114 SIR DAVID BREWSTER ON THE MOTION, EQUILIBRIUM, 



of the lens. The curious bag shape of the film in this latter form of the experiment, 

 while thus passing from the wine-glass to the watch-glass, is shown in fig. 4. 



(5.) The lens, when obtained upon the watch-glass, may be restored to the 

 wine-glass in the form of the concave film, by merely replacing the watch-glass 

 so that the lens shall touch the edge of the wine-glass, and it may be taken up and 

 replaced several times, and that whether the complementary film has remained 

 on the wine-glass or not. 



(6.) If, when the complementary film has remained on the wine-glass after 

 removing the lens upon the watch-glass, we replace the lens so as to form the 

 concave film, we can, by lifting the watch-glass, or causing it to rotate, as in the 

 previous experiments, reproduce the original single film, which in this case consists 

 of the same film which was taken up as a lens upon the watch-glass. 



II. On the Motions and Figures of Equilibriums of Films within Single Hollow Cones. 

 In the following experiments, a glass cone of the form in the annexed diagram 

 was used — the perpendicular height of the cone being 3 inches, the diameter 

 of the base being 1 inch. The aperture at the apex can be opened 

 or closed at pleasure, by inserting a plug at MX. When this vessel 

 is dipped in the soap solution (MN being open), it gives, when 

 raised, a plane film at CD. This film (as shown in the previous 

 paper on " Liquid Films," vol. xxiv. p. 503, of the " Transactions") 

 does not remain at CD, but at once commences to ascend towards 

 A B, with a velocity increasing— -firstly, with the angle of the cone 

 itself; and, secondly, with the angle of inclination at which the 

 cone is held. Arrived at A B, where the cone ends in the cylin- 

 drical tube, the film becomes stationary. 



The motions and disposition of films within the cone may be 

 well studied, by blowing small bubbles from a quill or small tube, 

 and inserting them within the vessel. Thus, if a bubble of moderate size be 

 placed on the side of the cone near its base, it will gradually ascend till its convex ' 

 surface comes in contact with the opposite side of the cone, Avhen it will separate 

 into two plane films, the lower of which will remain stationary at AB, the upper 

 a little way up the tube. This movement of the bubble is represented in fig. 5. 



Again, having obtained a plane film, a little way up the cone, insert a small 

 bubble against the side of the cone, touching the under surface of the plane film, 

 the upper surface of the bubble will unite with the adjacent portion of the plane 

 film to form a single film, and produce the system shown in fig. 6. Insert now, on 

 the opposite side, a second bubble of the same size with the first, and we obtain 

 the system shown in fig. 7, the upper surface of each of the two hollow figures 

 thus produced being convex, the lower concave, their surface of contact being a 



