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Vox.3 MAY 1930 No. 27

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11 TELEVISION for May, 1930

I% p

THE

OFFICIAL ORGAN OFTHE TELEVISION SOCIETY

FOR TABLE OF CONTENTS

see page 152

MAY 193o [No. 27

Notes of the MonthTelevision at No. .ro

A Baird receiver was installed at No. 1o, DowningStreet in time for Mr. Ramsay MacDonald and hishousehold to enjoy the inaugural sight and soundbroadcast programme on the morning of March 31stlast.

On April 1st a large number of the Delegates to theLondon Naval Conference, at Mr. MacDonald's invita-tion, witnessed a demonstration on his instrument.Among those present were the following :Commonwealth of Australia :

THE HoN. J. E. FENTON, M.P., Minister for Tradeand Customs.

Canada :THE HON. J. t. RALSTON, C.M.G., D.S.O., K.C.,

Minister for National Defence.France :

MONSIEUR RENt MASSIGLI, Ministre Plenipoten-tiaire, Chef du Service de la Societe desNations au Ministere des Affaires etrangeres.

Great Britain :THE RT. HON. J. RAMSAY MACDONALD, M.P.,

Prime Minister and First Lord of the Treasury.MR. R. L. CRAIGIE, C.M.G., Head of the American

Department.MR. MALCOLM MACDONALD, M.P.

TELEVISION for May, 1930 1*

India :SIR ATUL C. CHATTERJEE, High Commis-

sioner for India in London.Irish Free State.

PROFESSOR T. A. SMIDDY, High Commissioner forthe Irish Free State in London.

Union of South Africa :MR. C. T. TE WATER, High Commissioner for the

Union of South Africa in London.Secretary -General :

COLONEL SIR MAURICE HAMMY, G.C.B., G.C.M.G.

Chief Interpreter :MONSIEUR G. J. MATHIEU.

MISS JOAN MACDONALD.MISS SHEILA MACDONALD.

Baird Television MergerOn April 7th a series of meetings were held of the

various classes of shareholders in the Baird TelevisionDevelopment Co., Ltd., and Baird InternationalTelevision, Ltd., for the purpose of considering andpassing resolutions approving a scheme of amalgama-tion of the interests of the two undertakings. The fulldetails of the scheme have appeared in the daily press,

105

and it is of interest to note that the necessary resolu-tions were passed unanimously. The name of the newCompany, which will take over all the joint assets andliabilities of the Development and Internationalcompanies, is Baird Television, Ltd.

During the course of the speeches made by theChairmen of the Companies it was announced that inorder to afford further facilities to those in possessionof Baird " televisor " receivers the new Companyproposed to build two broadcast stations of its own.The necessary licence to do this had been procuredfrom the Post Office. The two wave lengths employedwill be 155 metres for speech and 5o metres for television.The power of both stations will be i kw. By meansof these two stations the Company will be enabledto transmit programmes during ordinary broadcasthours without causing any interference to the B.B.C.stations. In addition, by transmitting television on5o metres the Company will not be limited as atpresent to a 9 -kilocycle wave band, and will thus beable to send larger images and give improved detail.

In answer to questions, Mr. Baird announced thatalthough the light spot transmitter at presentemployed, using visible light, does not as a rulecause inconvenience to artistes sitting before it, inorder still, further to eliminate any possible chance ofembarrassment it was proposed to substitute infra -redrays for visible light in the near future. Since theserays are invisible, artistes would then experience noembarrassment.

Mr. Baird further announced that work wasproceeding in the laboratory on a larger receivingscreen, the object of which was to make it possible fora larger number of people to watch to received images.

Television in ManchesterMessrs. A. Franks, Ltd., of Manchester, are nothing

if not up to date. Three years ago they approachedthe Baird Company with a view to giving a practicaldemonstration in the North. It was felt, however, atthat time that television had not advanced sufficientlyto give a big demonstration. There was no televisionbroadcast and televisors were not available to thepublic.

To -day, however, the situation is changed, andFranks, who have kept in close touch with progressall the time, recently gave a particularly good twodays' demonstration. A transmitter was installed attheir main showrooms in Deansgate, and thus continu-ous reception was possible at their demonstration hallin Market Street.

Manchester has thus been given its first oppor-tunity of witnessing practical television by the pioneerfirm who introduced wireless to that city and, later,were able to give the first demonstration of stillpicture reception.

io6

Television Broadcasts in AmericaThe Jenkins Television Corporation, acting in

conjunction with the de Forest Company, are broad-casting sound and vision simultaneously from theirstations W2XCR and W2XCD ; the sound signalscome from the latter station on 187 metres and thetelevision signals from the former on 107 metres. Thevision signals consist of cinematograph films. Hori-zontal scanning is employed, using a 48 -hole disc, andscanning is carried out at the rate of 15 pictures persecond. No details are available as to the times ofthese transmissions.

A New Photo -Electric Cell

The General Electric Co. announce a new type ofphoto -electric cell known as the Type CM, which ismuch superior for most purposes than those whichhave been offered hitherto. The active material onthe cathode consists of a thin (monatomic) layer ofCaesium carried on a suitably prepared silver con-ductor. This CM cell, which is in a sense a " Caesium "cell, must not be confused with the old Caesium cellsin which the active material was a thick layer of

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Caesium ; these old cells were definitely inferior to theordinary potassium cell for all but a very few specialpurposes, whereas the older cells gave an emission ofone microampere per lumen, the CM cell gives about12 microamperes per lumen.

Particulars and prices of the new cell, which is madein two types, Vacuum and Gas -Filled, can be had onapplication to the G.E.C.

A New Loud Speaker ChassisFrom the Shaftesbury Radio Co. we have received

one of their Wates Double Cone Loud Speaker Chassis.This consists of two cones, one large and one small,connected together at their apices. The whole chassisis so arranged that a number of standard units can beconnected to it without difficulty. On test thisspeaker gives the most pleasing results.

MisleadingWe recently came across an item in a newspaper

describing the inaugural ripening by the NationalBroadcasting Company of America of a new studiowhich the Company has built on the roof of the NewAmsterdam Theatre in Times Square, New York.This studio really consists of a specially arrangedstage at one end of a large auditorium to which thepublic are admitted. While broadcasting is in progressa huge glass screen weighing six tons is lowered acrossthe front of the stage to prevent noises from theaudience reaching the microphone,time permitting the audience to watch the performersand hear them by means of loud speakers distributedthroughout the auditorium.

In describing the inaugural broadcast from thisnovel studio, the newspaper in question described it asan exhibition of television. Not only was it in nosense a demonstration of television, but the NationalBroadcasting Company have recently announced thatfor the time being they do not propose to participatein television broadcast experiments.

Brookman's Park nve-length ChangeAccording to a newspaper report a plan is under

discussion to change the wavelength of Brookman'sPark National Programme transmitter from 261metres to 288 metres. There are two arguments infavour of this step. Many old receiving sets fail totune down to 261 metres without alteration, whereas288 metres may just come within their range. Theother objection to the existing wave -length is that itis liable to fading. This trouble would be lessened on288 metres. Before this change can take place,however, a number of the relay stations which are atpresent operating on 288 metres will have to be givenalternative accommodation.

As the 261 -metre transmitter is at present used tobroadcast television signals, many distant televisionenthusiasts will benefit by the change.


Television DemonstrationsBetween March 24th and April 17th successful

demonstrations of television were given at the DailyMail Ideal Home Exhibition at Olympia. Thesedemonstrations were by land line, the transmitterbeing located at the premises of Major W. H. Oates,at 195, Hammersmith Road. Major Oates is a veryenthusiastic wireless and television amateur. It isestimated that about 30,000 members of the publicwitnessed the demonstrations at Olympia.

Successful public demonstrations were also given atSunderland from the 8th to the loth April, and atManchester on April 16th and 17th.

Further public demonstrations will be given atSouthampton from April 24th to May 3rd, and atBournemouth from May 8th to r7th. under theauspices of the Southern Daily Echo.

German Television SocietyRecently, due to private initiative, a German

Television Society was formed in Berlin with the title" Allgemeiner Deutscher Fernsehverein." Unlike theEnglish Society, which is rather frowned on in officialcircles, the German Society has as members theGerman Postmaster -General ; and Dr. Banneitz,Director of the P.O. Television Laboratory, Dr. Feyer-al:II-end, Under Secretary of State, Dr. Magnus, who isVice -President of the Society, and Professor Dr.Leithaeuser, Director Knoepfke of the Berlin Broad-casting Company, while the Broadcasting Companiesof Berlin, Breslau, Koenigsberg, and Leipzig havejoined as bodies.

The Society aims at assisting in every wty possiblethe development of television in Germany, and isreceiving support from all sections of the wirelessindustry, whether government or trade.

Its immediate task is the checking of televisiontransmissions from the Berlin Broadcast Station witha view to ascertaining to what extent, if any, tele-vision can be included as a regular item of the broad-cast programme. In this connection considerableattention will be given to the selection of suitableprogrammes so that public sympathies may not bejeopardised by the inclusion of unsuitable subjects.

At a meeting of the Technical Committee of theSociety there were present representatives of thewireless industry, wireless constructors, prominentmembers of the German P.O., the Technical ResearchDept. of the P.O., the Broadcast Companies andProfessors of wireless science.

Professor Dr. G. Leithaeuser took the chair andexpressed the pleasure of the Society at being able towelcome such well-known men as Dr. Knickow,Director of the German P.O., and Dr. K. W. Wagner,President of the Heinrich Hertz Institute.

The immediate tasks of television were discussed atthe meeting and it was generally agreed that cautionwould have to be used in putting the first televisors onthe market lest a reaction likely to jeopardise theultimate adoption of television be created.

The official organ of the Society is the recentlyfounded monthly magazine, Fernsehen.

107

Television in ScotlandBy Normal/ Turner,

Consulting and Radio Service, Ltd., Glasgow.

GREAT stuff this television 1 At least it wouldbe if we had more of it. Two half hours a weekrequirean enthusiast to enthuse, two half hours

that pass like lightning, when people are so keen tolook in that you daren't alter a connection or try a newstunt. Of course I'm talking of Scotland, where themorning transmission is totally inaudible and if it wereaudible it would be blotted out by the ghastly induc-tion of all the carpet sweepers that beat as they sweep.

What a thrill to get long-distance vision, not juston your doorstep, but the authentic long distance stuffwith all its atmospheric disturbances . and its fadingand its blot out by the local oscillating fiend. It'sfunny how accustomed the ear has become to outsidedisturbances ; it's only brought home to us by thecriticism of the eye. We see the disturbances. We seea lady with a beautiful top knot of extremely blackhair, her mouth becomes a most unpleasant gap, hernose a thing of caricature and then for a few momentsa perfect picture with every detail down to hereyelashes clearly discernible. Ah, for a local stationtransmission, what entertainment value there is insight and sound allied 1 But what a lot remains to bedone ; what a field there is for the experimenter withbright ideas, a brighter lamp, a wider projection, amore instant response to speed control.

In Glasgow I have been using a Columbia standardA.C. set, which has three screened grid valves, an anodebend detector and a resistance coupled low frequencyvalve, this coupled in turn to a single stage push-pullamplifier using two L.S.5A valves with only twohundred volts on the plates. The neon and thesynchronising coils are in series with the outputtransformer and are excited with two hundred voltsderived from the same high tension source as theL.S.5A valves. Why this talk about three and fourhundred volts I don't understand. I get perfectlyclear reception, atmospherics permitting, and goodsynchronising control with a total high tension voltageof two hundred applied as I have mentioned. TheL.S.5A valves are directly A.C. fed and although ona loud -speaker there certainly is a slight hum, thepicture only shows the faintest interference bars whichin no way mar reception.

What puzzles me, however, is why at the very startof television the Germans, who I presume are usingBaird's general system, should use different scanning,horizontal instead of vertical. A divergence ofopinion such as this makes television seem veryexperimental. The Fultograph people were able tostandardise the pitch of their thread at the outset,making reception possible from all countries. The

Io8

merits or demerits of horizontal or vertical scanningI am not able to 'discuss, but having received both Iam very much inclined to favour the Berlin method.The eye does not appear to appreciate horizontal linesnearly so much as the vertical ones, and shadowsappear more natural. In any event, after two hoursof canting my head to one side to see the Berlin trans-mission I am greatly in favour of having a standardisedsystem through Europe. If the aperture were at thetop of the Baird televisor, two loud -speakers could befitted, one on each side, giving a better impression ofspeech or music from the image.

Rome, however, was not built in a day, and no doubtthese points are appreciated by the very able Bairdstaff and we should be extremely thankful to be gettingeven the small crumbs we are getting. We must not,however, be satisfied ; two nights a week, thoughhelpful, are not enough for experiment, and it is mosttrying to have to wait so long to get the results of anychange you may have made in your apparatus, hopingfor still better results. If Berlin can steadily pour outtelevision for hours on end, I cannot see why in thecountry of its origin equal facilities cannot be given.The interest shown in Glasgow in television is clearevidence of the desire of the public to have blindbroadcasting unbandaged.

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Television and

Your Wireless ReceiverPART III.

By H. J. Barton Chapple5

Wh.Sch., B.Sc. (Hons.), A.C.G.I., D.I.C., A.M.I.E.E.

IN the second instalment of this series (whichby the way appeared in the January issue ofTELEVISION, so that an apology is due to readers

for the delay in preparing the present article) weconcluded by introducing the high -frequency stagesuitable for use in a wireless set that is to receive thetelevision signals. While there are several methodsfor coupling this stage to the detector valve whichgive good results, I stated that my preference, basedon a number of exhaustive tests, was for a choke feedcoupled arrangement with the tuned circuit directlyin the grid circuit of the detector valve. A skeletondiagram was given, and I now propose to elaborateon this somewhat.

We have traced the advantages of anode bendrectification coupled with an absence of reaction ifat all possible. Again, since it is desirable to avoidcircuits which are too selective in order to obtainthe sideband frequencies, it shows that the wirelessreceiver calls for a due measure of careful thoughtand design.

Selectivity.In Fig. I I have indicated the bare essentials for

a circuit which has enabled me to receive good tele-vision images, and it is hoped that it may prove helpfulto some readers. If troubled with problems ofselectivity which may arise from the reception of boththe Brookman's Park transmissions now that fromMarch 31st both speech and image will be sent outby these stations, I think it by far the better planto use a wave trap in conj unction with the picture set.If the set is made so selective that it will separateeasily the two stations concerned, then you are upagainst the sideband cut-off problem, but if youarrange to trap out any likely speech interferencefrom the pictures, matters will be quite satisfactory.With this proviso, it will be seen that on the aerialside the circuit is a plain straightforward one, thefixed condenser in the aerial lead being optionalaccording to the type of aerial in use for receivingpurposes.


Six -volt valves are used throughout, except for thescreened grid valve and this is a four -volt one. Theresistance It, in the negative filament lead is thenadjusted so that the voltage is just four across thefilament, and the drop in volts thus acts as a negativebias for the high -frequency valve. While a negativebias is often included in a screened grid valve for

Receiving a Television transmission on a Baird Dual Exhibi-tion Receiver. The apparatus shown contains two wirelessreceiving sets, one for speech and one for vision. The"televisor" is fitted with a Baird automatic synchronising

apparatus.

109

reasons of selectivity, since one can better tune out apowerful interfering station by reducing any possibilityof grid current flow, its use is recommended here, asit is advantageous.

De -coupling.

The resistance R2 in the screen grid connection shouldbe variable, so that the correct screen voltage can beapplied to this electrode without having to recourseto a separate high-tension feed. The maximum valueof this resistance will depend upon the main H.T.feed, but assuming this to be from 300 to 40o volts,then a Ioo,000 ohm variable resistance will suitnicely. Incidentally, this resistance, in conjunctionwith the i mfd. condenser joined up as shown, acts asan effective de -coupler. Another factor which can beborne in mind is that adjustments of the screen gridvolts through the medium of R2 serves as a goodvolume control.

In the plate circuit of the screened grid valve wehave a high -frequency choke of high impedance andpossessing characteristics differing from that of thehigh -frequency choke inserted in the plate circuitof the detector valve. The resistance R3 serves todrop the plate volts to the correct value and, as inthe previous case, acts as a de -coupler with the2 mfd. condenser.

A High Ideal.A mica fixed condenser of ooi mfd. capacity

couples the screened grid valve anode to the grid endof the tuned circuit preceding the detector valve,and here we have shown an arrangement about whichI discoursed at length in the Part II instalment. Itwill therefore be unnecessary to reiterate my previous

remarks, and we can accordingly pass on to the low-frequency side.

There is one golden rule which must be kept upper-most here, and that is the fact that distortion will beavoided if the increased signal from the output stagediffers from the original only in magnitude. In otherwords, the output plate current of each valve must bedirectly proportional to the input grid volts. This isa high ideal, but unless one aims high you cannot besure of obtaining even a relatively moderate level ofperformance.

First of all then, the total input grid volts swing toeach valve must operate well within that part of thestraight characteristic situated on the negative side ofthe datum line. This will ensure that the grid does notassume a positive charge and cause grid current toflow. It is therefore obvious that the valves mustbe chosen with care to see that they can handleadequately the power necessary, and a little time spentin examining the characteristics will be repaid four-fold when it comes to operation.

Resistance Capacity Coupling.

It will be seen from Fig. I that I have placed myfaith in resistance capacity coupling. This does notmean that any other form of coupling such as trans-former, choke capacity, push-pull, etc., is ruled out ofcourt, for from experience I know that good imagesare obtainable with sets using these types of coupling.What I am anxious to emphasise, however, is that fortelevision work, where the frequency range to becovered exceeds that of the audio -frequency range, itis found that resistance capacity coupling so far meetsthe case in a really excellent manner.

(Continued on page 114.)

Fig. 1.-A wireless circuit for receiving Television.


Amateurs' ii,xhibition.1Cew Ideas on Scanning and Receiver Construction

THE second annual exhibition -of members' workheld by the Television Society at the GowerStreet College, University of London, on

Wednesday, April 9th, was regarded by all as anunqualified success.

Although called formally an exhibition, it was amost friendly affair. Exhibitors, when they couldleave their stands, visited other exhibitors anddiscussed problems and schemes for getting bettertelevision reception-a topic that exhibitors andvisitors alike found of absorbing interest.

Although many knobs and dials were on view,there was no " knob twiddling " or a single case ofapparatus being damaged by unauthorised handling.

The exhibition was open from 2 p.m. to 9 p.m., andthe members showing competed for the Tuke Cup, asilver cup presented by Captain B. S. Tuke, to beawarded to, and held for a year, by the membershowing the best apparatus.

The exhibition was staged in the Physics Theatreat the College, a historic and very appropriate spot,for not only did the President of the Society, SirAmbrose Fleming, work for many years at theCollege on the measurement of wave -length and thethermionic valve, each of which ultimately madetelevision possible, but other items which play animportant part were discovered there.

In the chemical side, Lord Rayleigh worked onargon, an important item in photo -electric cells ;Sir William Ramsay in the physics laboratories, dueto his work with liquid air, discovered helium andneon. Mr. J. J. Denton, Joint Hon. Secretary of theTelevision Society, played a part in this work.

In a laboratory not very far away from the PhysicsTheatre, Professor C. G. Carey Foster, F.R.S., did allhis work on extremely fine electrical measurements,culminating in what is now known as " The Carey -Foster " method of electrical measurement.

The apparatus shown by members displayed aningenuity and determination not to be beaten bydifficulties, worthy of the great workers who hadused the laboratories.

The judges for the award of the Tuke Cup wereProfessor F. J. Cheshire, Dr. C. Tierney (Chairman ofthe Society), and Dr. H. Monteagle. They found theexhibit of Captain R. Wilson, who co-operates withE. L. Gardiner, B.Sc., and A. A. Waters, the mostmeritorious, and awarded him the Cup, a decisionwhich was approved by all. Honourable mentionwas awarded to the Southend-on-Sea District Tele-vision Society and East Essex Group Centre repre-sented by Mr. R. F. Cowley, Mr. D. L. Plaistowe,


Mr. L. Bounds, and Mr. A. F. Knipe for a variety ofexhibits, and to Mr. H. J. Peachey who showed anelaborate receiver combining a three -valve set forspeech and a four -valve vision set.

Captain Wilson's exhibit consisted of : -(a) A television transmitter and check receiver for

supplying a vision signal for testing the televisionreceivers exhibited for the Tuke Cup Competition.

(b) An independent television receiver fitted withsynchronising device.

(c) Horizontally arranged television receiver.(d) Experimental scanning device. '

(e) Wireless receiver and amplifier specially designedfor television reception.

(f) Heterodyne beat -frequency oscillator used indesigning the transmitting amplifiers.

General view of the exhibition. A very keen interest was takenby members in the various exhibits.

The whole of this exhibit was most workmanlikeand professional in finish, but by far the mostinteresting item was the experimental scanning device.

The mechanism for working this was housed in asmall box about 6 in. by 6 in. by 9 in., and driven bya motor, but how it was arranged or worked CaptainWilson would not say.

In effect, the light spot was caused to zigzag overthe scanned area, the strips appearing to be closertogether at the sides than in the centre.

The idea apparently was to secure even scanningand avoid the jump of the scanning beam from thefinishing strip to the starting strip as is usual with thedisc. This, if workable, would do much to get rid of

III

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flicker. It can, Captain Wilson explained, be arrangedto work with the present synchronising arrangements.

The Southend exhibit included an experimentaltelevisor, complete with magnetic toothed -wheelsynchroniser, an automatic jig for marking andcutting discs and discs made by this piece of apparatus.This jig was the subject of a recent article in TELE-VISION by Mr. Knipe, who also had on view his

A close-up view of Capt. R. Wilson's transmitter. Capt.Wilson is on the left and Mr. A. A. Waters, our well-known

contributor, is on the right. ,

" water lens "-two clock glasses cemented togetherand the enclosed space filled with water.

An interesting side -line of this exhibit was a strobo-scopically controlled device for measuring camerashutter speeds.

It consisted of a motor -driven drum and a neontube fed from the A.C. mains. The motor speed isadjusted by a stroboscopic device in conjunction withthe neon tube. When the motor speed is fixed, astrip of bromide paper on the drum is exposed to abright light by the shutter whose speed is beingtested. This gives a dark band on the bromide paper,and from the length of this the shutter speed can becalculated.

The most unconventional exhibit was that of Mr.C. E. C. Roberts, who was showing " tubes " fortelevision scanning and receiving.

His " receiver " looked something like a photo-electric cell in that there was a movable backing witha wire mesh grid in front of it.

By applying a suitable potential to these a visibledischarge can be made to take place.

The light given out by this is intense and very local.Its size is easily controllable by the voltage applied,while its position can be varied by suitable magneticfields as in the case of a cathode ray tube.

For his transmitter he proposes to use a large tubecontaining a photo -electric surface at one end. Somedistance away is placed a screen with a small hole inthe centre and further away again is the " grid."These three surfaces are all parallel to one another.In use, the image to be televised is condensed by a

TELEVISION for May, 1930 2*

lens and thrown on to the photo -electric surface, whereit gives rise to streams of electrons directly propor-tional to the light values.

This electron stream is " scanned " by magnetsplaced outside the tube and so fed as to cause everypart of the stream in turn to pass through the centrehole in the screen. Electrons passing the centre holefall on the " grid " and so give rise to electric variationswhich can be amplified in the ordinary way.

All this apparatus was very much in the experi-mental stage Mr. Roberts being hampered by lackof suitable assistance and funds.

Another interesting exhibit on this stand was atelevision receiver in which the disc was made to actas the diaphragm of a cone loud -speaker. The rodactuating the cone passed through the centre of themotor spindle, while the reed unit was carried on theend of the motor body. This arrangement, Mr.Roberts stated, worked quite well, th, rotation of thecone apparently having no effect on the reproductionof speech and music.

Next to this exhibit was that of Mr. Colin P. Garside,who was showing a complete receiver with standardsynchronising gear, several forms of scanning apparatusand some models of synchronising gear which he hopesto try out. In one arrangement of this, the inertia ofthe disc was employed to control resistances to speedup or slow down the motor, the object being to getrid of the " hunting " of the received image.

A " head -phone " receiver was shown by Mr. R. W.Corkling, the complete apparatus taking up very littlemore space than a couple of ordinary 6o -volt hightension batteries placed one above another. It gavea picture about 31 to 4 inches wide, and in place of adisc a drum was employed. The neon tube is placedinside, and gives an intense line of light the full

O.P.O. exhibit of photographs received from Germany andDenmark by the recently opened continental photo -telegraphy

service.

width of the drum, the image being thrown on atranslucent screen.

That a costly workshop with machine tools andpower was not necessary to the building of televisionapparatus was proved by Mr. Ian Vaughan -Jones, a

"3

student of Eastbourne College, who showed a " tele-visor " constructed from Meccano parts and tin sheet.Even the toothed -wheel was made from tin and,what is perhaps more surprising, the apparatusworked.

Mr. G. C. Cato, who had travelled from Aberdeento exhibit, had an ingenious device which made useof a 29 -hole integrating disc working with a 3o -holescanning disc to give apparent motion to any station-ary object being scanned. As an object for hisdemonstration, he had a stationary arrow, but asseen in the " televisor " this appeared as a successionof arrows following one another.

While not connected directly with television, he

General view of Capt. 'Wilson's exhibit.

suggests that his apparatus might be used as atelevision advertiser for use in shop windows.

Those who found it hard to realise that a varyingamount of light is reflected from any surface had alltheir difficulties brushed away by the exhibit ofMr. T. M. C. Lance, who had a hand adjustable spot-light playing on a photograph. The reflected lightwas picked up by a photo cell and the output recordedon a meter. With this simple device it was possibleto see why the size of the scanning spot -light controlsthe definition of the received image. (When the spotrested on half black and half white its response washalf that of pure white, yet more than that of pureblack, and would have given rise to a grey tint in a" televisor.")

These were the original or outstanding exhibitsamong many.

Sir Ambrose Fleming visited the exhibition and waspleased with the signs of activity and progress whichhe saw. The time had now come, he said, for team-work and concentration of groups of workers on aparticular line of work.

He indicated as suitable subjects the Kerr celleffect and the measurement of the light intensitiesreflected from the human features at different angles.

Mr. W. Woodroffe, who was due to show a colourtelevision receiver on mechanical principles, and atalkie film apparatus, flew from Manchester toLondon for the exhibition, but as his apparatus wasdamaged in transit was unable to exhibit.

"4

Television and Your Wireless Receiver.(Concluded from page izo.)

To avoid distortion here it is necessary to selectsuitable valves and component values which combinein an efficient manner. Although the overall ampli-fication may be less than could be secured with othertypes of coupling, it is A.' quality we are seeking.

Without actually specifying exact valves, resistancevalues, etc., it is impossible to be specific with thelow -frequency side of the circuit shown in Fig. I, andthe experimenter is called upon to exercise a certainamount of discretion on his own part. Note theinclusion of a potentiometer as the resistance Re(about meg.) to act as an efficient volume controlwhere such is desired, and also the stopper resistanceR, which may be any value between Ioo,000 and250,000 ohms. R5, R9, and R11 are de -couplingresistances, and it will be noticed that only onevoltage is used on the H.T. side.

A Single H.T. Feed.This form of working is most advantageous, as it

does away with eliminator or high-tension batterytappings and ensures a constant and steady drainon the H.T. source. This uniform load is to bepreferred always where it is possible to incorporate it,and back coupling effects are avoided, thus promotingstability and overcoming any tendency to motorboating or low -frequency oscillation. The values ofthe de -coupling resistances are calculated quite easilyby using Ohms law.

In many respects the low -frequency side resemblesthat of the amplier specified in William J. Richardson'sconstructional article of last month, and the compo-nent values suggested there suit this circuit very well.While inclined to be heavy in consumption from theL.T. point of view, valves of the LS5 class shouldbe used if circumstances permit. An LS5B, LS5 and14,55A or LS6A work well in the V3, V4 and Vg positions.As far as the dutput stage is concerned a chokecoupled filter will certainly reduce the total voltagenecessary, but even with the neon and cogged wheelsynchronising coils in series excellent images can beobtained with 35o volts or even 1pwer. So much willdepend upon the efficiency of the synchronisingmechanism and the type of motor, the better theworkmanship the smaller the power necessary tohold the picture steady.

The circuit arrangement suggested will ensure thatthe resultant image is a positive one with the normalBaird television transmissions now going out throughthe Brookman's Park Station. In view of this noprovision has been made for changing the image frompositive to negative or vice versa. While appreciatingthat the circuit submitted is reasonably straight-forward, I shall be glad to hear from any readers whotry it out for themselves, so that experiences in differentdistricts may be compared.

A newspaper informs us that " London broadcastson 84.2,000 cycles."-No wonder we get " jams."

TELEVISION for Mcly, 1930

Assembling and Working a BairdKit of Components

By William J.

WHEN the kits of Baird branded componentsbecame available to the general public afew weeks ago I felt it would be an excellent

scheme to obtain one and make up a machine formyself to use in conjunction with the amplifier whichI described in the March issue of this magazine. Thethought was father to the deed, and it was with quitea thrill that I unpacked my carton of goods to preparefor action. Naturally, out of the complete list whichthe Baird Company are prepared to supply there arecertain items which are either already in the possessionof the constructor or, alternatively, in the interests ofeconomy, he can make them himself.

The Items ObtainedThe kit which I secured was as follows :-

IIII

*1II

*1

II

Lens box assembly (six pieces).Spindle assembly.Large lens.Small lens.Variable resistance, bracket and knob.Zenite resistance and ebonite supports.Graduated receiving disc.Terminal board assembly.I mfd. mica condenser.Flexible lead and adapter.Motoi- bracket and strops.Flat electrode neon tube.

The complete kit assembled and wired ready for use.

TELEVISION for May', 1930

Richardson

Notice the positioning of the neon lamp andterminal board.

*I Neon tube holder.Universal motor, complete with synchronising

gear.

Of these items, those marked with an asterisk caneither be made up quite simply by the amateurhimself or he can no doubt unearth suitable substitutesfrom amongst his own gear at home. In additionto the list just given, a length of rubber -coveredflexible wire and sundry screws must be got togetheras detailed below.

II ft. 3 mm. rubber -covered flex.12 No. 6 ft in. round head wood screws.2 No. 6 j< in. round head wood screws.236No. 10 21 in. round head wood screws.

24 No. 6 BA screws.One ordinary tumbler switch has been used, as can

be seen in'the photographs, but if preferred the normalhouse lighting switch will serve for switching themotor on and off. I felt it was convenient to includeone on the baseboard, however, and can recommendthis policy to you.

Positioning ComponentsWhen the kit was obtained there was no definite

information concerning the positioning of the variousparts on a baseboard, and a good deal of time wasspent on finding the correct places for the motor

stand, neon holder, and lens assembly. I understandthat these dimensions are now available in a kitbrochure issued by the Baird Company, but a completelayout of these important items is given in Fig. I.

The wooden baseboard is 26 in. by 12 in. by in.,and the best wood for this purpose is gettelboard orfive-ply. A slot Ili in. by in. must be cut outin the position shown to give freedom of movementto the disc, and this should be your first task. Theaid of a keyhole saw makes this a very simpleproposition.

Now position the motor bracket and neon holderby marking out the baseboard holes to the dimensionsgiven in Fig. 1. Make sure that the holder is correctlyplaced, so that the flat plate of the neon is exactlyparallel to the disc. You must next assemble thelens box, and this is quite straightforward if youexamine the accompanying photographs. The smalllens is held in place on a partition clipped in the mainframe while the large lens is screwed on to the front,convex side towards the observer. All the holes arethreaded to take the 6 BA screws, and, when complete,screw this down to the baseboard in the positionindicated in Fig. 1.

Allowing for FramingClamp the motor and synchronising gear to the

bracket with the strops provided, being careful to

FOR A 20' SCAWindoO 0,5C CUT A NOI.0by BASEBOARD /4,...."B

2.,_ _lagrigs.~... ../..f.

F 2444-.r o k--_081

.I2 v

,-

sttennamoOISC 227 IU___

- _

tt -11ME / 6.

31'i ;

a

4iVotA zs 1.4 r«..-3.s 4srss,

,^! .!

12r 2%''k/sseN..6L__ I_ _

As W.SCREW3

. RE"

Fig. 1.-Detailed dimensions for the baseboard layout.

insert the spindle with collar and pinion so that the. framing of the image is allowed for by rotating thesynchronising coils and their holding bracket. Theterminal board, variable resistance and bracket,Zenite resistance and -1 mfd. mica condenser, mustnow be placed in position and screwed to the base-board. The exact arrangement of these is not veryimportant, and that is why no dimensions are givenfor them in Fig. 1, but you will gather, from thephotographs what I have done and can pursue asimilar line of action.

The tumbler switch is held under the baseboardabout 8 in. from the left-hand end, two holes beingdrilled through the wood to allow the pair of wiresto join on to the switch points. At this juncture itwill be advisable to raise the base off the table byfour wooden feet, 5 in. long and in. square. Thisis essential for the disc passes through the slotyou, have already cut out, and projects over 4 in.downwards.

116

SEEINGIt

BELIEVINGWE HAVE IN STOCK

Baird TelevisorComplete or Parts

Build a TELEVISORwith Genuine BAIRD Parts

Motor and Synchronising Gear- £7 7 0Lens, large 13 6

small 7 6Neon Lamp 1 5 0Baird Discs 2 2 0

THESE ARE THE MAIN ESSENTIAL PARTS TO BUILDYOUR TELEVISOR.

Full List of other Accessories on application

Build your own AmplifierWe recommend RICHARDSON'S Amplifier

(See Television, March Issue)

Complete Kit of Parts costs only £5 6 0Any parts supplied separately. Detailed Lists on application.

CASH OR EASY TERMSIF IT'S TELEVISION OR RADIOSend us a list of your requirements for a quotation by return. Send

post card for our magnificent 48 pp. catalogue.

PETO SCOTT Co.Ltd.

Free demonstrations and advice by Qualified Engineers atour Shops: 77. City Road, London, E.C.I. Telephone

Cleekenwell 9406-7-8. 62, High Holborn, London,W.C.I. Telephone : Chancery 8266. 4, Manchester

Street, Liverpool. Telephone: Central 2134.33, Whitelow Road, Chorlton - cum - Hardy,

Manchester. Tel.: Chorlton-cum-Hardy 2028.


Little Wring NecessaryAll should now be in readiness for the small amount

of wiring up that is required, and Fig. 2 shows you

This plan view will help you to make your connections.

the complete circuit. An actual wiring diagram isunnecessary for the illustrations indicate quite clearlyhow the various points are connected together by theflexible leads and held in place by small cleats. Theonly wires passing under the baseboard are thosefrom the lamp terminals to the neon tube holderitself. Beaded leads are joined to the tap pointsof the Zenite resistance, and you must be careful toattach them to the lettered terminals in the ordershown in Fig. 2, and also see that they clear the discedge.

A point which you should be careful over is in thelinking together of the two synchronising coils. Thewindings must be so placed in series that if one coilacquires a north polarity when a current is flowing,the other coil acquires a south polarity. Beforefinally making your connections, therefore, just twista wire from each coil together and apply a smallbattery voltage, say 4 or 6 volts, across the free ends.Bring a compass needle near each coil, and if the rightpair of wires have been linked the coils will indicate

Showing how the motor is run up to speed while watching theimage formation.

opposite polarities on the compass needle. If not,then the linked wires must be changed to rectifymatters.


Finding the Correct Tap PointOne of the leads to a mains terminal passes through

the T hole in the terminal board and finishes off in aspade tag. This enables you to connect on to theappropriate terminal for running your motor at itscorrect speed according to the house mains supplyvoltage available. The motor is of the universaltype, that is to say, it will run on either direct oralternating current, and is wound to run at 75o r.p.m.at ioo volts 5o cycles A.C. or 45 volts D.C. Thus, thecorrect Zenite resistance tap must be joined to bythe spade tag in order to " drop " your voltage therequired amount.

Check over your connections to make sure that oneor more leads have not been omitted, and if satisfiedthat this is the case, place the disc on the motor shaftwith the bush portion away from the motor carcase.This will ensure that the spiral of scanning holes

Coa.

LAMP 0--

A

5rvrrC

Neon,LANIP

VAR/ABLE\ ArTMAAA1 wCEz En/ /7"C RES'S l'ApvcE

0000000090.90Moro R.

SYNCooRCINISWG

'/A1F0

Fig. 2.-The complete circuit for wiring up the Baird kitof components.

moves in the right direction, and gives you an explora-tion of the neon plate from bottom to top and rightto left.

Details to FollowNext try out the motor and see that it runs by

joining the free ends of the flex leads to the appropriateterminals on the board. For a first test join the spadetag under terminal head A, place your plug in theelectric supply socket, and switch on both at thesource and the tumbler switch under the baseboard.If your motor runs smoothly in an anti -clockwisedirection then you will be safe in assuming that yourmotor is satisfactory.

Next month I will give a table to show you whichterminal you should join the spade tag to in orderto get the speed of the motor approximately correctfor your own particular voltage supply. In addition,the results of tests made in conjunction with theamplifier I mentioned previously will be described,together with a suitable detector unit coupled to it

117

Simultaneous Sight and Sound

Broadcast. Television Makes a further advance

SIGHT TRANSMISSION 261FROM BROOKMANS PARK.SPEECH TRANSMISSION 356 m.}

ONLY those who have taken a keen interest in,or have been intimately connected with thedevelopment of television, can realise the

anxieties that assail the members of the staff whenan important demonstration is about to be given.

Every: weak link, imaginary or real, is known, anddue care taken to safeguard it ; still the possibilitiespile up in the mind to an alarming mountain ; tempers,even the most equable, become strained to breakingpoint, and even the best of friends may quarrel-for a moment.

Knowing these things, yet not suffering from them,TELEVISION'S representative went with considerableinterest to the Baird Company's experimental stationat Hendon on Monday, March 31st, to see and hearthe first complete broadcast of television, i.e., sightand sound, from the dual stations of the B.B.C. atBrookmans Park.

To say that nothing happened would, perhaps, bemisleading ; but it is also correct, for nothing in theway of trouble or disappointment did happen. Thetransmission was a complete success.

Since the opening of the two B.B.C. stations atBrookmans Park one has read so much in the wirelesspapers of the difficulties of broadcast fans in getting onestation without the other that the question naturallyarose : " As the sight and sound signals are to go outfrom these stations, is it not likely that a little of thesight signal may stray into the loud -speaker, and alittle of the sound signal find its way on to the screenof the receiving ' televisor ' ? "

It has also often been stated by some critics thattelevision wants such a wide band that it would maketransmissions on a large number of adjacent wave-lengths impossible, even if only a limited image wasbeing sent.

These doubts made the demonstration additionallyinteresting and important, for neither image nor soundinterfered in the least with one another.

At the request of our representative, first, loud-speaker and associated circuits and then the " tele-visor " and its associated circuits were cut out. Thefact of either being on or off had no effect whatsoeveron the other.

Promptly at II a.m. the blank screen of the" televisor " showed signs of a signal coming along,and it Was synchronised just as Mr. S. A. Moseley,

118

Miss Gracie Fields and Miss Annie Croft before theTelevisor.

who was announced to open the programme, beganto say :-

" Ladies and Gentlemen,-This inaugurates anepoch in television transmission. For the first time inhistory we are putting over television simultaneouslywith sound. I want to explain, as simply as possible,what is happening. I am seated in the Baird studioin Long Acre before a microphone and the televisiontransmitter. My voice is being carried along one line,and the vision along another line to the B.B.C. controlroom at Savoy Hill. There both voice and vision areconnected to the Brookmans Park BroadcastingStations, where, in turn, they are radiated through twoseparate wave -lengths.

" Those of you who are looking -in should be ableto see me as I make this announcement."

At Hendon there were a good many who knewMr. Moseley. Judging by their comments, they hadno difficulty in seeing and recognising him-in fact,they found his appearance on the " televisor " screena " speaking " likeness. But to go back to hisremarks :-

" The interest in these proceedings has been 'verygreat," he continued. " Several eminent people havesome specially to the studio to take part in whatthey regard as an historic occasion. I now propose tomake way for Sir Ambrose Fleming. Sir Ambrose's


wonderful invention of the thermionic valve madewireless in the home possible. His interest in televisionis so well-known that an occasion such as this would beincomplete without his presence.

" After Sir Ambrose has spoken I shall ask theRight Hon. Lord Ampthill, Chairman of the BairdInternational Television Company, to say a fewwords. His pioneer work in bringing television beforethe public will occupy a proud position in the historyof this remarkable new science.

" Nor am I forgetting Mr. John Baird, the manwho made practical television possible, but whoseinnate modesty makes it uncertain whether he willappear before you publicly or not. At any rate, Ihope I may persuade him to come and reveal himselfto you before the end of this transmission.

" In order to balance the experiment, on the enter-tainment side we have procured the services of thepopular stars, Miss Annie Croft and Miss GracieFields.

" I have now great pleasure in introducing SirAmbrose Fleming. . . ."

Sir Ambrose Fleming's Speech.After a brief pause, the head and shoulders of Sir

Ambrose appeared, and he said :-" We are assembled here to -day, in the Baird

Laboratories in Long Acre, London, to conduct avery interesting demonstration of a simultaneousbroadcast of speech and visible images of the speaker,with two frequencies, as arranged by the BritishBroadcasting Corporation.

" We have now had, for some time, the broadcastof speech and music, but there is no manner of doubtthat appeal to the eye is, in general, more interestingthan appeal to the ear alone, and appeal to both eyeand ear at once is much more powerful than appealto the eye alone.

" All advertisers know that a visible image orpicture holds attention far better than a mere printedsentence or even happy verbal slogan.

" The celebrated picture by Sir John Millais, called' Bubbles,' with its curly -headed little boy blowing

Lord Ampthill, Mr. Baird and Miss Lulu Stanley (one ofthe artistes) lookingin at Long Acre, on March 31st.


Just before 11 a.m. at the Baird Laboratory at Hendon-waiting for the signal to receive the first simultaneous broad-

cast of sound and vision.

bubbles, was vastly more successful in capturingpopular interest than any mere recitation of thesaponaceous virtues of an article in frequent domesticuse.

" To be able to see the speaker adds something tothe effect of his speech, not only because we all do acertain amount of lip-reading, but because muchmeaning can be better conveyed by the looks than bywords alone.

" To be able, then, to see as well as hear will adda new interest to broadcasting.

" Most persons gain more knowledge by the eyethan by the ear. Anything moving or giving evidenceof being alive at once exercises an attraction, and weall know how quickly a crowd gathers round a shopwindow when there is anything to see in it which isin motion.

" It is, then, one of the latest achievements ofapplied science to be able to give this simultaneousbroadcast of audible speech or song and visible repro-duction of images of the faces of living speakers orsingers.

" I beg to congratulate heartily all those whoseingenious scientific labours have made possible thisremarkable feat."

Sir Ambrose was followed by the Right Hon. LordAmpthill, who, to judge by his appearance in thetelevisor, has a remarkably good " television face."His speech, too, was clear and deliberate, and cameover well. He said :-


119

Television fir Bthe eginnerPART \

By John W. Woodford

IT is gratifying to learn from several quarters thatthis elementary series has enabled many readersto better understand the working of the Baird

television system, and I hope that readers not clearon any points will write and let me know so that Ican deal with them. At present we are still engrossedwith matters at the transmitting end, and saw inour last instalment how it was possible to turn lightinto electricity.

A Standard Photo -electric Cell.Undoubtedly the modern photo -electric cell can

be looked upon as a sort of wonderful Aladdin'slamp, for its characteristics to the ordinary lay mindborder on the miraculous. It would not be in keepingwith the aims and objects of this series to examinethe photo -electric cell from the scientific point of viewand delve into its intricate properties. You willhave to take all this for granted and accept the barestatement of facts.

As we have said before, its prime function is toconvert light variations into current variations.Some of the best types for this purpose are manu-factured by the G.E.C., and one of the accompanyingillustrations will enable you to get an idea of theappearance of what is known as their standard type.For television purposes it is easy to imagine thatsensitivity is of the utmost importance because ofthe very small proportion of light which is reflectedback from the illuminated areas of the object beingtelevised. Gas -filled cells are therefore preferred, andin these the normal primary current is magnified bythe production of secondary electrons when theprimary electrons travel through the gas.

Removing a Misunderstanding.Unfortunately, the non -technical reader is liable

to run away with the idea that one or more photo-electric cells, since they transform light into electricity,should be capable of converting an entire scene orimage into terms of electrical current variations.Just expose the flood -lighted scene to the activesurface of the cells in much the same way as you woulda camera, and there you are !

But no, the problem is not such a simple one asthat, and a few moments rumination should serve toshow why. Any one scene or even a person's head

and shoulders if illuminated is found to be made upof countless differing light values spread over thewhole area. Now the photo -electric cell gives aproportional current response for every light valueto which it is exposed, and our large area wouldtherefore only produce one average light value which,of course, is useless. No, we must split up our subjectinto elemental light areas, and let the cell deal witheach one in turn.

Justifying the Light Spot.Now we can see the reason for installing our

travelling light spot. ' By imposing upon it a definitemovement so that it sweeps over every part in turn,it gives the cells a chance to perform their naturalfunction. At any one instant during the travel ofthe beam of light passing through the rotating disc,we have a minute area illuminated and the lightreflected from the subject produces a current variationin the circuit containing the one or more photo-electric cells.

At the very next instanta neighbouring elementalarea is illuminated in thelight strip being described,and our cell makes a responseas an instantaneous currentvariation. This process iscontinued spot byspot and strip bystrip until thewhole of theimage has beenexplored andanalysed or"broken up"into definite values of light andshade, which in turn bring aboutcorresponding current values.

In effect, we disembody oursubject and pass it piecemeal intoa valve amplifier to be handledas an electrical signal. This canbe heard as a note in a pair ofheadphones or even a loud -speaker,and the next time you tune -inthe home wireless set to thetelevision signals which are now

AG.E.C.photo-electriccell.


la unretottehedPhotograph of a television image, taken in 1926.

being broadcast by the B.B.C. remember that youare " listening " to some artist's face !

Making Movement Possible.I can quite imagine the reader saying to himself

that this is no doubt all right for subjects which arelifeless or quite steady, but how are you goino-b to takeaccount of movement ? It is fairly obvious that themain source of entertainment at present providedthrough the medium of television will be from artistswho cannot be expected to keep still, even if onlytheir lips move to speak or sing. Quite right, butthis is at. provided for.

When you patronise the cinema theatre and watchyour favourite hero or heroine performing on thescreen do you realise that the movement portrayedis actually an optical illusion ? What you really seeis a series of still pictures rapidly thrown on the screen,but your eye, owing to the property known as visualpersistence, conveys a harmonious movement to thebrain. About sixteen complete pictures per secondare shown, each one portraying a movement justslightly removed from its immediate predecessor, butthe rapidity of the process gives the impression ofcontinuous and not disjointed action.

TELZVISION for May, 1930 3*

Of Similar Character.Exactly the same sort of thing happens with

television. By arranging the speed of the trans-mitting disc it is possible to have as many completeexplorations of the subject in one second as desired.In practice twelve and a half pictures per second arecatered for, in other words, the disc is driven at 750revolutions per minute, and this rapid scanning issufficient to give all the movement that is requiredin normal practice. The mechanics of the processbecome lost on the observer, and he sees the visionof the moving image in his television screen, althoughthat movement takes place many miles away.

Now isn't that an intriguing process, and yet sosimple when it is shorn of all its technicalities. Manypeople are under the impression that this method isincapable of producing sufficient detail to give recog-nisable images, but let me say immediately that thisis quite erroneous. Admittedly, the amount of detailwhich can be put over in the present stage of develop-ment of the art is not unlimited, but even so theresultant images are far from being distorted,and resemble the original in a most remarkablemanner.

An amateur photograph of a modern television 'image. Theimprovement is very apparent.

A Softening Effect.Where is the method likely to fall short of giving

almost faithful replicas of the subject posing beforethe transmitter ? Why, only when an effort is madeto televise an object possessing intimate detail whichis much smaller in comparison with the travellinglight spot which is dissecting it.

For example, objects with sharply defined outlineswhen televised come over with a somewhat softenedeffect, but in ordinary television practice this is notnoticeable. Most of the characters are undergoingcontinuous movement during the course of theirturn before the " light microphone," and this, coupledwith the self -accommodating character of the humaneye and its tolerance, impart to the observer animage with quite a wealth of detail. In any case,the position of the hands on a watch can be seen quitereadily, so surely this is sufficient to prove that thesystem is capable of handling quite small things.

Modifications ?Of course, one could increase the number of holes

in the disc and thus get greater detail, but this wouldbring in its train many other alterations, such asdisc size, picture shape, etc. Then, again, one mustalways bear in mind that at the moment televisionbroadcasts are transmitted into space as wirelesssignals which must conform to regulations drawnup for aural broadcasting, and this artificially imposesa limit of nine kilocycles for the sideband owing tostation interference. Once this matter has beendealt with by the authorities on its own merits, thenwe can look forward to pictures of greater dimensionsor more detail.

The light and shade in our received image is dis-tributed throughout its area in the form of a washdrawing or continuous surface. This explodes allthose dot theories which were formulated in the pastto prove that television was quite impracticable asa commercial proposition. It is necessary merelyto see that the frequencies present in the originaltelevision signal are maintained.

Progress Made..As proof of what the image looks like and what

progress has been made, witness two of the accom-panying illustrations. One shows a man's head, andis reproduced from a photograph of the first realtelevision image ever taken, this actually being inthe year 1926. Defects were present then, for theapparatus at both the transmitting and receivingends had not been properly developed. Now comparethis with the photograph of the young lady. Isn'tthat recognisable ? And yet this is only a repro-duced photograph of the actual image, and the eyeitself would see a much better one than is recorded bythe camera, owing to the length of the plate exposure.

This alone should be sufficient to awaken enthu-siasm, and next month we shall migrate to thereceiving end and see what takes place there, for, afterall, to the " looker -in " this is perhaps of the greatestinterest.

Simultaneous Sight and Sound Broadcast.(Continued from page 119.)

" This is a very memorable occasion for all thosewho are interested in television, or, indeed, in theprogress of science, as we have reached a goal atwhich we have been striving for a long time and areactually inaugurating the double-wae transmission.

" I desire to offer my hearty congratulations tomy friend, Mr. Baird, and to all those who haveassisted him in the development of his wonderfulinvention.

" As Chairman of the Baird. International TelevisionCompany, I welcome this opportunity of thankingthe B.B.C. for all that they have done to assist us.As you may know, this transmission has been madepossible by the close co-operation of the B.B.C.engineers with the engineers of the Baird Companies.

" I greatly regret that my colleague, Sir EdwardManville, cannot be present this morning, as he wasconcerned with the development of television longbefore I had the privilege of being associated with theBaird Companies. Sir Edward Manville has a betterright than I have to speak about the progress andprospects of television, and I hope that on somefuture occasion you will both see and hear him withthe aid of your televisors.

" Meanwhile, I must not delay you any longer, asthere are others who are as proud'as I am to be presenton this occasion whom you ought to see and hear."

After Lord Ampthill came the variety section of theprogramme, opened by Miss Annie Croft, who sanga medley of popular songs from musical comedies.

An Entertaining Programme.Miss Grade Fields was the next performer ; she

gave " Nowt about Owt '" and " Three GreenBonnets," and left no doubt in anyone's mind that itwas Grade Fields and not a clever impersonator.

Mr. R. C. Sheriff, author of " Journey's End," wasto have concluded the programme, but was unable toattend. His place was taken, at a moment's notice,

by Miss Lulu Stanley, and so ended the first completetelevision broadcast.

Throughout the reception was uneventful. Thesynchronising scarcely varied from start to finish,and did not require adjustment. There was no inter-ference with the picture through fading, local" howlers," or any unwanted atmospherics or otherelectrical disturbances.

The programme was received on two " televisors "at Hendon, while one loud -speaker served for both.The room in which they were placed was not speciallyprepared, and might equally well have been any roomin any house. The blinds were drawn to cut outexcess daylight, and that was all.

Any amateur could have done what was done atHendon, and, in fact, many did, as reports elsewherein this issue prove.

The demonstration was but another proof addedto the many already given, that Baird television cando what it claims to do, and do it successfully, withoutany fuss or special attention. W. C. F.

TZLEVISION for May, 1930

Enthusiasm

in Newcastle

BY

Sydney A.

Moseley

FROM the many enthusiastic letters which havebeen received since the dual transmissionsstarted on March 31st, one of the most

interesting comes from Mr. Thomas Payne, of Payneand Hornsby, the radio and gramophone engineersof Gallowgate, Newcastle -on -Tyne, who writes to meas follows :-

" It is with very great pleasure that I write toyou with reference to our first reception of tele-vision on our premises last evening.

" As one of the pioneer station directors I havefollowed very attentively the progress of television,and also the great fight you have made for itsrecognition.

" Allow me to wish you and television the greatsuccess which I am now quite sure is coming.Perhaps you would also extend the hearty con-gratulations of this humble pioneer to Mr. Baird."

Mr. Payne encloses a copy of a letter he has sentto many trade papers and also to Sir John Reith withwhom " I was intimately connected at the commence-ment of broadcasting."

Messrs. Payne and Hornsby were delighted topick up the first transmission picture ever receivedin Newcastle. Indeed, they claim that this picturewas the first of the northern counties. Their firstattempt had been nullified by faults in their amplifier.

The second attempt had been nullified by the factthat the motor in the televisor had not been runningat the correct speed.


We used the " G.E.C. Stabilised Six " set, con-sisting of two stages of H.F., leaky grid detector,one stage of L.F. transformer coupled, followed bytwo stages of choke coupling with an I,S6A in thelast stage using 400 volts H.T.

" So far as the detection and amplification side isconcerned this is not considered orthodox for thereception of television. Anode bend detection andthree stages of resistance capacity coupling is con-sidered the most likely to bring satisfactory results.All the more satisfactory, therefore, to receive tele-vision on a standard wireless set."

Television was received on Messrs. Payne andHornsby's business premises in a notoriously bad partof Newcastle for any sort of wireless reception.They are situated in the business centre, tram wirespassing the premises, and screened all round withhigh buildings. They are 30o miles from the trans-mitter and can, therefore, say that they are practi-cally 200 miles outside the service area.

This is Mr. Henry Dixon, the secretary's report ofthe transmission :

The first picture was that of a lady singing, followedby a gentleman, then a lady and gentleman singingalternately. We cannot claim that the picture wasby any means perfect, but at times the features wereclearly distinguishable, and at these times syn-chronising with speech and music was perfect.

We were picking up speech and music off the356 meter wave -length with a 3 -valve set and anindoor aerial put up in the same room in which thetelevision picture was being received.

123

A group of interested journalists looking -in to the first combinedsight and sound broadcast on March 31st last.

Fading from the televising transmitter on the261 meter wave -length was our biggest trouble, thisfading was the sole cause of our losing the picturecompletely at times. A stable transmission wouldhave meant a stable picture.

It was quite thrilling, when the strength of thetransmission signal improved, to hear the synchronis-ing impulse from the transmitter effecting the runningof the motor of our receiver and pulling our receiverinto synchronisation with the transmitter. Whenthis happened the picture was fairly distinct.

For distant reception of television fading mustremain the bugbear for some time to come. On topof this our picture was affected by the distortionfrom the tram wires and perhaps an isolated motoror so still running in the vicinity of our premises.

Our electric current here is D.C., which, we think,is not helpful.

Speaking from the general interest point of view,since receiving our televisor we have found thatthere is a tremendous amount of public interest, andwe have had hundreds of inquiries as to when we willbe able to demonstrate to the public.

The journalists who looked -in on March 31st, taken outside theBaird Laboratories at Hendon.

124

We envy the people of the south who now havea transmitter on their " door step." Considering ourexperiences of last evening in the north with all ourdisabilities, we think that the reception of televisionin London and its immediate vicinity should nowbe easy. For the sake of the many thousands ofnorth country experimenters who are anxious totake up television for its extreme interest from theexperimental point of view, we are hoping that wewill soon have a northern transmitter in operationworking on twin wave ; until this is going the northwill be placed at a great disadvantage.

Naturally the well-known northern firm is veryproud of the fact that the first television pictureever received in the. north was tuned -in by theirmanaging director, Mr. Tom Payne, better knownas " Uncle Tom." " Uncle Tom," by the way, isbecoming a notable personage in the North of England,being able to claim the honour of being :-

The first director of the first B.B.C. station (5NO).The first to broadcast speech from 5NO.The first to broadcast music (on his violin) from the

,same station, and nowThe first in the North to tune in a television picture.Congratulations to " Uncle Tom."

Drawings from blue prints, processBlocks in Line & Halftone, CommercialPhotography-Skilled Operators

AVIERYS37-41, LOWER MARS41

WATER LOOLONDON, SZ.I

uz,


Te,evision

I o-day and To-morrow"Reviewed by Dr. Clarence Tierney, D.Sc., F.R.M.S.

T has been said, and said quite truly, that televisionas we know it to -day is as yet in its infancy, thoughit is equally true to say that our knowledge of the

problems involved in this subject and of their practicalsolution is infinitely in advance of our knowledge ofwireless signalling when that first started.

On the subject of television there is, too, a certainpaucity of authoritative publications. We welcome,therefore, this present work asindicating in a comprehensiveand readable manner thepresent state of developmentand future expectation oftelevision upon the lines of ourpresent knowledge.

The work deals at lengthwith the system of Baird,which, after all, is the onlypractical system known, andwhich it must be franklyadmitted is alone in survivingboth scientific and commercialtests and application. It isthe authors' declared intentionto place in the hands of readers' the most up-to-date, first-hand information concerningthe Baird system of television,"and in this they have admirablysucceeded.

A chapter is devoted to thetransmitter, in which suchproblems as the scanning disc,the number, shape and disposi-tion of the holes, their relationto the available frequency bandand to the problem of flicker,are discussed, while in a chapteron the receiver helpful andexperienced suggestions aregiven as to the types ofcomponents best suited to accomplish good results.The all-important problem of synchronism isadequately dealt with in a special chapter, givinga well -illustrated description of the magnetic toothed -wheel system of synchronising, which for wirelessreception has proved to be the most effective methodof steadily holding the received image.

TELEVISION

-.ANDTOMORROWsYDNr1 'A MOSE11:H...1,8A

CHAN>

JOH ts

SILilAIR

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Photo -electric cells and their couplings are also welldescribed, while in a chapter devoted to the wirelessreceiver for television the reader will find much helpfulinformation, with diagrams of tested and successfulcircuits.

In a chapter on the cinematograph and talkingfilm the authors describe the latest and far-reachingapplication of television and the development of

what is called the " tele-cinema," by means of whichthe film, either silent or talking,is televised and transmitted forwireless reception.

The more specialised applica-tions of television, such astelevision of objects in totaldarkness by the utilisationof infra -red rays, and also thetelevision of objects in naturalcolours, as well as phonovision,the method of recording a.hdstoring the televised image, areall fully dealt with, while in aconcluding chapter a briefreview is given of the efforts ofother workers in Europe andAmerica, and of the resultsachieved.

The book is prefaced byan excellent foreword byJ. L. Baird, in which he indi-cates the utilisation a n ddevelopment of short wave-lengths for the transmissionof extended scenes. The wholework is well written and pro-fusely illustrated and contains ahelpful index. It should be readby all desiring an instructiveand authoritative account ofthe recent advances and

development in this all-important subject of televisionand its practical application. C. T.

"TELEVISION TO -DAY AND TO -MORROW." By SydneyA. Moseley and H. J. Barton Chapple. With a forewordby John L. Baird. 193o. xxiii-I-13o pp., 86 plates andfigures. Published by Sir Isaac Pitman & Sons, Limited.Price 7s. 6d. net.

TELEvisioN for May, 193o 125

Some of the filmous zirtistes you Trill see on your Telibision Screen during the month of May.

No. 1. Miss Cecile Maule Colt. No. 2. Miss Dorothy. Dickson. No. 3. Miss Jean Colin. No. 4. Reginald Stewart.LNo. 5. Miss Mercia Stotesbury. No. 6. Ben awes. No. 7. Miss Madeline Carroll. No. 8. Miss Mary Brough.

Baird Studio TopicsBy Harold RraGly,

Studio Director

ULLO, everybody 1 Baird Television calling."Yes, I feel I want to start this article on acheerful note-and why not ?

The interesting event of television, combining soundwith vision, is going on merrily, and day after day theinterest in our transmissions increases.

I want here, however, to tell you, not about thetechnical branch of television, which more able pensthan mine have set down on the other pages of thismagazine, but about the artistes who have givenlookers -in so much pleasure during the short time thedual transmission has been in operation.

First, there is charming Miss Annie Croft, whosevoice is as sweet as anything to be heard on the Londonstage to -day. Miss Croft, who was the first artiste toappear in these new programmes, gave a delightfulrendering of numbers from popular musical comedies.And Gracie Fields-who could resist the temptationof investing in a televisor in order to take an admiringpeep at such an electrical personality ? Miss Fields,who gave up the first day of her well-earned holidayto appear in our initial programme, " blew in "shortly before II a.m., with hat on the back of herhead, and said, in best Lancashire dialect, " Ee, I'vecoom ! " Then she sang " Nowt About Owt " and" Three Green Bonnets." When I asked her later todescribe her feelings while being transmitted, thetypical reply was : " I was unconscious."

Lookers -in have had an opportunity of seeing andhearing Sybil Thorndike. Miss Thorndike, who is agreat worker, as all real artistes are, gave a perfectrendering of three of Robert Louis Stevenson's poems.I was with her once under Mr. Charles B. Cochran'smanagement at the Pavilion Theatre during the timethat Morton, the French comedian, was a ragingfavourite over here. I well remember how, during ascene with her, Morton would often grimace at usfrom the wings 'in an effort to " dry us up." To thebest of my belief Sybil was quite impervious, but itwas a great effort on my part to keep a straight face.I imagine she was too intent on her part to give amoment's thought to anything outside her work.Wasn't her performance in " To Meet the King " agem?

TEL VISION /or May, 193o

I had an interesting talk with Miss Desiree Effingerduring a visit she paid to our studio. It appears thatshe had been filming at Elstree the day before, andhad had a really strenuous time before going on to theDominion Theatre, where she is appearing so success-fully in Herbert Clayton and Jack Waller's " SilverWings." It was only natural that she should feel theeffects of her efforts of the previous day, but in spiteof this she insisted upon being televised, and even sanga few bars of some of her songs. Those who werelooking -in when she appeared on the televisor a fewdays afterwards beheld a dainty picture singingenchantingly.

Mr. George Clarke is surely the funniest " dude "comedian we have to -day. He appeared, completewith monocle and minute moustache, and put over avery amusing number. He is in " Darling, I LoveYou," at the Gaiety.

Pretty Miss Mamie Watson and Neta Underwood,both charming people who sing delightfully, havealready given enjoyment to lookers -in.

Mr. De Groot, than whom there is no more popularviolinist to -day, played excerpts from his extensiverepertoire in his own inimitable style.

Miss Jean Colin, who made a successful first appear-ance as leading lady in " The Five O'clock Girl " atthe Hippodrome a short time ago, sang her way intothe hearts of lookers -in, on April 15th.

Mr. Bransby Williams, that great character actor,appeared on April 9th, and put over one of his famousimpressions. It was a splendid test for television,which came out with high honours, every movementof the face and the gestures of the hands beingperfectly reproduced.

Miss Dorothy Dickson, who has a personality andcharm all her own, gave a singularly delightfulperformance here. I met her first at the WinterGarden Theatre in 1924 when I joined the cast of" The Cabaret Girl " during Mr. George Grossmith'sabsence in America. It was a great pleasure to dancewith her in that big number, " Dancing Time." Sheis a perfect and graceful dancer with a wonderfulsense of rhythm.

127

H ow Television zs being ReceivedReports from Czechoslovakia, Birmingham, Manchester, Leeds,

Glasgow and Sunderland.

TELEVISION is steadily marching on andgrowing. Not that any amateur needs to bereminded of or told that fact, but it is pleasant

to be able to record it, and at the same time paytribute to those who have fought the battle fortelevision.

Up to last month it was the amateurs who weredoing all the receiving of television. Now the wire-less agents all over the country are getting " tele-visors," and they are as keen as the amateurs andwrite just as enthusiastically.

Before dealing with them, however, there is anotherlong-distance reception of television to record.

Mr. Pranti;ek Pilat, who lives at Brno in Czecho-slovakia, and is a representative of the firm of Trans -radio, writes to say that the English television signalsare received at good strength in his country. Hesays :-

" Towards the end of December we began withtests of receiving television from London. Thesetests were most satisfactory, and it can be statedthat London television can be received daily inCzechoslovakia."

Mr. Fiat sends photographs of his apparatus, butdoes not give a description of it (in English).

Not content with receiving television, however, hehas been busy with his pen writing about televisionin a number of Czechoslovakian wireless papers, and,from a diagram given in one of these, it appears thathe uses in the output stage of his receiver a screengrid valve, choke fed, and couples his neon to theplate by a couple of 2 m.f. condensers, one in eachlead, with a 500,000 ohm variable resistance in seriesto regulate the voltage. He apparently uses about25o v. H.T.

In addition to his other activities, he gave a broad-cast talk on " Baird's Television " from the Brnostation, 342 metres ; from 19.55 to 20.10 (Continentaltime), on " Utery, rijna, 1929."

As none of my friends and acquaintances have anyknowledge of Czechoslovakian, it has not beenpossible to translate the date, but when shall we havea lecture on " Baird's Television," or even " Tele-vision," from a B.B.C. station ? Czechoslovakia hasstolen a march on us.

We congratulate Mr. Pilat on his good work onbehalf of television, and wish him every success.

A student member of the Television Society, Mr.E. H. Traub, living at Brondesbury, has been getting

128

into domestic hot water-with a friend-through histelevision experiments. Needing a motor to drivetheir disc, the domestic vacuum cleaner was raided.This was the cause of somewhat strained domesticrelations. Unfortunately, the motor was not suit-able. It sparked badly at the brushes and causedinterference with the image. They next got a II() A.C.fan motor which behaved better, as far as sparkingwas concerned, but ran somewhat uncertainly. Theirdisc is of cardboard and the neon a simple com-mercial beehive. With this, fed from an S.G. Det.and i L.F. set, results were obtained on April 9th" after many setbacks," as Mr. Traub puts it.

Their neon, through its beehive construction, gavea very uneven field of illumination, and having triedmirrors, ground glass, lenses and other expedients,they finally got over the difficulty by coating one-halfof the bulb with silver paper and " frosting " theremaining half.

The " frosting " was done with fine emery paper,turpentine being used as a lubricant, and took abouthalf an hour's careful papeting to complete. Thisarrangement gave a nice flat field of illumination anddid not lose too much light.

Like many other experimenters, they have learnedthat " volts " is another term for " cash," and theyfind themselves hampered by a shortage of both.

This photograph of his amateur -built television receiver has beensent to us by one of our readers, Mr. FrantCeek Pildt, of Brno,Czechoslovakia. In his covering letter he claims that this is thefirst experimental television apparatus used for receiving televisionfrom London in Czechoslovakia. He says: "These tests weremost satisfactory. London television can be received daily."

We congratulate our reader on his success.


Also, like most other experimenters, they do notlet a small thing like that upset their work, and so,to make use of the dual transmissions, they arefixing up a crystal set for speech reception. Theyhave the sympathy of all true amateurs in theirstruggles with adversity.

Birmingham has been mildly excited since the dualbroadcasts started from Brookman's Park, for Mr.J. B. Kramer, working a Baird " televisor " at theUniversity, Bournbrook, succeeded in receiving theLondon transmissions.

Mr. Kramer is a keen television experimenter, andin his present experiments is being helped by Messrs.L. G. A. Sims and T. Havekin, lecturers in electricalengineering at the University.

The Birmingham newspapers claim the ioo milesreception as a record, but close on the heels of theirclaim comes the Manchester papers with a " Home-made Television Set Triumph." A Manchesterjournalist saw Mr. A. E. Kay's apparatus and waspresent at a morning reception. Like his colleaguesin Birmingham, he was impressed, and had no diffi-culty in recognising what he saw, or realising thattelevision was genuine and of definite interest.

Birmingham and Manchester, however, are hope-lessly beaten, for at Newcastle Mr. Tom Payne, ofthe firm of Payne & Hornsby, wireless dealers, usinga " G.E.C. Stabilised Six " in conjunction with aBaird " televisor," has had consistently good tele-vision reception and demonstrated it to his customers.

The G.E.C. set consists of two stages of H.F.,leaky grid detector, one stage of L.P. transformercoupled, followed by two stages of choke coupling,with an L.S.6A in the last stage and 400 v. on theplate.. An indoor aerial and a three -valve set in thesame room as the " televisor " looked after the speechand music. Despite the fact that Messrs. Payne andHornsby's business premises are in the heart ofNewcastle and very badly situated from a wirelessreception point of view, they had, little or no troublewith their television and could recognise the peopletelevised.

Mr. Tom Payne is becoming a unique personage inthe North of England, for he was the first director ofthe Newcastle Station (5 NO), the first to broadcastspeech from it, and the first to broadcast music fromit. He now claims to be the first to tune -in a tele-vision image in the North, and if he bases his claimon having done it all on such commercial apparatusas can be purchased by anyone, he would seem to bejustified ; but he must look to his laurels, for Mr.Norman Turner, of Hope Street, Glasgow, of Con-sulting & Radio Service, Ltd., reported on March 26ththat he had received Baird television transmissions,and proved the accuracy of what he had seen bydescribing all that had been transmitted. Mr. Turnerused a Columbia Three, a screened grid set with anodebend detector and a P625 raw A.C. fed power valve.The output went to a push-pull L.S.5A amplifierraw A.C. fed filaments with 200 volts on the plates.Later he succeeded in getting the Berlin transmis-

The television receiver built by Mr. W raight, of Funchal,Madeira, a letter from whom appears on our correspondence page.

sions, a length of cinema film of two girls, and sotakes his place beside Mr. Hewel, of Berlin, as a long-distance amateur.

He describes the definition as very good.In addition to these firms, wireless dealers in Leeds,

Bristol and Lincoln have reported commercial recep-tion of television, and in each place there is the sametale of tremendous enthusiasm among the localwireless amateurs.

Sunderland, thanks to the enterprise of the Sunder-land Echo, has had a demonstration of Baird tele-vision all to itself, for a transmitter and receivers wereinstalled at the Festival of Youth Exhibition in theVictoria Hall, and people visiting the exhibition wereable to talk to and see their friends in front of thetransmitter in another part of the building. Theironly trouble seems to have been an insufficiency ofwords with which to describe their surprise andwonderment at this latest achievement of science.

The Sunderland Echo has done its best to helpthem, and devoted a considerable amount of space todescribing the demonstrations. There should be noexcuse for Sunderland residents asking, " What istelevision ? " or saying, " It cannot be done."

The Echo has earned the gratitude of all amateursfor having come out so boldly in the cause oftelevision.

W. C. F.

TELEVISION for May, 1930 129

Faithful ImagesBy W. F. F. Shearcroft, A.I.C.

HE process of Television resembles to someextent that of photography, and encounterssimilar difficulties which the photographer has

faced and solved.In both processes something, which we may

conveniently call the object, is placed before suitableapparatus. Energy, in the form of light, is given outby this object and collected by the apparatus. Onthe photographic plate this light energy is transformedinto chemical energy, which brings about certainmolecular changes of the substances imbedded in thefilm on the plate. These changes are not visible to theeye.

Similarly in Television, the apparatus at thetransmitting station collects the light energy given outby the object and transforms it into electrical energy,which again has no effect upon the human eye.

The photographer, having exposed his plate andobtained the necessary chemical changes, then proceedsby a series of chemical actions, collectively knownas development, to produce a final result which isvisible to the human eye. Similarly, the receivingstation in television transmision collects the electricalenergy and converts it into results which are visible.

In both cases the final result is seen and judgedby the human eye. It would be more accurate to saythat the result is judged by the process of humanvision ; because the eye is only concerned in receivingphysical stimuli which are transmitted as nervousimpulses to the brain, where what we call ourintelligence proceeds to interpret them in the light ofpast experience and education.

Photograph of a picture taken with ordinary film.

130

The value of the final result obtained in both casesobviously depends upon the correlation which we areable to obtain between the various transformationswhich take place. The camera, without proper control,lacks this co-ordination to a marked extent. Thus, forexample, if we view a bunch of scarlet poppies besidesa bunch of violets then we see the former as " flaming "while the latter are " modest." Red is, to our vision,a bright colour ; violet a dull one. Any representationor image of these must reproduce this brightness ordullness, or by some means must suggest it to give us atrue impression of the real thing.

A simple unaided photograph will reproduce thepoppies as " modest " and the violets as " flaming."The light energy given out by the violets is capable ofproducing more chemical change on the plate in anygiven time than can be produced by the light from thepoppies. This is an inherent defect in the process ofphotography, a defect very evident in the majorityof amateur snapshots. The camera does not ". see "things as we do.

In Television the same holds true. The receivingapparatus does not " see " the object as the human eyewould. Normally, the object is illuminated by whitelight, and only light reflected by the object reaches thephoto -electric cells. All natural objects exhibitselective reflection. Seldom do they reflect just thelight which they receive. A red object absorbs mostof the components of white light, and reflects apreponderance of red. Thus the lips of a human facewill send a message to the receiver in red light. Theelectrical impulses, set up by the light received, depend

[Photos by KodakPhotograph of same picture, using special colour sensitive

film and appropriate screen.


Photograph of a cabinet taken with ordinary film,without screen.

upon the portion of the spectrum which gives rise tothem. These differences will be faithfully reproduced atthe receiving end of the transmission-reproducedas the transmitter " sees " them, not necessarilyas the human eye would record them.

Short of reprodution in natural colours, the onlydifferences observable at the receiving end aredifferences of intensity of light. For faithful repro-duction we should require that the things we callbright should be represented by intense light, andthe dull things by dimmer light. Actually the reverseis quite possible in Television as in photography.

The photographer has solved this difficulty by aprocess of screening. Transparent screens are placedbetween the object and the plate. These screens aretinted so that they " filter " out some of the morechemically active rays of light coming from the objectThey impose a handicap on these rays, and thuspermit the less active rays to compete successfullywith them during the time which the image is actingon the plate. The illustrations show the differencewhich is obtained in this way.

In work in the studio much is possible by variationof the composition of the light used to illuminate theobject, and in the case of the human face by suitable


[Photos by KodakPhotograph of same cabinet taken on special colour sensitive

film, using appropriate screen.

make-up. This, however, will be impossible whenthe televisor is taken into the open. There thenatural objects will have their natural colours andselective reflections beyond the control of the operator.They will be lighted by daylight normally, which iswhat it is and again beyond the control of theoperator.

Screening alone is not the only possibility as far asphotography is concerned. The nature of the photo-graphic plate can be altered, and it is possible toproduce plates which are more sensitive to the lessactive rays than the ordinary plate. The sensitivityis produced by various means. Similarly, it will bepossible to produce photo -electric cells that willreact to various parts of the spectrum in such a manneras to produce a true image.

This aspect of the production of true images willhave to receive much attention, because human visionis much more critical and much more highly trainedthan human hearing. The vast majority of us do notmiss the finer points of music which are lost in theaverage bad reception on wireless outfits, and we arecontent with what we suppose is reality. We shall nottolerate beyond the experimental stage visual imageswhich are similarly lacking in faithful reproduction.

131

Where are the Sidebands?By R. S.

AFUR having several pet :theories upset bythe sideband theory of modulated carrierfrequencies, the writer, determined to try and

overcome the difficulties, but succeeded in provingthat sidebands are mythical, being only a mathe-matical theory advanced to explain certain defectsin radio engineering. A great deal has been writtenon the subject from both sides, but to date no con-clusive experimental corroboration has been putforward. Below is a brief explanation of two experi-ments performed by the writer, which leave noreasonable excuse for the continuance of the sidebandtheory.

The First Experiment.In the first experiment a radio frequency of 6,000

kcs. was modulated by another radio frequency of500 kcs., the circuit used being given in Fig. 1. Themedium and high frequency oscillators (shown atA and B respectively) are conventional tuned grid-tuned anode circuits, their outputs being led to themodulator and output valves as shown. A highfrequency choke (H.F.C.) is connected in the anodecircuit of the modulator valve, consistingof thirty spaced turns on a two-inch former. Thisprevents the 6,000 kcs. frequency from reachingthe anode of the modulator valve, whilst offering littleimpedance to the 500 kcs. frequency. The modulated6,000 kcs. frequency is fed direct to the aerial terminalof a short wave receiver, through an adjustableneutrodyne condenser.

The formula for sideband frequencies is given asn-m and n+m, where n is the frequency in cyclesper second, modulated by a frequency of m cycles persecond. If, therefore, sidebands exist, a signal shouldbe picked up in the receiver when tuned to either5,50o kcs. or 6,50o kcs.

The first trial produced signals on the tuning scaleat two points, one of these signals being, however,

Neu ;woo nve cavo To 'A"TERMINAL

HT ON RECEIVER.

rvur

Fig. 1.

132

Spreadbury

Fig. 2.

very weak. The frequencies for these settings wasascertained, being 6,000 kcs. for the stronger signaland 5,500 kcs. for the weaker, no signal being coaxedout of the receiver at 6,50o kcs. Having presumablydiscovered one sideband, the absence of the otherwas puzzling, until finally the discovery was madethat whilst the 6,000 kcs. was modulated by 500 kcs.,the two frequencies were superimposed, and partialrectification of these superimposed frequencies by theoutput valve of the oscillator produced an inter-mediate frequency equal to the difference of thetwo individual frequencies (as in superheterodynereceivers). A readjustment of circuit values remediedthe error, no signal remaining at the 5,50o kcs. settingof the receiver.

Another Experiment_Not content with one proof, work was started on

another experiment, this time to test the existenceof sidebands in a carrier frequency modulated byaudio frequencies, by neutralising the actual carrierfrequency.

Fig. za shows a circuit in which two high fre-quency valves are energised by a common aerial,one through an inductance, the other through acapacity. The acceptance of a circuit containinginductance varies inversely as the frequency (seeFig. 2b)-acceptance being the reciprocal of impedance-whilst the acceptance of a circuit containing capacity

TELVIISION for May, 1930

fi

varies directly as the frequency (see Fig. 2c), fromwhich it will be appreciated that as the frequencyincreases, oscillations from Vi decrease, whilst thosefrom V2 increase in strength, the two being equalat one critical frequency, this frequency producing noresponse in the secondary of the transformer T inthe anode circuit, since the individual signals in theprimary are opposed to each other. Fig. 2d showsthe response produced in the secondary of T, plotted

FREQUENCY I

Y z

Fig. 3.

against frequency, where x is the frequency at whichthere is no response.

Phase Reversal.A further increase in frequency results in an increas-

ing response in T secondary, but the phase is reversedas signals from V2 now predominate. In Fig. 2aa capacity and inductance are shown dotted, con-nected between the grids and filaments of the twovalves, their inclusion serving two purposes : firstly,to by-pass unwanted frequencies, thus makingthe circuit characteristics more pronounced ; and,secondly, to adjust the phase, counteracting any lagor lead in other parts of the circuit.

Fig. 3a shows the same circuit but with the inclusionof the detector valve, DET and the addition of twotuned circuits y and z, y being tuned to a frequency2 kcs. lower than the carrier wave (x), whilst z istuned to a frequency 2 kcs. higher than x. Theresponse -frequency graph for this circuit is given inFig. 3b, whence it will be seen that, whilst the carrierfrequency is neutralised, sidebands having a separationof a few cycles from this frequency will be received atgood volume.

When the receiver was tested on the local broad-cast it was found that the signals were impossible

MI,EVISION for May, 193o

to cut out completely, as presumably the modulatorvalve at the transmitter varied the carrier frequency.A modulated carrier frequency from a crystal -controlled oscillator was next tried, but even thisproduced the same trouble. Finally, a special crystal -controlled oscillator was designed in which themodulator did not upset the carrier frequency. Partof the circuit of this oscillator is shown in Fig. 4, avery brief description of which will be given.

Special Modulator.The circuit was designed so that as far as possible

no variations of circuit constants resulted frommodulation. The two tuned circuits, p and q, aretuned to the exact carrier frequency, but whereasthe current in q is in phase with the applied voltage,the current in p lags approximately 90° behind theapplied voltage, this lag being a characteristic ofsuch parallel tuned circuits. Thus there is a phasedifference of approximately 90° between the currentsflowing in r and s, these currents being fed to themodulator M. This modulator may be described asa capacity microphone where the diaphragms-ofwhich there are two-are vibrated mechanically.There are altogether five plates, three stationary,between which are the two vibrating plates ordiaphragms. The scope of this article does not permitof a detailed explanation of this modulator, and itsuffices to say that the amplitudes of the oscillationsin the two respective phases are not appreciablyaffected, but that the phase relation varies in responseto the vibration of the diaphragms. For instance,with a modulation per cent. the phasedifference of the two currents would alternate between45° and 135°, in step with the diaphragm vibrations.The output circuit combines these phases, producingan extremely constant frequency of varying amplitude.

On tuning -in the receiver described beforehandto the frequency from this oscillator, difficulty wasfound in cutting out the signals, but when the exactvalues were found no signals could be heard, provingthat no sidebands existed in the transmission.

It is thought that the foregoing proves the non-existence of sidebands, but still inherent defects ofpresent-day receivers remain to be eliminated.Possible lines of research may form the basis of asubsequent article.

133

Lt. Col. CH ETWODE(Chief Inspector of Wireless Telegraphy, G.P .0 .)

PART XVI.

WIRELESS TELEPHONY (2)

THE last article outlined the development ofwireless telephony from its birth to its presentproud position in the commercial field of long-

range communications, but the outline was far fromcomplete, as must have been obvious to all who areinterested in broadcast programmes ; and are there anywho are not ? There may be, but none of them atany rate can be a reader of TELEVISION. He wouldhave to read something else, and indeed avoid readingmost things published within the last seven years.

The Birth of Broadcasting.But even seven years is not nearly far enough back

to search for the birth of broadcasting. We mustmore than treble the seven, and get back as far as1907. In that year tests of broadcasting by wirelesstelephony were carried out in our Navy, and thefirst song then broadcast, possibly the first song everbroadcast, was " God Save the King." But we can-not by any means take all the credit for the birth, asour friends across the Atlantic were broadcastingsongs and music in the United States Fleet when theymade their world tour in 1907-8.

In those early days, arc transmission was theonly suitable arrangement, or it would be more-..,aesvrate to say, the least unsuitable ; and in America,de Forest, as usual, was well to the fore. In 1909 heinstalled a microphone in the Metropolitan OperaHouse, and broadcast the finest voice that has everbeen broadcast, the voice of Caruso.

With such a start as that, is there any wonder,one may ask, that broadcasting took the world bystorm ? But there was no use trying to storm froman arc, and nothing was heard of broadcasting untilthe possibilities arising from de Forest's addition ofa third electrode to 'Fleming's valve were more fullyunderstood than they were in 1909. It was, in fact,

134

another ten years before sufficient data had beencollected for broadcasting to have any chance ofbeing reckoned as a possible competitor with otherforms of entertainment.

Many of the readers of this journal are impatientwith the growth of television, and it might be wellfor them to reflect a little on broadcasting, whichmost people think grew up in a night. Successfulexperimental broadcasting took place in 1907, butit was not until 1920 that a start was made withbroadcasting as an entertainment for the public. Itlooks as if the growth of television may not be soslow after all when compared with its elder brotherwho is always held up as a perfect marvel of rapiddevelopment.

The Commencement of Programmes.So many individuals of so many countries claim to

have been the first to introduce broadcasting pro -

kw. wireless telephone set installed at Humber coast stationfor communication with fishing craft.


grammes that it is impossible to give a generallyaccepted name, but one which is accepted by some,though unknown to most, is Steringa Idzerda, of TheHague. Idzerda gave a public demonstration in 1919at the Third Dutch Trade Fair in Utrecht, certainlyone of the first successful public demonstrations ofbroadcasting as we know it to -day.

In November, 1920, the Westinghouse Electric andManufacturing Company at Pittsburgh obtained aGovernment licence to broadcast information andmusic. This is generally taken as the beginning ofbroadcasting, though as a matter of fact the Dutchconcerts had become a weekly feature earlier in thesame year, and a time -table of them appeared in aBritish journal in June. There is little doubt butthat the Dutch have a fair claim to the kick off,though the American forwards at once dominatedthe game. About the same time there were our ownfamous broadcasts from the Marconi Company'sstation at Writtle, inseparable from the name ofCaptain P. P. Eckersley, and in the spring of 1922the company were giving regular broadcasting pro-grammes from Marconi House in the Strand.

In the United States broadcasting was let looseall over the country, and the more cautious attitudeof the Post Office here came in for a lot of adversecriticism, not unprecedented, from those who were notfully informed of the circumstances. But the con-ditions in the United States were totally different fromthose in this small thickly -populated country, and itwas not really sensible to consider that the best linesof development there would be necessarily the besthere. Development was far more restricted herethan in America, but the net result was that bothcountries soon obtained what best met their needs,while retaining enough elasticity to allow for change,not only in needs but in technical development.

The B.B.Cs.In the summer of 1922 some of the leading British

manufacturers of wireless apparatus approached thePost Office for permission to commence a service inthis country, and the result was the formation of theBritish Broadcasting Company. The agreement wasfinally executed on January 18th, 1923, but broad-casting services had actually commenced on provi-sional permission from the Postmaster -General inNovember, 1922. At first there were two forms ofreceiving licence, the broadcast and the con-structor's, but on January 1st, 1925, the uniformlos. licence was introduced for the listener, a wordfirst suggested by Sir Henry Norman as a com-promise between what some called a listener -in, andothers a listener -out. The company's licence expiredat the end of 1926, and the British BroadcastingCorporation, incorporated by Royal Charter andoperating under licence from the Postmaster -General,took over the business on January 1st, 1927.

When the company started broadcasting inNovember, 1922, there were about 20,000 licences,and now there are about 3,000,000. During the lastfour years there have been about 3,50o prosecutionsagainst persons receiving without a licence, so that


we are not yet in the happy position of some othercountries where there are no " pirates "-and nofees. But, after all, we are spared advertising bybroadcasting, and that is well worth " pirates " andfees. (Is it ?-ED.)

In considering the phenomenal growth of broad-casting during the last seven years it is interesting tonote that there are already about 20,000,000 sets inuse, of which nearly one-half are in the United States.The number of broadcast receiving sets has thusreached in seven years a total of nearly half thatattained by the ordinary telephone which startedon its career over fifty years ago.

Marconi wireless telephone transmitter type XMB1 installedon the new Dover lifeboat of the Royal National LifeboatInstitution. This lifeboat (which is the fastest in the world)has been specially designed for the rescue of aeroplanes which

have fallen into the sea.

It would be superfluous to say anything here ofthe technical development of broadcasting in theselast seven years, as the details are well known toreaders of this journal, so we shall pass on now toanother important development of wireless telephony.

Ships' Telephony.This is a development which bids fair to loom large

in the immediate future. Here, as in the wirelesstelegraphic communications of ships, there is a freefield for development, as there is no other methodby which conversations can be held between ships,or between ships and the shore. Indeed, the need


135

THE Proceedings OF

The Television SocietyApril 8th Meeting, held at University College,

Gower Street, London

Photo -electric Cells and their Applications

By T. H. Harrison, Ph.D., B.Sc., A.Inst.P.

Introduction.

TIGHT manifests itself through the agency ofmatter in many different ways. Perhaps themost important property of matter with respect

to its behaviour when light impinges on it is itspower of reflecting the light. Without such a property,matter would be invisible, and a state of affairs wouldexist which would be very difficult to imagine. Butonly a part of the light impinging on matter isreflected. The remainder is absorbed, and it hasbeen known for over two thousand years that lightabsorbed in this way is largely converted into heatand raises the temperature of the absorbing substances.In fact, nearly all the light energy which is absorbedis converted into heat. But some substances reactin a special manner with respect to light, and exhibitother phenomena than that of a rise in temperature.Phosphorescence and fluorescence are both propertiesof certain substances which are activated by lightand which have been known for centuries, althoughnothing was known of the mechanism of the process.A further important action of light on matter wasdiscovered by Willoughby Smith in 1873, when heaccidently found that whilst selenium was under theinfluence of light its electrical resistance underwentconsiderable variations, the higher the illuminationthe less being the resistance. Then, again, theexistence of photochemical actions has been knownfor centuries ; chemical actions are, in some cases,considerably accelerated by the action of light ;

certain mixtures of substances which do not reactwith each other whilst in darkness will explode with

136

great violence when exposed to light. Besides thiscatalytic, trigger -like photochemical action of light,there are slower photochemical actions in which theprogress of the change depends largely upon the rateat which light energy is being received by the sub-stance-i.e., upon the flux of light impinging on thesubstance-and in which the total change gives somemeasure of the total light energy that has beenacting, such cases being exemplified by the processesin ordinary photography, and particularly in photo-graphic photometry so largely used in astronomicalresearch. Another property of light with respect tomatter which was theoretically predicted during thelast century, and which was experimentally verifiedin 1900 by Lebedew and independently by Nicholsand Hull, is that it exerts a pressure. It is true thatthis pressure is much too small to be of practicalutility, but the experimental proof of its existencewas of considerable theoretical interest, since itconfirmed the electro-magnetic theory of light.

It was in experiments in which " wireless " electro-magnetic waves radiating through space were firstrealised and measured, and in which the identityin the nature of such waves and of visible light wasproved, that Hertz 1 in 1887 came across an unexpectedand undesired effect which caused him to digress fromthe normal course of his work. He was investigatingthe effects of spark discharge electric circuits uponeach other, and found that when the electrodes ofone .gap were illuminated from the spark of anothergap, the sparking potential of the first was reduced.Not being able to explain the effect in terms of theordinary electrical reactions of the circuits, he sought

TELEVISION for May, 193o

an explanation elsewhere and finally traced the effectas being due to ultra -violet radiation. Havingsatisfied himself that this bore no direct relation tohis main investigation, he merely recorded his obser-vations and returned to his wave experiments, leavinghis newly -discovered effect to be further explained byother people. These explanations were soon forth-coming. Hallwachs in the following year publisheda detailed account of the phenomenon, and concludedthat when a negatively electrified metal plate isilluminated, negatively electrified particles travelaway from it and follow the lines of the electricalfield. In view of the newly -discovered fact of the

HO COP -

electhat

Aeithphobeeor

DOW

NODE.

SENSITIVE SURFACE -

HO. CUP.

rical nature of light, it was not considered strangeit should effect the electric nature of matter.

these properties of light are being utilisedr directly or indirectly, and in particular theo -conductive and photo -electric properties havethe subject of much work during the last twenty

hirty years. There are also other effects, suchas the changes in ;efractive index or in conductivityof certain liquids when they are illuminated, whichare capable of practical application. The photo-electric cell is, however, the subject of this lecture,and I will turn now to a record of its development,only delaying in order to give in a few words a defini-tion of what is generally meant by the term " photo-electric " effect, in order that there shall be no con-fusion in the use of. terms. This is rendered speciallydesirable since, in spite of the fact that photo -electriccells have become so much more in evidence duringthe last few years, there are still many people whoare by no means clear as to what a photo -electriccell is, and as to its manner of functioning. Someof this confusion is due to the existence of its old butrather inconstant friend, the selenium cell. Theselenium cell is really a sort of resistance box orrheostat whose electrical resistance varies accordingto the degree of the illumination falling on it, and themethods of measurement of light with the seleniumcell are identical with those used for measuringmoderately high electrical resistances. The photo-electric cell, however, operates in an entirely differentmanner. If the analogue to the selenium cell is theresistance box, then that to the photo -electric cellis the two electrode thermionic valve. In fact thephoto -electric cell is a valve, and the term photo -ionic valve would be far more appropriate to it thanits present name. The thermionic valve and thephoto -electric cell are almost identical in their action,construction and appearance, and the only funda-mental difference is that whilst in the former theelectrons are ejected from the hot filament by theaction of heat, in the latter the electrons are ejectedfrom the photo -sensitive surface by the action oflight. There is also unfortunately a further differencein that the photo -electric current is only about


1/1,000 of the thermionic current given in a valve ofabout the same size. This, however, is only to beexpected, since the rate at which energy is suppliedto the photo -sensitive surface by the light is verymuch smaller than the power used to heat the filamentof a valve. The main point to notice, however, isthat the methods of dealing with photo -electric cellsare identical with those with thermionic valves.

Development of the Photo -electric Cell.

The discovery of Hertz was taken up with greatinterest by several workers, and in the following year(1888) there are papers describing the effect byArrhenius,2 Hallwachs,3 Hoor,4 Righi,5 Wiedmannand Ebert.6 The papers by Hallwachs were themost complete, with the result that the photo -electriceffect has often been termed the Hallwachs effect.Until about 1900, or even later, the real nature of thephoto -electric effect does not appear to have beengrasped, the general view being that the action wasanalogous to that in an electrolytic cell with the airin between the electrodes acting as an electrolyte.The misleading and rather unfortunate name " photo-electric cell " is an inheritance from these early falseideas.

The earliest photo -electric cells usually consistedof a metal plate which acted as one electrode, andwhich was exposed to ultra -violet radiation surroundedby a metal case which was the second electrode. Theintervening space was, of course, filled with air atatmospheric pressure, there being no glass or quartzbulb container. The real nature of the photo -electriceffect seems to have been grasped to some extent bysome workers. The statement by Hallwachs, forinstance, already referred to was quite correct, andHoor in 1888 used the type of cell just described,together with an energising battery and galvano-

Fig. 2.

meter in exactly the same way as the photo -electriccell is used to -day. Again, Righi in 1888 experimentedwith a primitive photo -electric cell at low pressuresof. air, but he used no energising battery so that hisresults are complicated on account of the contactpotential effect, the real nature of which was notproperly understood until 1912, when K. T. Comptonand 0. W. Richardson for the first time correctlyinterpreted its action, and when 0. W. Richardsongave a correct theoretical interpretation of itsmechanism on the basis of the electron theory ofmatter. J. Elster and H. Geitel, who are almostsolely responsible for the development of the photo-electric cell, commenced their extensive researchesin this direction, which continued for more thanthirty years-a wonderful record-in 1889.2 In theirfirst research they found that freshly polished zincand aluminium were effected by ordinary visible

137

radiation, whilst rubidium was sensitive to the lightfrom a glass rod just heated to redness. Stoletow 9in 1889 gave for the first time curves showing photo-electric current as a function of applied potential ona photo -electric cell at pressures of air ranging between2.5 and 96.5 mm. of mercury, and Hallwachs in thesame year published an account showing that severalorganic dyes are photo -electric. Much work has beendone on the photo -electric effect of dyes, metalliccompounds, and many other non-metallic substances,but since this has not much bearing upon the photo-electric cell as developed for purposes of utility onaccount of the fact that they are only affected veryslightly, and then only by ultra -violet radiation, it

Fig. 3.

P. E. CELL.

will not be described in this paper. Elster and Geitel '°in 1890 found that the application of a transversemagnetic field to a photo -electric cell operating atlow gas pressures diminished the current, thus pavingthe way for the establishment of the identity of photo-electrons and cathode rays in 1899 by J. J. Thomson,uand a little later by Lenard.12 The order of sensi-tivity of the more sensitive metals to sunlight wasgiven by Elster and Geitel in 189113 as follows :

rubidium (the most sensitive), potassium, sodium,lithium, magnesium, thallium and tin (the leastsensitive). Elster and Geitel'made a potassium photo-electric cell filled with hydrogen at a pressure of 0.3mm. of mercury in 1893,14 and made the very importantdiscovery that the current was proportional to theamount of visible illumination falling on the sensitivesurface. In no type of light-sensitive instrumentother than the photo -electric cell is the responselinearly proportional to the illumination. In thefollowing year they 15 found that the following metals(given in order of decreasing sensitivity) were affectedby sunlight-rubidium, potassium, sodium -potassiumalloy, lithium, magnesium, thallium, zinc-whilstother metals such as copper, platinum, lead, iron,cadmium, carbon and mercury require ultra -violetradiation. They also found that with the alloy ofsodium and potassium, which is liquid at atmospherictemperatures and with oblique incidence of light,there was a difference between the photo -electricbehaviour when the light was polarised with theelectric vector parallel to the plane of incidence, andthat when the electric vector was perpendicular tothe plane of incidence. The former was called theselective effect, and the latter the normal effect.These phenomena are very interesting, and have beenthe subject of much research, but in the utility photo-electric cell they are not of practical significance,since the surfaces are in general too rough whenconsidered in relation to the wave -length of light to

138

show any differences due to light polarised in differentdirections, and both effects are superimposed uponeach other. In 1898 E. von Schweidler,1° using apotassium photo -electric cell made by the Elster andGeitel method, investigated the voltage sensitivitycurve and found that from o to 2 volts the current wasproportional to the voltage ; from 2 to 70 volts, thecurrent increased more slowly, but could not be saidto approach saturation, and that above 70 volts theincrease in current was much more rapid, until finallya glow discharge was obtained. He continued hisexperiments later, and made an extensive investigationof the effects of ionization by collision with the con-sequent magnification of the primary photo -electriccurrent which are made use of nowadays in nearlyevery cell. In 1899, J. J. Thomson 17 and Lenard,"working independently with transverse magneticfields acting on specially designed photo -electric cells,definitely proved that the photo -electric effect wasdue to the emission of negatively changed particles

Fig. 1.

NEhich have a mass equal to 1/1,800 of that of thehydrogen atom and a charge equal to that of thesimple ion in electrolysis. The particles were foundto be identical with those occurring in the cathoderay discharge, but on account of the lower potentialapplied across the photo -electric tube they possessedvelocities of about ro7 cm. per second, which aremuch smaller than those for cathode ray or (3 particles.The particles of negative electricity, whose mass isentirely due to their electric charge, have come tobe known as electrons. These experiments havebeen subsequently repeated with various modifica-tions by, several investigators. A systematic andcomprehensive investigation on the effect of gaspressure in photo -electric cells, some containingplatinum cathodes with air and others having zinccathodes with either hydrogen or carbon -dioxide, wasmade by Varley in 19o4." Such cells, of course,require to be illuminated with ultra -violet radiation.In this case an arc discharge between iron terminalsin an atmosphere of hydrogen to prevent burning awayof the electrodes was used. A convenient and fairlysteady source of ultra -violet radiation is the quartzmercury vapour lamp, but this, though much moresteady than metallic arc discharges, is not nearly sorich in the shorter wave -lengths. Einstein 20 in 1905propounded his quantum law for the photo -electriceffect, that the energy of a photo -electron which canbe represented either by the product of its electricalcharge and the potential required to reduce its velocity


to zero (eV), or by the product of half its mass andthe square of its velocity (i mv2), is equal to thefrequency of the exciting radiation times a constant(v x h), less the energy required for the electron toescape from its position inside the surface of the sub-stance to just outside this surface (p.). Expressed inmathematical symbols, this loss is given by the equationeV =by-150. The quantity " h " is a universal andvery fundamental constant which occurs in Planck'sradiation law (propounded in 1901), and is, therefore,known as Planck's constant. The Einstein lawwas not definitely experimentally verified for someyears, and there was another one, known as Laden -burg's law, that the photo -electric energy varied asthe square of the frequency of the light which seemedequally well to fit the observed facts to the degree ofexperimental accuracy that was at that time obtain-able. Both of these laws make the tacit assumptionthat the energy of the photo -electrons is independent

of the intensityof illumination ;an assumptionwhich is quitecontrary to theideas involved inclassical mechan-ics which wouldmake one expectthe energy of thephoto - electronsto be propor-tional to theintensity of illu-

PIN5 FOR iNsoznori urination.The above -

Fig. 5. made assump-tion, however,

was the outcome of Planck's ideas upon the m.. -charismof light, and had some justification in the cumulativeresults on photo -electricity that had been obtainedat that time. Special tests upon this question weremade in 1907 by R. Ladenburg,2' by R. A. Millikanand G. Winchester,22 and by Mohlin,23 whose experi-mental results proved conclusively that the energyof a photo -electron was independent of the intensityof the light concerned in causing its emission. Thefirst experimental work definitely establishing theEinstein law and disproving that of Ladenburg wasmade by A. Li. Hughes" and by K. T. Compton and0. W. Richardson 25 in 1912, and since then the Einsteinenergy equation has been generally accepted. Toreturn from this digression to the chronological orderof events in the development of the photo -electriccell and the discovery of its properties, we find thatthe well-known fact of the independence of the photo-electric effect of temperature was first suggested inexperiments by Lienhop 28 in 1906, where it wasobserved that the velocity of photo -electrons wasindependent of temperature within the region between20° and 180° C. (temperature of liquid air). Anotheruseful result was obtained in 1907 22 by Bergwitz,who, despite the existence of the much -talked ofphoto -electric fatigue due to almost infinitesimalchemical changes at the surface of the sensitive

STRAIGHT WIREANODE,

'EBONITE BASE.

SEMI CYLINDRICALCATHODE.

INTO VALVE HOLDER


material, found that for sodium potassium andrubidium in hydrogen at a pressure of 0.3 mm. ofmercury, the rate of fatigue was inappreciable-aresult which paved the way towards the belief thatphoto -electric cells could be constructed to givereliable results in the measurement of illumination.In the same year H. Dember 28found that for potassium, sodiumand potassium sodium alloy invacuum, the photo -electric currentwas independent of temperaturefrom 15° to II0° C., notwithstand-ing the fact that the change fromthe solid to the liquid stateoccurs within this range, an&furthermore that the sensitivityof a sodium potassium vacuumphoto -electric cell was constantduring a period of twelve months.It was at about this time thatthe controversy commenced as tothe accuracy of the linear relationbetween the number of photo-electrons emitted per unit timeand the intensity of illumination.F. K. Richtmyer,28 with a sodiumcell, verified this linear relationship over a tremendous range of illuminations, and suggested several photometric applications.Nowadays it is generally accepted that the photo-electric emission i is proportial to the illumination I,except wheh disturbing influences which unfortunatelyoccur only too frequently render this proportionalityapproximate rather than exact. For good specimensof well -made photo -electric cells, this proportionalityis accurate enough for all purposes providing the cellsare used under suitable working conditions. Theeffect of producing a glow discharge in a photo -electriccell was studied in 1908 by Chrisler,3° who foundthat this produced pronounced permanent changesin the sensitivity, a result which led the way to thesensitising process introduced by Elster and Geitel31a year later. The theory held by some physicistsof the photo -electric effect being due to chemicalaction produced by light rather than to direct actionof the light itself, as also that of the photo -electriccell operating in a sort of electrolytic manner, received

a severe blow from the dis-covery by Dember 32 in 1909that photo - electric currentswere produced under the bestvacuum conditions. The Elsterand Geitel sensitisation processfor alkali metal cells was de-scribed in 1909 83 and 1910.84The cells were filled with hy-drogen at a pressure of about

t k mm. of mercury, heated to350° C, and then a glow dischargepassed through them. Thehydrogen was left inside thecell to provide amplificationby ionisation. Unfortunately,in such cells the hydrogen wasFig. 7.

Fig. 6.

139

gradually absorbed by the metal surfaces. In 1911,however, Elster and Geite135 described a means ofovercoming this effect by pumping out the hydrogenand filling with either argon or helium, which are notcleaned up in the same manner. This completed thedevelopment of the alkali metal sensitised gas -filledphoto -electric cell, and no further marked improve-ment in design took place until three or four years

ago, when attention became directedupon the high sensitivity of thin invisiblefilms of metal only a few molecules thick.Work on thin films of metal commencedin 1910 when Kleeman 36 experimentedwith thin films of platinum.

Hughes 37 in. 1913 described a specialdesign of cell in which he found errorsin proportionality between photo -electriccurrent and illumination were reducedto a minimum, and in the same yearJ. G. Kemp," who was using an Elsterand Geitel cell for the purposes of stellarphotometry, calculated that the cell hewas using would give a detectable current

zige;)

Fig. 8.Visitron 53(Actual size)

of io-" amperes when illuminated by acandle over two and a half miles away.This statement has led many people tothe impression that the photo -electric cellis more sensitive than it really is. Suchcalculations are very often misleading,since they assume conditions of maximumsensitivity, which in practice are oftenunrealisable on account of instability and

unreliability. In addition, in this case, while io-"amperes can be detected under really goodconditions, it is at the very limit of practicalmeasurements and far from the region where resultsof precision can be obtained. Marx and Lichte-necker 39 found that there was no sign of lagin a photo -electric cell even when exposed to lightfor such a short period as Io-7 seconds. H. E.Ives 4° desctibed methods of making photo -electriccells in 1914, and gave diagrams of some that hemade of special design in order to avoid surfaceleakage of electricity over the glass. He found thateven with the use of long glass tubes and earthedguard rings, ordinary soda -glass allowed the passageof leakage currents. The use of cobalt glass was,however, entirely satisfactory. That common soda -glass is an insufficiently good insulator is also theexperience of the author, who, however, finds thatpyrex and other similar hard glasses are quite satis-factory. J. Kunz and Stebbins 41 in 1916 gave amethod of making photo -electric cells improvingupon the technique of Elster and Geitel, cells of thistype having been used very successfully in manypractical applications even up to the present time,and in 1917 Kunz," who mentioned that photo-electric cells had already been applied to stellarphotometry and to researches on plant physiology,phosphorescence, transmission, absorption, reflectionand radiation of light in various forms, first describedthe thermionic valve method of amplification ofphoto -electric current, and stated that with thismethod cells could with advantage be used withpotentials higher than that required in the ordinary

140

way to produce a glow discharge. Methods of makinguse of this Tact have been developed by N. R.Campbell." In 192o Miss Seiler 44 made a detailedand extended investigation in the colour sensitivityof alkali metal photo -electric cells. The wave -lengthsfor maximum sensitivity were as follows for theunsensitised pure metals, and the sensitisation process

in each casemoved the posi-tion of themaximum to-wards longerwave -lengths.Thus in the

authors' experience a potassium sensitised cell has acolour sensitivity almost identical with that of arubidium unsensitised one. All of these photo -electriccells already discussed are really of the Elster andGeitel type. An entirely new type of cell, sensitiveto visual light, was discovered by Case 45 in . 1921while working with oxide -coated valve filaments.After glowing, these filaments were decidedly photo-electric, and it was found that by using the plate ofthese valves as a photo -electric cathode considerablesensitivity to light was obtained. Apparently calcium,barium or strontium, according to which oxide isused for coating the platinum filament, is undergood vacuum conditions and at certain temperatures-

sputtered on the nickel plate, which plate then becomesphoto -electric. The strontium cell is stated to bequite stable, but the others are not. The coloursensitivities are about the same as that for a potassiumhydride cell, and the sensitivity is stated to be ioamicro -amperes in bright sunlight. Cells of the Casetype do not appear tohave been used verymuch, but they havebeen used by J. E. Ives 46for daylight recording.The author unfortunatelyhas no experience ofthem, and considers it I OuAizo RING.strange that cells of suchhigh sensitivity and easein construction shouldbe rather neglected.I. Langmuir and King -don 47 in 1923 discoveredthat caesium has theremarkable property ofadhering to other metalsin a thin invisible layereven above its melting and boiling point, whichdiscovery, together with that in 1924 by H. E. Ives,"that thin layers of potassium, only a few atoms ormolecules thick, are very phott-electrically sensitive,and particularly so at longer wave -lengths, has ledthe way to the modern highly sensitive thin film alkalimetal cells.

Another method of making photo -electric cellswas discovered in 1925 by R. C. Burt," namely,that in which sodium is passed through thewalls of a hot soda -glass bulb by a process ofelectrolysis. For potassium, a potash glass sodium -free bulb has to be used as described by

li Na K Rb Cs

mil 405 420 441 473 539

Fig. 9.

TELEVISION for, May, 1930

V. Zworykin 5° in 1926. Such cells are very sensitiveand reliable.

In 1927 N. R. Campbell 51 developed four methodsof using gas -filled cells above their arcing potentials,using a thermionic valve in series for the purpose oflimiting the current flowing. Such methods lead toa very high sensitivity, but are more suitable for thedetection of faint illuminations or for operating relaycircuits than for measurements of precision. In1928 N. R. Campbell 52 introduced thin film potassiumcells with a high red -sensitivity, and more recentlythe caesium thin layer cells described by L. R. Koller

have been introduced, both in Americaand in England. In these cells thethin film of alkali metal is formed ona metal plate, such as silver or copperor silver-plated copper. The produc-tion of a suitable surf ace conditionis an intricate matter, since veryslight, almost imperceptible, variationsin the various sensitisation processeslead to very large differences in thefinal total and in the colour sensitivity.V. Zworykin and E. D. Wilson 54 haverecently described a caesium -magnesium photo -electric cell inwhich a layer of caesium is formedon a freshly evaporated layer ofmagnesium on the internal surfaceof a glass bulb. This cell is highlysensitive, more particularly in thegreen and blue region. In additionto the different forms of cells withnature of the photo -sensitive surface

and to the methods of preparation of the same,there are also many different forms with respectto the geometrical design of the electrodes.Differences in geometrical design do not appear toaffect very greatly the ordinary behaviour of photo-electric cells, but certain forms are preferable forspecial purposes-for instance, a double convexcollapsed sphere form as recently described by Kunzand Shelford,55 and which is shown in Fig. r, is statedto be particularly useful in investigations upon theeffect of sun and daylight on plants and animals.

Fig. 10.Grid, Type G.E.

respect to the

Methods of Making Photo -electric Cells.Only those cells will be discussed here which are

reasonably sensitive to visible light. This restrictsone to alkali metal cells, except for the alkaline earthcells made by Case in which these metals appear tohave been given an exceptional " long wave " sensi-tivity in a manner perhaps similar to that obtainedin the potassium and caesium thin film infra -redsensitive cells. With the exception, then, of thesealkaline earth-calcium, barium and strontium cellswhich have already been sufficiently described-thereare three main types of photo -electric cell.

(I) The ordinary alkali metal hydride Elster andGeitel cells as developed by Kunz, Hughes, Richtmyer,H. E. Ives, The Telefunken Co. of Germany, andmany other makers.

(2) The Burt cell.

TELEVISION /or May, 1930

(3) The thin film alkali metal cell as developed byN. R. Campbell and others.

In the first type, and sometimes perhaps for thethird type, the alkali metal is purified and sealed undervacuum conditions in small glass capsules, in thefollowing manner. The alkali metal, which can bepurchased commercially, contained in bottles andimmersed in paraffin, naphtha or some other non-oxygen containing liquid, is taken out, dried withblotting paper, scraped to remove the surface film ofoxide and the mixture of this with the naphtha andcut up into small pellets. These are inserted into atube of pyrex or some other hard heat -resistingglass; A (Fig. 2). It is then gently warmed to removeexcess of naphtha, and until the metal is just molten.The molten metal is then poured into another tube, B,which is then sealed on to C. The combined tube,B C D, is then joined to evacuating apparatus, and themetal is distilled from B to C, after which the junctionbetween B and C is sealed off and B removed. Themetal is thenedistilled into D, and finally into the littlebottles which are suspended from D and which areabout 1 inches long. The little bottles which thencontain the fairly pure silvery metal are finally sealedoff.

The bulb of the photo -electric cell is made with aheat resisting and high insulating glass, accordingto the particular shape required, and the leads to theelectrodes are sealed in to it. Different kinds of glassrequire wire of different metals for the glass to metalseal, e.g., soda -glass which isno longer used owing to itspoor insulation properties andits great liability to crack inthe process of making the cellrequires platinum leads to besealed in to it, since the coefficientof expansion of soda -glass isequal to that of platinum ;while pyrex glass, which is verysuitable for photo -electric cells,requires the sealing in leads tobe of tungsten. It will beassumed that pyrex glass isbeing used. When the bulb ofthe cell with the desired elec-trodes and seals is complete, itmay be desired to silver part ofthe inside surface to form aconducting layer upon whichthe alkali metal is to be de-posited, and in order in somecases to prevent too largean area of insulated glass surface which in thefinished cell may become charged, influencing in anundesired manner the electric field inside the cell.This silvering is, therefore, the next process, and iseffected chemically by the reduction of silver nitratewith rochelle salt. The now complete cell bulb isthen joined to the purifying bulbs r, 2 and 3, shownin Fig. 3, and this set of tubes is joined to evacuatingapparatus by means of a ground -glass joint, thisbeing convenient for joining the hard glass of the cellto the soft soda -glass usually used in the vacuum

Fig. 11. Type S.

141

apparatus. The ground -glass joint also allows theset of bulbs to be rotated about an axis passingthrough the joint and perpendicular to the planeof the paper. One of the little bottles containing thealkali metal is then opened by breaking off the tipand inserted upside down into the wide tube abovethe bulb 1. This tube is then sealed off at the upperend, the whole series of bulbs evacuated and thetubes 2 and 3 and the cell itself are heated to driveoff occluded gases. The tube above i containing thealkali metal is then heated, and the metal runs downinto 1, after which the upper tube is sealed off. Thealkali metal is then distilled from i to 2 and so on,and can either be distilled or poured into the photo-electric cell, the side tube of which must be providedwith a small electric heater in order to preventdeposition of the metal on the insulating glass surfaceswhich would make the cell susceptible to electricalleakage. If the cell were now sealed off, we shouldhave a vacuum unsensitised photo -electric cell whichwould be quite satisfactory in its behaviour, but whosesensitivity would be rather small. In order toincrease the sensitivity, hydrogen is introduced at apressure of about i mm. of Hg. using a palladiumtube attached to the evacuating system for thispurpose. A glow discharge is then passed for severalseconds through the cell with the alkali metal surfaceacting as the cathode, a small induction coil or high -voltage generator being used for this purpose. Thealkali metal becomes coloured during this process,and this coloured surface is about four times assensitive to light as that of the pure metal. Thehydrogen is then pumped out, and an inert gas suchas argon, neon or helium introduced at a pressureof about mm. of mercury. The cell is then sealedoff from the apparatus and is complete.

The Burt Cell.The method of making the Burt cell is illustrated

in Fig. 4. The cell, which is in the form of an electric

Fig. 12.Type T.

lamp made of soda -glass, but with an additionallead sealed into it, is placed in a vessel containingmolten sodium nitrate. A positive electrode isimmersed in the sodium nitrate, and the filament ofthe cell is heated to white heat. The filament emitselectrons which charges the inside surface of the bulbnegatively. The glass of the bulb under the conditionsobtained here does not act as a perfect insulator,but allows the outside surface to become also nega-tively charged. The bulb .therefore acts as thecathode in an electrolytic action in the sodium nitrate,while the above -mentioned positive electrode is theanode. In this action, sodium ions pass to the glassbulb and replace sodium atoms in the glass whichdiffuse inwards, finally reaching the inside of the cellwhich becomes filled with sodium vapour. Thisvapour can be made to condense on any desired partof the cell by cooling this part.

142

The Thin Film Cell.The caesium thin film infra -red sensitive type of

cell, which is also extremely sensitive to visible light,possesses a silver-plated copper plate upon which thesensitive layers are deposited, and an anode whichmay be of any metal which does not react unfavourablywith the caesium or with the gases used in the sensi-tisation processes. The caesium is most easilyintroduced in the form of a chemical compound, andreleased in its metallic state by such reactions as

zCs CI±Ca=Ca Cld-2Csor that occurring when a mixture of caesium dichro-mate and silicon is made red hot in vacuo. In cells

PALLPEITusc

Fig. 13.

made at the B.T.H. lamp works at Rugby, a diagramof one of which is shown in Fig. 5, a mixture ofcaesium dichromate and silicon is introduced intothe small metal capsule at the upper end of the stiffstraight wire which forms the anode. The cell isattached to the vacuum system and evacuated. Thecylindrical plate is then made red hot by means of anelectric induction heater as used in the manufactureof thermionic valves, in order to drive off occludedgases. Oxygen at a pressure of a few mm. is thenintroduced, and an electric discharge from a smallinduction coil passed between the plate and a coilwhich is placed over the bulb, this discharge passingthrough the walls of the bulb and producing a glowdischarge inside it. This process oxidises the silverplating of the cathode plate, a coat of this oxidebeing necessary to secure the adherence of the caesium.When the coat of oxide has been formed the oxygenis pumped out, and the capsule containing the caesiummixture is heated to red heat until a violent actionoccurs, releasing caesium vapour which condenseson the walls of the bulb. The bulb is then heated inan oven for about a minute to a temperature of about300°C. and the caesium is driven from the walls of thebulb on to the cathode. Argon is then introducedat a low pressure and an arc discharge passed fromthe cathode to the straight wire anode. The cell isthen sealed off leaving a suitable pressure of argoninside it and mounted as shown in the figure on avalve base. The temperatures, intensities of thevarious discharges, the pressures of the gases, andthe lengths of time allowed for each process are allrather critical and slight variations lead to enormousdifferences in the behaviour of the finished cell.Considerable experience is therefore necessary inorder to make satisfactory photo -electric cells of thistype.


Types of Photo -electric Cells now encountered.There are several varieties of the older Elster and

Geitel type of cell met with at the present day, andmost of them are very efficient. Three differentdesigns of such cells made by one firm are shown inFigs. 6, 7 and 8. Cells such as that in Fig. 7 can beobtained in sizes up to 12 inches in diameter. Thesensitivity of these cells is about 5 micro -amperes perlumen, which gives for a small cell with a window ofabout if inches diameter 5 x 10-6 amperes for a candleat a distance of i metre. The sensitivity of the12 inch cell should, according to these figures, beabout o5 p. A for a candle at a distance of i metre.Of course if the cell is operated at a potential nearerto that for the glow discharge the sensitivity is con-siderably higher, but in general this is a state to beavoided. Another manufacturer makes cells of thetype shown in Fig. 9. These have a gauze anodewhich allows the field inside the cell to be moreuniform than is the case for the spherical cell, and isfor some purposes to be preferred to the other type.They are made with sodium, potassium or rubidium,and can be obtained either gas -filled or evacuated.

A third manufacturer supplies photo -electric cellsas shown in Figs. 10, II and 12. These cells are ofpotassium, and can be obtained either evacuated orfilled with neon. There is also a choice of threedifferent kinds of glass used for the bulb :

(a) Ordinary glass for work in the visible region.(b) Uviol glass for work in the near ultra -violet.(c) Fused silica for work in the ultra -violet.The Burt cell is procurable and is advertised in

Science.The red and infra -red sensitive cells of various types

are now also obtainable.Red sensitive thin film potassium cells are made at

the G.E.C. research laboratories at Wembley, and adiagram of one of these is shown in Fig. 13. Theyare filled with hydrogen, since neon, helium or argonseem to destroy the red sensitiveness of the surface.Unfortunately hydrogen, as mentioned before, iscleaned up (i.e., absorbed) gradually by the metalsurfaces, and in order to keep the pressure of hydrogenat a convenient value, the cell is provided with apalladium tube which, when heated in a bunsen flame,allows the passage of hydrogen into the cell. Highlyefficient caesium infra -red sensitive cells are also madeby the same manufacturers according to the designshown in Fig. 14. A description of a caesium thinfilm cell as made by the B.T.H. Co. has already beengiven and a diagram of such a cell given in Fig. 5.

Application of Photo -electric Cells.

(1) To Photometry and Stellar Photometry.The measurement of variations in intensity of

monochromatic light of sufficient intensity is a verysimple procedure with the photo -electric cell. Forlight which is not monochromatic, however, it is tobe borne in mind that the colour sensitivity of thephoto -electric cell is generally far different from thatof the eye, and ;that in consequence any results


obtained by the photo -electric method must beviewed in the light of this fact. To obtain results inphoto -electric photometry for illuminations of dif-ferent colours is perfectly simple ; to interpret themcorrectly or to design the apparatus in order to obtaindirectly results which agree with those of vigualphotometry is a matter of considerable difficulty.The measurement of the photo -electric current isquite simple : for higher illuminations (at any ratewith gas -filled cells which in the writer's experiencare practically as reliable as vacuum ones) a sensitivegalvanometer is used, for lower illuminations eitheran electrometer or a valve amplifier must be used.As early as 1906 a photo -electric cell was used forstudying changes of intensity of light during a solareclipse. The methods used in stellar photometry aresimple. The photo -electric cell is placed at the focusof the objective of the telescope and the currentmeasured with an electrometer. In order to avoidcapacity effects in the leads to the electrometer, thelatter is usually of the string type, or else that designedspecially for the purpose by Lindemann, which areboth capable of functioning when attached to themovable telescope. A thermionic valve could alsobe used as an electrometer, and a special valve hasrecently been made for thispurpose by Philips whichhas special quartz insulationand to which they havegiven the name " the electro-meter triode."

The problem of measuringthe candle powers satis-factory of electric lamps runat different colour tempera-tures has now been solvedfairly satisfactorily, theadvent of the red -sensitivecells having helped the pro-cess considerably, since theolder type had insufficientsensitivity in the red toallow the use of a colouredfilter which would reducethe colour sensitivity tothat of the eye withoutcutting out an undue amountof the active light. It isimpossible here to go fur-ther into details, but tworecently described automaticphotometers are of parti-cular interest. Fig. 14.

(2) Automatic. Photometers.

A diagram of a " recording photo -electric colouranalyser," designed by A. C. Hardy,56 is given inFig. 15. This instrument is designed to measure ona graphical record the variation of the reflectingpower for all wave -lengths of light of a sample ofmaterial. The photo -electric cell is alternately exposedto light reflected from a surface of known reflectingpower, such as magnesium carbonate, and that fromthe sample to be tested. The frequency of alternation

143

is about that of low sound waves. In general, thetwo light intensities are not equal, and the photo-electric cell gives an intermittent current effectwhich, when greatly amplified with valves, producesan alternating current sufficiently large to operate asniall electric motor through its field coil. Thismotor controls a shutter in front of the standardsample, and continues to operate until the shutter issufficiently closed (or open) that the light receivedby the cell from the standard reflection material isequal to that from the test sample. When thiscondition is realised, the photo -electric current ceasesto be of an intermittent nature, and the output from theamplifier ceases, with the result that the motor stops.

Exit SlitPhotoelectric. Sample

Cell

Shutter Motor

Arm.o 50".

Fig. 15.

Entranc,t

Disc`

Standard

0

The shutter is connected with a recorder pen, and thedesign is such that the position of the pen to whichit is driven by the motor gives a measure of thereflecting power of the sample of material used.Another motor worked from the same source of alter-nating supply as that used for the armature of thefirst operates a recording drum and the wave -lengthchanging mechanism. In a period of time of aboutone minute a complete chart is produced showing thereflecting power of the sample throughout the visiblespectrum.

Another interesting automatic photometer is onedesigned by M. Horioka 57 for giving a visible recordshowing the candle powers of an electric lamp indifferent directions. Fig. 16 shows the apparatusdiagrammatically. Light from the lamp 1, the dis-tribution of candle power from which in all directionsgiven by the radii of a circle with centre at 1 and ina plane perpendicular to the paper is required, passesto the mirror M, from which it is reflected to thephoto -electric cell d. A screen B prevents lightpassing directly from the lamp to the cell. Themirror M, is connected to a system which also hasanother mirror M3 attached to it. This system iscaused to rotate as suggested by the pulley wheelsand belt shown in the figure. The current from thecell is amplified by the valve amplifier j which operatesthe oscillographic galvanometer, the mirror of whichis shown as M.,. The deflection of the galvanometeris obtained on the frosted glass screen S. The screen Sshowing the galvanometer deflection is observed inthe direction indicated by the eye shown in thediagram through the rotating mirror M3. Thevelocity of rotation of the system is made to be about

144

12 revs. per second in order to avoid fficker effect,and the trace shown in the revolving mirror is apolar curve of the distribution of candle power fromthe lamp 1 in the plane indicated by the diagram.

(3) Control of Printing and Textile Machines by meansof Stencils.

This, together with control of chemical reactions(e.g., titration) of smoke production and colourchanges, also with optical alarm systems, automaticstreet light control, picture gallery blind control,illumination control in buildings and with burglarand fire alarms, is performed by making the currentfrom a photo -electric cell, when the illuminationpasses through a critical value, operate a relaywhereby a large electric current is brought intooperation in order to control any taps, bells or motorsthat may be required to be automatically controlled.If very large illuminations are available and verysensitive cells can be used the cell may be made tooperate a galvanometer relay directly, but generallyspeaking the use of a thermionic valve or a dischargetube relay is required. If a valve is used, it may beused in the ordinary way as an amplifier, or it maybe used as a current limiter with the photo -electriccell operating above its normal glow potential in themanner described by N. R. Campbell." The GeneralElectric Co. manufacture a photo -electric cell relayon this principle and designed specially for the auto-matic control of street lighting.

In the control of machines by means of stencils, abeam of light passes through the stencil on to a photo-electric cell. The stencil moves along as the work isbeing done until of it intercepts the beam oflight, when the photo -electric current ceases, thusoperating a relay which effects the required adjust-ments to the machine. In the control of titration,the beam of light passes through the solution andadjustments are so made that when the solutionsattain the required colour the illumination on thecell reaches the value at which the relay operates.

For detection of smoke or dust in the air a strongbeam is made to pass through the air. If there isdust or smoke present, the path of the beam is visible.A photo -electric cell is placed so that it views part ofthe beam, so that it receives the light scattered fromthe dust particles.

The measurement of colour temperature of electriclamps and the automatic rating of them are reallyidentical. Two photo -electric cells of different coloursensitivity are exposed to the same source of illumina-tion and are connected so that the current from oneis in opposition to that from the other. By suitablyadjusting the apertures of the cells, a balance isobtained for a certain colour. For bluer light thanthis the balance will be upset in one direction, andfor redder light in the other direction. For changesof intensity, without change in colour, the balance is.unaffected, since in this case the changes in currentin one cell are equal to those in the other.

The measurement of absorption of light in lampbulbs can also be measured conveniently by thephoto -electric method. The bulbs to be tested-leftopen-are placed in succession over a small electric


lamp andand the measurements made by any of themethods used in ordinary photo -electric photometry.

Measurements of spectroscopic plates can be con-venientlyi made, using a photo -electric microphoto-meter asklesigned in the first place by P. Koch.58 Apoint source of light is focussed on the plate fromwhich it diverges on to the cell, and in this way thephotographic density of a spot of exceedingly smallarea can be measured.

The methods of using photo -electric cells for thetransmission of pictures for television, for transmis-sion of signals by light, for talking pictures and forgramophone recording all involve the same principles.A flux of light of oscillating intensity affects a photo-electric cell which is capable of responding to epremelyhigh frequencies, and the response is amplified withan ordinary valve amplifier. In some cases wherethe quantity of light available is very small, or wherethe time of illumination is very small indeed, it maybe desirable to use the larger cells (up to i foot indiameter) obtainable nowadays in order to collect asufficient quantity of light, but in most cases the

same quantity of light can with advantage be col-lected by lens or mirror systems and concentrated ona smaller cell. Of course, the larger size cells arecapable of dealing with a much larger flux of light,and will give very large photo -electric currents, butthe electrical capacity of the cathode is rather large,and unless a very large flux of light is to be dealtwith it is better to use lenses or mirrors to collect it.For transmission of pictures and television, lightselected from a small area of the object to be trans-mitted is passed to the cell. The small area is madeto traverse the whole object, and when this is com-plete the object can be said to be recorded in the formof a series of electrical oscillations. These oscilla-tions are amplified and transmitted by telephone orwireless, converted again into light oscillationswith the aid of a discharge tube such as the neonlamp or of the Kerr cell or of some sort of light valve,and the light oscillations are directed on to a plateor screen by means of an apparatus similar to thatused for collecting the light and working synchron-ously with it. No special type of photo -electric cellis required.

In the talking pictures, gramophone recording andtransmission of signals by light, there is a variableillumination falling on the cell, and this produces avariable current which is amplified and passed to aloud speaker. Some sort of microphone is used inthe first place in producing the oscillations in thelight, and of course in the talking pictures these arerecorded at the side of the ordinary film.

TELEVISION /Or May, 1930

In conclusion, it may be remarked that there are,no doubt, many further applications of photo -electriccells which will come to mind as new problems arise.The photo -electric cell, as at present made, is quite arobust little instrument ; if not required to work atthe very maximum of its powers, it is very constant,responds instantaneously to fluctuations of light, hasa response proportional to the quantity of lightaffecting it, and will give good service for manyyears. The fact that its sensitivity is not quite sohigh as some people would wish is no real detriment,since with the aid of a single thermionic valve thiscan easily be amplified several thousand times with-out appreciable loss of accuracy.

References.1. Hertz : A. d. P., xxxi, p. 383, 1887.2. Arrhenius : A. d. P., xxxiii, p. 638, 1888.3. Hallwachs, W. : A. d. P., xxxiii, p. 301, 1888.4. Hoor : Wien Berichte, xcvii p. 719, 1888.5. Righi : S. Accad. dei lincei, March, 1888.6. Wiedmann and Ebert : A. d. P., xxxiii, p. 241, 1888.7. Compton, K. T., and Richardson, 0. W.: P.M., xxiv,

p. 577, 1912.8. Elster, J., and Geitel, H.: A. d. P., pp. 40 and 497, 1889.9. Stpletow : Comptes Rendus, cviii, p. 1241, 1889.

1o. Elster, J., and Geitel, H.: A. d. P., xli, p. 16r, 1890.ii. Thomson, J. J.: Phil. Mag., xlviii, p. 547, 1899.12. Lenard : Wien Berichte, cviii, p. 1649, 1899.13. Elster, J., and Geitel H. : A. d. P., xliii, p. 225, 1891.14. Elster, J., and Geitel, H.: A. d. P., xlviii, p. 625, 1893.15. Elster, J., and Geitel, H. : Nature, I, p. 451, 1894 ; A. d. P.,

p. 433, 1894.16. Schweidler, E. v. : Wien Ber., cvii, p. 881, 1898.17. Thomson, J. J.: Loc. cit.18. Lenard : Loc. cit.19. Varley : Phil. Trans. Roy. Soc., A202, p. 439, 1904.20. Einstein7A. : A. d. P., xvii, p. 132, 1905.21. Ladenburg, R.: Verh. d. Deut. Phys. Gesell., ix, pp. 165

and 504, 1907.22. Millikan, R. A., and Winchester, s.: Phil. Mag., xiv,

p. 188, 1907.23. Mohlin : Akad. Abhandl. Upsala, 1907.24. Hughes, A. LI. : Phil. Trans. Roy. Soc., A212, p. 205, 1912 .25. Compton, K. T., and Richardson, 0. W.: Loc. cit.26. Lienhop : A. d. P., xxi, p. 281, 1906.27. Bergwitz : Physikalische Zeitschrift, viii, p. 373, 1907.28. Dember, H.: A. d. P., xxiii, p. 957, 1907.29. Richtmyer, F. K.: Phil. Mag., xiv, p. 297, 1907.30. Chrisler : Phys. Rev., xxvii, p. 267, 1908.31. Elster, J., and Geitel, H.: Phys. Rev., xxix, pp. 71 and

404, 1909.32. Dember : A. d. P., xxx, p. 152, 1909.33. Elster, J., and Geitel, H.: Loc. cit.34. Elster, J., and Geitel, H. : Physikalische Zeitschrift, xi,

pp. 257 and 1082, 191o.35. Elster, J., and Geitel, H.: Phys. Zeits., xii, p. 609, 1911,36. Kleeman : Proc. Roy. Soc., A84, p. 92, 1910.37. Hughes, A. LI. : Phil. Mag., xxv, p. 679, 1913.38. Kemp, J. G.: Fhys. Rev., i, p. 274, 1913.39. Marx and Lichtenecker : A. d. P., xli, p. 124, 1913.40. Ives, H. E.: Astrophys. Journ., xxxix, p. 428, 1914.41. Kunz, J., and Stebbins, J.: Phys. Rev., vii, p. 62, 1916.42. Kunz, J., Phys. Rev., x, p. 205, 1917.43. Campbell, N. R.: Phil. Mag., iii, p. 2041, 1927.44. Seiler, Miss : Astrophys. Journ., fii, p. 129, 1920.45. Case, T. W.: Trans. Am. Electrochem. Soc., xxxix, p. 423,

1921.

145

46. Ives, J. E.: Trans. Ilium. Eng. Soc., N.Y., xx, p. 493,1925.

47. Langmuir, I., and Kingdon : Phys. Rev., xxi, p. 330,1923.

48. Ives, H. E.: Astrophys. Journ., lx, p. 209, 1924.49. Burt, R. C.: Jaunt. Opt. Soc. America, xi, p. 87, 1925.5o. Zworykin, V.: Phys. Rev., xxvii, p. 813, 1926.51. Campbell, N. R.: Phil. Mag., iii, p. 1041, 1927.52. Campbell, N. R.: Phil. Mag., vi, p. 633, 1928.53. Koller, L. R.: Gen. Elect. Rev., xxxi,,p. 476, 1928.54. Zworykin, V., and Wilson, E. D.: Joum. Opt. Soc. Am.,

xix, p. 81, 1929.55. Kunz, J., and Shelford, V. E.: Rev. Sci. Insts., i, p. ,o5,

193o.56. Hardy, A. C.: Journ. Opt. Soc. Am., xviii, p. 96, 1929.57. Horioka, N.: Researches Electro-Tech. Lab., Tokio,

No. 268, 1929.58. Koch, P.: A. d. P., xxxix, p. 705, 1912.

The Story of Electrical Communications.(Continued from page 135.)

is so obvious, and the field of action so apparentlyfree, that we must first explain why this developmenthas Jagged so far behind that of wireless telegraphy.

The main reason lies in the phenomenal success ofwireless telegraphy for ships' communications. Wehave seen that this was the first application of wire-less telegraphy for commercial purposes, and we haveseen how rapidly it was developed for these purposes,as well as in connection with the safety of life at sea.So rapid and successful were these developmentsthat telegraphy was established in an extraordinarilystrong position before the invention of the thermionicvalve made telephony a practical proposition.

Technically, telegraphy had several importantadvantages. It was in a high state of development,it was cheaper to install, was more economical ofpower, and used a universal code which to a greatextent disposed of the language difficulty inherentin telephony. Many people were obsessed with theseadvantages of telegraphy; and even thought thattelephony would never find a strong commercialfooting for ships' communications. It has not doneso yet, but there is really no doubt now, and therenever should have been any doubt, that the over-whelming advantage of the spoken ward for com-munication must eventually break its way throughall difficulties.

Early Experiments in Ships.Experiments with wireless telephony for ships'

communications commenced immediately after thewar, and in this country the Marconi Company weresoon in the field. In the summer of 1920 they arrangedfor conversations with the shore to be held by pressdelegates in s.s. " Victorian " when proceeding fromEngland to Canada, and conversations were held atdistances as great as i,000 miles. In August, 1923,the company fitted a cross -channel boat, s.s. " Lorina,"belonging to the Southern Railway Company, and, inco-operation with the Post Office, conversations wereheld between passengers on board and telephonesubscribers in England. This was probably the first

146

time that conversations took place between pas-sengers in a ship and telephone subscribers on shore.The system was then improved so that ordinaryduplex telephone working could be maintained, andanother steamer, the " Princess Ena," was fitted.There proved, however, to be little demand fortelephone facilities at that time, and the wholescheme was abandoned.

Short Waves for Ships.Later, the company fitted a number of whalers

and lightships, etc., with telephony, and theseinstallations have proved of great value, but it wasonly within the last year or so, when short waveworking had become better understood, that ship andshore telephony has showed signs of seriously enter-ing the commercial arena.

On December 8th last year the " Leviathan," whenone day out from New York on her way to South-ampton, opened a commercial telephone service onshort waves with the United States, and Sir ThomasLipton in the " Leviathan " was the first to use theservice by 'phoning through to Mr. Rankin in AtlanticCity to express his [and our] hopes of bringing homethe yacht race cup when he visited the States againthis summer Satisfactory working was maintainedup to a range of 2,600 miles.

The Post Office here opened a service with the" Majestic " on February 24th, and has since arrangedthat a service is available to and from any ship onthe North Atlantic route which is fitted with suitableapparatus. The minimum charge is L4 ios. for threeminutes' conversation with L1 los. for each additionalminute or fraction thereof. In place of the normalcharge a report charge of los. is payable when forany reason beyond the control of the Post Office theperson asked for cannot be found.

The Post Office, indeed, has been fully alive to thepossibilities of telephone 'services for a long time, andits station at the Humber has been fitted with wire-less telephony, in addition to telegraphy, for someyears, but very little use has been made of it by theshipping community. Germany and some othercountries have also recently fitted a few shipsand stations ; in fact, it is now at last generallyrecognised that telephony, in spite of its inherentdisadvantages for ship -and -shore work, has madea real start, and before long will settle down onordinary commercial lines.

Long Range Services.Since the last article (which dealt with long range

commercial wireless telephone services) appeared,the Government has announced its policy with regardto the development of these services. As alreadymentioned, the late Government transferred theBeam wireless telegraph services, which work over-seas, to the Imperial and International Communica-tions Company, but left the development of wirelesstelephone services in the hands of the Post Office,and the present Government has now decided thatthese services will be worked from the Post Officetransmitting station at Rugby in conjunction withits receiving station at Baldock.


Letters to the EditorThe Editor does not hold himself responsible for the opinions of his correspondents.Correspondence should be addressed to the Editor, TELEVISION, 26, Charing CrossRoad, W.C.2, and must be accompanied by the writer's name and address.

A CORRECTION.

To the Editor of TELEVISION.

DEAR SIR, -I should like to point out one or twoslight typographical errors in your issue of April,1930. I refer to an article entitled " Reproductionand Amplification in Television Receivers," by Dr.Fritz Schroter ; page 72, second column, line Io from;he bottom :

" intensity for 1=1 " should read " intensity for:=T."

Page 73 equations (1) and (2) should read respec-tively :-

H=Ci .1- td1=-C (T-7)2 (I)2

T

and H=-Ci ftdt + CiTT -L -Ti (7 -2d -r2+277-) . . (2)2

instead of :-

H=Ci tdt=e1c. and H=Ci tdt+etc.

Similarly, on page 74, first column, the equationon line 9 from the top should read :-

CifT

td1=-Ci T2 (I-f)=3H,.T/2

Yours faithfully,C. WILSON,

Technical Department,Baird Television Development Company, Limited.

April 1st, 1930.

HOW IT HAPPENED.


DEAR SIR,-Just happen to be looking around forsome sort of a magazine on television, and justhappen to run across your magazine, TELEVISION ;sure did enjoy it very much.

Although I have just started to experiment ontelevision, I find it more interesting than radio.

I will be looking for your next issue.Yours faithfully,

M. DEPPS.

4149A, Grove Street, St. Louis, i1lo., U.S.A.March 21st, 193o.


CO-OPERATION WANTED.


DEAR SIR,-About five weeks ago I started toconstruct a televisor, which took me about threehours to build, and since then I am -almost' regularlyseeing in to the night transmissions. A Metro- -Vickers fan motor (r/16th H.P.) is used to rotate thedisc, synchronising being maintained by a variableresistance. The disc is made of aluminium, beingdrilled with thirty round holes. An Osram " Osglim "is used as a neon lamp, and I have had the bulbfrosted (host, about 3d.) to obscure the filaments.

Last night (April 4th) the images did not comethrough as clear as on previous occasions, as I hadtrouble in maintaining synchronism, but after" National " had closed at 12.3o p.m., and I hadconnected the loud -speaker to the set, I was surprisedto hear television signals on a wave -length of about40o metres. Naturally I reconnected the televisor,and with the disc revolving at about 600 r.p.m.,succeeded in seeing what appeared to be a ratherbeautiful lady. This picture appeared to be slightlycoloured. The images altered every few minutes,but unfortunately they were not clear enough todistinguish any detail. At 2.45 a.m. pictures werestill coming through. Can you please tell me whichstation was doing this transmission and the correctspeed for disc ?

Up to the present I have been unable to get intouch with any other television enthusiasts in thisdistrict, and as it would be very useful to comparenotes with someone, should very much appreciateany help you could give in this direction.

With the hope of more frequent and earlier nighttransmissions and best wishes for the success of yourmagazine,

Yours faithfully,

A. J. STAINES.

" Aghancon," Kingsfield Avenue, Harrow,Middlesex. April 5th, 1930.

[The station picked up by our correspondent wasprobably Witzleben, Berlin, which operates on418 metres, and broadcasts cinema films regularlyfrom 9 to 9.3o a.m. and I to 1.30 p.m. On Tuesdaysand Thursdays the morning transmission is omitted.

Witzleben uses a 3o -hole disc and scans at therate of I2i pictures per second, as in this country,but employs horizontal scanning and a 3 to 4 pictureratio.-ED.]

147

.

PROGRAMME CRITICISMS.To the Editor of TELEVISION.

DEAR SIR,-I have constructed a televisor mainlyfrom Baird parts and get splendid results using theamplifier described in TELEVISION by W. J. Richardson.

I find that by using two L.S.5A valves in parallel inthe last stage and running the neon and synchronisingcoils in series the synchronism is all that can bedesired, and when once adjusted the image can beheld for the whole of the half-hour transmissionperiods ; in fact, it is rather difficult to gently speedup or slow down the motor with the rheostat whenit is required to get the image properly centred. Theneon glows very brightly with about 350 -volt H.T.

I have a few criticisms to make with regard to thedual wave transmissions. First and foremost, thetransmission periods are far too short. Then thespeech part of the transmission is of very poor qualitycompared with the B.B.C. transmissions from theirstudios, and gives people a very poor opinion of thereceiving apparatus when giving demonstrations.

Yours faithfully,A. A. KEEN.

48, Broad Street, Chesham, Bucks.April 4th, 193o.

TELEVISION MAGAZINE IN AMERICA.To the Editor of TELEVISION.

DEAR SIR,-Television with us in the U.S.A. is" just around the corner." At least so they tell us.At any rate we have several systems and as manytypes of scanning discs. There are some twentyvisual broadcasts on in various parts of the country,but we have not reached the stage where a magazinedevoted to television is evidence of a widespreadfollowing. I am' sure that there are many here, likemyself, that eagerly look forward to the appearanceof TELEVISION on the news-stands.

Yours faithfully,M. E. EISENBVRG.

9333 Main Street, Kansas City, Missouri, U.S.A.March 5th, 1930.

AMATEUR RESULTS.To the Editor of TELEVISION.

DEAR SIR,-We have pleasure in sending you aphoto of our latest televisor in the hope thatyou will see fit to publish same in May issue of TELE-visION. You will doubtless notice the likeness toyour first televisor. All the parts of this apparatushave been made from the old model published inyour first March, 1928, issue.

The motor stand is as original, but the baseboardis cut to half width, as all the back portion was wastedspace due to the taking away of the transmitter,projector lamp, etc., whilst the viewing tunnel is cutto almost half length, as we found that not morethan two people could see the image at the same time.with the tunnel at the original length.

148

Cutting down the transmitting motor stand wefound made quite a good and solid job as a stand forthe viewing tunnel, whilst a reading glass inserted inthe tunnel brings the image up to quite good dimen-sions. At the disc end of the tunnel we inserted apiece of cardboard with a hole to the shape of thepicture, as this cuts out all unwanted illumination,as we found that all stray leaks of light, no matterhow small, tended to make the image less bright.

Our next problem was the neon stand, etc., as wefound that unless this was mounted on a solid basethe received picture suffered owing to vibration set

up on the neon by the disc pulling itself to true whilstrevolving.

A crate formerly used for housing one of the smalltype 20 -volt wet H.T. accumulators was cut down tosize and mounted on end with a baseboard about6 inches by 6 inches screwed to it as a platform forthe neon, mirror, etc. The neon (Commercial Osglim)is then screwed to the platform well to one side (theleft) so that no part of the glass can be seen throughthe holes when the disc is revolving, after which themangin mirror (as specified in the old televisor) ismounted in a picture frame and screwed to the samebase at an angle, so that the projected light from theneon falls on the holes in the disc. After this is com-pleted the whole is boxed in, and a piece of cardboardpinned on the front by drawing pins with a hole cutout slightly larger than the received image, so thatno unwanted illumination can escape to interfere withthe operator's vision.

We found also that tin foil on the back of the neontended to brighten the image to a certain extent,although this not absolutely necessary. We wentto all this trouble with the neon box, as we foundthat the more illumination one can keep out of one'seyes was all to the good of the image brightness.


At present we are using a discarded fan motor,regulated by hand, but are busy on a simple syn-chronising gear, with a standard hole aluminium disc.The disc, as you will see, has been painted black for2 inches round the circumference, which preventslight leaking across the image due to the polish onthe disc.

Our radio receiver is a standard " Music Magnet,"with a further two stages of L.F., one transformerand one R.C., with 35o volts H.T. We are at present'using two L.S.5A's, and find these quite suitable.

Results.April 5th was the first time we had a chance to

try out the new apparatus, and the results wereastonishing, considering that this was the first timewe had tried this new idea. Making slight adjust-ments during the Baird transmission accounted forat least half of the transmission time, but later theantics of the Moustache manipulator made it wellworth the trouble. After the Baird Co. closed downwe succeeded in picking up the transmissions fromBerlin, and were very surprised to find that we couldmake out the images being transmitted, this duringa burst of atmospherics which, however, faded awayand left the image almost as clear as the one we sawat the Baird demonstration last year.

Our results were so good that we have written theGerman station offering to pick out the artistes fromas many portraits as they care to send. A over-heated motor forced us to close down at 3.45 a.m.after holding the film transmission for 3f hours.

Since writing the first part of this letter we havehad a visit from the wireless correspondent of theDaily Dispatch, with which paper is incorporated theSunday Chronicle and Empire News, ManchesterEvening Chronicle, etc., and we enclose report of hisvisit. Although we are situated on what we thinkto be the worst car track in the country, we canduring intervals of the interference bring up theimages to recognisable proportions.

We mention the visit of the above correspondentto prove that others beside ourselves have seen imagesin daylight under worse than average difficulties.May I mention at this point that we are also sur-rounded by hills of the Pennine Range.

Further Results.Saturday, April 12th (12 to 12.30 a.m.). Better

results than before from B.B.C. transmissions, everydetail of both announcer and lady artiste beingvisible. Interference from our own motor cut downto nil with condensers and resistances similar to theones specified in your article on Cutting out Inter-ference. We have not as yet received a reply fromBerlin, but are expecting one daily.

We shall be pleased to report further results asthey come to hand.

Yours faithfully,FRED ANIL> FRANK B. PARRY.

58, Church Street, Littleborough.P.S.-Please understand that car interference is

only in daylight, as they finish at 11.45 p.m.



DEAR SIR,-I hope to interest you and the readersof TELEVISION by giving you the results of my firstexperiments in television which started three weeksago.

My receiving set is of the superhet type withoutreaction, two valves in the last stage, and Ferrantiequipped, fed by accumulators 16o volts or 220 voltsD.C. from the mains, giving the necessary outputpower.

I started with a disc as described by Mr. Knipe,but with holes of i mm. square and a bad electricmotor. The disc is of zinc and as thick as 1/16 inch,weighs 235 grammes, but is easily punched. Nodifficulty was encountered to make the drift with agasoline motor valve.

My neon lamp is a commercial one, similarlyarranged to that of Mr. Neal. When I started threeweeks ago, at my second trial I was able to see blackshadows, but as the picture was so small, the greatdifficulty consisted in holding the picture steady.My only speed and synchronising controls were mytwo finger tips, one for speed and the other one tokeep the image steady.

I made a speed -regulating device of my own.Experimenting succeeded in keeping the picture stillsimply by an occasional adjustment of the regulatingnut. (The speed of the electric driving motor mustof course be regulated by a resistance and made torun a little faster than required, to be able to adjustthe adjustment of the regulating nut.) This deviceacts as a frame and is not subject to variations causedby heat like a resistance ; the motor must be run alittle bit before the " look in " to make resistance andoiling system uniform.

By night I always had a good reception, but in thedaytine the reception suffers from atmospherics, andmostly from interference caused by big industrialmotors in the vicinity as well as tram lines. Duringthe transmission of Friday, March 28th, I saw dis-tinctly two arms and hands on the screen doing whatappeared to me like playing with little cards andletting them fall one after the other.

149

persons moving about in the background. At thebeginning of the transmission of April 1st I saw theprofile of two heads moving and facing each other.Afterwards I think'I saw a group of persons playingmusical instruments. I could never read the letters.

My bad reception is, of course, due to a leaky gridrectification and transformer coupled L.F. amplifica-tion, which gave some distortion. I think a superhetis not the ideal set because of the abnormal atmo-spherics produced when giving the power requiredto light the neon lamp. The small image is also dueto the fact that I am using 1 mm. holes instead of0.75 mm. holes.

I am busy now making a well -designed set withscreened grid, and anode bend rectification and aproper R.C.L.F. amplifier like that described in yourApril number ; I am sure to have fine results with thistransformation. I make also a new disc. I say openlythat it is thanks to the interesting articles of your maga-zine that I was able to realise reception.

I would feel obliged if you give me the address ofa British manufacturer or dealer of neon lamps witha flat plate, because here in this country none areavailable, and let me know the hours of transmission,as I have been disappointed more than once afterhaving waited till midnight, to get only Fultographtransmission or no television at all.

I avail myself of this opportunity to congratulateyou on your very interesting and well conceivedmagazine.

Yours faithfully,GEORGES VERDI'N.

9, rue du Moulin, Anvers, Belgique.April loth, 1930.

[The night transmissions are from midnight to12.30 a.m. (Summer Time) on Tuesdays and Fridays.-ED.]


DEAR SIR,-In the April issue of TELEVISION,which I have just received, I note you publish extractsfrom a report I sent to Messrs. Baird's with referenceto my reception of the London transmissions. Ithought the enclosed photographs might prove ofinterest to you and perhaps to your readers. Fullplate enlargements of these are, incidentally, beingexhibited at the annual exhibition of members' workat University College on April 9th.

The four photographs illustrate the complete tele-viser, radio receiver, etc., and I give below a generalspecification of the instrument.

Televisor.-Disc, 20 inches diameter, 3o aperturesof 033 inches square, ratio approximately 7 by 3.Constructed of thin sheet tin. Motor, G.E.C., serieswound, 23o volt D.C., 1/17 h.p. Series resistance,G.E.C., 500 ohms, fitted with micrometer adjustmentfor fine control. Synchroniser, standard tooth wheeltype, constructed in accordance with the articles pub-lished in TELEVISION. Coils wound to 2,000 ohms

150

Rear view of Mr. TVraight's receiver.

each. Operates very efficiently indeed with 15 m.a.current from separate power valve. Neon, G.E.C.plate type Osglim, chole coupled to output of receiver.

Television Receiver.-Four-valve receiver, compris-ing one screen grid H.F., anode bend detector coupledto three resistance capacity valves. This amplifierbuilt according to details published in March issue ofTELEVISION. Have not got this to function properlyyet owing to grid paralysis effects.

Telephony Receiver.-One screen grid H.F., leakygrid detector, coupled to 2 L.F., transformer coupled,choke capacity output.

Both receivers are capable of working on a rangeof 10-5,000 metres. Until recently the latter receiverhas been used for the reception of the televisionsignals and within reason has given quite good results.

Reception in these latitudes is, of course, largelya combination of hope and despair. Static is veryprevalent and interference from passing ships extremelybad. One has sometimes to wait weeks before afavourable Tuesday or Friday night rolls along. Itis strange to note how the transmissions on the othernights of the week, which you have not much use for,come through so clear and strong. Seriously speak-ing, however, the present two half-hours a week areridiculous for such a subject.

Heads and shoulders appeared frequently on thescreen during the transmissions, as well as several


Showing Mr. Wraight's synchronising gear.

I should much appreciate the help of your contri-butor or your readers on the following.

I have tried all the various combinations of circuitspossible to endeavour to cure the interference frommy televisor motor. I have found unfortunately thatany additions in the way of filter circuits tend tomake matters much worse. The series of remediespublished in TELEVISION a couple of months backhave all been tried, of course, and gave no results.

distance to be notless than: -

3',

I find, however, that I cancompletely cut out the inter-erence if I place the televisorat right angles to the wirelessreceiver. It must also be atthe aerial end of the receiver.In fact its exact position isquite critical. In this positionI can bring in the interferenceby touching the motor casing orshaft. Perhaps these details

TELEVISION far May, 1930

will help towards a solution of the trouble.Any other position will immediately bring in theinterference.

Wishing TELEVISION continued success,

Yours faithfully,W. L. WRAIGHT,

Associate Television Society.c/o The Madeira Electric Lighting Co., Ltd.,

Campo do Almirante Reis, Funchal, Madeira.9th April, 1930.


DEAR SIR,-On March 31st I witnessed, at MajorOates' Works at Hammersmith, the reception oftelevision pictures combined with broadcast speech,and I wish to congratulate the Baird TelevisionDevelopment Company on the excellent results andthe distinct and successful step forward in theirventure.

The whole arrangement and layout of this receivingstation gave one at once the impression that the artof receiving broadcast television pictures and speechcombined was not any longer an amateurish orexperimental attempt, with untidy apparatus anda maze of wiring and all sorts of instruments, but aclean-cut, tidy and well -arranged equipment, which atonce gave one confidence that what we were about tosee and hear was of first-class and high quality.

Right from the tuning signal, throughout theprogramme and until the 3o minutes' transmissionwas over, everything worked splendidly andapparently with ease and simplicity of control.

The announcer came through very clearly and washeard at the same time most distinctly.

His place was taken by Sir Ambrose Fleming, whosefamiliar face was at once recognised, and you couldsee distinctly every movement of his face when helooked down upon his notes and up again, and onewas almost touched to see and hear this great man,who had already given much to the world by hisprevious work, and to hear him propound the causeof television with all sincerity, and which made himour trusty friend right from the inception, whenMr. Baird started out in his early days in his pioneerwork.

Lord Ampthill, who came next, was as distinguishedand dignified as he ever is, and again you couldobserve every detail and movement in his face.

The two lady artistes-Miss Gracie Fields andMiss Annie Croft-were as charming to look at throughthe television lens as they are in reality, and theirgreat vivaciousness in their expressions was quitewonderful. But I also wish to speak, and I do so inthe interests of development, of a few points whichstill require improvement.

151

We could observe a kind of white halo on top of theheads and the appearance of which I could not accountfor.

Then there was similarly strong reflected whitelight on the lower part of the face, particularly ofMiss Field's face, which looked like shaving soaplather on that part of her face. Perhaps there isa particular way of holding your head when beingtelevised to avoid those reflections as mentioned,and that artistes, who are accustomed to appear onpublic stages, usually tilt their heads upwards,I believe, slightly, so that they can be more easilyseen and heard by people ,in the galleries. I amquite certain, however, that these few defects will bedetected and cured before very long.

There, was also a kind of " V " shaped darkishpart in the middle of their foreheads, which seemedto persist in everyone's pictures.

Apart from these, I do not think, in all honesty, onecould criticise any other details.

The television apparatus was a standard BairdTelevision Receiver and the amplifiers employed weresimple and unpretentious. The pictures and thespeech were, I believe, received from one and thesame aerial.

Major Oates has rendered, undoubtedly, signalservice to the cause of television to have given ussuch a pleasant and well -arranged performance of analmost historical event.

After the performance I left immediately forBirmingham, with ardent intentions and inspired

by what I saw, to repeat a similar reception here,112 miles away from the London station.

With the permission of Professor W. Cramp, Iendeavoured, at the Birmingham University, twodays later, to pick up the London television trans-mission and speech, and I am glad to inform you,although I was not so completely successful asMajor Oates, who by now is an " old hand " at it,that I was successful in receiving the pictures andspeech with a standard Baird Television Receiverand a special amplifier which was hurriedly constructedat the university.

Ever since that date we have improved every day,and before long I hope to report to you that we willhave a successful appliance working here, as atMajor Oates' place on that memorable day...

I shall then give you more technical details aboutthe difficulties experienced, and which I am over-coming from day to day with greater success. I haveno hesitation in firmly believing that broadcasttelevision and speech will, before very long, becomea practical success, and with a little more patiencebe a valuable adjunct and an indispensable means ofinterest in the home.

I only wish that those " thirty minutes " can soonbe doubled by the B.B.C.

Yours faithfully,J. B. KRAMER,

M.R.I., M.I.E.E., M.I.MEcrr.E.Witton, Birmingham.

Table of Principal Content

NOTES OF THE MONTH .

TELEVISION AND YOUR WIRELESS RECEIVERBy H. J. Barton Chapple, B.Sc. (Hons.), A.M.I.E.E. 109

AMATEURS' EXHIBITION . IIIASSEMBLING AND WORKING A BAIRD KIT OF COMPONENTS.

By William J. Richardson 115

SIMULTANEOUS SIGHT AND SOUND BROADCASTTELEVISION FOR THE BEGINNERENTHUSIASM IN NEWCASTLE .

HOW TELEVISION IS BEING RECEIVEDFAITHFUL IMAGES . .

WHERE ARE THE SIDEBANDS ? .

THE STORY OF ELECTRICAL COMMUNICATIONS.

THE PROCEEDINGS OF THE TELEVISION SOCIETYLETTERS TO THE EDITOR .

is8By John W. Woodford 120

123

128

By W. F. F. Shearcroft, B.Sc., A.I.C. 13o

By R. S. Spreadbury 132

By Sydney A. Moseley

PAGE

105

By Lt. -Col. Chetwode Crawley, M.I.E.E. 134

136

147


,cori%S1/

15 "EREAt last tne greatest Radio achievement of the era-the Baird Televisor becomes a " home " proposition.Everyone has been eagerly awaiting the adventof this apparatus, at a reasonable price, and itscoming heralds the commencement of the greatestradio boom in history.The wonder of ordinary radio is now amplifiedby the additional wonder of the Baird Televisor.To SEE and HEAR is the expressed desire ofeveryone interested in radio, and only the BairdTelevisor with its actual reproduction of everymovement of living things can solve the problem.No laborious building up of " still " pictures canever be more than experiment of limited interest.The Baird Televisor Home Reception Set alonecan give permanent satisfaction.

Daily broadcasts both from the National andRegional Stations at Brookman's Park have been afeature since March 31st.The Baird Television Company has given greatthought and care in producing a Kit of Parts bearingthe BAIRD brand. This will interest the HomeConstructor and Experimenter, and will open upa new wonder to tax his ingenuity. Ample " Service "is arranged for.Prices for the complete Receiver and Televisor,Televisor only, and Kit of Baird branded partswill be sent on application to :THE BAIRD TELEVISIONDEVELOPMENT COMPANY LTD.133, Long Acre, London, W.C.2

thE birth of a wonderful radio EraTELEVISION for May, 1930 iii

TELEVISIONiaDAY AND%MORROWS1)NrY A NIOSELEY

GiAPpLE

"TELEVISION

TO -DAY & TO -MORROW"

HAVE YOUSEEN IT?

By SYDNEY A. MOSELEY andH. J. BARTON CH APPLE, B.Sc. <Hons.>, A.M.I.E.E.

WITH SPECIAL PREFACE BY

JOHN L. BAIRD

AUTHENTIC !LUCID !

PRICE

7/6 UP.TODATE /4I OSTAGE

SIXPENCEEXTRA

This new and comprehensive work contains thevery latest information on the subject. Profuselyillustrated, it presents all the essential facts in aneminently handy and readable form.

si-i:cuRE YOUR COPY NOWPublished by

SIR ISAAC PITMANSONS, LIMITEDand obtainable from

TELEVISION PRESS LIMITED26, CHARING CROSS ROAD, W.C.2

Printed by HAZELL, WATSON & VINEY, LTD., 52, Long Acre, London, W.C. 2, and published for the Proprietors, TELEVISION PRESS, LTD., 26, Charing CrossRoad, Loudon, W.C.2, by Tide ALDINE PUBLISHING CO., LTD., Crown Court, Chancery Lane, London, W.C. 2. Address for advertisements, "TELEVISIONADVERTISEMENT DEPT., 26, Charing Cross Road, London, W.C.2. Sole Agents for America. THE INTERNATIONAL NEWS COMPANY, LTD., 131, Varick Street, NewYork, U.S.A. Registered for transmission by Canadian Magazine Post. Entered as Second Class Matter, March 15, 1929, at the Post Office at poston, Mass.,

under the Act of March 3, 1879 (Sec. 397, P.L. and R.).

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