Electricity carried by a Gaseous Ton. 349 



In order to make the expansion take place with sufficient 

 rapidity the piston was made of very light glass. The vessel H 

 was exhausted until the pressure in it was but little greater 

 than that due to the water vapour, and especial care was 

 taken that all the tubes, through which air had to rush during 



the expansion, were of as wide a bore as possible and without 

 any constrictions; when these precautions were taken, it was 

 found that the expansion was rapid enough to catch all the 

 positive ions. This is shown by the following results, which are 

 a sample of those obtained in a large number of experiments. 



Ionization produced by a sample of radium A placed at a 

 height 10 cms. above the top of the vessel in which the 

 cloud is formed. 



Pressure of atmosphere 768 mm. Temperature 19*5. 



jxpansion. 



Time taken by drops in 

 cloud to fall 1 centmi. 



1-346 



1-333 



1-32 



1-31 



1-29 



1-28 



1-27 



1-257 



9-7 



9-8 



9-1 



8-25 



7-1 



7-12 



7 



6*5 



Number of drops in cloud 



reckoned per c.c. of the volume 



of the gas before expansion. 



6-6X10 1 



6-7 „ 



5-7 „ 



4-8 „ 



3-6 „ 



3*6 „ 



3*55 „ 



2-9 . 



