330 Messrs. Moseley and Robinson on the Number of 



unless completely surrounded by earthed conductors it col- 

 lected a large number of ions from the air, even when at a 

 considerable distance from the charged chamber. The 

 values found for n, after subtracting the effect of the 

 natural ionization, were corrected so as to give the values 

 in air at 76 cm. pressure and 15° C. The actual distance, r, 

 traversed by the radiation was, when considering the absorp- 

 tion of the (3 rays, replaced by the equivalent distance r', 

 which was corrected to this standard density of the air and 

 included a small correction for the absorption by the glass 

 walls of the emanation-tube. 



The Ionization by the /3 rays from Radium B and 

 Radium C together. 

 The values found for nr 2 with no aluminium screen are 

 plotted in fig. 1 against r' '. The ionization in the distance 



10x8 



k 



Ffc. 1. 



1 











! 





\ 













■ 



\ 









o cm 



+ C/VA/ 



1BE/I B 





\ 









X CHAA 



18£f?C 



















































/ 



a 









i 2 3 Metres 



up to 10 cm., in which measurements were not made, was 

 mainly due to the a particles, but excluding the effect of 



