﻿374 Dr. Norman Campbell on the 



discharge have I been able to reduce R lower than 2'31 ; I 

 am not at all sure that this value corresponds to state B, 

 because further action of the discharge increased R again 

 to 2*47. The lack of alteration in aluminium by the 

 discharge is doubtless connected with the absence of 

 sputtering. 



It will be observed that these conclusions agree in all but 

 one respect with those advanced in the first paper. It has 

 not been found, however, that state A can be regained from 

 state B by bombardment with cathode rays in a high 

 vacuum. It was thought that this result had been obtained 

 because, in platinum and with the low speeds of the incident 

 rays then employed, the ionization in state B does not differ 

 very much from that in state A. Further experiments have 

 shown that it does differ certainly, and that the only certain 

 way to reproduce state A is to take the metal out of the 

 tube and polish its surface. Long-continued standing in 

 mixtures of gases or vapours has little or no effect. 



4. There seems to be a simple and plausible explanation 

 of these changes. We may suppose that the state A is that 

 in which the metal is covered by a layer of gas, and that the 

 state B is that in which this layer is removed. It is, of 

 course, known that heat or the action of the discharge 

 removes the layers of condensed gas adhering to the surface, 

 and there are several lines of evidence which seem to show 

 that the layer once removed is not easily restored. This 

 idea would account for (1) the similarity of the values of R 

 for different metals in state A ; (2) the methods of changing 

 from state A to state B; (3) the difficulty of restoring 

 state A, though perhaps the difficulty is rather greater than 

 would have been anticipated. The reduction of the ioniza- 

 tion below that corresponding to state B would then be due 

 to some other change in the metal ; it might represent either 

 a roughening of the surface by the sputtering and a 

 consequent entanglement of the electrons liberated, or it 

 might represent the effect of double-layers such as Seeliger 

 has shown to exist. The second alternative is supported by 

 the fact that the change is reversed by the action of cathode 

 rays which Seeliger has shown to restore the double-layer 

 removed by the discharge. It is difficult to suppose that the 

 mere bombardment with cathode rays would have much 

 effect in changing the molecular structure of the surface *. 



* The surface was examined with a microscope in states A, B, and in 

 states giving less ionization than B. When the changes had been 

 -effected by the discharge the appearance of the surface was always 

 different from that in state A, but no difference could be seen between 

 the surface in state B and in the state giving less ionization than B. 



