182 



Professor Sir James Dewar 



[Jan. 19, 



tube B leads from the vessel A to a mercury U-tube manometer, and 

 to the stop-cock to which the air-pump is attached ; while another 

 tube carries at its lower end the constriction C and the funnel on 

 which the bubble is to be formed, and at the upper end the small 

 reservoir G of soap solution. Air passing through the purifying 

 bulbs F is admitted by the regulating stop-cock D, through tlie 



reservoir G to the funnel-mouth C. 

 A capillary tube between D and Gr 

 assists in the control of air when the 

 pressure in A is very small. By 

 slightly tilting a few drops of the 

 solution in G down the tube to C, 

 bubbles are easily blown within the 

 flask A, even at a pressure less than 

 1 mm. Hg. At this pressure the con- 

 traction of the bubble proceeded 

 visibly, and was accelerated as the 

 diameter was reduced. 



In Fig. 8 various forms of bubble- 

 support tubes are shown, convenient 

 for different purposes : (a) permits 

 the insertion of a long fine tube or 

 rod into the bubble ; (b) allows the 

 apparatus to be inverted, without loss 

 of soap solution, so as to have the 

 bubble supported from below : (c) 

 permits the formation of bubbles in 

 otherwise inaccessible places (this 

 form has a dropping funnel and stop- 

 cock attachment to the reservoir) ; 

 {(l) is useful for forming a succession 

 of bubbles (by a series of slight 

 regulated jerks of the reservoir, a 

 series of films form in its exit-tube, 

 which pass down to the thistle-shaped 

 funnel, and there produce a chain of 

 bubbles). 



An ordinary tubulated aspirator, 

 of about 12 litres capacity, is very 

 convenient for the study of bubbles 

 up to nearly 20 cm. in diameter. For 

 careful measurements a plane-sided vessel is necessary to prevent optical 

 distortion. For this purpose a metal-framed plate glass box, 1 foot 

 length of side, was used. The sheet of glass forming the top was 

 nearly 6 mm. thick ; it was pierced with three or four holes from 

 J cm. to 8 cm. diameter, besides the central hole, 3 cm. in diameter, 

 for supporting the blowing tube. These extra holes allow the 



Fig. 2. 



