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ROYAL SOCIETY OF CANADA 



from a preliminary set of observations for the activity of the tinfoil 

 sheets which were found to emit an extremely feeble though measur- 

 able radiation. From the values given in Table VIII it will be seen 

 that it was necessary to cover the salt with foil representing a total 

 thickness of .06 mm. before the radiation from the salt was reduced 

 to one-half its original intensity. 



TABLE VIII. 



TABLE IX. 

 Absorption by Tinfoil. 



The mean values of the absorption constant A for the different 

 thicknesses were deduced from the formula I = lo e ^ ^> where 

 lo was the ionisation current obtained with the unscreened salt and 

 I the current when d centimetres was the thickness of the tinfoil 

 traversed. The deduced values of A are given in Table IX and as 

 will be seen these shew a gradual decrease as the number of sheets of 



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