﻿382 The Ionization of Metals by Cathode Rays. 



some cause more complicated than an opposition to the 

 emergence of the electrons liberated, for this cause should 

 produce the same proportional decrease whatever the speed 

 of the incident rays. But I have no further suggestion to 

 make as to the nature of this change. 



Summary. 



The experiments described in a recent paper on "The 

 Ionization of Platinum by Cathode Rays" have been extended 

 to other metals and to higher speeds of the incident rays. 



It is shown that the changes in the ionization which were 

 found to take place on heating the platinum can be produced 

 in that metal and in copper and nickel by making the metal 

 one electrode of an electric discharge in air, oxygen, 

 hydrogen, or petrol vapour at about 2 mm. pressure. The 

 changes were greatest in copper; in aluminium hardly any 

 change could be produced. The changes seem connected 

 with " spluttering.'"' 



It appears that, in respect of this ionization, the surface 

 of the metal can be in the following states : — (1) State A, 

 which is that of the metal after it has been polished, (2) a 

 series of states W which are produced by the discharge. 

 The ionization in the states B' is smaller for all speeds of 

 the incident rays than in state A. Of the states B', one, 

 called B, is distinguished (1) because the ionization in that 

 state is greater (for all speeds of the incident rays) than in 

 any other of the states B', (2) because it can always be 

 reproduced from any of the states B' by subjecting the 

 surface to cathode ray bombardment. State A cannot (as 

 was stated previously) be reproduced from state B by such 

 treatment. 



It is uncertain whether the ionization potential in states 

 B' is different from that in state A ; if it is different, it is 

 lower. It is also uncertain whether the speed of the 

 electrons liberated varies with the state of the surface ; it 

 does not vary with the metal (in state A) or with the speed 

 of the incident rays. 



The ionization produced by rays of any speed in a metal 

 in the various states B' becomes more nearly equal and less 

 nearly equal to the ionization by those rays in the metal in 

 state A as the speed of the rays is increased. 



It is suggested that the difference between state A and 

 the states B' lies in the fact that in the former the metal is, 

 and in the latter it is not, covered with a layer of gas. If 

 this explanation is correct, the ionization potential of a 



