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VIII. On the Electrical Resistance of Thin Liquid Films, with a revision of Newton’s 
Table of Colours. 
By A. W. Reinold, M.A., Professor of Physics in the Royal Naval College, Greenwich, 
and A. W. Rucker, M.A., Professor of Physics in the Yorkshire College, Leeds. 
Communicated by Professor W. Grylls Adams, F.R.S. 
Received March. 3,—Read March 17, 1881. 
[Plates 59, 60.] 
I. 
In a preliminary note read before the Royal Society in June, 1877,'“' we stated the 
results of some observations in which an electric current was used in investigating the 
properties of soap films. These observations were made in the course of an enquiry 
(then incomplete) as to whether the resistance offered by a soap film to an electric 
current is inversely proportional to its thickness, and our object in undertaking this 
was to obtain, by a novel method, evidence as to the value of previous experiments 
by which various physicists had from time to time attempted “to obtain from the 
phenomena of capillarity, or from observations on liquid films, an indication of the 
magnitude of the radius of molecular attraction.” 
Since that date we have had but few opportunities of carrying out our research in 
common (as was necessary), and hence the long delay which has taken place ; but we 
are now in a position to state the results of our later experiments, in which the method 
has been in several respects altered, and the apparatus considerably improved. 
In the first place, it will be well to give a summary of the conclusions of previous 
observers. QuiNCKE,t as the result of a welhknown research, conducted by immersing 
in water and mercury plates of glass covered by wedge-shaped films of silver, collodion, 
and other convenient substances, arrived at the conclusion that the radius of molecular 
attraction is approximately equal to 50 X 10~ 7 centims. Plateau! estimates it at less 
than 59 X 10 -7 centims. Ludtge,§ on the other hand, asserts that the thickness of a 
soap film becomes almost immediately after its formation less than twice the radius 
* Proc. Roy. Soc., No. 182, 1877. 
t Pogg. Ann., 1869, Bd. cxxxvii., p. 402. 
X ‘ Statiqne des Liquides,’ 1873, tom. i., p. 210, 
§ Pogg. Ann., 1870, Bd. cxxxix., n. 620. 
