THE ELECTRICAL RESISTANCE OF THIN LIQUID FILMS. 
489 
and it provides, as it were, a means of analysing the films, such as measurements on no 
other of their physical properties afford. 
It has been suggested that it would be impossible for a soap film to exist, the thick¬ 
ness of part of which is less than twice the radius of molecular attraction. The surface 
tension being in this part less than in the remainder, rupture, it is contended, must 
ensue. This argument might perhaps be conclusive if it were known that the differ¬ 
ence of surface tension was considerable. If however it is small while the surface 
viscosity is high, the force thus set up might for a long time only accelerate the 
thinning of the film without actually tearing it asunder. In any case while soap 
films present so many paradoxical phenomena, such as the sudden augmentation of 
thickness noticed by us in the paper already referred to, it seems unsafe to rest 
satisfied with conclusions for which direct experimental evidence cannot be adduced. 
In conclusion we must express our thanks to Mr. A. Haddon, Demonstrator in the 
Physical Laboratory of the Royal Naval College, Greenwich, for the ready and able 
assistance which he has rendered to us during the whole of our investigation. 
Our acknowledgments are also due to the late Mr. F. Wentworth and to 
Mr. C. C. Starling, both of the Yorkshire College, for aid in the tedious calculations 
required for the revision of the table of colours. 
