48 Mr. J. LeConte on the Apparent Attractions 



This class of phenomena seems to have been first explained 

 by the celebrated Mariotte about 1655; but more particularly 

 by the great geometer Monge*, who distinctly and correctly 

 referred them to the action of the surface-film of the liquid, 

 as modified by the presence of the partially immersed solid 

 bodies. In more modern times the improved theory of capil- 

 lary action of Young f and Laplace J, as modified by the re- 

 fined physico-mathematical investigations of Gauss § and of 

 Poisson||, refers all capillary phenomena not only to the reci- 

 procal attractions between the liquid and the solid, but also to 

 the existence of a tense superficial film at the free surface of 

 every liquid, which gives origin to a tensile elastic reaction 

 resulting in the development of a force tending to elevate or 

 depress the liquid according as its terminal surface adjacent 

 to the solid is concave or convex. The actual existence of 

 such an elastic contractile film at the bounding surfaces of 

 liquids is abundantly verified by numerous conclusive experi- 

 ments with films of soapy water, as well as by the whole class 

 of striking phenomena rendered prominent by the admirable 

 researches of Plateau If, and the equally satisfactory investiga- 

 tions of Dupre** and of Quincke ft- 



Even according to the more exact mathematical theories of 

 capillarity of Laplace and of Poisson, the explanation of this 

 class of phenomena is not altogether free from ambiguity. 

 Thus, in Laplace's investigation, as the pressure of the atmo- 

 sphere appears as a prominent element in producing the 

 motions of such floating bodies, the student is naturally per- 

 plexed when he is confronted by the somewhat awkward fact 

 that capillary phenomena are entirely independent of the pres- 

 sure to which the apparatus is exposed, as was long ago proved 

 by the experiments in vacuo, executed by the members of the 

 Accademia del Cimento of Florence. It is proper to add, 

 however, that a critical examination of the explanation given 

 by Laplace, as well as by Poisson J J, very clearly indicates that 



* Memoires de VAcad. des Sciences for 1787, p. 506 et seq. 



t Phil. Trans, for 1805, p. 65 et seq., on the " Cohesion of Liquids." 



X Mecanique Celeste, tome iv., " Supplement au Livre x.," " Sur l'Action 

 capillaire (1806). Also " Supplement a la Theorie de l'Action capillaire " 

 (1807). 



§ Principia Generalia Theories Figurce Fluidorum in Statu JEquilibrii : 

 Gottingen, 1830. 



|| Nouvelle Theorie de V Action capillaire : Paris, 1831. 



*jf Statique Experimentale et Theorique des Liquides. 



** Theorie Mecanique de la Chaleur, chapitre ix., u Capillarite," p. 206 

 et seq. : Paris, 1869. 



It Phil. Mag. [4] xxxviii. p. 81, and xli. pp. 245, 370, 454 ; [5] v. pp. 

 321, 415, and vii. p. 301. 



XX Laplace, Mecanique Celeste, tome iv. "Supplement au Livre x." art. 

 11, p. 41 et seq. Poisson, op. cit. supra, arts. 81-85, pp. 162-173. 



