472 Prof. 0. Lodge on the Controversy 



handier, so introducing the migration ratio r = ujv we get 



1 + 



dT 



and so on for II and E as before when two metals are em- 

 ployed, only with the new relative migration factor which 

 permits ready change of sign ; and it must be remembered 

 that the corpuscular migration ratio r, as well as the corpus- 

 cular detachment number n, may differ in the two metals. 



Helmlioltz 's View of Electric Mass- Affinity. 



The doctrine that matter has a specific attraction for 

 electricity * leads to many of the same conclusions as the sup- 

 position that positive or negative electricity inside a substance 

 has a real specific heat, and the two modes of statement may 

 be considered together ; but we may speak in the language of 

 Helmhollz's hypothesis as being the more important of the 

 two, indeed the only one seriously upheld as a physical 

 reality. As has been suggested above, p. 369, it is to some 

 extent ambiguous, however ; for it is not certain whether the 

 affinity or attraction is effective at a metal-gether free surface 

 or at a metal-metal junction. As usually stated, the attraction 

 is supposed to be an affair of mass or bulk and not of surface, 

 though no doubt any such internal volume electric stress 

 would give rise to something analogous to electrical surface- 

 tension ; but the whole may be really and essentially super- 

 ficial, having to do with the free surface only; and in that 

 case it is difficult to distinguish it from chemical affinity, 

 unless it can truly be shown to be independent of the pre- 

 sence and nature of surrounding adjacent matter. Even so 

 it may be considered as an early and crude statement of 

 certain consequences of the electron theory of matter, rather 

 than as a distinct and independent theory (cf. J. Larmor, 

 Phil. Trans. 1897, vol. cxc. p. 271). 



However it be regarded, it is plain that the effect of an 

 attraction between matter and electricity must display itself 

 at a transition or boundary layer, and although it has been 

 customary to concentrate attention on the metallic (e.g. the 

 copper-zinc) junction in this connexion, it is by no means 

 probable that that is so efficient or complete a transition as 

 the free air or sether surface of either metal ; nevertheless these 

 surface actions have secured too little attention. 



The proofs that have been given, for instance, of the value 

 of the Peltier effect, and its connexion with contact force, 

 * For references see Phil. Mao-. October 1885, p. 377. 



