6'6 8 
PROFESSORS A. W. REINOLD AND A. W. RUCKER 
Experiment VIII. 
Three measurements were made when the films were in similar states. 
t 
C, 
Ch 
s 
Mean. 
m. 
24 
{2'5&, G (2, 2)} 
{0-56, B (3, 0)} 
-0-83 
32 
{46, B (2, 3) j 
{26, G (2, 9)1 
-0-86 
37 
{56, R (1, 0)} 
{36, B (2, 6)} 
-0-84 
-0-84 
The films were then separated, and the current was sent up the left film till the 
colours of the third order reached the top. This operation was repeated at 70 m . The 
current was taken off at 7 4 1,1 ; at 88 ni the films were again connected, and the following 
observations were taken :— 
t 
C r 
V 
£ 
Mean. 
h. m. 
1 30 
All black 
{16, G (2, 0)} 
-0-52 
35 
?5 
5? 
{2-56, B (2, 2)} 
-0-78 
40 
J? * 
>5 
{46, O (1, 8)} 
-0-69 
-0-66 
In this case the final measurements gave a comparison between two films, of which 
one was black and the other displayed on the average 2'5 mm. of black only. The 
difference between the principal diameters was, however, only 0T8 mm. different from 
what it was when the films were in very similar states, the change being such as to 
prove that the left film had contracted a little, i.e., that the surface tension of the 
right film when black was a little less than when it was coloured. 
If this were so, however, since 2'5 mm. of the left film were black, the effective 
difference between the tensions of the two films was 0'98 of what it would have 
been, had the left film been coloured throughout. The sensitiveness is therefore 
4’51 X 0 , 98 = 4 , 42, and thus 
dT/T= -0-018/4-42= —0-0041. 
Hence according to this experiment the surface tension of a black film is less than 
that of a coloured one by 0‘41 per cent. 
Experiment IX. 
In this case one of the films which had become partly black in a previous experi¬ 
ment was used. Hence no initial zero was obtained. The thicker film was again 
thickened by the current 14 m after the films were first put into communication. The 
