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II.— On the Motion, Equilibrium, and Forms of Liquid Films. By the late Sir 

 David Brewster, K.H., D.C.L., &c. (Plates I. and II.) Communicated 

 by Francis Deas, Esq., LL.B. 



(Read 6th April 1868.) 



[This paper was transmitted to the Council by Sir David Brewster, on the 

 8th February 1868, with the following remarks : — " I have tried in vain to finish 

 the two most important of my papers on Liquid Films, but the most beautiful 

 drawings of all the phenomena which its purpose was to describe have been 

 finished. I think, therefore, that my friend Mr Deas will, by means of these 

 drawings, produce an interesting paper. The drawings are numerous and large, 

 but many of them may be reduced in size. As this is the last of my papers, I hope 

 the Council will not grudge the expense of having them well lithographed." 



In another letter, Sir David Brewster expresses a wish, that in the event of 

 the paper being printed in the " Transactions, " notice should be taken of the 

 fact that the drawings were executed by his friend Miss Dickenson.] 



I. On some Transformations in Films when brought in contact ivith Surfaces of Glass.* 



(1.) Let a film be formed on the rim of a cylindrical wine-glass, at or very near 

 its margin ; cover it immediately with a watch-glass, and holding the latter firmly 

 in its place, invert the whole, so that the film is placed in a vertical position. 

 The film will now attach itself to the watch-glass at the lowest point where it is 

 in contact with the margin of the wine-glass, and will run up the concave surface 

 of the former. At the same time, the film will leave the margin of the wine- 

 glass at its upper edge, and retreat into the glass, running down its inner sur- 

 face. A film of the form of the segment of a sphere will thus be produced, which, 

 with the upper portions of the inner surfaces of the watch-glass and wine-glass, 

 will form a hollow filled with air, as shown in fig. 1 . This state of matters will 

 remain the same, in whatever position we now place the wine-glass, the figure 

 which has thus been produced being one of equilibrium. The phenomenon 

 produced arises from the fact, that when the original film is first taken up on 

 the margin of the wine-glass, a drop of liquid always remains in the bottom of 

 the glass, and when the glass is inverted, so as to bring the film into the vertical 



* The experiments under Head 1, are best performed by using a watch-glass of considerable 

 concavity, but they will all succeed more or less perfectly by using a piece of perfectly flat glass, or 

 even by employing the convex instead of the concave surface of the watch-glass, provided we take 

 care that the surface of the film on the wine-glass does not project in any part above its rim. 



VOL. XXV. P^RT I. 2 F 



