ADHESION OF BODIES TO FLUIDS. 173 



body therefore must compensate the vacuum it produces by 



capillary action ; or, if it raise the fluid by this action, its 



inferior specific gravity must compensate the weight of the 



fiuid raised. In the first case this action raises the body, 



which by this means may be retained on the surface, though 



specifically heavier than the fluid: in the second case it has 



a tendency to sink the body in the fluid. It is thus that a Steel floating 



very slender cylinder of steel, the contact of which with on wa,er - 



water is prevented either by a varnish, or a thin stratum of 



air surrounding it, is supported on the surface of the fluid. 



If we place thus two equal and parallel cylinders, touching Two equal 



each other, but the extremity of one passing beyond that l )ieces of thlrl 

 . . . . w ""e, partly in 



of the other, we perceive them immediately sliding by each contact, -will 



other to bring their extremities on a level. The reason of bec0I "e so 



... . . throughout 



this phenomenon is visible. The fluid is more depressed by their whole 



the capillary action of the two cylinders at that extremity of ^"g^ 1 - 

 each which is in contact with the other cylinder, than at the 

 opposite extremity. The base of the latter extremity there- 

 fore experiences greater pressure than the other base, since 

 the fluid around it is more elevated. Consequently each cy- 

 linder tends to unite with the other more and more: and as 

 the accelerating forces always carry a system of bodies, the 

 equilibrium of which is deranged, beyond the state of equi- 

 libration; the two cylinders must alternately pass each other, 

 producing an oscillation, which, diminishing incessantly, by 

 the resistance the cylinders experience, will at length be an- 

 nihilated. The cylinders, being thus arrived at a state of 

 rest, will have their extremities parallel. These oscillations 

 may be determined by analysis, and we may compare the 

 theory of capillary action on this point with experiment. 

 These comparisons are the true touchstone of theories, which Theory should 

 leave nothing to be wished, when by means of them we can experiment! 

 not only foresee all the effects that must result from given 

 circumstances, but determine their quantities with accu- 

 racy. 



If we consider the whole of the phenomena of capillary Capillary at- 

 action, and their dependance on one single principle of an traction de- 

 attraction between the molecules ot bodies decreasing in a of the mole . 

 very rapid ratio, it is impossible to call this principle in cules of bodies, 



question. This attraction is the cause of chemical affinities : which is the 



•f cause of che- 

 mical *ffinitie% 



