4!)8 



liKi'oiiT — 1881. 



A to T? '•/(' W, m* '•/'•(' /•<>••.•(/, no work is done on llic wlioh'. Qaite true; 

 but thu conclusion that no work \h done at llic- jnuclidii, by no me is 

 follows. Work viiist bo ilono at; tho junction in propoi-tion to the foiot! 

 thpro (l)y inspection of the diaf^nun), and acf-ordinj^l^- the existence or 

 non-cxistenco of a I'dtier otlbct 1ms ivcnith'ni'j to do with thopxistiiicc op 

 non-existonccf of a local E.M.F. 'J'his controverts the sci'ond form of the 

 nr^nraent. 



It' tho ai'^unipnt bo now considered upset, are we to proceed to assi it 

 that tho dilferonco of potential, or force, concerned in the Volta ell'ect, aud 

 the heat dcistruction or <;enei'iition concerned ii, tlic^ Peltier ell'ect. arc 

 closely connected, and in fact dillerent ways of observitij,' tho same thiiiL^'r 

 \\y no means. All wo have proved is that tho Peltier elfect accurately 

 and necessarily represents and measures tho true contact force at a June- 

 tion. True, wo havo considered a dill'erenc(! of potential V— \'' as jmi- 

 duccd by this contact force in an incomplete circuit, and so it is; hut 

 iiothini>' has boon, said to imply that this ditteronco of potential has any- 

 thinj^ to do with what is observed in electrostatic experiments as tiio 

 Volta etfcct. So far from this I will assert that what is usually observed 

 when two motals are touched and separated is not ])rimarily a difference 

 of potential between tho metals at all. They are at dilfereii) poteiitiuls 

 when separated, no doubt, because they are oppositely charged ; Imt 

 they may havo been at the same potential until sepjirated. T'he riiil 

 \'olta eU'ect is almost indejiendcntof tho true contact force, and of the dif- 

 ference of potential which it produces. In other words, a good Volta 

 effect can bo observed when there was no difference ol' potential whati vir 

 between the metals when in contact. 



According to my view the Volta effect is produced, not by a coiitiCt 

 force at tho junction of the two motals, but by a contact force at thuir 



c 

 Kk;. 1.-.. 



Hydrost.'ido nnaloffiK! of tho Volta oft'oct.or a]>p(nrnfA\Vicvo\\i^<io[. potcnti;iI proiliu'eil 

 l)y inct.'iUic cdiitiict, and of the oupositu cliiu-y:fs but unifcjiiu iiotentuil wliioli ii 

 iii;iiiitiiiiis liflwcen two iiu'ials in contact. The vcs.scls are coverc<l Ijv a:i-ti,.,l'' 

 ela.-l if has^s (lill'tTcntly strL'tcheil. 



free surfaces, between tho metals and the air or other medium surround- 

 ing them. To represent this hypothesis by a hydro.static model we .sliall 

 have to maintain the diffei'ence of level in the two connected vessels, 

 not by a force at the junction, but by a force at the surftices ; say by usinL' 

 closed vessels and compressed air, or more pictorially by diffcrentiv 

 stretched clastic meuibranes or bladders tied over the tops of the vesseli*' 



