36 Mr. C. Tomlinson on the Motions of certain 



the surface-tension of that part of the liquid immediately below 

 the tube becomes less than on the surrounding portions, and 

 these exert on that part a traction which is made evident by the 

 apparent repulsion of the particles of powder floating on A ; or, 

 by this same force of traction, the superficial layer drags away 

 the molecules situate below the tube and thus produces a de- 

 pression. If this force be sufficiently energetic, waves are pro- 

 pagated on the surface of the liquid. When, on the contrary, 

 b is greater than a, the subjacent portion of A acquires a greater 

 surface-tension and attracts the surrounding layer, unless the 

 resistance be too great. 



10. Let A be distilled water at 20° C, when the tension a = 7S 

 milligrammes per millimetre of length; B ether; b = 1'88; 



= 0*74. When the interior diameter of the ether-tube is 



a 



less than a millimetre, the depression on the surface of the water 

 is well marked ; with a tube 2 millims. in diameter the concavity 

 is from 4 to 6 centims. wide, and the particles floating on the 

 surface are powerfully repelled towards the edge of the vessel. 

 If the ether-sponge (la) or a finger wet with ether be held 

 over the water, the effect is still more energetic, and a sys- 

 tem of waves is propagated on the surface of the water. If 

 the water be in the form of a stratum not more than 2 millims. 

 thick, the part below the sponge will fly open and leave the por- 

 tion of the bottom of the vessel thus exposed quite dry so long 

 as the vapour of ether pours down 10 . If the water be made to 

 rest on the surface of pure clean mercury, a much thicker stra- 

 tum may be used ; the ether-sponge will act at considerable dis- 

 tances, producing sensible motions in the well-defined perfectly 

 circular iris of water. That vapour of ether will act at a dis- 

 tance and produce motions on the surface of water, was pointed 

 out by B. Prevost in his controversy with Carradori, noticed in 

 my former paper 11 . Fragments of gold leaf or of tinfoil floating 

 on water became agitated as soon as a capsule of ether was 

 placed at some height over the surface. 



11. It will be understood that the above experiments cannot 

 be performed if the water be previously saturated with ether, 

 or if the water be soiled with the finger or otherwise, because in 

 such cases the surface-tension or contractile force of A becomes 



10 Draparnaud (Ann. de Chim. vol. xlvii. p. 303) noticed that a thin 

 layer of water at the bottom of a capsule flies open when touched by a drop 

 of alcohol at the end of a glass rod, leaving the bottom of the vessel un- 

 covered. The water slowly closes in again as the alcohol evaporates. The 

 bottom of the capsule should not be convex. Carradori (Mem. Soc. Ital. 

 vol. xii. p. 94) says this is an old observation, and refers to Ann. di Ch. di 

 Pavia, vols, xviii. & xix. 



11 Phil. Mag. for December 1869. 



