468 Prof. 0. Lodge on the Controversy 



ions, conductivity in a metal may mean greater mobility of 

 the corpuscles ; " hence perhaps the E.M.F. of a metallic 

 junction might be something like this : 



E 



• m K>g 



m' ' jp' 



rolt. 



where the k are conductivities and the m atomic weights and 

 the p densities. 



I would suggest that the curious deterioration suffered by 

 some thermo-electric piles with lapse of time, especially those 

 used for generating a fair amount of power, has never so far 

 as I know attracted much attention or been thoroughly 

 investigated. It may be merely mechanical, due to alternate 

 heating and cooling, "but it may possibly be due to something 

 of greater interest. 



The corpuscles clinging to atoms are rather like ions 

 clinging to solvent; so perhaps in a metal the negative 

 corpuscles move with velocity 



/±cipdV\ 



Ul \Xedz dx) 



where the intrinsic velocity u x is large, 

 corpuscles move with velocity 



diile the positive 



/ 1 dp dV\ 



their intrinsic velocity v x being very small. 



But in a homogeneous metal itself these speeds u and v are 

 perhaps equal ; indeed where there is no potential gradient or 

 driven current they must be equal. 



Are they equal at a metallic junction too ?, or is anything 

 kinetic occurring there at all ? 



There must be a stress or polarisation or double layer or 

 something statical at such a junction ; and a statical 

 condition can be simulated by kinetic equilibrium. What 

 are the arguments ? 



When a zinc surface is illuminated with ultra-violet light 

 J. J. Thomson found that it does not throw off corpuscles 

 unless it is negatively electrified. The ultra-violet light may 

 be said to detach them, but it takes electrification to throw 

 them off. 



So at a junction of two metals when no current is being 

 passed it may be that there is no interchange of substance ; 

 but the interchange may or must begin as soon as a current 

 flows ; and if the A aggregation has more potential energy 



