258 Duane—IIeat Generated by Radio-active Substances. 



usually much too long, and to reduce its length all that is 

 necessary is to tilt the apparatus up a little so as to cause a 

 current of the liquid to pass through the tube. This current 

 pushes the bubble down into the portion of tube below and at 

 the side, which is larger than the capillary portion. The 

 bubble remains in this portion of the tube, and the current of 

 the liquid passing it carries along the air little by little, thus 

 reducing the bubble's volume. On repeating this process, 



Fig. 1. 



causing the current to flow first in one direction and then in 

 the other, one can reduce the bubble to any desired length. 



After the bubble has been replaced in the tube, and the 

 apparatus has been prepared for the experiment, the bubble 

 remains in the horizontal part of the tube. It never descends 

 into the large portion, no matter how much the temperature 

 of the room may vary: but it slowly disappears. The air in 

 the bubble dissolves in the liquid more or less rapidly accord- 

 ing to the nature of the liquid, the pressure of the air and the 

 dimensions of the apparatus. In my experiments it is neces- 

 sary to renew the bubble once in two or three weeks : and this 

 is a process requiring about five minutes time. 



The form and dimensions of the capillary tube B have been 

 carefully studied. The length of the horizontal part is 4|- cm 



