﻿798 



Mr. Gr. Shearer on the 



It is clear that the efficiency of a metal as a source of 

 electrons increases with its atomic weight or number. Fig. 2 

 shows the results graphically. The relation between the 

 number of electrons escaping from a metal and its atomic 

 number is very nearly a linear one. The electron emission 

 may be expressed with considerable accuracy by an equation 

 of the form 



n' = *(N-a),' 



where n' is the number of electrons escaping from the metal, 

 N is the atomic number, and k and a are constants, the value 

 of a being approximately 10. 



Fte. 2. 



ZOO 



50 



z 



^ too 



50 



cu 











/ 















/ 



/& 







/ 



/ 









20 



40 

 ^Atomic 



60 

 Number. 



SO 



400 



Since N denotes the number of electrons in the atom, it 

 might appear that this result implies that the number of 

 electrons emitted from an atom is proportional to the 

 number of electrons in the atom with a small correction due 

 to the presence of the term a in the equation. Such an 

 interpretation is, however, not permissible, as what has been 

 measured in these experiments is the number of electrons 

 which succeed in escaping, and not the number liberated 

 from the atoms under bombardment. 



In the present state of knowledge of the laws governing 

 the passage of electrons through matter, it is not possible 

 accurately to deduce the number of electrons liberated from 

 an atom from the observed number actually escaping from 

 the surface. An approximation may, howeyer, be obtained 

 by making certain assumptions which are probably near the 

 truth. 



