676 
PKOFESSORS A. W. REINOLD AND A. W. RUCKER 
Experiment XIX. 
When both films were colourless the following observations were made :— 
t 
a 
1 
Mean. 
7 
19-08 
8 
19-25 
19-16 
Successive readings gave afterwards 
§=19-08, 19-03, 19-12, 19-19, 18-94, 19-26, and 1914. 
The last two observations were as follows :— 
t 
C s 
c. 
0 
Mean. 
47 
{15, G(5, 6)} 
{235, Y (1, 5)} 
19-29 
51 
{16, Gt (5, 6)} 
{255, W (1, 5)} 
19-08 
19-18 
Hence 
cH/T = 0"002/3-7X 0-98=0-06 per cent. 
Results of the Experiments. 
The above experiments give no indication of a continuous change in the surface 
tension as the film becomes thinner. The differences observed are irregular and such 
as would arise from accidental causes. 
Thus, in Experiment VII., the black film showed a deficiency of surface tension of 
0'41 per cent, when balanced against a film which displayed the blue and green of the 
second order. In Experiment IX. the surface tension of the black film, also balanced 
against another, which showed the blue of the second order, was in excess by 1*5 per 
cent. 
In all cases where the same experiment has furnished two results they make dT of 
opposite signs, thereby indicating that the difference between the two films is not due 
to the fact that one is thicker than the other. 
The results are summed up in the following table :— 
