Radioactivity and Ionization of the Atmosphere* 71a 



The large cylinder was closed at the top by a zinc plate, in 

 the centre of which was a circular opening slightly larger 

 than the internal cvlinder. A metal flange, fixed round the 

 top of the inner cylinder, rested on an ebonite ring C. 



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Between the ebonite and the zinc plate D was placed a ring 

 of thinfmetal E. connected to earth, which rested on a similar 

 ring of a partial insulator like cardboard. The thin metal 

 ring, connected to earth, -erred as a guard ring and ensured 

 that even with a large P.D. between the cylinders, no current 



