334 



Profs. Remold and Riicker on the 



[June 21 , 



Plate 2. 



Fig. 4. A " giant cell " from the ascending frontal convolution in man. Obtained 

 from recent brain by means of the new freezing microtome. X 105 dia- 

 meters. 



Fig. 5. Section from the ascending frontal convolution in a case of senile atrophy. 



Obtained, by means of the new freezing microtome, from fresh brain. The 

 proliferation of connective cells of the upper cortical layers is seen invading 

 the vascular tracts and nervous elements. X 180 diameters. 



Fig. 6. A cluster of amceboid connective cells from the third layer of the ascending 

 frontal convolution, in a case of senile atrophy. Section obtained from 

 fresh brain by pressure and teasing. 



III. " On the Thickness of Soap Films." By A. W. Reinold, 

 M.A., Professor of Physics in the Royal Naval College, 

 Greenwich, and A. W. RiicKER, M.A., Professor of Physics 

 in the Yorkshire College of Science, Leeds. Communicated 

 by R. B. Clifton, F.R.S., Professor of Experimental Phi- 

 losophy in the University of Oxford. Received June 13, 1877. 



Attempts have from time to time been made by various pl^sicists to 

 obtain from the phenomena of capillarity, or from observations on liquid 

 films, an indication of the magnitude of the radius of molecular attrac- 

 tion. The authors of this note have, with the same object in view, 

 lately made a series of experiments to determine whether the law that 

 the resistance offered to the electric current by a uniformly thick homo- 

 genous body varies inversely as the section is or is not apparently 

 obeyed by liquid films, as any apparent departure from that law might 

 be taken to indicate a want of homogeneity, or that the thickness of the 

 film was comparable with the magnitude of the radius of molecular 

 attraction. 



Their investigations on this point are not as yet sufficiently advanced for 

 publication ; but in the course of their work they have made some obser- 

 vations on the forms of soap films, which they venture to lay before the 

 Royal Society in a preliminary note. 



A liquid film, inclined to the horizontal so as to become gradually 

 thinner by the slow descent of the liquid, will, under favourable con- 

 ditions, appear black, as in the central portion of Newton's rings. By 

 optical methods it is only possible to obtain a superior limit to the thick- 

 ness of the black portion of such a film ; but there is no doubt that at 

 the lower boundary of the black the thickness of the film increases with 

 extraordinary rapidity. 



As a general rule no trace of the blue of the first order can be per- 

 ceived ; but when the colour next below the black is the white of the first 

 order, the line of s3paration between the two is very definite ; and if the 

 film be moved so as to change the angle of incidence of the light by 



