the /3 Rays from a Thick Layer of Radium E. 871 



rays from such thin layers as they used are absorbed 

 according to an exponential law. 



Gray * by the same method showed that the /3 rays from 

 a thick layer of radium E are distinctly heterogeneous, 

 although they are absorbed according to an exponential law 

 by aluminium. In view of the experiments of v. Baeyer and 

 Hahn the following experiments were performed. 



The apparatus is shown in fig. 1 and is similar to that 

 used by Wilson (loc. cit.). 



Fig. 1. 



The rays from the radium E which was placed at B could 

 pass through a hole in a lead block A and into a magnetic 

 field perpendicular to the plane of the diagram. They were 

 bent round in circular paths and passed through holes 

 and P in lead screens into an electroscope E. The mean 

 radius of the path of the rays was 4 cm. and the diameters 

 of the holes and P *8 cm. The ionization in the electro- 

 scope was determined for several strengths of the magnetic 

 field, and the results obtained are shown in fig. 2 a, where 

 the ionization in the electroscope is plotted against the 

 product of the field strength and the radius of curvature of 

 the path of the rays. If the rays were homogeneous and 

 the holes and P and the source infinitely small, we should 

 only get ionization in the electroscope for one definite 

 strength of field. Experimentally however, even if the 



* Gray, Proc. Koy. Soc, A. lxxxiv. 1910, p. 136. 



