84 ROYAL SOCIETY OF CANADA 



from deposits of polonium, to wliicli radiation attention was first drawn 

 by the experiments of Sir J. J. 'Thomson,^ Logeman,^ Ewers/^ and otliers. 



Makower has also recently used it to measure the beta radiation 

 from radium and from the measurements to deduce the number of beta 

 particles emitted per gram of that substance. 



By applying this method to the radiation from potassium salts the 

 writer has observed in certain cases that potassium salts, when insulated 

 in high vacua, acquire a positive charge, but up to the present it has not 

 been found possible from the characteristics of the acquired charge to 

 decide whether this charge arises from the radiation being wholly of the 

 beta type or whether it is due to the emission of rays of both the alpha 

 and beta type with the beta type of radiation in excess. 



Among other phenomena observed when applying the method are 

 those associated with the volta effect. If a metallic rod or vessel con- 

 nected to an electrometer be placed within and insulated from a second 

 metallic vessel, it will be found when both the containing vessel and the 

 insulated vessel are joined to earth, that generally a potential difference 

 will exist between them. This potential difference will, of course, be 

 more marked when the two vessels are made of different metals. It will 

 also, however, be observable ordinarily when the two vessels are made of 

 'metals supposedly the same, but in this case the existence of the effect 

 only goes to show that some slight difference exists in the composition 

 of the two pieces of metal used in the construction of the two vessels. 



If now with the arrangement just described where one vessel is 

 placed within and insulated from a second the earth connection of the 

 electrometer be removed it will be found that the insulated body or vessel 

 more or less rapidly acquires an electrical charge, the sign of the charge 

 being determined by the direction of the potential gradient. This charge 

 arises from the air or gas between the two vessels possessing a conduc- 

 tivity which is imparted to it either by radiations emitted from the walls 

 of the containing and contained vessels or from the passage through the 

 gas of the penetrating radiation whicli is known to be present at the sur- 

 face of the earth. The conductivity possessed by the air will tend to 

 diminish the potential difference set up between the two bodies when 

 they were both joined to earth, and the charge acquired by the electro- 

 meter under the action of the conductivity when the earth connection to 

 the inner vessel is removed, will give a measure of the magnitude of the 

 volta effect. 



1 Thomson, Camb. Phil. Soc, Proc. 13, pp. 49-54, Feb. 18, 1905. 



2 Logeman, Proc. Roy. Soc, Series A, Vol. 78, No. A. 523, p. 212. 



3 Ewers, Phys. Zeit. March, 1906, pp. 148-152. 



