r.l.K( TltOMOTIVE FORCES IN THE VOITAIC CKIX. 



497 



I l)y the 

 ■e9 very 



quoted, 



1 botWCL'U 



\\y vepvt'- 

 liem. No 

 raiust till' 



act. 

 ao-clectric 



tVorcncc of 



uiubor 2 is 

 motliods of 

 ■store tl\eii' 

 us n\ duty 

 ■encvality of 

 cticuloiusl 



Olid pi^i't of 

 called oil to 

 3 accept any 

 lou liow one 

 ect tbom al-. 

 part of and 

 d substitute 

 ty first men- 

 lity. IS umbo'.' 

 |tJ tbo foiu'tli 



atiereffoctto 

 f'. of contact. 

 ttly plausible 

 ), and wbicli 

 [it it is wortli 

 statement of 

 t abbreviated, 

 lotentials, the 

 vet. Thereis 

 pqual opposite 



fitlieroftbese 



tjtlio junction, 

 lotliing of tlie 

 Imall rcsidnal 

 listinct cause. 

 ■hi tbink be 

 ^tbis. When 

 IbctNVCCU K and 

 let K.M.F. with 

 llty in motift' 



Q units of electricity aro tnmumitted apjaiust a force E, work J'] Q is dmio ; 

 al.so ^\ hen tlicy aro transmitted up a differejico of potential V — V, work 

 Q (V — V) is done; but, in an open circuit coiitaiuinf? an clectromotivo 

 junction, V — V is produced by and is equal to K. llenco at an electro- 

 motive junction no work need be done by a current ; in other words, the 

 existence or non-existenco of a Peltier effect has nothing to do will, tho 

 oxistenco or non-existence of a local I'j.^M.F. 



Tho fallacy of tho ar<;umen4, in either form, lies in ovcr-prcoiso 

 specification of locality ; gratuitously asserts as true for tho JiDicJlun. 

 what is only proved to bo true for tho whole circuit. It assumes Ihat 

 ilu-ro can be no work done at a junction if it bo perfectly easy to drive 

 electricity cither way across it — /.»'., if there be no work d(jno on Iho 

 whole. 



1 1. To exhibit tho fallacy, consider a hydrostatic analogy. Two vessels 

 of water connecteil by a l)ipe in which is a motor of some kind, \v!ii(;h 

 without leakage e.xcrts a specified t'orco on tho water and maintains a 

 constant dillerenco of potentials, but then remains stationary, doing no 

 further work. Wo typify it feebly in tho diagram by an impracticable 

 close-iitting water-wheel driven by a weight without friction. 



Hydrostatic analofjue <ji! (Ik; true contact or Socbeck force, it nd ol' llie n^al tliouj;h 

 small 'litt'creiieo of jiolential which it iiiaiiitiiiiis Ijctween two iiutals in contact. 

 W is a weight dris'inij: a water-tight wheel until slo])i)cd by the (Utfcrcnco of 

 jiotcntial set uj). Tin; livdraulic raising or lowering of tlu! weiuht represents the 

 Peltier i^lfect. 



V— V is the equivalent of the force exerted at the junction, and every- 

 thing is in equilibrium. It is perfectly ea.sy for water to flow from one 

 vessel into the other under tho influence of the slightest extra force, for 

 W helps the water up the bill V — V", when the flow is in that direc- 

 tion ; and, whenever the flow is reversed, it lets the water gently down 

 again, taking all its energy out of it. If water is made to flow from A 

 to B, say by pouring more into A, the weight W is lowered, or energy 

 disappears (heat absorbed) at tho jnncfion ; if it is made to How from 

 B to A tho weight is raised, or energy (say heat) is generated at the 

 junction. Thus there is a true Peltier effect at the junction despite tho 

 existence of V — V and its equality to the junction force, and yet no re- 

 sistance is offered to the flow of water either way. Thus is tho tirst form 

 of the argument controverted. 



To pnmp water from A to B by any other pipe wonld need work ia 

 be done equal to Q (V — V), and to pump water against the force of W, 

 acting alone, would also need work E Q ; but when the water goes fi-om 



1884. K K 



