Professor Sir James Dewar 



[Jan. 21, 



capacity of about a litre, and the straight tul»e was al)Out 60 cm. in 

 length \ind 4 cm. in diameter. Both are sealed after exhausting to 

 a traction of a mm., the part containing the soap solution being 

 meanwhile cooled to about - 20' C. When the bulb A is then 

 gently warn^ed on either side by tlie finger and thumb, a regular 

 succession of bubbles rise from two opposite points of A, which are 

 thus at a slightly higher temperature. The growing bubbles pass 

 in their expansion to and fro across the liquid surface almost with 



A 



c^A 



Fig. 4. 



the regularity of a pendulum, and rise up the tube as a series of 

 fiat films. In a similar manner, if the side tube (filled with the 

 solution) be warmed by the fingers, saddle-backed films emerge and 

 divide into flat films up and down the straight neck (see Fig. 9). An 

 alternatiye method more applicable to the straight tube form is to 

 agitate the liquid until it is largely a mass of froth, the bulb A being 

 Avarmed in the hand during the shaking. When the tube is then set 

 vertical, the slight warmth imparted to the liquid mass in A causes 

 a steady and extensive evolution of interlacing bubbles to pass 



