usually think in terms of large lecture halls or certainly a lecture hall as large as this. This scheme at the U. S. Naval Academy was something different. I would like to call on Dr. Woodcock who has had only a little time to assemble a report on this ques-tion. Woodcock:

When he says a little time, he meant that yesterday

50

Vernet Eaton passed me this sheaf of papers and told me that I was to read it and prepare a summary. We shall try to hit some of the high points. I think the best way to do this is to check these reports chronologically. The first one is dated 1954. The Naval Academy had just received a television system which was installed in the summer of 1953. The purpose of it, as has already been pointed out, is somewhat different than the ones we have discussed so far. They established a studio con-trol room and had it piped by the way of coaxial cables to some nineteen classrooms and the large lecture room which seats approximately a thousand. It was under the jurisdiction of the Electrical Engineering Department which teaches such subjects as General Chemistry, Physics, Basic Electrical Engineering, and Electronics. They have some 97 instructors. The hardcore, pro-fessional teachers are in general civilians. The sec-tions average about fourteen midshipmen each and there are enough instructors so that each section will have its own instructor in both laboratory and recitation. When one tries to introduce television into such a system which is working properly and securing excellent results it becomes merely another training aid to assist the in-structor. If faced with this situation, on the one hand, successful strong recitation teaching with enough good instructors and on the other hand a closed-circuit tele-vision system for experimental educational purposes, what should be done? They found that the best results came from programs generally of about 10 to 20 minutes in length with occasionally one from 30 to 35 minutes but never longer. We find that they have finished ap-proximately one program per week-each program being presented six times because of the number involved. What are some of the advantages of this closed television system? First you have a captive audience, already in place in the classroom, an audience that does not have to be moved from one place to another to see chalk-talks, demonstrations or training film. Secondly, you can use the best instructors with a well-prepared script with the proper facilities and apparatus to develop and stress the concepts you want. Thirdly, well worked-out TV presentations can be used to show all your instruc-tors the proper methods of teaching. Fourthly, tele-vision can be used to show many things that cannot be taken into the classroom.

I was quite interested in the split screen system demonstrated today. Incidentally, I was one of those who got up at six-thirty all winter long. In fact I bought a television set just to see it because I thought the way most of you did, that if this was a new technique, that as a physics teacher I just could not afford to ignore it.

Now to return to the script. What are some of the disadvantages of television? First, the additional per-sonnel required to operate such a station and the fact that all this personnel must be trained. Secondly, scheduling difficulties, particularly when the station is run on a cooperative basis. Thirdly, the initial and maintenance costs. Cameras and circuits have only a short life and are complicated. We've been asked by representatives of two other services if television is a success in education, and secondly, whether it could be used profitably? The 1954 answer to this was a quali-fied Yes. Use of television as a unique method .of pres-entation is an advantage but television should not be used when talk, movies, slides, and demonstrations can do it just as well or better. Above all do not use tele-vision to replace the laboratpry or work on real appara-tus. This, of course, applies to the Naval Academy. Where then in the services would education by television be an advantage? And the answer to that is: Where you have large groups, where the instructors were not suffi-ciently well trained, where time is very short, or when you have to cover many concepts. Television could be used for a review or preview or to. show things that cannot be shown to large groups.

The Head of the Department of Electrical Engineering who was given this assignment reports, "Experience in-dicates that the benefits derived from the use of TV are not commensurate with the effort required." His prin-cipal criticisms had to do with cost, time required for preparation, and acoustic reverberation. For example, he reports, "In order to put a 15-minute program before the midshipmen of one class it is estimated that from 60 to 200 man hours must be used in the preparation of the script, rehearsals. and actual presentation. This saves no time as regular section instructors are avail-able in each classroom."

DISCUSSION

Zemansky: Are there any comments in connection with this par-

ticular method whereby the television program is de-livered to a small classroom while the teacher is there? Elsewhere in that report it mentioned that a fifteen-minute period or at most thirty minutes are taken up with the television program and then the remaining time is taken up for discussion. The teacher who is there has to see the television program with his audience and, therefore, he cannot ignore the lectures which the stu-dents have seen. Where I teach, for example, the stu-dents have to hear one lecture a week and four recita-tions and there may be twenty-five sections and the

young people who teach those sections do not have the faintest idea what the lecturer has said or done. There-fore the whole pedagogical value of the lecture is lost because the teacher in the classroom does not refer to it, does not make use of it. Here they have to, it's put right in front of them. So it seems to me that although this particular Naval Academy experiment was not car-ried very far, it does seem to have possibilities. At least it does contain the germ of an idea which may be one of the better ways of using television.

Does that report say that the balance of the Academy did not necessarily feel compelled to cooperate with the course of instruction?

Woodcock: Just those in the EE Department. Physics and Elec-

tronics are taught in the Electrical Engineering Depart-ment. Overbeck:

I wonder if there isn't going to be the same kind of feeling towards TV as already exists toward films. A teacher looks at say thirty minutes of television and then takes over the class. I know of a number of people who refuse to use films. They say, "I'm trained as a physics teacher. Why should I sit back as if incapable of doing the first thirty minutes and then take over for the question period." Eaton:

I want to remind this group that some years ago, Mark Zemansky was chairman of the Audio-Visual Aids Committee of AAPT and during that time they turned out some excellent films. The cost was about fifty dol-lars for about eight minutes and, therefore, they did not sell, and so there is a real problem of cost in this. Overbeck:

I think it is well to call attention to another thing that is going on and in which we should be very much inter-ested as teachers. My attention was called last year to something which is going on. This is an attempt in chemistry to substitute motion picture film for the lab-oratory experience. This is being recorded at length in the papers, whole columns of it, in which the state-ment is actually being made that tests show that the students learn just as much by going to a movie labora-tory as by actually getting their hands on equipment. I have had a bit of correspondence with the individual who is doing this and I've had him send his examination questions since I told him frankly that I believed he was not testing for what the laboratory was supposed to do.

Those who have seen the questions agree with me. Olsen:

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Mr. Eaton asked me to say a few words about the Case project. We haven't arrived at the point where we are ready to draw conclusions especially as it pertains to lecture work. The project under Professor Jack Martin ran about three years. They did several things-teaching graphics to various sections at the same time with two-way communication, teaching humanities in the same way to a number of sections simultaneously, and teaching some electrical engineering courses to say 100 or 150. They made rather elaborate studies of how television could be used to aid in lecture demonstrations, the sort of thing Miss Hoyt showed here and others have referred to. The end product of this study, I think, is that no one now at Case, although the equipment is there, is teaching humanities or graphics by television. The only thing they are using the television equipment for now is to make lecture demonstrations better in the area in which you can display things on television screens that you cannot see otherwise. The Electrical Engineering Department is willing to provide a service now with the equipment they have to any department that wants to do a particular demonstration. They will come in and supply the technical equipment and service with the receivers and help with a demonstration. We use this in the Physics Department several times a year. One case is to show domain walls and the movement of domain walls on the television screen. It's the only way I know to do this and it's rather difficult but it can be done. And so I would say in summary, the real benefit they have found as a result of this rather elaborate equipment was an expensive way to improve lecture demonstrations by showing things you cannot otherwise see.

BROADCASTING

R. Rippen and M. Einhorn, National Broadcasting Company

Zemansky: All of you know, of course, that this year Continental

Classroom was broadcast over the NBC television net-work. Many of the audience actually got up 6:30 in the morning, staggered to their television sets, and watched physics at this ungodly hour. I would like to say that a very lovely person, Dorothy Culbertson, was the pro-ducer. The associate producer was Mr. Marvin Rippen whom we have over here, and the director was Robert Einhorn over here. Present in this august assembly are no less than six people who participated on this program as guests. As you know, most of the lectures were given by Harvey White. Guests included: Winston Cram, Vernet Eaton, Paul Kirkpatrick, Harold Schilling, Eric Rogers and myself among, of course, many others. But at least six of those who participated are here as well as the producer and the director. (Note: There were 32 different guests who gave a total of 42 lessons.) We now have a chance to hear the producer Mr. Rippen and the director Mr. Einhorn.

Rippen and Einhorn: Before we start, Harvey asked us to extend his best

wishes to everybody here. His heart is in what we are doing today but we think he is in Venezuela.

There will be a short introduction before and a ques-tion period after each excerpt. I want to remind you of one thing, this is a 16 mm kinescope and the quality leaves something to be desired. The original show was recorded on video tape and we think the results were excellent. Editor's note:

The excerpts shown were chosen to illustrate the various special techniques used in television. These included the use of the cellomatic screen for animation, light diffraction patterns directly on the face of the image tube, the split screen, and special problems en-countered with cloud chambers. One excerpt was a laboratory-type experiment but there was general agree-ment that TV should not be used to replace laboratory experiments.

Session V

SPACE AND EQUIPMENT

Presiding: J. K. Major

THE LECTURE ROOM AND ITS FACILITIES

R. R. Palmer, Beloit College

I understand that my function on the program this afternoon is two-fold: first, to acquaint members of the Conference more fully with our Project on Design of Physics Facilities; and secondly, to initiate a discussion which will yield helpful information for the Project. In particular, in line with the interests of this conference I hope to learn what you consider are essential charac-teristics of a good lecture room.

As most of you know, our Project had its inception in the activity of the AAPT Committee on the Design of Physics Buildings. As the result of a card questionnaire conducted early last year, the Committee discovered that about a quarter of a billion dollars was scheduled to be spent for physics construction in colleges in the next few years. The Ford Foundation was approached for funds to expand the study, and this subsequently led to a grant from the Educational Facilities Laboratories, Inc. for the support of our 18-month Project on the De-sign of Physics Buildings. It is to be hoped that our Project will help make possible the construction of more efficient facilities for both teaching and research.

The Project has been established in the Education Department at the American Institute of Physics, and I have been serving as the Director on a part-time basis since the first of the year and full time since just last week. Mr. William M. Rice, a member of the American Institute of Architects, joined the Project in February. He is on leave from the Lawrence Radiation Laboratory in Berkeley. Dr. John, Major will spend one month with us this summer on a special study of building services, with emphasis on the distribution of electrical power. Miss Nancy Zlobik, who was AAPT administrative as-sistant this past year, is serving as Secretary for the Project. We expect to employ a draftsman at a later date when such services are required.

Our Advisory Committee has as its nucleus the for-mer members of the AAPT Committee: Yale Roots as Chairman, Albert Baez, J. W. Buchta, and Carl Howe. The committee has been augmented by Thomas P. Mur-tagh of the large electrical contracting firm, L. K. Comstock and Co., Inc., Benjamin L. Smith of the New York architectural firm of Voorhees, Walker, Smith, Smith and Haines, and William W. Walker of Yale Uni-versity. These gentlemen together with a secondary school administrator, who has since found it necessary to resign, were added to represent primarily interests other than college teaching.

One of our first activities was to send out letters to about a thousand schools announcing the Project and seeking information. Those schools known to have new facilities were asked to describe them briefly and to identify those features they believed to be particularly good. The schools known to be planning new facilities were asked to describe their plans, and to give us a list

55

of items about which to seek information. Other schools received a more general letter. Follow-up letters are being sent to schools we have not heard from, and which we believe may have facilities of interest to the Project. On the whole, the response has been very good.

A bibliography on physics buildings, largely compiled by John Major, has been mimeographed and is being sent to those who request it. And to provide still more help for those who cannot wait for our final report, a 200-page volume of reprints of selected articles on physics buildings has been assembled and is now available from the American Institute of Physics at $2 each.

It is planned that the final report of the Project will appear as a single volume. The introduction will at-tempt to describe how physics is taught and serve as a primer for architects and administration. This con-ference is supplying material for this section. It will contain separate sections dealing with different facilities such as lecture rooms, elementary and advanced labora-tories and research laboratories. Good examples of each type of facility will be given together with an evalu-ation by those who use them. A variety of floor plans which have been found to be efficient for various types of institutions will be included. A list of "do's" and "don'ts" is also being assembled for inclusion in the final report. Finally, we plan to have a special chapter which deals with physics facilities at the secondary school level.

Mr. Rice and I have each visited several schools in-dividually. However, for most of our visits we will go together, with each assuming certain areas of interest. We have already made test visitations together on two occasions. We visited three schools in the Philadelphia area in April; and in May, four schools in the Washington area. As an experiment, the last afternoon in each case was devoted to a conference on building problems with representatives from the respective schools participat-ing. So far we feel we have been received most hospita-bly and have had excellent cooperation.

Our visits will, of course, be concerned with the whole range of physics facilities. But one of the most important and one with which this conference is vitally concerned is the physics lecture room. I have taken some pictures of various facilities, and to help initiate discussion, I have brought along a few slides of some of tpe lecture rooms we have seen. I hope the discussion will serve to let me know what you regard as the good and bad features of a lecture room, and also what we should look for in lecture rooms during our visits to various institutions.

Slide 1 - Small college. Rectangular room, about 32 X 50; 122 seats; 10 rows, 4-1/2 inch risers; rear exit (down 5 steps) as well as front; small

56

left section of 3-section blackboard can be raised and opens into storeroom and also makes available a hood; two movable sections to lecture table; large window area; room used by both physics and chemistry.

Slides 2 and 3 - Large university. Square room, about 50 X 50, with lecture table in one corner and coat rooms and projection room in rear corner; 186 seats in quarter-circle rows with varying pitch for seeing; motor driven screen, slow; automatic projection from rear rarely used; 22ft-candles on lecture table increases to 32 ft-candles when 4 flood lights are turned on; slide-up blackboards (glass) with aluminum channels to clear erasers, provides wide opening into storeroom in addition to door; dimmer for room illumination; no windows.

Slides 4, 5, 6, 7 - Large university. Pie-shaped lecture room (one of three, each with 60° between side walls--all air conditioned); motor driven chalkboards and motor driven screen; variable overhead lights; lecture room shown seats 100 in theater-type seats with folding tablet arms; 8-inch rise and 33-inch separation between rows; 30 x 36 inch movable tables to match small fixed lecture table; no windows; lighting controls at lecture tables installed subsequent to initial construction at cost of $1600 for the three rooms; side-wall spotlights bother lecturer; coat racks in rear.

Slides 8, 9, 10 -Medium size university. Rec-tangular room, about 30 x 60, determined by

structure of building, with five rows of seats to seat 130 parallel to long dimension and curved at each end; pitch 14 inches per row; 42 inch separation between rows; pair of heavy center movable black-boards have zero clearance, dangerous to fingers; illumination about 70ft-candles throughout; dim-ming only in steps near one of the front entrances; availability of apparatus storage through side door and narrow passage; height above lecture table, 9 ft (acoustic ceiling depressed).

These lecture rooms do not have certain features which some consider important, such as left-hand chairs, a built-in translucent screen, a catwalk above the lec-ture table, provision for closed-circuit TV, as well as other things mentioned at this conference, the past few days. I have seen an installation where the entire lec-ture table can be rolled from the preparation room into the lecture room where all connections to utilities are then made through flexible tubes and cables located be-neath the floors. Several schools are considering the installation of a "lazy-susan" system, with two or three identical lecture tables mounted on a rotatable platform, so that while one of the tables is in use, apparatus can be assembled on one of the others in preparation for a lecture the next hour.

I am pleased to have had this opportunity to describe some of our initial activity in connection with the Project on Design of Physics Buildings. We will appreciate receiving any suggestions that any of you have.

DISCUSSION

Kirkpatrick: I want to ask if that square room at Northwestern

where you set the lecture table in the corner, is that satisfactory for projection? Bockstahler:

I think the angle is too wide. It holds 186 seats. I wouldn't want more than 100 people in it. I keep the wings clear if possible. Eaton:

As a thirty-four year expert, I can explain what is wrong with this lecture room and I think this is a good place to start. Since the apparatus is usually on the table, the side seats near the front are at a bad angle and are not used-those seats are wasted. It has always seemed to me that if the lecture table were across the corner, we would save quite a bit of space. Although we have our water and things of that kind on the lecture table, they sometimes get in the way. I see of no reason why these things couldn't be mounted along the side wall here with some sinks and things of that kind. I would also suggest that along the wall we would have some translucent screens of flashed glass illuminated from behind. We should have some ordinary chalkboards like these, perhaps of green glass, and in addition one of white glass. If a clear space were provided through the

apparatus cases behind the white board, it would be pos-sible to project from behind onto the white board. You might project rectangular coordinates onto your screen and draw your graphs on the board. Turn off your lan-tern and your coordinates are gone. You might project a certain piece of equipment and then show the electri-cal connections. Now these are some things I would like to have if I were making this room over. The most im-portant item would be the complete absence of windows. For example, if all these walls were white plaster, what beautiful projection surfaces you would have. Rogers:

What you are really doing there is converting the lecture room to one that is deeper and narrower. Eaton:

No, I don't think so. What I'm saying is that I am simply doing away with these seats I am not using. They represent waste space. Kirkpatrick:

Would you use curved rows of seats in which case the seats cannot be one behind the other which makes it difficult to give examinations? Overbeck:

I have a plan of seating for our room which is quite effective for examinations.

Rogers: But you lose about 30%. May I cite an ancient insti-

tution. The Royal Institution of London, projects a spectrum from way back in the apparatus room onto a translucent screen. Eaton:

The fact is I project a mercury spectrum in this room. I put the mercury vapor source near the back of the room and I project on this beaded screen and every-body in the room can see the two yellow lines separated on the screen. Rogers:

I would like to suggest as a criterion you stand at the center of the lecture desk look up at the audience and swing out 45 degrees on either side. I find it is a cri-terion architects can remember. Kirkpatrick:

When one has the table crowded with equipment it sometimes gets in the way of the blackboard. You can

57

avoid this interference by a scheme that I accidentally worked out by having the lecturer step up onto a step this high when he goes from his table back to his board. It puts all the written work up where everybody can see it. I don't believe I have been in a lecture room with enough board space. Furthermore, there are few lec-ture halls that are well designed for permitting projec-tion of slides and motion pictures while maintaining illumination for people to take notes and for the black-boards to be used at the same time. Overbeck:

I notice that Eaton has a projector which could be used on the table and a mechanism for writing on the projector and projecting it on the screen. Do you ever use it that way? Eaton:

No.

THE SHOP IN A PHYSICS DEMONSTRATION LECTURE PROGRAM

Lester I. Bockstahler, Northwestern University

In preparing this paper I have been guided by certain principles or deep seated convictions. These I list as axioms or self-evident truths.

1) Physics is essentially an experimental science. Demonstrations are indispensible in forming and fixing fundamental concepts in the minds of undergraduate students. Good demonstrations discourage sheer memorization.

2) Allowing for the fact that "mute inglorious demonstrators" are to be found among the fraternity of physics teachers, it seems to me that there is a real need for more inspiring demonstration lecturers. Per-haps this group is destined to follow into oblivion the "chautauqua lecturer" and the "4th of July orator." If this be the case, I wish to be counted among those who mourn their passing.

3) Any demonstration lecture can be only as ef-fective as the suitability of the equipment at the dis-posal of the lecturer.

4) The apparatus should be tailored to match the skill, the dexterity, and the objectives of the teacher.

5) In few cases can a hand-me-down piece of equipment substitute for apparatus designed and tested by the lecturer. He knows the peculiarities, the lim ita-tions, and the possibilities of such pieces. Through such media his inner feeling, understanding, and enthu-siasm is conveyed to the student.

If we accept these statements and their implications, even in part, no further argument need be made for an effective shop as a necessary accessory to a successful demonstration program.

I shall consider what may be called a typical shop associated with a physical laboratory or department in which demonstration lectures (elementary as well as on an advanced level) are accepted as an integral part of

instruction in physics. It is clearly recognized that no one ideal shop layout or organization will fit all possible circumstances. Every case must be considered in light of local conditions. Furthermore such a shop cannot be completely disengaged from other interests of the labo-ratory. Service to all undergraduate instruction (in-cluding introductory research) is an inevitable activity of the shop. If graduate and project research as well as services to other departments (i.e., chemistry, biology, astronomy) are to be included in the shop duties, the proper facilities must be added. I shall consider con-crete and what appear to me to be the basic needs and characteristics of a shop which can effectively support a good demonstration lecture program. Three points will be covered: (a) space, (b) personnel, (c) equipment.

(a) Space. The main shop will occupy about 1500 square fe~ x 50'). Floor space should be subdi-vided to provide for a wood shop, adequate student work space, and a paint room with ventilated spray booth and drying oven. These rooms should be independent but communicate directly with the main shop. The usual service utilities are taken for granted. Ample raw stock and general storage space should be considered carefully. (Minimum shelf length 16 feet.)

(b) Personnel. Among the skills, talents, knowl-edge, and competence to be sought in the shop staff are: machinist, fine mechanics, welding, hard soldering, basic electronic circuitry, electrical repair, rudimen-tary glass blowing, a range of experience--including, if possible, instrument manufacture. The foreman should have a generous measure of imagination and some knowledge of drawing and design. If student instruction in shop practice is to be included in the program, apti-tudes for this are not to be overlooked. Personality is of greater importance here than in an industrial position.

58

In many cases the demonstration lecture assistant and the curator of supplies and apparatus may well be included in the shop staff. The question of providing and training of competent shop personnel and demon-stration lecture assistants might well be studied seri-ously by a national committee. Such positions are in-deed essential and can be made very attractive.

Depending on local activities and interests some pro-vision for optical grinding, polishing, etc. may be de-sirable ..

(c) Basic equipment with approximate cost. 1) Milling machine (Shaper) $ 7500 2) Lathe, large, -12" swing, 30" bed 8500 3) Lathe, small, bench 3200 4) Band saw 2400 5) Drill press, large 800 6) Drill press, small 140 7) Drill press, precision 250 8) Pedestal Grinder - buffer 320 9) Welding - oxy - aceteylene 150

10) Paint spray gun gear 60 11) Sheet metal shear 200 12) Sheet metal brake 350 13) Circular wood saw 300 14) Glass saw 500 15) Stock cut off saw 400 16) Spot welder 600 1 7) Sander 150 18) Gauges, calipers, tools etc. 3000 19) Accessories for machines

(chucks, collets) 20) Student shop machines

2500

(used or low precision) 3000 With this basic equipment clever members of a shop staff will provide themselves with many other necessary and helpful contrivances.

The cost of a well equipped shop may, at current prices, approach forty thousand dollars. At the other extreme one may omit, substitute, compromise and come up with a surprisingly useful shop consisting of a "mail order" drill press, a table lathe, and an electric soldering iron manned by the lecturer himself and some student help.

A supplemental shop located in or near the prepara-tion room will be a decided convenience. Since this is not to be primarily a construction shop the equipment need not all be of precision grade - some even second hand.

Bench lathe $400 Bench & Vise Drill press 100 Chest & Tools Emery Wheel 25 Miscellaneous tools

$ 75 100

Soldering gun 15 and gauges 100 The cost of fitting this shop will be in the neighborhood of a thousand dollars.

The advantage of shop made apparatus does not lie

in its lower cost. I doubt that locally fabricated equip-ment can compete cost-wise with many standard items available on the open market. In my opinion shop made equipment reflects the understanding, the enthusiasm, the warmth, and the deep seated interest of the demon-strator in good physics. Granted of course that he has had a major part in conceiving and designing the demon-stration gear. Unless the lecturer has this experience his demonstrations are likely to have the earmarks of "sounding brass and a tinkling cymbal." We need simply to recall such inspiring examples as D. C. Miller's projection of the fringes of a Michelson interferometer, the elegant spectacle of electrical discharge through gases by C. T. Knipp, not to mention many stimulating demonstrations by members of this association at re-cent meetings.

It is proper at this point to call attention to the many reports and papers which have treated with the design and construction of demonstration apparatus. Size, simplicity, color, visibility, etc. must be given careful consideration. Shoddy, malfunctioning, poorly designed pieces have no place on the demonstration lecture table.

This paper must in no way be construed as opposing or discrediting factory built apparatus. In the area of standard items, of mass production, of meters, and in service to schools which cannot maintain an adequate shop the apparatus manufacturer will always be indis-pensable. The physics shop can in fact do much de-velopment research for the manufacturer.

To summarize: a) Physics is an experimental science and as such

lends itself exceptionaUy well to the use of demonstra-tions.

b) The demonstration lecture is unexcelled in clarifying and fixing concepts. It must never be used solely to mystify or simply to entertain.

c) Good demonstrating is at best an art but it can be only as effective and inspiring as the equipment available is appropriate and timely.

d) The effective demonstrator must be a student and a researcher in the field of demonstrating. This covers the entire gamut of physics. To this end a well equipped shop is as essential in this area as in any other field of research.

e) At first glance the initial cost of a good shop seems high. Relative to the cost of other projects car-ried on in the physical sciences it is really modest. When one considers that it is in the demonstration lee-ture that the basis is usually laid-the seed implanted-for future interest and genuine understanding of physics, the cost is fully justifiable.

Grateful acknowledgement is made to Mr. Petzel of our shop, and to certain members of the shop staffs of neighbouring physical laboratories who have given valu-able suggestions as to minimal equipment requirements.

DISCUSSION

Kelly: I would like to ask this question: Is it possible for

cooperation to exist among small colleges and large universities in the making of equipment for demonstra-

tion? I believe that at Northwestern it has been possi-ble to do this to a limited degree? Overbeck:

Yes, there have been requests to duplicate some of

our equipment. It has been done by the shopman on his own, if he wishes to do it on his own time in the evening. As a usual thing, however, these requests have been turned down. Kelly:

I think some of the major universities have a policy of allowing their staff people to do work in the evenings on their own time. I wonder how wide-spread this is and whether it could be exploited to help some of the smaller colleges. Could we arrange cooperation among colleges and universities in various areas? Bockstahler:

I suppose it could be arranged but I would caution against allowing your shopman to do outside work. The shopman is likely to get so interested in something that Mr. X is doing that he will forget all about you. Zemansky:

Has there been a problem in working outside of work-ing hours? Bockstahler:

Yes, he's using your equipment-so I should caution against doing that kind of thing. Rogers:

I would like to ask Dr. Kelly if the AIP would write to colleges with shops and ask what they are prepared to do. I know for instance the Princeton Physics De-partment would not make apparatus in their own shop for a commercial outfit, but they would make it for another college. They would charge the shop rate plus overhead. We do this between departments and with neighboring institutions quite a lot. Overbeck:

I agree with Bockstahler that if it is going to be done at all it has to be very carefully controlled so that the shopman not only doesn't become too interested in his extra-pay work but uses so much of his evening and night time that the next day he's too tired. Bockstahler:

How does your general shop differ from your re-search shop? Kirkpatrick:

I think for every lecture room, back there with the appa:ratus there should be a shop-some places it's only

59 a soldering tool, some places it's more ambitious. What should that shop be like? Bockstahler:

I would list the curator as a member of the shop so that he could go down to the main shop. He might have a soldering iron or hammer here, but to do your repair work I would send him downstairs as a member of the main shop and he would have access to all of the material. Kirkpatrick:

I would certainly recommend a more ambitious shop attached to the lecture system. I have found a great ad-vantage in having a shop adjacent to the apparatus room and someone in the backstage staff who knows how to use it. Comment:

I thought I would mention another way to get demon-stration equipment. Many of the students in our school take shop courses and the overwhelming majority do a thesis before getting the bachelor's degree. In many cases, the projects have been such that we have gained laboratory pieces from their work. Some of our best work actually has been done by well-trained under-graduate students getting course credit and building equipment for the school. Can we exploit that? Olson:

I am a bit confused here, because I started thinking this was a list of equipment for a special shop associ-ated with the lecture. There is another shop perhaps a bigger shop that was utilized for all the other functions of the physics department, specifically the research function. Is this a list for a shop for the teaching course? Bockstahler:

I am talking about a shop to support the lecture table. If in addition you want to have personnel to do your re-search shop work, it's okay with me. I am pleading for a shop that will support effectively the lecture-demon-stration program of a man who is going to make the thing go. It wouldn't necessarily have to be separate. Overbeck:

I would like to support what Dr. Kirkpatrick brought up that each of the laboratories, the lecture room and so on, have a work table with a vise, bit and brace, saw and soldering material.

NEW DEMONSTRATION APPARATUS MANUFACTURERS SHOULD PROVIDE

Howard A. Robinson, Adelphi College

I have been asked to talk to you today on the subject "New Demonstration Apparatus Manufacturers Should Provide." I have chosen to understand that wording somewhat liberally and intend to go off on several tan-gents.

First I must tell you that I returned to teaching only two years ago to a school that has had no tradition in the teaching of physics and therefore no equipment. During this two year period we have increased the number of physics majors from 50 students to 400; the number of problems which has consequently arisen have been so large and so diverse that the matter of demonstration

apparatus has had to play a rather minor role. I am, therefore, not well qualified to talk to you on this sub-ject and feel that most of you are experts while I cer-tainly am not. When I reminded Dr. Kelly of the Ameri-can Institute of Physics of this fact, when he asked me to handle this particular subject, the answer I got was "Well you will at least furnish a fresh viewpoint." What you are going to get is just that, a fresh viewpoint.

There is no question but that a problem concerning new demonstration apparatus exists, for we certainly do not have available to us all of the equipment that we would like to have; the problem possesses a number of

60

facets some of which I would like to mention in some de-tail and on some of which I would particularly like to comment. My first comment is on the matter of size and visibility. We have been over this today in detail and at the risk of some repetition I would like to point out that the three things that we have talked about so far are large-scale apparatus, such as Dr. Kenworthy dis-cussed this morning; projection-type apparatus such as that described by Dr. Pohl; and the television-type of magnification which Dr. Hoyt discussed at some length. Now when I was requested to give this talk I was pre-sented with the results of a survey which the American Association of Physics Teachers made some two years ago, in 1956-57, and in which a number of you here par-ticipated. Physicists from one hundred colleges in the country were asked a number of questions and it's of interest that in the tabulation the need for better large-scale apparatus was mentioned by 24 of the 100 people; the need for projection-type apparatus was mentioned by 15 of the 100 people, and better use of television was mentioned by 10 of the 100 people. These figures give you the order of magnitude perhaps of interest in these various types of things. But I think we can also say that the type of magnification that we must use will depend upon the size of the school and certainly on such aux-iliary problems as the design of lecture halls and things like that. These factors must certainly have a bearing in the future on the design of demonstration apparatus and this is one thing which I am sure the manufacturers will want to take some notice of. Furthermore I con-clude from what has gone on here today that first, noth-ing on the demonstration lecture table can probably be made too large, and that second, the imaginative use of color is certainly lacking. It is clear that both color and size certainly play a large part in the visibility problem and these are things that perhaps have not been carefully enough considered by the suppliers.

Now the second aspect of the problem is the fact that there should be a trend away from a purely qualitative type of demonstration apparatus. We should as far as possible emphasize quantitative results and apparatus should be made to read in numbers which the whole class can see; for example, temperatures should be readable and force tables should give forces which can be read. Apparatus which only illustrates a principle qualitatively is probably of less interest to this group than many things which can be made more quantitative.

A third part of the problem which complicates our lives is the fact of (to quote the title of a famous book by Henry Crew) "The Rise of Modern Physics." This is something which probably plagues us more than any other single thing in the lecture room. It's no longer possible, in my opinion, to hold class interest by dis-cussing how trolley cars, steam engines and steam shovels work. And as time has gone on I think that the tendency in most places has been to try to use, as illus-trative subject matter, material from the body of mod-ern physics. That is, we measure masses and things like that and almost immediately talk about masses of electrons. We have to expect that apparatus which was developed during the 19th century and which many of us are still using, while perhaps satisfactory from a tradi-tional point of view, is now no longer as useful as it

once was. A somewhat far-fetched example of this per-haps is the famous Guinea and Feather Tube. Recently several of us were going over lists of apparatus which should be purchasable for high schools. This famous item appeared on that list and during the discussion it came out that the historical reason for this particular name was due to the fact that sometime during the late 19th century, Tyndall came to this country and gave a series of lecture demonstrations. One of the things which he demonstrated was this famous Guinea and Feather Tube. Now guineas are no longer legal tender even in England so it's about time we did something to bring this situation a little more up to date. I don't feel in all cases that apparatus which is being offered has necessarily kept pace with the developments of physics. We have seen a number of such things today and have talked of a number of things the past few days that cer-tainly will bear this out.

As mentioned previously one of the great problems has always been the making of temperature measure-ments on a scale that is visible to an audience. Now at the Apparatus Competition, which we held in January in New York, one of the rather interesting exhibits was one from the City College of New York in which they showed temperature changes due to adiabatic expansion and compression. A transistorized amplifier circuit was used which made the temperature changes clearly visible. There must be a number of cases where the use of transistors would be useful. There certainly isn't a person in this room who doesn't have the prob-lem of measuring temperature during demonstrations and making the reading visible; this is one way in which it could be done.

One of the things that I have found very useful is the old ampere-frame type of apparatus where you can set up a coil which makes contact in a pool of mercury on the bottom and some kind of a rotation contact on the top. The thing supposedly rotates, but of course, it never does. The apparatus is very fragile and no matter how carefully you pack it away it gets bent. It's a hope-less situation to use one over any extended period of time. Apparatus which is important as this, and which can be used to show so many of the electrical magnetic interaction laws, is something which should certainly be redesigned.

Now one of the reasons why this lag in design occurs is probably due to the innate conservatism not only of the manufacturer but also of the physicist. I read with a great deal of interest in the last issue of Physics Today a review of a new textbook which has just come out which happened to have been reviewed by a man who had returned to physics teaching after an absence of 20 years. He expressed himself as being horrified at the fact that many textbooks, of which the one under review was an example, are still in essentially the same form they were 20 years ago when he went to school. Now I think you only have to look at a textbook in chemistry to realize how drastically the teaching of chemistry has changed in 20 years and how perhaps much less drastically the teaching or the textbook writ-ing in physics has changed in this same period. This is very startling because, of course, the change in chemistry was due to the change in physics and it

certainly seems curious that our own texts reflect so little change. I am quite sure that many schools when they teach physics take some textbook and get their ideas for lecture demonstrations out of things which are in this book and I would suppose that the manufacturer often does the same thing. So I think the conservatism here is partly our fault.

Now on an even worse scale perhaps is the fact that there are a number of experiments in Modern Physics which would be very useful if we could demonstrate them to large classes but which are, so far as I know, wholly impossible of being demonstrated today. I real-ize that this is a strong statement and may very well be due to my own inexperience; I have picked four such ex-amples at random any one of which seems to me to be fairly important. For example, I don't suppose it would be possible to demonstrate Rutherford scattering·. It seems that this would be difficult to demonstrate without spending a great deal of money and, of course, this is a complication for all of us. Another example is the Thompson experiment on electron diffraction. The Stern-Gerlach effect would be a wonderful thing to demonstrate and certainly this in itself would be diffi-cult as things now stand. One would also like to show Maxwell's distribution of velocities. There is certainly room for a lot more to be done and it is this lag which does worry me a little bit.

I would now like to switch very abruptly at this point to talk about the economics of the whole apparatus situ-ation. This is partially meant as an apology for the situation in which the manufacturers find themselves. Let us first look at the results of the AAPT study. The 100 colleges, who were questioned, spent among them-selves, including work in their own shops $380,000 a year for demonstration apparatus. Now if you multiply this by 5.4 (this magic figure arises because of the fact that there are 543 physics departments in colleges in the United States at the present time according to the AlP figures) you come out with a total business includ-ing shop work in the college laboratories of something like two million dollars. Now if we are to increase this to include high schools I would suppose the figure would go up to between three and four million dollars as the amount of business that is available to manufacturers. I understand from talking with Mr. O'Connor and Dr. Picard and some of the others here today that the total business of Cenco and Welch (which I take simply be-cause they are presumably the main suppliers in this field) combined is in the neighborhood of $25 million a year. Clearly the 3-4 million dollars which the physics departments give to these companies is certainly not a major portion of their endeavor. Now I would like to do one minor calculation. If I write down here this magic figure of four million dollars as roughly the amount of the economic market we are talking about, I'd like to remind you that for many American manufacturing companies, one can estimate as a good round average figure that one per cent of the sales dollar can be spent on research and development. Now one per cent of four million dollars is $40,000 and we cannot expect that with this order of magnitude of money available that the instrument makers are going to be in a position to fi-nance and develop all of the things which we would like

61 to do. In addition to this complication, there are cer-tain complications in the market itself. The market is highly individualistic and one piece of apparatus which College A may think is absolutely indispensable, Col-lege B may think isn't worth a hill of beans. In addition it turns out that marketing costs in this field are high in proportion to sales; there is, therefore, an economic problem here which I think we must be cognizant of and sympathetic with.

Now on the other side it does seem that the matter of contact between us as consumers and the apparatus makers as suppliers is probably not as good as it ought to be. If this small amount of development money is all that there is available we certainly must do some-thing to improve our liaison and help insure that what we want and what the suppliers are going to give us are the same thing. It is possible that AAPT can be of some assistance in this matter.

Now to return to the manufacturers, and here again my comments may well reflect my lack of experience. I have a number of salesmen call on me for apparatus houses and I have a number of salesmen call on me for textbooks. I am continually being struck by the differ-ence in attitude between these two groups. I don't sup-pose that a textbook salesman ever comes into my office but what he doesn't do everything he can to find someone in the department who wants to write a textbook that he can sell and he's just begging for ideas which they can invest in. I have never had (and this may well be due to our situation), a representative of an apparatus manu-facturer ask me for a single idea. Now I don't want to say that this is general, but there is certainly a great difference in the approach of these two types of business organizations to a somewhat similar problem.

Now to go back for the moment to what the Apparatus Committee of the AAPT might do, I would like to point out two things which are already underway and which could be useful in this respect. One of these, of course, is the publication of the Taylor Memorial Manual. Cer-tainly in that manual there are going to be a great num-ber of experiments described which will be very im-portant and for which some market presumably will be available. The second thing is the Apparatus Drawing project which the AAPT is now sponsoring. Out of this will surely come a wealth of information on things which would be useful to have. My one comment to the people who sell apparatus is that the study of projects such as these by them could well be helpful to all of us. The only thing I am pleading for is that somehow the channel of communication should be opened further to their and our mutual advantage.

Now there is another complication in this picture which we ourselves are imposing on the apparatus market. The survey showed by almost 2 to 1 that com-pletely assembled pieces of apparatus were more de-sirable for demonstration use than were unit parts which one could assemble by himself. This means, of course, that terrific duplication is necessary; it is cer-tainly one of the major factors in complicating the ap-paratus market.

In closing I would like to mention a few specific types of apparatus, which seemed to me to be needed. This is a very dangerous thing to do for as I have

62 already said, something which may seem desirable at College A is anathema to College B. I will start out by mentioning a few facts which the apparatus survey brought to light. (The report, incidentally, also brought forth two conclusions which I think perhaps should be stressed. First, the manufacturer concluded very defi-nitely from our study that physics professors just don't study catalogues, and that many things are available which those involved in the survey seemed to think un-available. Physics professors on the other hand con-cluded from studying the survey that the apparatus manufacturers just didn't understand what is wanted. As you see, the conclusions which you draw depend on which viewpoint you take.) Now to go back to some of the facts. There were five pieces of apparatus which were in greater demand than any of the others. These five items are those to which the greatest number of institutions gave a high rating without stipulating cost; they are thus the items which to many men in the field seem to be most conspicuously lacking. The first of these is a projection apparatus for Brownian motion. The second apparatus listed is a simple projection spec-troscope. Now surely there must be ways of projecting spectra. The third listing was a projection cloud cham-ber which I think you will all agree would be something useful. The fourth item actually covers several pieces of equipment and has already been mentioned previously; that is simple apparatus for experiments in Nuclear Physics. Actually there is a lot of such apparatus if you care to look for it. But much such apparatus is not inexpensive. Now the fifth item is something which brings with it a number of specific problems about which I would like to comment; this was a photoelectric tube for measuring Planck's constant. I understand in talk-ing with manufacturers of equipment that it is very dif-ficult for them to furnish special tubes of any descrip-tion; I think that the only solution to this problem is to find some manufacturing concern willing to produce special tubes on order. Certainly a tube for Planck's constant is one of our prime needs, although it is pos-sible to import them. In any case, some solution of the special tube problem is certainly indicated as a result of this survey.

I would like now to mention just a few of the other things which received a double star rather than a triple star in the survey. There seems to be a great deal of trouble with carbon arcs. And people would like a more versatile automatic-feeding carbon arc. I don't know if they are available or not. The second one is a bright projection galvanometer. It would seem that this prob-lem must have been solved some place although perhaps not. A third thing was a wave demonstration apparatus showing impedance matching. The whole wave concept is a very important one and improved apparatus would be highly desirable in this field. Another item which is very important (and I wouldn't know how to demonstrate the effect on a lecture table), is a black body radiation apparatus giving energy data as a function of wave length. Another thing which I am sure we have all run up against is a high level signal generator of variable frequency. This I am sure would be useful.

At the apparatus contest in New York, there were at least five pieces of apparatus which would be useful to

have and which might conceivably find a market. The first of these was Mr. Waage's very successful alpha particle counter which has been demonstrated to you here. This is a piece of apparatus which, it would seem, would fill a number of requirements. With its use an important modern physics concept becomes not only visible but audible and one can both see and hear a very small scale phenomena. Another thing which has been suggested is that the electro-magnetic pump which also won a prize in the competition might be something which would be useful in teaching the laws of electro-magnetic induction. The third thing is the adiabatic temperature-change apparatus which we have already mentioned earlier. The fourth thing was the air cush-ioned puck which has been developed at MIT which seems to me to be highly important. I would like to digress here for a moment to go back to the subject of textbooks. There will shortly appear from MIT a new textbook on Mechanics which we are going to use by special arrange-ment at our college next year in special courses that we are giving. This book develops mechanics from the study of momentum and the text is developed completely around the use of this puck. Now this textbook may not gain wide acceptance, but if it does, the absence of the air cushioned puck may be serious indeed. In any case, the device is novel and highly useful. Available models need further development work. Now the fifth thing which I have picked out was the Doppler effect apparatus which also was developed at the City College of New York. This seems to be the only Doppler apparatus in existence which really demonstrates a true effect. So there were at least five items in the apparatus compe-tition which would certainly serve as useful things to consider.

I understand that the manufacturing companies even though they only have this small amount of money at their disposal usually consider something of the order of magnitude of twenty pieces of apparatus per year and of these approximately ten actually see daylight. Now in addition we may also say that it takes probably on the average of about a year for one of these pieces of apparatus to be developed and to reach the markets so this gives the time scale we are faced with.

Author's note on revising notes for publication: In the original presentation a number of extra ap-

paratus needs were mentioned at the end of this paper. These needs were drawn up as a result of a verbal dis-cuss ion with a number of other physicists. Except for apparatus capable of demonstrating the relativistic change in e/m and a less expensive set up for measur-ing nuclear magnetic resonance, it turns out that sources are actually available for the other items.

Note prepared by W. C. Kelly at the request of the editor:

The Study of Apparatus for the Teaching of Physics yielded materials that would be helpful to physics de-partments that are reviewing their stock of laboratory and demonstration equipment. Included are reports on visits to institutions that participated in the Study; copies of laboratory manuals, experiment sheets, and

lists of apparatus; photographs of apparatus built in de-partmental shops; and catalogs and facilities booklets of apparatus manufacturers. Supplementary materials are constantly being added to these by the Committee on Apparatus. The materials are stored at the American

63 Institute of Physics, 335 East 45 Street, New York 17, New York. They are available for use at the Institute by appointment by representatives of physics depart-ments, by committees of the American Association of Physics Teachers, and by apparatus manufacturers.

DISCUSSION

O'Connor: I thank you, Dr. Robinson, for giving these matters

very careful thought, and you should be commended for having covered so many different points so well. Our major need now is not suggestions for new pieces of equipment but to figure out which one to start working on. This is a very real problem and probably our greatest. There is another problem, namely, that some things are wanted that we don't know how to make. We need a closer relationship between manufacturer and teachers. We would like to have people go out and call on teachers, but we can't do that. However, letters, even if only three lines long, telling us that a certain piece of equipment could be a lot better if we did such and such receive careful attention. So we are very sin-cere in wanting this kind of help. Kelly:

I would like to comment on the remarks Mr. O'Connor made, but first let me say that Dr. Robinson did a very good job on reporting on work that he had not done him-self. I would like to remind you that the study of appa-ratus which was carried on by the AAPT Committee on Apparatus consisted of several parts. The question-naire to which Dr. Robinson referred was first sum-marized by a post card survey and then we sent out a questionnaire to 98 physics departments. The survey indicated the need to call to the attention of our col-leagues sources of information about apparatus of which they are not aware. There may be a number of these things which are commercially available but, obviously,

it isn't going to do a physics teacher any good if he doesn't know about it. As far as the other needed items of equipment are concerned, I must point to the second part of the study which was a series of visits I made to the colleges and universities. I visited about thirty-six, making notes and taking photographs. As a result I think we were able to offer rather specific suggestions to manufacturers about existing prototype equipment of many kinds. There are further problems, however, and these are problems of cooperation. In some cases the manufacturer may make a bona fide attempt to borrow the equipment to look it over, but for one reason or another the physics department was not able to furnish the prototype equipment. It is obvious also that re-search and development funds for new equipment will go a lot further if we supply ideas in rather specific form, prototype equipment which can be lent to the manufacturer perhaps. We have been able to make sug-gestions in many of these cases to the apparatus manu-facturers so we must look at the record then in terms of the availability of some rather specific ideas that were furnished to the manufacturers. Eaton:

I would just say that as far as the low friction pucks are concerned, they are on the market. I have had my order in for two weeks and I hoped they would be in be-fore today but they haven't arrived yet.

Session VI

INEXPENSIVE AND SIMPLE APPARATUS

Presiding: R. R. Palmer

An evening session was spent on the kind of entertainment that a demonstration lecturer likes best, simple equipment demonstrating both important and minor physical principles.

Each member of the conference, with his very best showmanship, performed one or more experiments with a piece of apparatus of his own selection that cost less than a dollar and could be demonstrated in less than two minutes. Many pieces were "home-made," but the limit on cost did not include the value of the conference member's time spent in design and construction.

Session Vll

DEVELOPING SKILLED DEMONSTRATORS

Presiding: R. J. Seeger

TRAINING JUNIOR STAFF MEMBERS

Leonard 0. Olsen, Case Institute of Technology

I am not an advocate of the lecture method. If there is no "give and take" between student and instructor there may be some learning but little teaching. The use of well-written books in a quiet room is a much better method of acquiring knowledge than the large packed lecture hall. Good books, and small recitation sections for discussion of subtle and difficult concepts, form the most effective, efficient system for the acquisition of knowledge. Motivation and interest rise in direct rela-tionship to knowledge gained and understanding of the concepts mastered.

We start with the wrong approach if we assume we are going to have so many students and so few instruc-tors that we can't do anything but shove more and more students into bigger and bigger lecture rooms. This approach will inevitably produce fewer teachers, more films, more video tapes and certain stagnation. Per-haps we need to be more critical about who goes to col-lege and what is required of them to stay there. With favorable teaching conditions, more good teachers will be available and our educational system can move to a higher level of achievement. We really have made practically no effort along the line of producing quanti-ties of good teachers.

Certainly if the large lecture section is inevitable, much more emphasis must be placed on demonstrations as well as on other visual aids. The physics instructor is in an advantageous position compared with his hu-manities colleague for many of the topics he wishes to discuss can be illustrated with good demonstrations.

Good physics teachers who are ardent enthusiasts for demonstration lecturing are undoubtedly presenting good and interesting physics courses. Such physics lecturers are born. They are certainly not made in our graduate schools, which so intensely stress the impor-tance of research. In fact potential lecturers are prob-ably being converted into researchers and it is difficult to visualize that there will be any trend away from this research emphasis in the near future. Physics teaching by demonstration lecturing is a full time job in even a modest size college. It can be successfully done only if the physicist makes a career of it.

We are quite enthusiastic about the General Physics instruction method which we developed at Case because of our dissatisfaction with the more conventional lec-ture demonstration-recitation section method which we formerly used. Our lectures seemed to be quite good but we became convinced that our students learned their physics from the text and the infrequent recitation sec-tions. In my 20 years at Case there has not been one capable staff member interested in or agreeable to de-veloping a lecture demonstration course for even one-half of our two year physics course! Yet, all of these staff members have always been interested in teaching

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a recitation section of General Physics and are willing to develop a few demonstration lectures for this course.

Our present two-year course is essentially taught in small recitation sections. We give about five demon-stration lectures per semester and some of the demon-strations are quantitative, requiring analysis and some report writing by the students. Each\senior staff mem-ber is responsible for about two of these lectures and usually gives each lecture four or five times to the several larger groups of students who are scheduled together for lectures. The lectures have retained their high quality and have been changed often, sometimes in part or in total, both to meet the interest of the lecturer and to meet new developments in physics. Student in-terest has been high.

Instruction in the recitation sections is given by senior and junior staff members with considerable supervision by one senior man. The entire general course is under the continuous scrutiny of a small de-partmental committee. Junior instructors are previous top level graduate assistants who have demonstrated teaching ability in our laboratory and have also demon-strated academic ability. The junior instructors are also involved in the lecture demonstrations we give. They are all assigned to understudy the responsible senior men. They aid in planning and setting up the lectures and usually give each lecture once after ob-serving at least one of the lectures of the senior man.

Careful attention to these junior instructors by the course supervisor materially aids their development. We are proud of the good teachers who have earned Ph.D's at Case and are certain that more of them would have stayed in academic circles if the climate there was more attractive. It is perhaps obvious that most of these good young teachers would have missed the opportunity to learn about teaching and its thrills if our general course were taught by the lecture method with a capable career lecturer.

Admittedly the Case plan of heavy emphasis on small informal sections and relatively small use of lecture demonstrations is a compromise, but I suppose we will always have compromises. Ideally, every small class-room would be equipped with demonstration gear so that each instructor could readily show his students how physics works. Few institutions could afford the space, equipment and staff required. Case can't afford this approach. We have therefore reduced the time for more formal demonstrations to a minimum and show only those experiments and effects which we feel con-tribute greatly to ease and speed of learning. We do encourage the section instructors to use demonstrations in their teaching but not enough of this is done.

Demonstrations can and should be utilized by the recitation section instructor. If we can preserve small

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section teaching, we must improve the method by more use of better demonstrations. A convenient central sup-ply of good, easily portable equipment with which the instructor is fully familiar is one rather obvious im-provement.

There is obviously nothing wrong with good demon-strations. If their use does not conflict with student participation in small, informal study and discussion

classes they add strength and elegance to any course. Unfortunately, as with television and motion pictures, thinking about demonstrations becomes entangled with thoughts of inexpensive solutions to problems of mass education. If we can have good demonstrations without large lecture sections I imagine nearly every physics teacher would be for them!

DISCUSSION

(Q): I gather from your remarks that on occasion a graduate student may give a demonstration lecture. Is this correct?

Olsen: Yes, a top level graduate assistant who has demon-

strated academic and teaching ability usually gives one lecture after having seen a senior man give the lecture in an earlier lecture section. Comment:

It is common practice to use the College Physics laboratory as a first step in teaching experience. Suc-cess in this field may lead to the assignment of a Dis-cuss ion Class in the following year. The last stage is certainly the lecture demonstration. Comment:

I have reservations about giving so few demonstra-tion lectures. I think the demonstration ought to come when you are discussing the physical principle. A lot is lost if you, at intervals, use a period just to give a whole lot of demonstrations. Olsen:

I agree and we do try to correlate. For example, the lecture on gyroscopic motion comes the week when we study it in class. We rarely go back and demonstrate subjects already discussed. If we think a topic is im-portant enough, we schedule the demonstration lecture; otherwise, we don't demonstrate. (Q): Do you use demonstration equipment in recitation

classes? Olsen:

We encourage this, but I've seen too few instructors carry things to the classroom-a few do. (Q): How do you correlate with the laboratory? Olsen:

It is not coordinated with the course. Our laboratory course is an independent one-year course given in the sophomore year concurrent with the second half of our

two-year General Physics Course. The experiments range from mechanics, heat-sound, and electricity through modern physics. We only have two or three set-ups of each experiment and a variety of experiments are set up at the same time. The theory for experi-ments has always been covered in class before the stu-dent meets the material in the laboratory but he may have studied the material as much as a year earlier. The few demonstration lectures that we give are very closely coordinated to the recitation class work. Comment:

My experience with the single vs multiple lecturers in a course has been that the continuity of the course is lost when you have a series of "visiting" lecturers. I have, too often, seen many of these men go off on the tangents of their specific interests. I have seen no ade-quate way of informing the group of the background in order to maintain the desired continuity of the work. Olsen:

We don't have this trouble because we assign the subject matter for the day. We would have opposition trying to staff the course with an assignment of all the lectures to one or two men. The staff men will accept one or two lectures but not the whole course. They do a good job in their special lectures. In addition, our students meet many of our staff, and our staff learns what is going on in these courses. This, I think, is valuable. Comment:

I think we must be careful in these remarks to give a clear picture. Essentially, we need to recognize that there is no one system which alone can be labelled good or otherwise. A good lecture is good, a poor discussion class is poor; but this does not mean lectures are good and discussion classes are poor and vice versa. It is essential for each institution to work out its best sys-tem under existing conditions.

LITERATURE AND TRAINING FOR THE DEMONSTRATOR

Harald C. Jensen, Lake Forest College

Up to this point, this conference has been addressing itself primarily to the problems associated with provid-ing facilities for demonstrations. Techniques, methods, space and associated equipment and the kinds and sources of apparatus have been the objects of discus-sion. It goes almost without saying, however, that no

matter how much time, effort and money are devoted to these aspects, a successful and meaningful program of teaching physics by demonstration cannot exist in the absence of a skilled and enthusiastic demonstrator.

We have made occasional (almost incidental) refer-ence to the demonstrator, but it seems fair to say that

we have been making an implicit assumption that good demonstrators are to be found wherever physics is taught and that the primary need is to supply them with the proper environment and tools. This attitude is not at all surprising in view of the fact that this is a group of teachers who believe in demonstrations and are prac-ticed demonstrators. But it is entirely possible that another group of physics teachers could be assembled that would contend that physics could be successfully taught without the use of demonstrations. This group might even suggest that the time spent on a demonstra-tion might be better used in other ways. I am suggest-ing that the group of individuals assembled here is a unique one. We are advocates of demonstration teaching and as such must be concerned with the means by which those who are not can be persuaded to become demon-strators.

I would like to emphasize these introductory remarks by describing four different teachers with whom I am acquainted. The first of these is a young man who came to work with me this year. He is a mathematical physi-cist, an enthusiastic person and a very bright young chap. One of his assignments was to teach a class of beginning physics students which was to meet at the same time that I met another class of beginners. We have only one physics lecture room at Lake Forest Col-lege, so I apologized to him and said, "I'm sorry. I have the prerogative of using the lecture room and you'll have to meet your class in some other room. It will be very difficult for you to demonstrate." He re-plied, "That's OK. It doesn't make a bit of difference to me, Harald, I wouldn't demonstrate anyway." So he did teach beginning physics without using a single demonstration. You may be interested to know that he spent the first week or two of this course introducing formal vector analysis and used it as a tool throughout the year. He also succeeded in interesting a large per-centage of his class in becoming physics majors. This seems to indicate that he has some of the qualifications of a successful physics teacher, but the members of this conference would probably insist that he would be a better one if he did some demonstrating and that his students missed something.

The second teacher I would like to describe is my-self and how I came to be as much of a demonstrator as I am. I remember that the first book I bought for my professional library was the Sutton book entitled "Dem-onstration Experiments in Physics." Many hours were spent leafing through it in order to find something of interest to me in the hope that because it interested me it would also interest my students. As you know, many of the demonstrations described there are simple and inexpensive and so those are the ones that I began to use first. Then as my shop ability became a little more sophisticated I was able to build and use more and more pieces. Also as I began to know more physics, more of the descriptions of demonstrations had meaning for me. So now I have developed a library of demonstrations of such a number that I can put out two or three pieces three times a week thirty weeks a year. This has been a do-it-yourself experience. I accepted the value of demonstrating without question (probably because this method of thinking and teaching appealed to me and

71 suited me) and became a demonstrator inspired by Sutton and using, in the main, homemade apparatus. The members of this conference would probably agree that I could have used the demonstration method uf teaching to far greater advantage had I been able to proceed in a more professional manner.

My third subject of description is Vernet Eaton. Vernet is a professional and a perfectionist. He has at his disposal facilities making it possible for him to really demonstrate including a curator who makes and repairs apparatus and assists during the demonstration lecture, a room that is used for this one purpose only and is equipped for this special purpose, a shop staffed with competent technicians who can make and modify apparatus and, finally, a budget making the entire ac-tivity possible. The fact that this conference is being held on Professor Eaton's home grounds is an indica-tion that a group of teachers interested in demonstrat-ing know what the proper environment for demonstration teaching is. This is the kind of a situation I would like to be in. Since I am not, and there are many others who are not, it seems imperative that some kind of feedback from places like this to those like mine can take place so that the latter could become more professional.

The fourth person I want to include in this set of descriptions is Professor Pohl. It needs only to be said that he has convinced us by his presentations at this conference that he is a real expert. He is the kind of a demonstrator that could give lessons to Eaton.

I believe that these four descriptions point out two important needs. The first is that there is, in general, no planned, concerted or any type of formal effort in use making possible a feedback of the skills, techniques and other results of the work of demonstrating physics teachers such as Pohl and Eaton to persons like myself and my young associate. It seems to me that this is a concern of vital importance to this conference and that its conclusions should include suggestions and recom-mendations with respect to it. That the need is real is shown by the relative paucity of the literature on demon-strations. The Sutton book, already thirty years old, is unique. I fear that only a very small percentage of the new developments in the demonstration field find their way into the American Journal of Physics. The UNESCO publications address themselves to problems different from the ones of concern to us here. I repeat that it seems to me that a concerted and well-planned effort needs to be made to provide the young, beginning demon-strator with up-to-date reference materials and that such an effort may well be an appropriate outcome of this conference.

A second need is to put the training of young demon-strators on a less haphazard basis. It probably would be quite difficult to describe how a person does at pres-ent become a demonstrator, but I suspect that a given individual uses demonstrations in his teaching because of his own approach to physics. That is, an experi-mentalist is more inclined toward demonstrating than a theoretician. If this is so, a tremendous problem exists. The young theoretical physicist starting out as an instructor in general physics must first be convinced that demonstration is not only a useful but also a neces-sary teaching method if physics is to be taught in the

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proper perspective. This may be quite difficult in view of the possibility that he has learned the physics he knows without the benefit of demonstrations. Even here at Wesleyan some youngsters can take a beginning physics course taught without the use of the wonderful facilities at the disposal of the teaching staff. But even if the young theoretical physicist can be converted to this approach to the teaching of physics, we still expect him to learn to demonstrate without the aid of any for-mal training in the art. His experimental colleague faces the same state of negligence and apathy. This

conference, I suggest, should give evidence that it is aware of these difficulties.

I would like to conclude by summarizing my remarks very briefly in this fashion: The participants of this conference have shown by the discussions here that they believe the demonstration to be an important, useful and necessary aspect of teaching physics. Granted that this is true, it seems unavoidable that more attention must be paid to the training of demonstrators and to putting in their hands the information necessary for carrying out a demonstration program.

DISCUSSION

Comment: A few years ago we had a similar experience to the

one you mentioned. We gave a young theoretical physi-cist, new in the department a special class of about fifteen men of very high ability in the freshman class. The instructor did practically nothing in the way of demonstration. Comment:

I teach in a teachers college where the students are prepared to teach physics in the high schools. We be-lieve that demonstrations are important but we do have difficulties, since some, at first, do not like this form of presentation; particularly the mathematical physicists. Comment:

I think Case is providing experience in demonstration to their students. We hired a man who was very enthu-siastic about the training he received there. Perhaps this should also be part of the program of other schools. One cannot adequately judge a method until he has had some experience with it. Comment:

May I talk to Harald's first example, the theoretical man? I want to quote Galileo. He said that in taking up the Copernican theory he noticed that there was no one who held the Copernican view who had not been on the other side first, but when he examined the Aristotelians he found that there were none of them that had been a Copernican first and had then gone back to Aristotle. I think if you can get the theoretical man to demonstrate he will continue to do so. Our last two theoretical men

at Princeton listened generously when we talked to them about demonstrating, but did not seem convinced. But with a year of experience they were more trouble in the stockroom and more delight to their students than any-one we've had in years. They were full of ideas of things to demonstrate. Comment:

The question is: How are we going to convince these people that demonstrations are important? This con-ference should try to make proposals for the solution of this problem. Comment:

The thing that worries me is that some of these prob-lems are much too big for an hour's discussion. There are hundreds of teachers in the country anxious and eager to get information to help improve their teaching. We have had fun here doing and watching new demon-strations. But this is a small audience and really not the group that needs the stimulation and the ideas. I think we are using our Journal inadequately as a means of communication in this field. Comment:

My training was in theoretical physics and I classify myself as a theoretical physicist. But I wish to speak in defense of that group. I was converted to the need of good demonstrations by seeing what a colleague was able to do with lecture apparatus. Perhaps we are not hostile to demonstrations but rather uninformed in not having seen good demonstrations performed.

SUMMER INSTITUTES AND THE PREPARATION OF DEMONSTRATORS

Harold K. Schilling, The Pennsylvania State University

1. Basic Definitions and Assumptions

It is my task to discuss the subject of the preparation of demonstrators, with special reference to summer in-stitutes for teachers. In developing my thesis I wish to employ, and distinguish between, three terms. There-fore, I begin with the following definitions:

Dl. Demonstration means the showing or exhibiting of an object or phenomenon, the illustrating of a principle or process by means of apparatus, the

performing of an experiment before a group of spectators.

D2. A physics demonstration lecture is a lecture liberally interspersed with demonstrations for the purpose of more effectively teaching a sub-ject of physics. (It is not a lecture for the sake of the demonstrations themselves.)

D3. Lecture demonstration (L. D.) is the highly developed and demanding art of presenting demonstrations, that requires much knowledge,

many skills, and most of all creative imagina-tion.

I shall also make some assumptions that are implied by these definitions and that embody points of view de-veloped earlier in this conference.

Al. Demonstrations constitute an important and in-dispensable resource and method for effective teaching of natural science at all levels of edu-cation.

It seems incredible that truly good teaching of science can be done anywhere-in school or college-un-less pupils are given the opportunity actually to "see for themselves" directly many of the phenomena or aspects of nature with which natural science is concerned.

A2. The knowledge and skills specific to L.D. extend far beyond those native to science per se, and, therefore, should not be assumed to follow auto-matically from the study of science itself. It constitutes a field of study and professional en-deavor in its own right.

This is evident from several undeniable facts. Most beginning teachers of physics are "all thumbs" when first confronted with the tasks of lecture demonstration. In general the apparatus they have used in laboratory courses and in research is not suitable for demonstra-tion purposes. Problems of visibility and audibility take on a new order of importance. Often they encounter physical effects they have never heard of before. Then there are the psychological difficulties of capturing the interest and intellectual participation of a group of very different spectator individuals, and the artistic ones of presenting the demonstrations elegantly-so that the im-portant aesthetic values and dimensions of physics are not misrepresented or lost sight of. Last, but not least, they are likely to be unaware of the large repertoire of famed demonstrations, the many standard "tricks of the trade," and the extensive literature on the subject that are available to them.

A3. The field of L.D. is extensive and sufficiently demanding intellectually to warrant the estab-lishment of programs of instruction designed specifically to provide opportunities for system-atic study and preparation in it.

Here there arises again the old, hoary issue of whether explicit training in method is desirable or nec-essary. Without attempting to resolve it, I simply urge that if the preceding assumption (A2) is valid, namely that L.D. is indeed "a field of study and professional endeavor in its own right," then it follows that to achieve competence in it requires systematic study and prepa-ration. Such preparation will generally be most fruitful and efficient if it is provided in a program of instruction designed for the purpose.

A4. Such a program of training should not be only pedagogical or methodological, but should con-tribute to the student's mastery of subject matter content.

That this is entirely feasible follows, it seems to me, from the well-known fact of experience, that anyone who takes seriously the business of preparing the best pos-sible demonstrations for a given subject, will thereby learn much about that subject. For greatest effective-ness, therefore, a course of study and instruction in

73 L.D. should be designed explicitly so as to maximize the increment in subject matter understanding. It would, of course, be much easier simply to build it around gadgetry and tricks of the trade!

A5. It is highly desirable to include the systematic study of L.D. in the curricular offerings of in-stitutes for teachers.

It should not be assumed that L.D. will be achieved automatically as a by-product by a sort of mental os-mosis. It should be planned for. And if institutes for teachers are designed to increase the competence and effectiveness of teachers, they should not ignore the subject of L.D.

2. Features of Proposed Program of Instruction

I suggest that such study should have both formal and informal features, and should introduce the trainee to both the theory and practice of L.D. It might well in-clude the following features each of which I shall discuss briefly: observation of a master demonstrator in ac-tion, practice, independent study of the pertinent litera-ture, tours, and a formal course on L.D. Six full weeks or its equivalent, with six semester hours of credit, could easily be devoted to such a program. An effective allocation of time and effort might devote three semes-ter hours to a formal course running throughout the six weeks, with the rest of the time going into the informal features of the program. Of course, in many situations and for many classes shorter programs would be de-sirable. The main thing I am urging is that teacher education programs provide for suitable, systematic training in lecture demonstration for all teachers of natural· science-suitable in amount and kind.

Probably there is no better introduction to L.D. than to watch a master demonstrator give a complete series of demonstration lectures, take copious notes on the apparatus (including photographs of set-ups) and methods he used, and discuss with him the whys and wherefores, as well as alternatives, of procedures. Unfortunately, many teachers-and even prospective teachers with doctoral training in physics-have never seen a signifi-cant number of demonstrations well done. Relatively few institutions have planned their curriculums and structured their instructional staffs in such a way as to assure every prospective teacher of physics--or any other of the natural sciences-an opportunity to observe directly the meaning and instructional power of lecture demonstration at its best. Therefore, in-service train-ing programs, such as summer institutes, might well endeavor to make up this deficiency among others.

Without doubt next to seeing a master in action, the most valuable training for the future demonstrator de-rives from actual practice. Under this heading a train-ing program should provide at least three kinds of supervised experience. First, a trainee should act as a lecture assistant, where he can work at close range with someone more experienced. Here he can "get a feel" for apparatus set-ups with special reference to the problems of L.D., and learn something about the many techniques peculiar to it. Second, he should be given the opportunity to give demonstration lectures, in part or whole, under supervision with subsequent critical

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evaluation. Third, he should be expected to devise original demonstrations and construct apparatus. Cer-tainly one of the most important abilities of the demon-strator is that of devising new demonstrations to keep abreast of modern developments in his science, or to meet the specific needs of particular classes or teach-ing situations.

Under the heading of informal, independent study of the pertinent literature the following sources and sub-jects are suggested: books and journal articles about demonstrations, descriptions of the famous demonstra-tions all demonstrators should be familiar with, catalogs of apparatus houses, the elements of public speaking, the elements of the psychology of L.D., educational tests and measurements with special reference to the objec-tives of L.D., the architecture and appointments of lec-ture rooms.

Tours to schools, colleges and universities, insti-tutes and science museums can also be of great value in acquainting a trainee with "how other people do it," with a variety of facilities and equipment, with various conditions under which demonstrations must be given, with different types of audiences. Often one of the most important gains is an appreciation of "how not to do it" and why.

3. Content of Proposed Course on L.D.

What I refer to here is a systematic, organized course of lectures, study, discussion and practicum ex-perience carefully planned to introduce the trainee to all the main parts of the subject of L.D. and which pro-vides the basic rationale that gives meaning and direc-tion to the more informal elements of a training pro-gram. The main topics in such a course might well be: A. the Rationale of L.D., its specific goals, how to achieve these goals, evaluation in terms of goals; B. Lecturing, the lecturer, the lecture, the lecture schedule as an integral part of a physics course; C. Facilities, the lecture room, stock room, shop; D. Apparatus, and instrumental techniques; E. Criteria of Effectiveness of apparatus, of the individual demon-stration, of the demonstration lecture as a whole, of the entire series of lectures, of lecture notes for use of class, of ways of testing for effectiveness of teaching by demonstrations; F. the Profession's Repertoire of dem-onstrations; G. the Lecturer's Own Repertoire.

With some hesitancy I present in section 5-for what it may be worth illustratively-a brief and partial sylla-bus for the kind of course proposed here.

4. Suggestions about In-Service Institutes

We must now consider more specifically the matter of institutes for teachers, such as are sponsored and supported, for instance, by the National Science Founda-tion. I would strongly urge that, in appropriate meas-ure, instruction in L.D. be included in these institutes.

The purpose of the institutes is to "up-grade" teach-ers, especially with regard to their mastery of subject matter content. In general it is assumed that what teachers need most is what they are not likely to have gotten from courses in Education or Educational Psy-

chology. Because of this justifiable subject matter em-phasis, there is a tendency to resist suggestions that point toward instruction in method-including the methods of L.D. This seems to me to be most unfortunate, be-cause in a very real sense L.D. is physics. Moreover, a program of instruction in L.D., if properly conceived and executed, with emphasis on subject matter as sug-gested, would definitely be a program of teaching physics.

Therefore I propose that every institute for science teachers (short or long, summer or winter) might well provide some opportunity for the systematic considera-tion of L.D. Furthermore, some of them might well be devoted from time to time to L.D. exclusively. This would be especially valuable in the case of a six-week summer institute for college teachers.

Directors of institutes should be encouraged to in-clude master demonstrators among their visiting lec-turers. Lists of available experts in L.D. should be made available to them by, say, the American Institute of Physics.

More thought needs to be given to the particular problems and needs, relative to L.D., of teachers at different levels, viz., elementary, secondary, collegiate levels. These differentiated approaches could conceiv-ably be worked out advantageously in institutes. It would be helpful, therefore, if there were prepared relatively brief manuals of instruction on L.D. appropriate to dif-ferent kinds of school situations and teachers' institutes.

These suggestions seem appropriate also relative to all-year institutes for teachers-as well as to the regu-lar curricular offerings of physics departments in col-leges and universities preparing teachers.

5. Suggested Partial Syllabus for Course on L.D.

1.0 Introduction. 1.1 Various aspects of a natural science. 1.2 Studying science is more than studying books

and listening to "blackboard and chalk" lec-tures.

1.3 Demonstration lectures meet certain unique needs not met in other ways.

2.0 Some whys-and corresponding goals. 2.1 To confront students with certain aspects of

nature itself; to let them observe basic phe-nomena directly.

2.2 To create favorable conditions for physical thinking. 2.21 To give students direct experience with

empirical situations that call for con-cepts that are new to them.

2.22 To give concrete meaning to difficult con-cepts.

2.23 To demonstrate the reality of what, in spite of logic and "proofs," may seem unbelievable or impossible.

2.24 Seeing, hearing, feeling aid in thinking. 2.3 To demonstrate how a scientist thinks and

proceeds; 2.31 When he attempts to isolate phenomena

for study. 2.32 When he tries to identify causes, effects,

and functional relationships.

2.33 When, confronted by a mystery, he guess-es and hypothesizes.

2.34 When his guesses lead to prediction, and experimental tests are called for.

2.4 To re-enact historic experiments or discov-eries.

2. 5 To exhibit, use, and explain basic instruments and methods referred to in books, but not stud-ied in laboratory courses.

2.6 To arouse genuine "physical" interest-not merely spectacle interest.

3.0 Some criteria for desirable and effective demon-strations and demonstration apparatus.

4.0

5.0

6.0

3.1 Teaching value-not merely entertainment. 3.11 Must illustrate basic principle.

3.2 3.3

3.4

3.5

3.6

3.7

3.12 Must facilitate isolation of variables. 3.13 Must facilitate control and variation of

critical factors. 3.14 Provide surprises. Clarity of purpose evident to students. Visibility (or audibility). 3.31 Size. 3.32 Contrasting colors for different parts. 3.33 Illumination, direct, indirect. 3.34 Proper arrangement and location. 3.35 Contrasting backgrounds. Simplicity. 3.41 Minimum number of parts. 3.42 Ease of operation during lecture. 3.43 Minimum distractions. Portability. 3.51 Light in weight. 3.52 Minimum set up and removal time. Sturdiness. 3.61 Obviating undue care in handling. 3.62 Reproducibility from lecture to lecture,

or from semester to semester. Attractiveness, aesthetic appeal (not always).

Some criteria for a good demonstration lecture. 4.1 Concentrates upon what needs to be demon-

strated, and is best taught that way. 4.2 Provides at least one intellectual thrill. 4.3 Not too many demonstrations; in general not

more than can be discussed thoroughly. 4.4 The usual characteristics of any good lecture,

such as: being well organized, ...... 4.5 Lecture notes for use of students. Evaluation of effectiveness of demonstration lee-tures, tests and examinations. 5.1 Indirect. 5.2 Direct. Particular techniques and equipment. 6.1 Optical projection.

6.11 Slides. 6.12 Moving picture films. 6.13 Repeating film strips. 6.14 Opaque projection of apparatus. 6.15 Transparent projection of apparatus. 6.16 Shadow projection. 6.17 Image inverter. 6.18 Magnification.

6.2 Charts. 6.3 Models.

7.0

8.0

6.4 Coordinate systems. 6. 5 Lighting systems.

6. 51 Indirect. 6.52 Floodlights. 6.53 Light backgrounds.

6.6 Public address system. 6.61 Lapel microphone. 6.62 Record player. 6.63 Special purpose amplifiers and trans-

ducers. 6.64 Special purpose oscillators. 6.65 Filters.

6. 7 utilities. 6. 71 High and low voltage supplies. 6.72 DC, AC. 6. 73 Gas. 6.74 Water. 6.75 High pressure air.

6.8 Lecture room facilities. 6.81 Movable tables. 6.82 Movable platforms. 6.83 High supports. 6.84 Screens for projections. 6.85 Movable backgrounds. 6.86 Wall galvanometers. 6.87 Heating and cooling devices. 6.88 Rods, clamps, tools. 6.89 Batteries.

6.9 Special devices for general use. 6.91 Pumps. 6.92 Mechanical rotators. 6.93 Mechanical oscillators. 6.94 Cathode ray oscilloscopes. 6.95 Stroboscopes. 6.96 Timers and clocks. 6.97 Meters and scales. 6.98 Temperature meters and indicators.

The traveling demonstration lecture "show." 7.1 Packaging. 7.2 Modes of transportation. 7.3 Vibration and shock problems. 7.4 Weather problems. 7.5 Strange and bare lecture rooms.

7.51 Tables. 7.52 Platforms. 7. 53 Electric outlets.

7.6 Adapting to different types of audiences. 7. 7 Arranging for assistance. TV. 8.1 Closed circuits, intra-mural. 8.2 Networks, extra-mural. 8.3 Special problems and techniques.

8.31 Timing. 8.32 Rehearsals. 8.33 Lighting and sound. 8.34 Blackboard and equivalents. 8.35 Framing. 8.36 Relations to director and studio crew.

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DISCUSSION

Comment: I wonder if we should consider means of providing a

traveling visiting demonstration lecturer. Sigma Xi, for example, arranges to have 2 or 3 scientists who give full time to college and university visits for science lectures. Comment:

May I remind you that we have a mechanism for just this kind of activity under the Visiting Scientist Pro-gram plan. The problem is, where can you find a scien-tist willing to take off a year for this important service to his profession? Comment:

The N.S.F. Visiting Scientist Program has operated such a plan from Oak Ridge. The demonstrators have station wagons outfitted with demonstration apparatus for their circuit of many schools. Visits to the N.S.F. Summer Institutes is another service we can give in helping in this work. One recognizes, however, that the short visits of 2 or 3 days each are not long enough to get down to the roots of the matter. Comment:

The increasing present sales of "Demonstration Ex-periments in Physics," (McGraw-Hill) edited by Sutton, twenty years after its publication shows the interest in the field of lecture demonstrations. Comment:

We must be concerned with science teaching at all levels. I think we should plan a progressive series of courses in science which start in the lower grades and continue throughout the elementary and secondary school classes in much the same way math is now taught. The most difficult element of such a program is trained staff. It may be necessary to use trained science advisors who, in turn, develop the subject mat-ter background of the teachers in their local school system. Comment:

The National Defense Education Act provides an un-precedented way of upgrading science. Teachers can now buy demonstration and class apparatus on a really adequate scale. There is one great danger, namely, that the money will not be wisely spent. There is, in my opinion, great need for all of us to help give guid-ance in this program. (Q) Has there been any official action of AlP or AAPT

in this matter?

(A) Yes. Various persons have helped in a number of ways. One, for example, was help given in the preparation of a purchase guide of apparatus to assist the state and local districts in the purchase of apparatus. We suggested the items of equipment particularly well-suited as teaching aids in physics.

Comment: Our first job in public school science teaching is not

to worry about how to teach people to demonstrate or to buy equipment--it is rather, how can we help provide training in subject matter. This is where they are par-ticularly weak and you can't demonstrate properly until you know what the demonstration means. Too many Summer Institutes do not stress subject matter. (A) I heartily disagree with this blanket statement. In

the first place there are a great many teachers at all levels who are quite competent. Some are not and these are the ones we tend to see from our ex-perience on the college level. There are good ones and these come to the Institutes to better their pro-fessional skills. They are thinking solid physics when they try to answer the question: how can I best teach these principles? I do not suggest re-peating types of demonstrations unsuited to their condition. Lets help them think of the kinds of demonstrations appropriate to their situation.

Comment: There are also workshops arranged by principals

and superintendents for their teachers. I helped in a 10 day workshop for 78 teachers of grades 1 to 6. This was a real challenge. Comment:

The pronouncements from national levels AlP; AAPT etc. frequently can not hit the differing local problems. We need to lend more support on a state or even local community level where we know the existing problems and how best to solve them. I wish more of our group would get into the fight at these levels where the spend-ing of the appropriated money really takes place. Comment:

I think we can summarize the morning's contribution by saying that we agree there should be articulate aggressiveness. If you believe in a thing you don't sit back but you get going to do your share of what needs to be done. The summation of these individual contribu-tions become large enough to solve the big problems.

Session VIII

PROBLEMS OF CURATOR AND ASSISTANTS

Presiding: C. N. Wall

PROBLEMS AND SOLUTIONS AT MIT

H. E. Anderson Curator of the Physics Department

Massachusetts Institute of Technology

There are many problems encountered in the prepa-ration of lecture demonstrations: problems such as the storage of equipment, development and building of new apparatus, time allotment for the preparation and re-hearsal of lecture demonstrations, purchase of appara-tus, maintenance of equipment and many others.

Some of these problems in the Physics Department at MIT were solved when we moved into a new modern air-conditioned lecture hall and preparation room. The lecture hall is provided with easily-accessible power outlets, as well as, gas, hot and cold water, compressed air, drain and an exhaust fan. There is also provided a portable sink with additional connectors which can be fastened easily to the movable lecture tables.

The preparation room, which is directly back of the front of the lecture hall, has entrances from either side. It is provided with six steel cases 7' x 4' x 1 0' high and six additional steel cases 4-1/2' x 4' x 8' high mounted above with a stairway and cat-walk. There is also a storage room below back of the lecture hall which has six steel cases 8' x 4' x 7' high, and floor space for storing heavy apparatus. This provides ample space for the storage of equipment which, I believe, is quite necessary.

Lecture demonstrations involve the use of many kinds of apparatus and its storage. A simple index system devised to show the location and description of the ap-paratus would be most useful.

New apparatus constitutes a problem in that some of the equipment is too small to be visible in large lecture group demonstrations. However, many small-scale ex-periments can be made visible by shadow projection. The help of graduate students in the development and testing of new demonstrations is of great importance.

Some equipment is not available in the open market, but with a good machine shop, it is possible to build ap-paratus to suit your own specifications and needs.

A great deal of time is spent in keeping the equip-ment in good working order. Breakage and damage can be cut down considerably by instruction in the use of the

equipment and by supervision in the lecture demonstra-tion set-ups.

Loaning apparatus, even to your own research people, is found not to be good practice. Many times the appa-ratus is returned in a damaged condition and, in some cases, this is not detected until it is going to be used in a set-up. Only if time permits can the damage be re-paired before the lecture. In the case of late decisions on lecture demonstrations, and the apparatus is out on loan, it is not always possible to get the equipment back in time. I have found that the best solution is to have the equipment in the preparation room and to let it be used for lecture demonstrations only.

Time allotment for the choice of demonstration, preparation, and rehearsal is another problem. Usually, the kind of demonstration is decided upon by the lec-turer on the day .before in a short meeting. The time for preparation depends on the type of demonstration, and this varies considerably. The lecture demonstra-tions are prepared on movable tables in the preparation room and rolled into the lecture room and connected, usually one hour before the lecture starts. This gives the lecturer time to try out the different set-ups before the lecture begins and also to make last minute changes. During the time the lecture is in progress, which usually runs for two consecutive periods, time is spent in pre-paring the next lecture set-up. Generally one hour is al-lowed to make a complete change-over. This carries on Monday through Thursday, leaving Friday as an open day.

Slides play an important part in lecture demonstra-tions. With the Polaroid slide-making kit it is now pos-sible to make slides in a comparatively short time.

In closing I would like to say that the number and type of lecture demonstrations depend upon several im-portant factors. Among them are the lecturer's point of view, time allowed in the course for demonstrations, and the lecturer's experience and interest.

The curator's time not spent in lecture preparation can be used advantageously in developing and building new experiments and in the general upkeep of equipment.

SOME OF PRINCETON'S SOLUTIONS

Harold M. Waage Curator of the Physics Department

Princeton University

A lecture curator is at once the architect, builder and demolisher of a temporary structure known as a

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lecture demonstration. Therefore he has problems connected with the storage, manufacture, purchase,

80

maintenance and repair of his raw materials. Some of his problems of building up and tearing down are solved by unitized construction because usually the same com-ponent parts are used in setting up a large variety of demonstrations.

Storage areas should be of adequate size and easily accessible for the transportation of much-used as well as heavy items. Due to the rapid expansion of certain branches of physics such as Electronics and Atomic Physics, extra shelf space should be available for the addition of much new equipment. One of the storage problems is concerned with the best arrangement so that items may be easily classified according to an index system such as mentioned by Mr. Anderson. The usual arrangement is to keep all experiments within one topi-cal classification in the same section of the storage cabinet. However, since proper storage is facilitated by keeping each particular item in a particular place, such items are best labelled in accordance with their location on the shelf rather than according to topical subdivision. The word "item" here also refers to boxes in which component parts of a demonstration are kept together. In Princeton we have items labelled accord-ing to their location in a certain cabinet, certain shelf and certain place on that shelf. Thus, the label A-3-7 indicates that the item belongs in Cabinet A, Shelf 3 and is the seventh item on that shelf. A cross reference index should also be made so that location can be related to topical classification.

The problem of manufacturing new demonstration pieces, if they are not available on the market, must be solved either by utilizing the services of shop personnel or by the curator himself designing and constructing some of the simpler forms of apparatus. The allocation of man hours and procurement of materials is merely a routine matter for the machine shop personnel when they are provided with well thought out details of con-struction indicated in a drawing. Such work can be well planned in advance. However it is a different matter when the need for new pieces of lecture apparatus arises at a time when the shop is busy with the construction of research- tools. At such times a machinist may feel

reluctant to drop what he is doing and proceed with the hasty construction of an item in accordance with a rough sketch, with the result that, even if beautifully made, it may not be adequate for the specific purpose the lec-turer has in mind. Therefore it is best that the curator be able to anticipate the need for new experiments so that he can devote time enough to get a servicable item made. Permanent makeshifts often waste time and ef-fort over the years that would have better been expended at the outset in working out improvements. For the same reasons the curator must order well in advance those pieces of apparatus for which he feels certain there will be a future need.

The problems of maintenance and repair of existing equipment are similar to those connected with the mak-ing of new equipment. A shop setup geared to the day-to-day needs of the lecture department has already been ably presented and need not be dwelt on further here.

Almost no problem so far considered can compare in seriousness to that which arises when equipment is borrowed and not returned in time for its use in lecture. The chief motive for such borrowing seems to be the desire on the part of a few research workers to try out a bread-board version of their research apparatus be-fore ordering more permanent equipment. What is more natural than for them to borrow from the curator's wonderful collection, those things they need. To aggra-vate matters further it sometimes happens that such equipment may still lie around the research areas long after the need for them has passed. Therefore they may remain unnoticed until the curator himself comes to get them.

The keeping of a notebook in which a sketch and de-scription is made of each new demonstration setup be-comes an invaluable aid in following years when the same arrangement is asked for by the lecturer. It is difficult, if not impossible, for the curator to draw upon memory alone in reconstructing some highly successful experiment after a lapse of months or even years, if such a record is not available.

Session IX

SUMMARY AND RESOLUTIONS

Presiding: P. Kirkpatrick

A spirited discussion resulted from the tentative report of the Resolutions Committee. The following was written subsequently by the Resolutions Committee as a result of this discussion and was circulated to the members of the conference. It has since been approved by the Resolutions, Planning, and Editorial Committees.

GENERAL SUMMARY

Wesleyan Conference on Demonstration Lectures

Wesleyan University, June 22-24, 1959

I. Purpose of the Conference

Demonstrations have been traditionally a part of physics teaching, especially at the introductory college level. Many of the great teachers of physics in the past and present are known primarily as masters of the demonstration lecture. Since physics is a developing subject, as the content of the subject grows it is appro-priate to examine and evaluate the teaching procedures used to transmit physics to new generations. The Wes-leyan Conference on Demonstration Lectures attempted to define the value of demonstrations and to set forth ideas on what makes a good demonstration, including the art and technique of presentation. Attention was also given to equipment and to the training of personnel nec-essary for good demonstrations. Finally, the Confer-ence attempted to look forward in expressing its con-victions on the values of demonstrations in the changing educational climate of the future.

II. Many Approaches to Learning Physics

The methods and techniques employed in the teaching of physics are many and varied. The procedures depend on many factors such as the educational level of the stu-dents, the numbers of students to be taught, the physical facilities available, the experience and skills of the in-structional staff as well as their prejudices, the educa-tional goals of the students, and the degree of under-standing and cooperation of persons administratively responsible for the program. One finds learning in physics taking place through (1) independent study, (2) colloquia, (3) seminars, (4) laboratory, (5) formal and informal discussion and problem sections, and (6) lectures with or without demonstrations. Since an effective program can evolve only through the combina-tion of several techniques, it is important that teachers of physics be aware of the various approaches and adapt their procedures to yield the maximum quality of in-struction.

III. Various Aspects of Demonstration Lectures

The Conference directed its attention to the role of demonstration lectures in the teaching of physics at various levels. Specifically, sessions were devoted to the consideration of (1) The Values and Purposes of Demonstration Lectures, (2) New Demonstrations, (3) Demonstration Techniques, (4) The Uses of Tele-vision, (5) Space and Equipment, (6) Inexpensive and Simple Demonstrations, (7) Sources of Materials and Information, (8) Problems of the Curator.

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IV. Value of the Demonstration Lecture

The principal value of a demonstration must be sought in the basic nature of the subject. Physics is an experimental science; the physicist is concerned with the world of nature and the observations made on it. In the demonstration where real objects are seen and ma-nipulated the student can observe the basic things of nature in the flesh thus making physics come alive. It is no longer merely a textbook subject, no longer merely a clever method of manipulating symbols on the chalk-board. It becomes in the student's experience an ob-servational science. Furthermore a demonstration lecture is perhaps the only place that a student can see a physicist in action-not only talking about his subject, but living his subject.

V. Features of a Good Demonstration Lecture

Since we learn by doing, a good demonstration gathers the audience into vicarious .participation with the ex-perimenter. A good demonstration can be effective in maintaining student motivation and interest in the way in which physicists deal with natural phenomena.

A good lecture demonstration should (1) be carefully planned and tested beforehand, (2) be simple and clear, (3) contain a minimum of "black box" components, (4) be constructed to a scale which will make it visible to every student in the audience or employ optical pro-jection techniques for clear viewing, and ( 5) be skill-fully presented. In addition, the experiment should not only give enjoyment to the audience but make the audi-ence realize that the lecturer is enjoying himself.

Several new demonstrations covering a wide range of physical principles were presented during the second session. The advantages of optical projection techniques were masterfully presented by Professor R. W. Pohl. The use of large scale equipment and special meter devices was described and discussed in the session devoted to techniques.

VI. Use of Television

The possible use of a television camera and screen for making small objects on the lecture table visible to a large audience was demonstrated. Such a procedure offers an alternative to the construction of large-scale demonstration equipment, but adds certain problems of special lighting and maintenance of electronic equip-ment. The experiences of two colleges with closed cir-cuit television in multiple rooms were reviewed and they in<licate that such programs are expensive in time

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and money. Certain phases of this form of instruction need further study and evaluation. The NBC program Continental Classroom was discussed and some experi-ments recorded on film were presented. It was pointed out that the content should be controlled by the lecturer, unhampered by rules and regulations. Further experi-ence and study is needed in all phases of television use in the teaching of physics.

VII. Training Demonstration Lecturers

The Wesleyan Conference discovered that there are no systematic procedures in wide use for training dem-onstrators. Those who have become skilled in the art of the demonstration lecture are ones who have enjoyed a combination of opportunity and talent. But undoubtedly in the training of demonstrators to meet the increased teaching load of the future, there is a need for a wider dissemination of information on the techniques and pro-cedures of the physics demonstration lecture. It is clear that this exchange of information on desirable demonstration techniques is not well organized.

VIII. Special Lecture Facilities

The final sessions considered the advisability of careful planning of physics buildings so as to provide facilities for lecture demonstrations. The necessity for specialfacilities in lecture halls as well as adequate shop and storage space was emphasized. Since much of the demonstration apparatus is not commercially avail-able it is essential that a good metal and woodworking shop be provided. Technical help should be available to assist in the construction and care of apparatus. One or more such assistants should be provided in a large department and at least part-time help from one assist-ant in the small department.

IX. Increasing Importance of the Demonstration Lecture

What is the future of the demonstration lecture? Has it outlived its usefulness? Although it is clear that the demonstration lecture is only one facet of the course in physics, it is an important facet. A course in physics must also involve first-hand contact with nature in the laboratory, as well as reading and pencil-and-paper operations. But in the total context of the physics course, the Wesleyan Conference felt that the demon-stration lecture has a real and unique place.

In its combination of experimental and theoretical approach, in its ability to teach by expert example, in the possibilities it offers for the efficient use of the small number of skilled teachers in teaching large num-bers of students, the demonstration lecture represents a technique of teaching that has a rightfully important place. Even the use of motion pictures and television cannot displace the demonstration lecture, because it is usually a demonstration lecturer who performs be-fore the camera. It seemed clear to the Conference that the demonstration lecture, far from being obso-lescent, was in need of more encouragement than ever; it was the hope of the Conference that in the future, ways could be found to encourage the development of skilled lecturers and to provide for them the assistance they need to do an effective job. At a time when more and more students are entering colleges, at a time when there is an increased general awareness of the value of physics, at a time when it is vitally important to train young people in the procedures and attitudes of physical science, we must not abandon an instructional technique that, in skilled hands, offers to large groups of people a first-hand association with the rich content of physics.

RECOMMENDATIONS

1. Since demonstration lectures can and do play a vital role in the teaching of physics, they should be used in all instructional programs including those of the ele-mentary and high school.

2. The American Association of Physics Teachers and the American Institute of Physics as organizations and physics teachers as individuals should bring to the attention of administrators the necessity for, and ad-vantages of, the use of demonstration lectures in the teaching of physics.

3. Educational institutions should provide time, building facilities, and funds for equipment and assist-ance, and should urge the members of their physics faculties to give lecture demonstrations as a regular part of instruction. As a minimum, the lecture table or room must be made available to the demonstrator for preparation during the period preceding his demon-stration lecture.

4. Graduate schools and institutions responsible for the training of college teachers in physics should provide guidance and instruction in the techniques of lecture demonstrations.

5. It is suggested that the resources of depart-ments of physics in colleges and universities be made available to assist teachers in neighboring elementary and high schools in the use and development of demon.,-stration lecture materials.

6. The American Association of Physics Teachers and the editorial staff of the American Journal of Physics should take steps to encourage increased publi-cation of articles relating to demonstration lectures.

7. The American Association of Physics Teachers and the American Institute of Physics should encourage the National Science Foundation to develop and support institutes which provide training to teachers in the techniques of demonstration lectures.

8. Since demonstrations should be seen by the entire class, physics teachers should critically review their demonstrations, with the recommendations of this Conference in mind, and should increase the size of demonstration equipment or resort to projection tech-niques and television cameras where the need for mag-nification exists.

9. The use of the television camera in lectures

and the development of closed circuit TV techniques for teaching in several rooms simultaneously offer possi-bilities for extending and improving existing methods used in demonstration lectures. Support and encourage-ment should be given to experiments in this field and objective studies made of the results to ascertain their value.

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10. Television broadcasting of demonstration lectures to large audiences is having a significant effect on the understanding of physics by many segments of the national population. Physics teachers should con-tinue, therefore, to give the television industry the ad-vantage of their counsel and experience.

APPENDIX

LIST OF APPARATUS EXHIBITED AT THE WESLEYAN CONFERENCE

ON LECTURE DEMONSTRATIONS

a) Catalog Items

80422 80429-3 80429-4 80434

82550

CENTRAL SCIENTIFIC COMPANY

Microwave Optics Equipment, with Double Dipole Antenna, and Double Parabolic Reflector w/stands, and Polarized Grid

Projection Voltmeter

b) Items in production but too new to be in the catalog

77722 8039082490 71866 74730 77430 83064

c) Experimental Models

Kinetic Theory Apparatus Transistor Analyzer Infinite Resistance Voltmeter Rayotron with Beam Tube (Atomic Laboratories) MITAC Gyroscope Cenco-Miller Forces in Thermal Expansion Apparatus Cenco-Miller Temperature Coefficient of Resistance Apparatus

Cenco-Miller Triple Track Inclined Plane Experiment Cenco-Miller Jet Propulsion Apparatus Large Lecture Table Multimeter Apparatus for Liquefying Permanent "Gases"Battery operated Transistor Amplifier and Speaker Combination (used to make

audible the output from the Microwave Receiver)

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J. KLINGER SCIENTIFIC APPARATUS

(E. LEYBOLD'S NACHFOLGER)

Catalogue

Wave Trough 40801/2 P H 32

Torsion Wave Machine 40110 P H 32

Discharge Tubes 55416 P H 32

High Vacuum Pump 11012s P H 32

e/m Apparatus 55557/8 P H 32

Photoelectric Cell for Planck's Constant 55877 P H 32

Deflection of [3 Rays P H 37

Counting Devices P H 37

Franck Hertz Experiment 55580 P H 32 and P H 37

Neutron Source(artificial radioactivity) 55930 P H 37

Half Life of Thoron P H 37

Demonstration of Exponential Decay

9 0

a) Catalog Items

812 7501 978 909B

3341 3341A 2164 40753978 7067A7067B7067

53 1663 1876 2692 30593671 38003818

b) New Apparatus

W. M. WELCH MANUFACTURING COMPANY

Large Stop Clock for Lecture Table or Wall Radian and Circle Demonstrator Maxwell's Top Oscillator Attachment for Rotator (Rotator 904A)Film Loops, Wave Motion, Set 1 Film Loops, Wave Motion, Set 2 Film Loops, Radioactivity Demonstration Dial Balance Beseler Master Vu-Graph Overhead Projector and accessories Coordinate System Slides (3-1/4 x 4-inch) Coordinate System Slides (10 X 10-inch)Coordinate System Slides (2 x 2-inch) Demonstration Projection Vernier Large Bimetallic Bar Demonstration Dip Needle Lecture-table Galvanometer Volt-ammeter Lecture-table Ohmmeter Singerman Color Mixer Interference Diffraction Resolution Kit (with extra slit films 3800A)Replica Diffraction Gratings

Three-body Center-of-Mass Apparatus Earth-Moon System Demonstration Archimedes' Principle Apparatus Mariotte Bottle

c) Experimental Models

Demonstration Jack Screw Apparatus Mystery Batons Spool Problem Beat Demonstration Demonstration YoYo Conservation of Angular Momentum Demonstration Linear Expansion Apparatus Lamp-bulb Wheatstone Bridge Series Parallel Lamp Board Polaroid Disks Motor-driven Color Disks Normal Distribution Curve

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