142 



ROYAL SOCIETY OF CANADA 



The apparatus is represented here by Fig. 1, and may be briefly 

 described as follows: 



An air-pump supplies a current of air through a tube of thorium 

 hj'droxide, where the emanation mixes with tlie air and thence passes 

 through tubes, containing absorbing or non-absorbing material, as the 

 case may 'be, into a testing vessel of the ordinary cylindrical type. An 

 accurately calibrated manometer in the circuit measures the velocity of 

 the air current. The testing vessel is connected to one pole of a battery 

 of E. ]\[. F. sufficient for complete saturation, the other pole of the battery 

 being earthed. The central rod of the testing vessel is connected with 

 a suitable electrometer, and a condenser of adjustable capacity is placed 

 in parallel "oàth it. It should be noticed that, with this arrangement, 



BflTTCfty 



»IR DOIYIC. 



BRflNCH CIRCUIT roft SPEED ^DJUSTMCNT 



Fig. 1. 



absorption of the emanation takes place when the charcoal has absorbed 

 its full amount of atmospheric gases, under the existing conditions. 



The weight of thorium hydroxide used was 37 gms. 



The ionization current in the testing vessel is proportional to the 

 number of emanation atoms breaking up per second in the testing 

 vessel, and this is A. times the number of emanation atoms present, A. 

 being the coefficient of decay of the emanation. Henco, the ionization 

 current is a measure of the amount of emanation in the testing vessel, 

 and by this means we can compare the amount of emanation present 

 when it has passed through non-absorbent and absorbent materials. 



Tn the paper referred to before, it has l)oen deduced that when 



