282 Sir E. Rutherford and Messrs. Robinson fy Rawlinson: 



give a veritable spectrum, consisting of a number o£ well- 

 marked bands. In a previous paper *, Rutherford and 

 Robinson have analysed in some detail the magnetic spectra 

 of the ft rays of both radium B and radium C, and have 

 measured the velocities and energies of a large number of 

 groups from each element. 



It is also well known that the <y rays of radium B and C 

 in passing through matter give rise to high-speed ft rays. 

 The penetrating power of these rays has been examined by 

 the electrical method, and has been shown to correspond 

 approximately with that of the primary ft rays from the 

 same radioactive substance. It is of great importance to 

 determine accurately the distribution of velocities of these 

 excited ft rays, and to trace their counexion, if any, with the 

 primary ft rays emitted by the radioactive substance. 



For this purpose, we have made a number of experiments 

 by a method similar to that described in the paper mentioned 

 above. The diagram, fig, 1, is reproduced from that paper. 



Fig. 1. 



The whole apparatus is placed in a uniform magnetic field 

 between the pole-pieces of a large electromagnet. The 

 ft rays issuing from the radioactive source S describe 



* Rutherford and Robinson, Phil. Mag. xxvi. p. 717 (1913). 



