ON THE THICKNESS AND SURFACE TENSION OE LIQUID FILMS. 
655 
Eight. 
Left. 
Diameter. 
23-05 
18-80 
2Y. 
22-213 
19-643 
2 dy 2 . 
+ 0-837 
-0-843 
f. 
25° 48' 
29° 10' 
Using equation (18), we find that the surface tension of one film exceeded that of 
the other by 8'8 per cent. 
Also, since 3 = 0*425 cm. and the limiting sensitiveness for the two cylinders is 4*51, 
<^T/T=0*425/4*51 = 0*094. 
So that by this formula the difference of surface tension is given as 9*4 per cent. 
Considering that both equation (18) and the limiting sensitiveness are here applied 
to films which differ considerably from cylinders, these results are in satisfactory agree¬ 
ment and prove that the greater part of the difference of form of the two films cannot 
be ascribed to any slipping of the liquid attachments to the solid supports. 
To show that this point needed careful investigation, we may remark that it seemed 
prima facie probable that the bulging film might be forced out and the contracting- 
film drawn in a little so that they were virtually attached to rings a little larger and 
a little smaller than those actually employed. If this had affected the radii only to 
the extent of 0*1 mm. the effect on the calculated difference of surface tension would 
have been very great. Thus, assuming the principal diameters to have remained 
unaltered, but the others to have been increased in the right and diminished in the 
left film by 0*2 mm., the values of 2Y in the above table would have been 22*346 and 
19*510. The difference of surface tension given by these numbers is 3*8 per cent., 
while that calculated from the sensitiveness remains, as before, 9*4 per cent. It is 
evident, therefore, that it was only by careful measurement that we could assure our¬ 
selves that the source of error we are now investigating was not affecting our results 
to a very serious amount. 
We have made a considerable number of similar experiments which prove that the 
method of measuring three ordinates generally gives results from 0*5 per cent, to 1 per 
cent, lower than those obtained from the sensitiveness. The following Table is a 
sample of our results when the films had settled down to a constant state. It shows 
the numbers obtained by a series of consecutive measurements on the same film. The 
value of rfT is given in percentages. The left film was flooded at three minute 
intervals. 
