672 
PROFESSORS A. W. REINOLD AND A. W. RUCKER 
The current was used to accelerate the thinning of the one film and to retard that 
of the other. The circuit was broken at 53 m , and afterwards the following measure¬ 
ments were made:— 
t 
C, 
Ci 
6 
Mean. 
h. m. 
1 18 
{66, 0(1,5)} 
1226, W (1, 5)} 
o-io 
21 
{86, Y (1, 5)} 
{256, W (1, 5)} 
0-02 
24 
{106, Y(l, 2)} 
All black 
010 
0-07 
59 
{246, Y (1, 5)} 
All black 
-0-14 
-0-14 
The effective change in the length of the black in the first comparison was from 
8 mm. to 24 mm., the alteration in S was 0'55 mm. in the direction indicating a 
falling-off in the surface tension of the black film. Hence 
dT/T=— 0-055/4*51 X 077=—1*59 per cent. 
From the second part of the experiment we get 
c^T/T=0-021/4-5lX 0-77=0-60 per cent. 
Second Method of Experiment. 
Our second group of experiments was intended to utilize a fact which we had 
observed, viz., that a spherical film thins more slowly than a cylinder. A cylinder of 
the usual dimensions (lengths 1 '25 X diameter) was formed on one of the smaller pairs 
of rings. The larger rings were used to form the sphere, and, since the ratio of their 
diameter to that of the smaller pair was very approximately 1*6, it is evident, if 
the distance between them was made =1‘2X2Y, that a sphere would be formed the 
radius of which was 2Y, and which would therefore be in equilibrium with the 
cylinder if the surface tensions were identical. In consequence of the slow thinning 
of the sphere, a longer interval could generally be allowed after flooding with this 
arrangement than when two cylinders were employed. 
It was found that, even when the films were newly formed, the ratio of the two 
diameters always differed appreciably from its theoretical value of 2:1. This was 
probably due to slight errors of adjustment and to the effect of the liquid rings. 
The experiment consisted in testing whether the difference between the diameters 
was the same when the two films were thick as it was when the cylinder was much 
thinner than the sphere. 
The sensitiveness was 3'7. 
The spherical film rarely showed more than one or two millimetres of black, the 
