4-t

For the .hmrnaI or the Franklia Institute.

_Part'ic~dars ~f the Ntcrn-wheel £'tea~er Ve~wcdor.

Ihdl built by Samuel Sncdcn & Co. Machinery by Ii. Ester g Co., New York. 1)csigucd hy T. F. Rowland, engineer. ()w~lers, Magdalena Steam ~avig:u im~ (2o. Intended service, Magdalem~ River.

I lcl ,T, .--I ,e ,glh (m deck, 155 ft. 1)o. at load line, 150 ft. Breadth of Imam (molded), 24 It. D~'pthof h o h t t o s p a r deck, 5 ft. Frame---molded, 6 ins . - - s ided , 4 i n s . - - a p a r t

fl'om centres, 24 ins . l~ulkhcads, two. l]ottom plank, 2 ft. 5 ins. thick, of yellow pine. Sides, 2 ins. lhiek, do. do. l)ecks, white pine, 2 ins. thick° Promenade deck, do., 1 in. thick, t lurr ieane do., do., 2-in. do. l)raft, forward and aft, loaded, 3 It. 6 ins. Area of immersed section at load d~aft of '/ ft. 5 ihs., 82 .~q. ft.

E.x(:ix~:s.--lnclined direct. Diameter of cylinder, 16 ins. Length of stroke, 6 ft. Maxinmm pressure of steam, 120 Ibm Cut-oil;variable. Maximum revolutions at above pressure, 35.

BofLvm--One-- lmeomotive. Length of boiler, 18 ft. S ins . Bread ' .hdo . ,8 ft. 1 in. l-leight do, exclusive of sleam chimney, 7 tL 6 ins. Number of furnaces, 2. Breadth do. ,3 ft. 6 ins. Length of gratelmrs, 6 ft. N u m b e r e r lubes, 138. Internal diameter of do,, 3 ins. Length of do., 12, fL I teat ing surface, 1500 sq. ft. Diameter of smoke- pilms, 3 ft.

P,~l~m,~:: Wnl,:l,~r,,~.--l)iameter over boards, 16 it. Lenglh of blades, 17 ft. Depth of do., 15 i ,e. / \ umber of do., 15. C. tI. II .

On Ziyllt-house /[llumb~atiom--The L'lectrie Zij]~t.* ]~y ~rof. F~I~A- I~AY, D. C.L., F. R. S.

[1/o5"al Institution of Great l~ritain.]

~he use of light to guide the mariner as he approaches land, or passes through intricate channels, has, with the advance of society and its ever increasing interests, caused such ,% necessity for means more and more perfect, as to tax to the utmost the powers both of the phi- losopher and the practical man, in the development of the principles concerned and their efficient application. Formerly the means were simple enough ; and if ~he light of a lantern or torch was not sufficient to point out a position, a fire had to be made in their place. As the system became developed, it soon appeared that power could be ob- *ainetl, not merely by increasing the light, but by directing the issuing rays ; and this was m many cases a more powerful and useful means than enlarging the combustion ; ]eadlng to the diminution of the volmne of the former with, at the same time, an increase in its intensity. Direc- tion was obtained, either by the use of lenses dependent altogether upon refi'aetion, or of' reflectors dependent upon metallic reflection. [And some ancient specimens of both were shown.] In modern times the principle of total reflection has also been employed, which involves the use of glans, and depends both upon refi'aetion and reflection. In all these appliances much light is lost ; if metal be used for reflection, a certain proportion is absorbed by the face of the metal ; if glass be used for refraction, light is lost at all the surfaces where the ray passes between the air and the glass ; and also in some degree by absorption in

* From the Loud. Ed, and Dub. l~hiI, Mug. April~ 1860.

Ou LigT~t-Twuse Illumination. 45

the body of the glass itself. There is, of course, no power of actually increasing the whole amount of light, by any optical arrangement as- sociated with it.

The light which issues forth into space must have a certain amount of divergence. The divergence in the vertical direction mustbe enough to cover the sea from the horizon, to within a certain moderate distance from the shore, so that all ships within that distance may have a view oi" thclr luminous guide. I f it have less, it may escape observation ~vhcre it ought to be seen ; if it have more, light is thrown away which ought to be directed within the useflfl degree of divergence; or, if the horizontal divergence be considered, it may be necessary so to construct the optical apparatus, that the light within an angle of 60 ° or 45 ° shall be compressed into a beam diverging only 15 °, that it may give in tile distunce o. bright flush having a cert'~in duration in- ~tcad of a continuous l igh t ,~or into one diverging only 5 ° or 6 °, which, though of f~r shorter duration, has greatly increased intensity and penetrating power in hazy weather. The amount of divergence de- 1)ends in a large degree upon tile bulk of the source of light,.and can- not be made less than a certain amount, with a flame of a given size. i f tile ilame of an Argand lamp, -~ of an inch wide and 1} inch high~ bc placed in the focus of an ordinary Trinity House parabolic reflector, it will supply a beam Mving about 15 ° divergence; if we wish to in- crease the efl'cct of brightness, we cannot properly do it by enlarging the lamp flame; for though lamps are made for the dioptrie arrange- ment of Fresnel, which have as many as four wicks, flames 8½ inches wide, and burn like intense furnaces, yet if one be put into the lamp place of the reflector referred to, its effect would chiefly be to give beam of wider divergence ; and if to correct this, the reflector were made with a greater focal distanc% then it must be altogether of a much larger size. The same general result occurs "~,ith the dioptric appara- tus ; and here, where the four-wicked lamps are used, they are placed ~t times nearly 40 inches distant from the lens, occasioning the neces- sity of a very large, though very fine, glass apparatus.

()u the other hand, if the light could be compressed, the necessity for such ]urge apparatus would cease, and it might be reduced f~om the size of a room to the size of a hat; and here it is that we seek in the electric spark, and such like concentrated sources of light, for aid in illumination. I t is very true, that by adding lamp to lamp, each with its reflector, upon one face or direction, power can be gained ; and in some of the revolving lights, ten lamps and reflectors unite to give the required flash. :But then not more than three of these faces can be placed in the whole circle; and if a fixed light be required in all directions round the light-house, nothing better has been yet established than the four-wicked Fresnel lamp in the centre of its dioptric and catadioptrie apparatus. :Now the electric light can be raised up easily to an equality with the oil lamp, and if then substituted for the latter, will give all the effect of the latter; or by expenditure of money it can be raised to a five or tenfold power, or more, and will then give five or tenfold effect. This cau be don% not merely without increase of the volume

46 3feel~anics, Physics, and ¢]~emistry. of the light, lint whilst the light shall have a volume scarcely the 2000th part of that of the oil flame, t:[ence the extraordinary assistance we may e×peet to obtain by diminishing tile size, and perfecting the optical part of the apparatus.

Many compressed intense lights have been submitted to the Trinity IIouse ; and that corporation has shown its great desire to advance all su_ch objects and hnprovo the lighting of the coast, by spending, upml various occasions, much money and much time for this end. It is manifest that the use of a light-house must be never failing, its service ever sure ; and that the latter cannot be interfered with by the intro- duction of any phm, or proposition, or apparatus, which has not beent developed to the fullest possible extent, as to the amount of light pro- duced,~the expense of such a ]ight,--the wear and tear of the appa- ratus employed,--the steadiness of the light for 16 hours,~its liability to extinetion,--the amount of necessary night eare,~the number of attendants,--thc nature of probable aeeidents,--its fitness for seclude4 places, and other contingent circumstances, which can as well be ascer- tained out of a light-house as in it. The electric spark which has bee~* placed in the South :Foreland, High :Light, t)y Prof. ttolmes, to do duty for the six winter months, had to go through all this preparatory edueatiort before it could be allowed this practical trial. It is not oh- rained from t¥ictional electricity, or from voltaic electricity, but fron-t magnetic action. The first spark (and even magnetic electricity as a, whole) was obtained twenty-eight years ago. (Faraday, Philosophical Transactions, 1832, p. 32.) I f an iron core be surrounded by xvir% and then moved in the right direction near the poles of a magnet, au current of electricity passes, or tends to pass, through it. Many power- ful magnets are therefore arranged on a wheel, that they may be ,'tssoeiated very near to another wheel, on which are fixed many he- lices with their cores like that described. Again, a third wheel con- sists of magnets arranged like the first ; next to this is another wheeI of the helices, and next to this again a fifth wheel carrying magnets. All the magnet-wheels are fixed to one axle, and all the helix wheels are held immovable in their place. The wires of the helices are con- joined and connected with a commutator, which, as the magnet-wheels are moved round, gathers the w~rious electric currents produced h~ the helices, and sends them up through two insulated wires in one com- men stream of electricity into the light-house lantern. So it will be seen that nothing more is required to produce the electricity than to revolve the magnet-wheels. There are two magneto-electric machines at the South Foreland, each being put in motion by a two horse power steam engine; and, excepting wear and tear, the whole consumptio~t of material to produce the light is the coke and water required to raise steam for the engines and carbon points for the lamp in the lantern1.

The lamp is a delicate arrangement of machinery, holding the two carbons between which the electric light exists, and regulating their adjustment; so that whilst they gradually consume away, the place of the light shall not be altered. The electric wires end in the two bars of • small railway; and upon these the lamp stands. When the carbons of ~ lamp are nearly gone, the lamp is lifted off and another

.British ~lodular Standard of Lengt]t. 47

instantly pushed into its place. The machines and lamp have done their duty during the past six months in a real and practical manner . The light has never gone out through any deficiency or cause in the engine and mt~ehine house ; and when it has become extinguished irt the l~ntern, a single touch of the keeper's hand has set it shinin~ as bright as ever. The llght shor~c up and down the Channel, and across into :France, with a power far surpassing that of any other fixed light within sight, or anywhere existent. The experiment has beer~ a good one. There is still the matter of experlse and some other circum- stances to be considered ; but it is the hope and desire of the Tr in i ty tI0usc, and all interested ia the subject, that it should ultim~ttely justify its full adoption.

For tlm Journal of the Franklin Institute.

Particulars of t]te Ntcamer -Daniel Drew. Hull built by Thomas Co]yet. Machinery by Neptune Iror~ Worlcs,

:New York. Owners~ D~niel Drew and others. HvL~.--Lengt[l on deck, 25t ft. 8 ins. ]Do. at load line, 244 ft. B read th o f b e a m

(molded), 30 ft. 6 ins. Depth of hold to spar deck, 9 ft. 3 ins. F r a m e s - - m o l d e d , 15.~ ins.--sided, 4 ins . --apart from centres, 30 ins. Keel, depth, 3 ins. Draft, f o r w a r d and

aft, 4 ft. 6 ins.

E ~ I ~ . - - ' V e r t l c a l beam. Diameter of cylinder, 60 ins. Length of s t roke , [0 ft: Maximum pressure of steam, 35 ibs. Cut-off, o~lc-half. Maximum re,~olutions a t above

pressure, 26.

BOILEr~s.--Two--Rcturn fined. Length of boilers, 29 it. Breadth do., a t f u r n a c e , 9 ft., at shell, 8 ft. Helgbt do., exclusive of steam chimney, 9 ft. ¢ ins. :Number o f fur- naces, two. Length of grate bars, 7 ft. Numbcr of flues, above, I4; below, 10. In ter - nal diametcr of do., above~ 9~ ins. Do. do., below, 2 ,)f 13~ ins., 1 each of 13, I l , and 7¼ ins. Length of do., above, 22 it. Heating surface, 3350 sq• it. Diameter o f s m o k e - pipes, 4: ft. t te ight do., 32 ft.

PADDIA~ WHEELs.--Diameter over boards, 29 ft. Length of blades, 9 ft. :Depth of do., 26 ins. ]Number of do., 24,

~emar/cs.--One independent steam, fire, and bilge pump. [l:his stc~mer has been built to attain a very high speed, having v.

very easy and a very superior model. The velocity of the per iphery of her water-wheel bl~dcs is 27 miles an hour.

Date of trial, May, 1860. C. I f . t:l[

~ritish Modular Standard of Length.* By 3. F. W. tInl~SC~IEL.

It may not be unwelcome to the scientific portion of your readers to have their attention directed to a simple numerical relation be tween our actual parliamentary standard of length a,nd the dimensions of the earth, which, in effect, pats us in easy ~)ossesslon of a "modular " sys-

• . . / i • (1 tem~ which might be deelmahzed , 'Lnd wh!ch, abstractedly c o n s l d e r e , • From the Lend. Atheamum~ April~ 18~0,