produced hy the Action of Thorium Compounds. 187 



Xo definite difference was observed whether the gas was free 

 from water- vapour or not. The amount of current due to the 

 emanation from thorium oxide was found, however, to vary 



Ficr. 1: 



100 

 90 

 80 

 70 



60 

 50 

 40 

 30 

 20 

 10 















/ 



/ 



































































k 





















i 





















a 























/ 



















/ 



/ 



















/ 







/w 



FSSO 



RE ( 



IF /7/ 



/? //V 



MA 



f S. 



o-rei 



100 200 500 MO 500 600 700 800 900 \000 

 atly with the gas. Taking the current due to air as unity 



with 50 volts acting, the currents due to the " emanation 



were 



Air 

 H 



C0 2 



1 

 •35 

 1-1 



These numbers are not necessarily proportional to the 

 ionization constants of the gas, as the current produced 

 depends on the relative absorption of the rays between the 

 cylinders. 



These results, together with those obtained for lowering of 

 the pressure in air, show that there is no evident quantitative 

 connexion between the current due to the emanation and the 

 amount of induced radioactivity. 



Chemical and Mechanical Actions on the Radio-active 

 Surface. 



We have previously considered the conditions which govern 

 the production and decay of the induced radioactivity. We 

 will now describe some experiments that have been made to 



