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XL VI. Experimental and Theoretical Researches into the Figures of 

 Equilibrium of a Liquid Mass without Weight. — Ninth, Tenth, 

 Eleventh and last Series. By Professor Plateau*. 



Ninth Series. — Secondary causes which affect the persistence of 

 liquid films. — Film- figures of great permanence. — Historical 

 survey of observations relating to liquid films. — Capillary ascen- 

 sion to great heights in tubes of large diameter. — Constitution 

 of a current of gas passing through a liquid. 



IN the last Series I endeavoured to show that, although cohe- 

 sion and internal viscosity play the chief part in the deve- 

 lopment of all liquid films, these causes are not sufficient when 

 we have to do with films which are both large and durable, like 

 those formed by soap- water, and that in such cases other and 

 entirely distinct conditions must concur — namely, great superfi- 

 cial viscosity and a comparatively weak tension. But when such 

 films have been actually produced, their duration is affected by a 

 certain number of secondary causes, which I pass in review in this 

 Series. 



The first of these causes consists in the small disturbances 

 communicated to the films by the movement of the surrounding 

 air and by the vibrations conducted by the ground. These small 

 disturbances no doubt act by overcoming the inertia and fric- 

 tional resistance of the molecules ; they thus hasten the descent 

 of the molecules, and consequently the attenuation of the film ; 

 and besides this, they cause the breakage of the parts that are 

 very thin. It is partly on this account that the films generally 

 last longer in closed vessels; for then one of the causes of disturb- 

 ance (namely the movement of the air) is got rid of. 



A second cause is evaporation (when the liquid constituting 

 the film is susceptible of it) . Prom the experiments described 

 in the last Series, I conclude that in the case of liquids which do 

 not admit of being blown into bubbles, evaporation is favourable 

 rather than hurtful to the permanence of the films. I try to 

 account for this singular fact, and I show that the contrary is true 

 in regard to liquids that are easily blown out into bubbles ; that 

 is to say, in the case of these the persistence of the films is dimi- 

 nished by evaporation. Por instance, hemispherical bubbles 

 about a centimetre in diameter, formed at the surface of a solu- 

 tion of Marseilles soap, last for several hours in an atmosphere 



* Translated from the Author's abstract, in the Annates de Chimie et de 

 Physique, S. 4. vol. xix. p. 369 (March 1870), of the complete memoir 

 published in the Memoires de VAcademie de Bruxelles, vol. xxxvii. Por 

 abstracts of the preceding Series see Taylor's Scientific Memoirs, vol. iv. 

 p. 16, vol. v. p. 584 ; and Phil. Mag. (S. 4.) vol. xiv. p. 1, vol. xvi. p. 23, 

 vol. xxii. p. 286, vol. xxiv. p. 128, vol. xxxiii. p. 39, and vol. xxxviii. p. 445, 



