670 
PROFESSORS A. W. REINOLD AND A. W. RUCKER 
t 
c. 
G 
c 
Mean. 
h. m. 
0 54 
{75, B (2, 3)} 
{235, W (1, 3)} 
+ 0-21 
0 58 
{8b, B (2, 0)} 
All black 
+ 0-11 
+ 0-16 
1 31 
{175, G(2, 0)} 
All black 
+ 021 
1 36 
{205, G (2, 2)} 
+ 0-20 
+ 0-20 
The first comparison showed that 8 had altered by 0’54 mm., the movement being 
such as to indicate an increase in the surface tension of the film which displayed the 
most black. Since the thicker film had 7 - 5 mm. of black, while the thinner had an 
average amount of 24‘5 mm., the difference of pressure could only have been 0 - 8 of its 
full amount. Hence 
riT/T=0'054/4 , 51 X 0'8 = 1'5 per cent. 
During the second part of the experiment the movement of the zero continued in 
the same direction, which must be interpreted as a falling-off in the surface tension of 
the right film, which was now becoming black. 
As the black extended only from 7'5 to 18 ‘5 nnn., 
clT/T= — 0-004/4-51 XO-6 = — 0T5 per cent. 
This experiment illustrates the importance of obtaining, if possible, two measure¬ 
ments with the same pair of films. The fact that the change in the magnitudes of 
the principal diameters went on without reference to the thinning of the films is 
strong evidence that that change was not caused by the alterations in their relative 
thicknesses. 
Experiment XI. 
The same films were used as in Experiment I. The final observations in that 
experiment gave 0T8 as the initial difference of the diameters. At the end both films 
were first thickened by the current and then flooded. The value of 8 found was 0'44. 
The mean of the two values is 0‘32. 
During the greater part of the time that the experiment lasted the current was 
passing. The circuit was broken at 2 h ll m after the films were first made, and the 
following observation was taken :— 
t 
O r 
0, 
8 
h. m. 
2 16 
{175, W (1, 0)} 
{0-55, W(l, 5), Y (1, 5)} 
0-41 
