﻿986 Theory of Ionization by Collision. 



no regard is paid to the energy required for the estab- 

 lishment or extinction of the directed molecular flow of 

 the electrons, which produces the transfer of energy in 

 question. Hence, in Prof. Richardson's calculation of the 

 Peltier effect — which he supposes to be quite general, i. e. in- 

 dependent of special assumptions about the forces between 

 the molecules and the electrons — only the part of the effect 

 which arises from a possible potential-difference between the 

 two sides of the surface separating the two metals, is 

 considered ; the other part arising from a possible difference 

 in the amount of kinetic energy transferred by the electric 

 current in the two metals is not taken into account. 



Quite similar considerations will hold for the Thomson 

 effect. 



It may finally be remarked that it can be shown that the 

 calculated values for the thermoelectric constants when the 

 above mentioned points are taken into account, will also 

 satisfy — at least for a very general case — the conditions 

 given by Lord Kelvin, — a result which does not seem to be 

 rigorously deducible from thermodynamic principles (cf. my 

 paper, pp. 71-75). 



I am, 

 Trinity College, Cambridge, Yours faithfully, 



Feb. 5, 1912. N. Bohr. 



P.S. — Since the above was written another paper by 

 Prof. Richardson has appeared (Phil. Mag. April 1912). 

 In the fifth paragraph of this very interesting paper Prof. 

 Richardson has generalized his calculation, no longer assuming 

 that the potential energy of the free electrons inside the 

 metal can be considered as constant. Quite similar remarks 

 to those stated in the above note will, however, for exactly 

 analogous reasons, hold for the relation between the results 

 of Prof. Richardson's new calculation and those of my own 

 calculations for the corresponding case. 



C. Theory of Ionization by Collision. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, — 



I MUST protest that Professor Townsendhas misunderstood 

 me completely and that I did not make the statements 

 which he attacks with such vigour. I was so far from 

 accusing him of holding the " older view " of ionization that 

 I suggested that he had dismissed it- from consideration 



