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



Table XVI. 



Thickness of lead over the top of chamber=*964 mm. 

 Thickness of aluminium over the top of chamber = 4*73 mms. 

 Lead above aluminium. 



/3 rays deflected towards 



(5 rays deflected away from 



chamber. 



1 



chamber. 



Current 





Current 





through 



Saturation 



through 



Saturation 



magnet 



Current. 



magnet 



Current. 



(amperes). 





(amperes). 





0-0 



10-85 



o-o 



1068 



2-5 



1094 



2-5 



10-74 



4-5 



10-87 



4-5 



10-37 



65 



10-89 



6-5 



10-10 



100 



10-70 



100 



9-88 



150 



10-67 



150 



9-74 



i 22-0 



10-65 



21-0 



9-60 



this table shows a slight gradual decrease in ionization as the 

 /3 rays were deflected downwards toward the chamber, and 

 the fourth column shows a greater decrease as the /3 rays were 

 deflected away from it. Here, again, it will be seen that the 

 difference in the ionizations for the directions of the magnetic 

 field was approximately of the same magnitude as when there 

 was 8*4 mm. of aluminium over the ionization-chamber. Since 

 none but 7 rays could enter the chamber, this difference in 

 ionization must have been due to the action of the magnetic 

 field in the chamber on the secondary radiation issuing from the 

 back of the aluminium screen under the excitation of the y rays. 

 (2) The next experiment was to place the radium protected 

 by the lead cylinder on the side of the ionization-chamber 

 directly opposite to its former position. The same aluminium 

 screen, 8 "14 mm. in thickness, was placed over the chamber 

 as before, and the /3 rays were again deflected down into the 

 chamber by a suitably directed magnetic field and afterwards 

 upward and away from it with the field reversed. The results 

 are given in Table XVII. The numbers thus recorded show 

 the same characteristics as when the radium was in the first 

 position. When the magnetic fields were such as to deflect 

 the f$ rays downwards into the chamber, the ionization 

 decreased but slightly. On the other hand, a considerabty 

 greater decrease took place when the /3 rays were deflected 

 in the opposite direction. 



