Readings for the displacement, shape and size of the bubble were ob- 

 tained by means of the Bausch and Lomb comparator using a magnification of ten. 

 The comparator can be used to measure displacements to within 0.01 cm. Suc- 

 cessive frames showing the bubble can be placed on the screen and the position 

 of the bubble determined for each. In order to determine the path and shape 

 of the bubble as it rose, the images of the bubble on the screen were traced 

 on a single sheet of paper, along with the reference scale. Such a trace is 

 shown in Figure 2 . 



The size of the bubbles was determined gravimetrically. This method 

 is more accurate than volumetric methods. A simple but rugged chemical bal- 

 ance reliable to about 2 mg was used. An inverted funnel, closed at the upper 

 end, was hung from one edge of the balance and immersed in the water. The 

 change in weight due to the displacement of the water by the air was obtained. 

 For the small bubbles, a sufficient number were collected so that the change 

 in weight was 0.1 gm or greater. The larger bubbles were weighed individually. 

 In order to verify uniformity in the size of the bubbles during a run, several 

 film records were obtained and compared. If the size of the bubble as deter- 

 mined with the comparator was different for different bubbles, the run was 



Figure 2 



Path and Shape of Bubble as Traced by Means 

 of a Bausch and Lomb Comparator 



The bubble radius is 1.15 cm. The scale is in centimeters. 

 The time interval between successive pictures is 0.0885 sec, 



