192 



Professor Sir James Dewar 



[Jan. 19, 



the tangent drawn at the desired point of the contraction curve. 

 The amount of the gas transference, in cubic centimetres per day 

 through unit area, is then equal to one half of the daily rate of 

 reduction in diameter, measured in centimetres. 



This follows directly from the simple properties of a sphere ; for 

 if S and Y be respectively the surface and volume, and 1) the 



diameter, then S ^ tt D^, and V = - D^, so that d Y 



6 



D2.^/D 



= I S.^D, therefore c?V/S, the rate of gas transference per unit 

 surface, = ^.^ D, which is half dy/dx, the daily rate of reduction in 

 diameter shown by the slope of the tangent already referred to. 



(Oem's 



3 6 C^ 12 15 18 ^l 2:^^ DAYS 

 Fig. 6.— Black Bubble in Hydrogen. 

 Decrease in size at 3-day intervals. 



Some of the results obtained are shown in the following 

 Tables 3, 4, 5, and 6, in which are given respectively (1) the diameter 

 of the bubble on which the measures were made ; (2) the corre- 

 sponding internal excess pressure, above the exterior air pr» ssure, 

 given in mm. water ; and (8) the measured value of d'D/2, representing, 

 as shown above, the rate of gas transference in c.c. per day pns^ing 

 out through each square centimetre of the bubble when at the 

 diameter given m line (1). 



Gas Transference through JUack Air llubhles. 

 Table 3. — 50 per cent, glycerine, 2^ per cent, soap ; hanging on glass tube. 



Diameter .... 

 Internal pressure 

 (laa transference rate 



