REPORT ON CAPILLARY ATTRACTION. 289 



inents of Gay-Lussac cited by Laplace for the same purpose. 

 The heights of the disc above the horizontal level of the fluid, at 

 the instants when the Meights of the elevated columns are at a 

 maximum, are determined at the same time by the theory, but 

 these were not measured in the experiments. 



Besides the usual problems in the capillary theory, M. Pois- 

 son has solved two others, not previously attempted, one relat- 

 ing to the form of fluid poured upon another fluid of greater 

 specific gravity ; the other relative to the adhesion of the base of 

 a capillary solid cylinder to a fluid from which it is raised with 

 its axis vertical. This question is similar to that of the adhesion 

 of a disc, but requires to be treated by a different analytical 

 process. 



The concluding chapter of the treatise contains notes and ad- 

 ditions, in which some points of the theory are further developed, 

 and new experiments compared. One section is devoted to a 

 full exposition of the author's views respecting " the interior 

 constitution of bodies, particularly of fluids, and the nature of 

 molecular forces;" another treats of "the general equations 

 of the equilibrium of fluids." It results from the complete 

 equation of the free surface of a fluid, obtained on the hypothesis 

 of disjoined molecules, held in equilibrium by attractive and re- 

 pulsive forces, that the resultant of the extraneous forces acting 

 on the fluid, is not exactly perpendicular to its surface, uijless it 

 be perfectly plane. The views advanced in these sections are for 

 the most part those we have had occasion to adduce in speaking 

 of the Menioir on the Equilibrium of Fluids. Some of the 

 other subjects of this chapter ought not to be passed over with- 

 out notice. 



The depression of mercury in the barometer cannot be con- 

 veniently calculated by the theory except the ratio of the radius 

 of the tube to the constant a be either small or great. In 

 other cases it is necessary to recur to the method of quadratures. 

 A table of depressions calculated in this way by M. Bouvard, 

 and inserted in the Connaissance des Tenis for 1812, is cited by 

 M. Poisson, and placed in comparison with a like table from 

 Lord Charles Cavendish's experiments, with which it is found 

 to agree as nearly as could be expected from the nature of the 

 observations. It is desirable, he remarks, that the calculations 

 should be repeated with the more exact values of the constant a 

 and the angle of contact determined by himself. 



Casbois, Professor of Physic at Metz, pointed out a method 

 of constructing barometers with plane or even concave surfaces, 

 having observed that by boiling mercury the convexity of its 

 capillary surface is diminished, and by continuing the "boiling 



1834. u 



