278 Messrs. Robinson and Rawlinson: Magnetic Spectrum 



in greater detail. It is now known that the spectrum o£ the 

 characteristic X radiation of an element consists of a series of 

 maxima of different wave-lengths, a large proportion of the 

 energy in the case of the K radiation being concentrated into 

 two or more strong lines. It is consequently of great im- 

 portance to determine how the energy of the /3 ray is 

 connected with frequency of the X ray which excites it. 

 According to Planck's theory the energy of the escaping 

 j3 ray should be given by E = liv, where h is Planck's element 

 of action, and v the frequency of the X radiation. The 

 experiments to be described here were made with the object 

 of testing this point. As the results already obtained, though 

 distinctly promising, indicate that a sufficiently complete 

 investigation will involve a very prolonged series of experi- 

 ments, it has been considered advisable to communicate this 

 preliminary account of the experimental methods adopted, 

 and of the general nature of the results. 



The method used consisted in the analysis by means of a 

 magnetic field of the groups of /3 rays ejected by different 

 metals when exposed to definite types of X radiation. The 

 source of radiation employed in these preliminary experi- 

 ments was the focus tube with nickel anticathode which has 

 been described by Mr. Rawlinson in a previous communication 

 (p. 274) , the slit only being removed. Nickel was chosen 

 as anticathode in spite of its known inefficiency as compared 

 with metals of higher atomic weight, such as platinum, 

 because of the relatively simple character of its X-ray 

 spectrum, and its comparative freedom, when run at a 

 suitable degree of hardness, from penetrating radiation. 



The arrangement of the main apparatus used for the 

 examination of the excited j3 rays will be obvious from the 

 diagram, fig. 1. The X rays from the anticathode A leave 



