' ' 



oOO 



REPORT — 1884. 



for every junction in tbo chain : neglecting magnetic or impressed E.M.F. 

 [Verified most completely by Ayrton and Perry.] 



]j. — Thomson. 



iv. The E M.F. in ary closed circnit is equal to the energy confencd 

 on unit electricity as it flows round it. 



[Neglect magnetic or impressed E.!M.F. in what follows.] 



V. At the junction of two metals any energy conferred on, or with- 

 drawn from, the ctirrent must be in the form of heat. At the junction 

 of any substance with an electrolj'te, energy may be convej'ed to or i'roui 

 the current at the expense of chemical action as well as of heat. 



vi. In a circuit of uniform temperature ; if metallic, the sum of tlie 

 E.M.F. 's is zero by the second law of thermodynamics ; if partly electro- 

 lytic, the sum of the E.^M.F.'s is equal to the sum of the energies d 

 chemical action going on per unit current per second. 



vii. In any closed conducting circuit the total intrinsic E.M.F. is eqna) 

 to the dyniiniical value of the sum of the chemical actions going on per 

 unit electricity convoyed (S'Jfic), diminished by the energy expended ii: 

 algebraically genorating reversible iieat. 



viii. The locality of any E.]\r. F. may be detected, and its amonii? 

 measured, by obsirving the reversible heat or other form of energy then 

 prodnced or absorbed per unit current per second. [This is held by 

 Afaxwell, but possibly not by Thomson,' though it.s establishment is dut 

 to him.] 



II. — Sr.\Ti:MENTS BELIKVKD RY TIIK WIMTKIl TO HE FALSE TIIODGII 



OIJTHODUX. 



ix. Two metals in air or water or dilute acid, but not in contact, art 

 practically at the same potential.- [Sir Wra. Thomson, Clifton, Pellat. 



X. Two metals in contact are at seriously different potentials (/.''. 

 differences of potential greater than such milli-volts as are concerned in 

 thermo-electricity.) [This is held by nearly everybody.]"* 



xi. The contact force between a metal and a dielectric, or between ii. 



' The only voason which I can tliink of as likely 1o havo caused Sir AVni. TljonisoM li' 

 doubt or deny the validity ot' this proposition is L;ivcu and, I hope, refuted at section: 

 (10) and (11). 



- The irutii or falsity of this statement may he held to depend on a (pie.stion of 

 words, viz.: — the deiiiHiun of potential. Sir Wni. Tiiomson at the mectinf^ said In 

 had always dflined potential as the work done in brinj^ing a unit charge close up If'- 

 but not ■iiifn, the body. Tliis delinition explains some apparent inconsistency in I'ln 

 or two of his utterances whicii 1 had never ipiite understood. Hut seeing that tlierui- 

 no dillieulty whaicver in givinga charge up to p lueial body, but rather the contrary, 

 why not d(vn(! its ])oteulial in the more simple uiaiUK'r whii'h followers of his have 

 unconsciously, and I beMevc universally, adopted, not knowing that they were tliii> 

 l)utting themsi'lves out of harmony with him. (iivc^n his delinition, so that tin- 

 potential of a l.od. means really not its potential but tlic potential of the miH^mii 

 close to it, stat'iuimts Xos. ix. and x. r.re undoubtedly true ; and No. xi. is also tnu'. 

 I sup]jose, for it thm only means that there is not much E.M.F. between the inediiiii- 

 closo to a nuMal and that at a little distance. 



' It is much more natural to suppose that the potential of a metallic conduclor i- 

 uniform, whei her it is homogeneous or not. Indeed it is not only more natural. 

 but it is true, that two jiarts of a conductor ea>i only differ in potential by rcasov. 

 of an E.M.F. located at the junction. Now there usually is an E.M.F. at a junc- 

 tion, but it is only of such a magnitude as is concerned in thiTmoelcctricity. !'• 

 indeed, dfjcs picduce a dillercnce of potential biitween the metals, but uotliin.i.' 

 olse can. N. 15. Always provided that by 'the potential of a metal' is niQun'. 

 that potential, and net the potential of air near it. 



