150 Mr. V. E. Pound on the Absorption of the 



the aluminium plate. If then the magnetic field were applied 

 in such a direction as to deflect the primary j3 rays down into 

 the chamber, this field, since the chamber was so situated as* 

 to be affected by the field, would deflect the secondary rays- 



JPiar. 17. 



issuing from the back of the aluminium screen in the same 

 direction. With the field in the opposite sense, the primary 

 /3 rays would be deflected upwards and away from the chamber, 

 and the secondary rays in the chamber would also be turned 

 by this field in a similar way, i. e., with one direction of the 

 field the axis of the pencil of secondary rays corresponding 

 to RA would be turned anti-clockwise, while with the field 

 reversed this pencil would undergo a clockwise deflexion. 

 From the diagram shown in fig. 17 it can be seen that when 

 the pencil of maximum intensity RA is given a clockwise 

 rotation, the air-path traversed by it will be lessened, and 

 consequently the ionization produced by it reduced. On the 

 other hand, with the anti-clockwise rotation the length of path 

 traversed by this pencil will be increased; and hence one should 

 not expect the magnitude of the decrease in ionization following 

 the application of the field producing this deflexion to be as 

 great as when the field applied caused the rays to be deflected 

 in the opposite sense. It is evident, too, that the tertiary rays 

 excited on the walls of the chamber by the aluminium secondary 

 rays would be greater in the case of the anti-clockwise rotation 

 of the secondary rays than in experiments when the rotation 

 of these rays was in the opposite direction. One naturally 



