~76 Mechanics, Physics, and Chemistry.

the mould which produced it. I wish to lay particular stress upon the fact that drawing touches can be thus rendered, anti an ettect rapidly produced, unattainable by modelling. Tile larger plaster casts were taken ti'om drawings freely made--as tile appearance of the touches will

~ rove---in commou brown soap. The finer kind of soap is, of course, etter fitted for fine work; but slmuhl the process now described be

adopted by the manufacturt?r---aml l trust it may never become the sub- jeer of any patent--s¢,ap bett~,r suited to the purpose than any now made will doubtless he slwcially manulhctured. In proof lhat line lines can be drawn upon the so:~p as well as broad vigorous touches, I can state that one of ll.clnl,rmJdt's vtchings has been eopied on soap, the soap pressed into g-tta lWrClm, ;rod an eletqrot)pe taken fi'om the gulta pervba cast, froth uhich a prima h:,s b,~'n oblained, very little inferior in ddicaey to the original etchir~g. I) lbl]ess~ persons en~ged in rnanu{aetures will see apptieatirms ,~f tb.,.' process which I have not contemplated, and l l e a v e i t t,,~ ttwir i ,gvmlity to discover them. [ would particularly call the attenti,m of ornamm,t:Jl ]{:ather and paper manutaeturers, bookbinders, and, possibly, manul~wturers of china, to the process; for it must be re- membered that .soap, when made, can be run into moulds of any form, so as to obtain curved as well a:s ilat sat[aces for the artist to d~aw upon. It has also occurred to me tlmt it would prove a very ready and expe- ditious method of ibrminl,~ r~,ised maps, pictures, mTd diagrams for the use of the blind. 'I'hc m:mipulation is very simple. A lead pencil drawing, if required, cam readily be transferred to the smoothed surface of the soap, by placing tim face of the drawing on the soap and rubbing the back of tile paper ; every line of the drawing is then distinctly visi- ble on tile soap. The imp!emel~ts used are equally simple : all the spe- cimens sent were drawn with ivory knittlng-needles, and small ivory netting-meshes for scoopiny~, out a'ger a l(l £1eeper touches. T e only caution necessary is Io av~;id uader-eutting. Having felt the greates~t interest in tim establishmel~t of schools of design, so well calculated to re-connect fine art wi!h ,nanuti~ctures, it will aflbrd me sincere gratifiea- lion if the shnple process now pointed out--and I trust its simplicity will be no bar to its being carefully tested~shall be in tile smallest de- gree instrumental in aceom t lishing the re-union.

She[field, December 231st, 1853. P .S . - -The date 1850 is on some of the illustrative speeimens.--Jour-

hal q'lhe 5bciel~j of jbls.

Identity of Dynamic or Voltaic Electricity with Static or Frictional Elec. tridty. By Professor F~aDAy.*

Tile F,-iday evening meetings, for the season_ commenced at the Royal Institution on Friday last, the opening lecture being delivered by Pro- lessor Faraday to a very crowded audience. The subject was the devel- opement of electrical principles produecd by the working of the electric lelegraph. To illustrate the subject, there was an extensive apparatus of voltaic batteries, consisting of 450 pai,'s of plates~ supplied by the Electric

*From the London Mechanics' Magazine, January 7.

Dynamic or Voltaic ElectHdt~. ! ~

c ~ , ~ nv, and eight miles of wire, covered With :tta' ere~a Telegraph ~ .... va . . . . . . ~P , four miles of which in cmls were immersed m tubs of water~ to Sh0W:the effects of submersion on the conducting properties of the wire in sub- marine operations. The principal point which Professor Faraday was anxious to illustrate, was the cm~firmation which experiments 0n the large scale of the electric telegraph have afforded of the identity o f dyna. ,sic or voltaic electrici@ with static or frictional electricity. In the'first place, however, he exemplitled the distinction between conductors and non-cot~dtmtors, impressing strongly on tile audience that no known substance is either a perfect conductor of electricity or a perfect non- conductor, the most perfect known insulator transmitting some portion of the electric fluid, whilst metals, the best conduetors, oflbr considera- ble resistance to its transmission. Thus the copper wires of the submarine elect"ie telegrq)h, iho]2gh covered with a thickness ofgutta pereha double the diameter o,t' the wire, permit an appreciable quantity.of the electricity transmitted to escape through the water; but the msulatmn ~s, nevertlae- less, so good that the wire retab~s a charge for more than half an hour after connexion with the voltaic battery has been broken. ProfeSsor l:araday stated that he had witnessed this effect at the Gutta Pereha Works, where one hundred miles of wire were immersed in the canal. .tfter communication wilh a volatic battery of great intensity, the wire became charged with electricity, in the same manner as a Leyden jar, and he received a succession of tort 2" small shocks from the wire, after it had been charged and the connexion with the battery broken. :No such et~bct lakes place when the coils of wire are suspended in the air, be- cause in the latter case there is no external conducting substance. The storing-up of the electricity in the wire when immersed in water is exactly similar to the retenti(m of electricity in a Leyden jar, and the phenomena exhibited correspond exactly with those of static electricity, proving in this manner, as had previously been proved by charging a Leyden j a r with a volatic battery, that dynamic anti static electricity are only differ' eat conditions of the same force; one being great in quantity, but of 10w intensity, whilst the latter is small in quantity, but of great intensity. Some interesting facts connected with the con~luction of electricity have also been disclosed by the working of the submarine telegraph, which Professor Faraday said confirmed the opinion l~e had expressed twenty )'ears ag% that the conducting power of bodies varies under different dreumstanees. In the original experiments by Professor "Wheatstone, to ascerlain the rapidity with which eleclricity is transmitted along copper wire, it was found that an electric spark passed through a space of 280,- 000 mites in a second. Subsequent experiments with telegraph wires have given diffi~rent results, not arising fl'om inaccuracy in the experiments, but from diitbrent conditions of the conducting ~'ires. It has been de- termined that the velocity of transmission through iron wire is !6~ 000 mites a second, whilst it does not exceed 2700 miles in the Same'sP ace 0fti ne in the telegraph wh'e between London and Brussels, a great por- lion of which is submer~ed in lhe German Ocean. The retardation o f

• • • '~ • ," " dinwater lscamu- the torte m its passage through insulated x~ u'e nnmerse lated to have an important practical bearing in eit}Ytinge~ ~ve~.:~{o0 . _ _,o~ , , ,n tdc aJ n,'u, ~'--~'" communica!ion with America; for it was stated that i m ~, ~

YoL. XXVIL--TInlt~ 8~au~s.--No. 4.~AeaIL, 1854. 24

2'78 ~]lechanics, Physics, and Chemist W.

miles, three or more waves of electric force might be transmitting at the same time, and that if the current be reversed, a signal sent through the wire might be recalled before it arrived at Amerb:a. Professor Faraday eoncludod by exhibiting a beautiful experiment illustrative of the identily of volatic and fiictional electricity. The terminal wires (~f a powerful secondary-coil apparatus were placed seven inches apart within the re- ceiver of an air pump, and when the receiver was exhausted, a stream of purple colored light passed between the wires, resembling, though more continuous and b~illiant, the imitation of the aurora borealis p'roduced '~'hen an electric spark is passt.d through an exhausted glass tube. The volatie power emplo)'ed to produce this effect of static electricity was only three cells of a Grove's battery.

Researches on Evaporalion. By Professor ~[ARCI::T, Of Geneva.*

'File following experimenls were instituted with the view of throwing some light on the tendency of" certain circumstances to promote or di- minish the evaporation of liquids. Water and alcohol were *he liquids chiefly used. The results obtained by the author may be recapitulated as follows : ~

1. The temperature of a liquid, allowed to evaporate fl'eely in an open vessel, is always inferior to that of the surrounding atmosphere. The higher the temperature of the atmosphere, the greater is the diftbrence between its temperature and 1hat of lhe liquid exposed to evaporation. Between 40 ° and 50 ° Centigrade the diftbrenee was found 1o x'ary from 5 ° to ../o ; between 20 ° and ~05° it varied fl'om 1½ ° to 1¼ ° ; at 1"2 ° it "was 0"8 ° only, and between 3 ° and zero about 0"2 °. The explanation of this result is obvious. The evaporation of a liquid diminishing with the external temperature, tile cold, which is the consequence of this eva- poration, must diminish in the same proportion ; "and if it were possible to prevent evaporation altogether, the author presumes that there would be no difference whatever between the temperature of a liquid and that of the surrounding medium.

2. The temperature of liquids, such as water and alcohol, as well as the rapidity with which they evaporate, varies, all other circumstances remaining the same, according to the nature of the vessel in which these liquids are contained. For instance, the temperature of the surrounding atmosphere being from 15 ° to 20 ° , water is, on the average, 0'3 ° warmer in an open metallic vessel than in a similar one of polished porcelain, and 0.g ° warmer than in a similar one of glass. It is the same with alcohol. Again, both water and alcohol evaporate more rapidly from a porcelain vessel than from a metallic or glass vessel of precisely the same size. For example--three similar vessels, one of metal, the second of porcelain, and the third of glass, containing each 600 grains of water, having been exposed to evaporation during seven days, the temperature of the surrounding atmosphere varying from 20 ° to 25 °, it was found, that at the end of that time, the porcelain vessel had lost 301:1 grains of its previous weight, the metallic one 277, and the glass vessel 275'5

" From the London Repertory of Patent Inventions, January, 1854.