368 Prof. 0. Lodge on the Controversy 



microscope (Discourse on Coherers. Journ. Roy. Inst. 1899) : 

 but what has all this to do with the location of contact fore? 

 at one junction rather than at another? What bearing has 

 it upon the present controversy? So far as I see. none. 



And further, I would ask, what has this dielectric attraction 

 got to do with the heat of formation of brass '? But in asking 

 this last question I do not pretend that it is an easy one. and I 

 would not dogmatise as to the answer. The question is briefly 

 treated at the end of the present chapter. I only wish to 

 indicate at this stage that the answer to the question is open 

 to doubt, and that it must not be taken as indisputable that 

 the heat of combination of metals has any connexion with their 

 voltaic force, or with their thermoelectric force either. 



There was a time when I fancied that though the heat of 

 formation of brass had no connexion with the Volta force, 

 vet it might have some connexion with the thermoelectric 

 force of contact, or. let us say. the Peltier effect. This idea, 

 too, I wish to abandon*, and for the same reason, viz.. that if 

 metallic affinity were an efficient agent in propelling the 

 current, then I should expect the transmission of the current 

 to result in some formation of alloy. Conceivably some 

 secondary influence may mask the display of this result : and 

 if thenumencal determinations of metallic heats of combination 

 correspond, when reduced to volts, with the E.M.F. anyhow 

 observed in connexion with circuits or partial circuits formed 

 of those metals, that would be a striking coincidence and one 

 to be carefully considered. So far as I am aware, no such 

 coincidence has yet been indisputably discovered, even with 

 a single pair of metals. 



Experiments on heats of metallic combination have been 

 made by Sir W. Roberts-Austen, by Dr. Gait, by Mr. F. 

 J. Baker, and by Mr. J. B. Tayler. Doubtless also br- 

 other workers whom I forget at the moment or do not know 

 of. The results obtained are not yet free from doubt and 

 difference of opinion. Some of the results agree neither with 

 the Volta nor the thermoelectric forces : and this discordance 

 is what I expect will ultimately be believed. On the other 

 hand, some determinations of the heat of alloying of zinc and 

 copper, taken in conjunction with the customary estimate of 

 the size of atoms, do appear approximately to coincide with 

 the order of magnitude of the Volta contact-force. (See end 

 of this chapter.) 



If this is truly so, it is very remarkable, and must greatly 



strengthen the ground of those commonly called " contact 



theorists/' It would seem unlikely to be the result solely of 



* Cf. Phil, Mag. 1885, p. 356, and Joura. Inst. E. E. xiv. 1885, p. 219. 



