524 Electrical Resistance of Thin Liquid Films. [Mar. 17^ 



March 17, 1881. 



THE PRESIDENT in the Chair. 



The Presents received were laid on the table and thanks ordered for 

 them. 



Professor J. Emerson Reynolds was admitted into the Society. 

 The following Papers were read : — 



I. " 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,. 

 1881. 



(Abstract.) 



The authors have made numerous measurements of the electrical 

 resistance of cylindrical liquid films. Their object was to determine 

 whether a thinning film gave evidence by change in its specific re- 

 sistance of an approach to a thickness equal to twice the radius of 

 molecular attraction, and also to devise a method of finding the amount 

 of water which might be absorbed by or evaporated from it. This 

 change of constitution had been neglected by previous observers of 

 the properties of films. 



The thickness of the films was determined from their colour. This 

 necessitated a revision of Newton's table of colours, which was carried 

 out partly by observations on Newton's rings, partly by more than 

 2,000 observations on the films themselves. Two simultaneous but 

 independent measures of the thickness of the film were made by 

 observing two portions illuminated by light incident at different 

 angles. In 84 per cent, of the measures made during the final series 

 of experiments described in the paper, the difference between the two- 

 values of the thickness thus obtained did not exceed 2 per cent, of its 

 value. 



The films were enclosed in a glass case in which they could be 

 formed without admitting any external air. Elaborate precautions 

 were taken to maintain the aqueous vapour within the case at the 

 tension proper to that in contact with the soap solution. 



The resistance of the films was measured by piercing them with- 



