ON THE THICKNESS AND SURFACE TENSION OF LIQUID FILMS. 
669 
circuit was broken at 23 m , and the stop-cock was opened at 32 m . The following 
observations were taken :— 
t 
c. 
cb 
& 
Mean. 
m. 
41 
All black 
{3b, B (3, 0)} 
+ 0-51 
45 
55 
{46, 0(2, 0)1 
+ 0-23 
49 
*5 
{56, G (2, 5)} 
+ 0-39 
+ 0-38 
The value of 8 fell as the left film thinned. The last two observations were as 
follows :—- 
t 
c. 
C i 
6 
Mean. 
h. m. 
1 39 
All black 
{21 b, W (1, 5)} 
-0-05 
0 44 
5> 
{236, W (1, 5)} 
-0-16 
-040 
The right film may be presumed to have remained in the same state throughout the 
experiment. The length of the black part of the left film increased from 4 mm. to 
22 mm. The difference of pressure must therefore have increased from 0‘05 dp' to 
0‘95 dp', i.e., by 0'9 of the total difference between a coloured and a black film. 
During the same time 8 changed by 0’48 mm., the movement being such as to indi¬ 
cate an increase in the diameter, i.e., a falling-off in the tension of the film which was 
becoming black. 
Hence 
fZT/T= —0-048/4-51 X0‘9 = — D18 per cent. 
Experiment X. 
The films were made as usual, and the following preliminary observations were 
taken :— 
t 
0 , 
Cb 
C 
Mean. 
m. 
5 
R (5, 5) 
R (5, 0) 
-0-34 
7 
R (4, 5) 
R (4, 5) 
-0-42 
12 
R (3, 5) 
R (3, 5) 
-0-38 
-0-38 
' The right film was then thickened by means of the current. The circuit was 
broken at 17 m , the stop-cock opened at 35 m . The first reading gave S=— 0T6, and 
the value of 8 increased (algebraically). The following observations were taken at the 
times indicated :— 
