ON THE THICKNESS AND SURFACE TENSION OF LIQUID FILMS. 
671 
The change in the value of 8 from the mean of the two values obtained when the 
films were in the same state was 0*09 mm. 
Hence 
dT/T= — 0*009/4*51 X 0*72 = — 0*28 per cent. 
Experiment XII. 
The following observations were made to determine the zero :— 
t 
Or 
Ci 
£ 
Mean. 
m. 
17 
Colourless 
Colourless 
1T6 
22 
{lb, B (2, 5)} 
R (2, 5) 
1-12 
1T4 
The current was then passed up the left film, but in spite of this it continued to 
become thinner. The circuit was broken at 31 m , the stop-cock was opened at 37 m , 
and the following observations taken :— 
t 
c. 
C; 
a 
m. 
39 
All black 
{56, T (1, 5), B(2, 5)} 
1T2 
53 
All black 
0-92 
The first comparison gives 
dT/T= + 0-002/4-5lX0'89 = + 0-05 per cent. 
The second gives 
cZT/T= — 0'020/4*51 X 0*90= — 0*49 per cent. 
Experiment XIII. 
On this occasion the films were allowed to thin for some time before one of them 
was thickened. The value of 8 changed considerably. Thus at 13 m 8=0*09, at 
16 m 8=0‘42, at 19 m 8=0*60. The last three readings gave the following results :— 
t 
c r 
u 
a 
Mean. 
m. 
24 
{0-756, T (3, 5)} 
{G (4, 0)} 
0-58 
29 
{0-756, G- (3, 0)} 
{G (3, 9)} 
0-61 
0-62 
33 
{0-756, R (2, 9)} 
{16, R (2, 6)} 
0-66 
