334 



Mr Wilson, On the Action of Uranium rays [Oct. 25, 



The thin- walled glass bulb A, about 5 centims. in diameter, 

 contains the air to be exposed to the action of the rays. 



The tube, at the end of which the bulb is blown, is about 2'5 

 centims. in diameter. It has its open end ground perpendicular 

 to the axis, and is wired tightly down in a vertical position against 

 the flat surface of an indiarubber stopper. 



ToPump 



Inside this tube there slides freely an inverted thin-walled 

 test-tube P, with the lip removed and the open end ground 

 smooth and perpendicular to the axis. The test-tube serves as a 

 piston. Its open end is always immersed in the water which fills 

 the lower part of the outer tube, in the way indicated in the 

 figure. 



By means of the arrangement B (described on p. 268 of the 

 paper in the Phil. Trans, already referred to) the air-space in 



