ELLt TltOMOTIVK FOIICKS IN TirE YOI.TAIC ('KF.L. 



4()9 



bccauso at 

 tliorc, two 

 •h were tlio 

 irco of tho 

 II ' Elect ro- 

 fvvution til' 

 as are not 

 in possihle 

 K.M.F. <'t' a 

 oti, bat i8 

 „'inical (lata 

 y, however, 

 H and acute 

 I tho voUaic 



•ity ') it was 

 ;od heat at a 

 other words, 

 "icebeck one. 

 lie, lor ever 

 current pro- 

 tho chemical 



1) at lliiit lUitP. 



oufjh it is no! 



fitly directly in 



; oiirly stii^'e o' 



lian<;es lire tlif 



nts of M. Vi'lt'' 



liul toiu'crtiiiii 



aiiotlu'i" pdwi r 



elect ritiiy cx- 



ms, [ifirticiilarly 



nost oxidisabic 



i\etals undergo 



icapplicntions 

 lotive Forces in 

 / (t)itl I'lii/ficiil 

 xrtvi. TiiiTuio- 

 j I ; Miith. and 



circuits in liis 

 Berlin, .Inly -';'. 

 Sh a great part 

 f the conserva- 

 nd shows, as is 

 ^ and sutticieni 

 uperscdcd ; bui 

 dianical theory 

 neto-uiachines ; 

 ent work of Sir 

 essiblc thrnugli 

 he ' new scries 



city, and in tl;c 

 On the electric 

 the heat disen- 

 sprint of Joutu' 



actions going on there ; but it was supposed, and is still supposed (thoiif.Mi, 

 as I venture to think, quite orroncouHly) to leave untouched the (jucstion 

 as to the precise^ Koat of tho E.M.F. in a battery. 



However that may bo, tho succ(>ss of tlu) chemical theory of tho 

 electric current naturally caused it to be Ktill iiiort! cerlainly assnnied 

 tliat tho apparent contact force of Volta could also bo accounted for by 

 aceiilental chemical action, and that without some chemical action some- 

 where no Volta effect could bo prodticod. This also I believe to ha qaito 

 false; provided always that tho i)hraso ' cheniical action' bo used In its 

 ordiiuiry sense as meaning combination, aiul that tho woitl 'aelion" bo 

 not explained away as meaning anythiug whatever. 



'J. 'I'lic triumph of tho chemical theorists with regard to tho Vnila 

 elTect wa.«, however, shortliveil, fiU', from istlo, the invention ol' tho 

 (|ua(lraiit electrometer put into the hiinds of electrostatic experinu iter8a 

 far nioio refined and delicate instrument than could have been tliought 

 possible a few years before ; and the illustrious inventor of that instru- 

 ment himself for ever put the truth of Volta's phenomenon boyouil doubt, 

 by the most simple and beautiful device of suspeiuling a charged tor 'ion 

 arm over a zinc-copper junction. JJy comparing the deflection so i)ro- 

 (Ineed with that cau.scsd by a Daniell cell, an absolute measure of tho so- 

 called contact force was made ; and it was shown that on uniting th(> corper 

 and zinc by a drop of water, instead of by a metal, no deflection was 

 produced. It was also shown that tho deflection was greatest \\l;(.'i' i.lio 

 zinc was clean and the coj)pcr oxidised.' 



But Sir William Thomson went further than this ; ho sound' d a, 

 theoretic note, and in a sentence revived the whole controversy a'lou^. 

 tlio seat of 2)ower in the pile. The sentence is this: 'For nearly two 

 years 1 have felt quite sure that tho proper explanation of voltaic aclion 

 in the common voltaic arrangement is something very near Volta's, w! ieh 

 fell into discredit because Volta or his followers neglected tho princi|)lo 

 of the conservation of force. I now think it quito certain that ^avo 

 metals di])pcd into one electrolytic liquid will (when polarisation is dono 

 away with) bo at the same potential.' And tlien ho goes on t j one of 

 those brilliant and extraordinary speculations characteristic of no oin; 

 else, and applies this apparcTit contact force to determine a lower limit 

 to the size of atoms — an application obviously of transcendent interest, 

 and of more importance! than all tho previous outcome of coniact 

 discussions put together.- 



The whole subject now acquired a fresh interest, and the new secies 

 of experimental determinations of contact force beoan. 



o. Ifankel's and Gerland's measurements belong to this period in point 

 of date (1801-18G!)), though in method and motive they probably aro the 

 outcome of the earlier period.'' llankel uses a nu)ditied Kohlrauseh mctliod 



' Proc. Lit. anil I'h'd. Soc , .Alanclicstcr. Letter from I'mf. W . Tliomsfin totVn 

 president, Dr. .Toule, .Tan. iM, 18(i2. ' New pronf oC contact elcctririty.' Hcc reprint 

 of jiiipcrs on Electrostatics and Maonotism, \\ •''"• 



- "Tlierc cannot be a doubt that the whole theory is .'^iinply clu'iiiical action .it ;) 

 distance. Zinc and cojipcr connected by a metal wire attract c;uli other fr.^m any 

 distance, sod<j platinum plates coat(>il with oxyj^cn and liy(lrog(Mi res]>ectively. ' can 

 now tell the amount of tlu- fotw, and calculate how great n ]iroi>ortion of clioi! ical 

 ■dlinity is used upelectrolylically before two such disks come within any .spccitied small 

 jli.stancc down to a limit within which molecular heterogencousticss becomes scn'-iblc. 

 This of course gives a detinite limit f.ir the size of atoms.' -Ia'I tor to Dr. Joule, 18(i2, 

 cited al)()vc. Wee also Tluunson and Tait, Xiit P/iil., Part 11., Aiii)endix F. 



'■' llankel : Electv.Untvrsuchuinjen: Ahh. tier KiinigL Silchx. O'csdhclinft. Math.- ■' hi 



