Residual Ionization in Air enclosed in a vessel of Ice. 42£ 



spontaneously in these molecules, or (3) ionization produced 

 by a radiation from the walls of the zinc containing-vessel, or 

 (4) ionization produced by some type of radiation far more 

 penetrating than any hitherto observed. 



With a view to testing the third of these hypotheses some 

 experiments 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 ionization 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 

 ionization in the air. 



II. Apparatus and Experiments. 

 In these experiments two types of measuring instrument 

 were used, namely : the 0. T. R. Wilson compensating con- 

 denser gold-leaf electrometer and the Wolff bifilar quartz- 



Fiff. 1. 



thread instrument 



in 



Bgs. 1 



ia grammatically 



and 2. As the theory of the former has been 



