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THE ROYAL SOCIETY OF CANADA 



or (2) ionisation occurring spontaneously in these molecules or (3) 

 ionisation produced by a radiation from the walls of the zinc con- 

 taining vessel or (4) ionisation produced by some type of radiation far 

 more penetrating than any hitherto observed. 



With a view to testing the third of these hypotheses some experi- 

 ments were undertaken during the past winter by the writers on the 

 electrical conductivity of air confined in a vessel of ice. It is known 

 that the water of Lake Ontario contains only an extremely small 

 trace of radium and it was thought that if the residual ionisation in air 

 confined in a vessel of zinc was due to a radiation from the zinc then 

 the conductivity of air enclosed in a vessel of ice would probably turn 

 out to be less. This conjecture has been found to be correct, for in the 

 experiments referred to the value of 2 • 6 ions per c.c. per second' was 

 obtained for the residual ionisation in the air. 



II. APPARATUS AND EXPERIMENTS. 



In these experiments two types of measuring instruments were 

 used, namely, the C.T.R. Wilson compensating condenser gold leaf 

 electrometer and the Wolff bifilar quartz thready instrument. These 

 are illustrated diagrammatically in Figs. 1 and 2. As the theory 



Fig 1. 



of the former has been given by Wright^ in a paper "On variations in 

 the conductivity of air enclosed in metallic receivers" and that of the 

 latter in a paper by McLennan and McLeod^ on "Measurements on 

 the earth's penetrating radiation with a Wolff electrometer." There 

 is no need of repeating them in this place. In the experiments the 



iWright. Phil. Mag. No. 17, p. 295, 1909. 



