﻿806 



Mr. G. Shearer on the 



negative potentials, the walls of the vessel being connected 

 to earth. 



Under the influence of a retarding field the electron 

 emission diminished rapidly at first, then more slowly, finally 

 reaching a constant value. This stage was reached when a 

 negative potential of about 20 volts had been applied. On 

 the other hand, an accelerating field produced an increase in 

 the emission, and the potential necessary to ensure constancy 

 of the emission was considerably greater than in the case of 



a retarding field. 



Fig. 3. 



Gl 









150 

















J 



100 



















50- 





Volts. 



13.0 



-SO 



"tO 



-*o 



£C 



■12.0 



The curve in fig. 3 is typical of the effects of accelerating 

 and retarding fields on the total electron emission. Such 

 curves were obtained for various metals and for some salts. 

 The results of these observations was that there did not 

 appear to be any change in the velocity distribution of these 

 slow electrons with a change in the nature of the matter 

 from which they came. Exact quantitative measurements 

 of the properties of these electrons were rendered difficult by 

 the large effect which the state of the surface had on the 

 emission. Especially in the case of the salts examined, 

 fatigue effects were observed which were presumably of 

 similar origin to those observed in the photo-electric effect. 

 No special precautions were taken to obtain very clean 

 surfaces. The state of the surface has very little effect on 

 the emission of high-speed electrons, whose properties were 

 the main object of this investigation. 



Experiments made on the ratio of the number of low- 

 speed electrons to the total emission showed that this was 

 also independent of the material bombarded. Table IV. shows 

 some of the results obtained in these measurements. The 

 numbers have been reduced so that they all show the same 

 electron emission with no field acting. 



