EQUILIBRIUM IN LIQUID FILMS. 



513 



If, when both ends of the cone are open, we take up, by immersion, a film 

 upon the larger side BC, it will rise to the top AB, gradually contracting itself, 

 and remaining at AB. If there happens to be a drop of fluid retained at F, its 

 weight will prevent the film from rising, but if we run off the drop F at one side, 

 the film will immediately rise to AB. The height of the glass cone ABDC is 1^ 

 inch, its breadth AB 1*1 inch, CD 1*7, and its angle 13°. 



When the bubble, placed at AB, is not much larger in diameter than AB, it 

 will descend with the film, leaving another film at AB. Upon breaking AB the 

 film CD will rise to AB. 



If we employ a glass funnel ABCD of the same size and form as the preceding 

 figure, and close it at E, the film which it takes up at CD will be 

 convex, but if we open it at E it will take up a plane film which will 

 ascend, breaking at AB, and leaving a film there. If we now take 

 up another film by dipping CD the eighth or tenth of an inch in 

 the solution, the compression of the air will drive the film AB 

 out of the tube at E. If we replace AB by making a film at CD 

 ascend to AB, and dip CD into the solution so slightly as not to 

 compress the air and drive out AB, we shall obtain a convex film 

 at CD, which will remain there. By breaking AB with a strip 

 of blotting paper, the convex film CD, with its coloured rings, 

 will become plane and rise to AB, the rings formed on the 

 convex film being changed to bands when the film has become 

 plane. 



I was anxious to ascertain what was the largest angle of a cone at which it 

 would raise the film at its mouth to the aperture at its apex. Upon using cones 

 made of thin card-board, I found that the film rose rapidly when the angle was 

 upwards of 90°, but when it reached 120° or 130°, a film could not be lifted from 

 the soap solution. It was probable, however, that the cone did lift the film and 

 carry it to its apex, as there was always the appearance of fluid at that place. 

 By placing the solution in a vessel shallower than the height of the cone, and ob- 

 serving that there was no film at the apex previous to lifting it out of the fluid, I 

 always found that a film was at the apex, and consequently that a film had been 

 formed at the mouth of the cone, but rushed so rapidly upwards that it could not 

 be seen there. 



VOL. XXIV. PART III. 



Qz 



