O.N <:OHESI0N-. 6io 



the elevatioi^ woukl he a whole inch; and if the distance were smaller than 

 this, ,tl>e. eleMatioQ would he greater in the same proportion ; so that when two 

 plates are placed in such a manner as to touch each other at one of their 

 upright edges, the outline of the water raised between them assumes the form 

 of a hyperbola. (Plate XXXIX. Fig. 535.) 



The weight S'upportcd by the cohesion of the water in a tube may be de- 

 termin-e<l.,in a similar manner, from the extent of the circumference ; the height 

 being an inch in a, tul>e, one twenty fifth of an inch in diameter, or as much 

 greater as the diameter of the tube is smaller: and iii a tube wetted with 

 mercmy the height would be half as ;great. It is obvious that if the Ipwer 

 part of the tube be either contracted or dilated, the height of the fluid will 

 remain unaltered, while its weight may be varied without limit; for the 

 hydrostatical pressure on the surface isthe same, in both these cases, as if .the 

 diameter of the tube were equal throughout its length. (Plate XXXIX. 

 Fig. 536.) 



The attractive force of glass, to misjcury is less than half as great as the 

 mutual attraction of the particles of mercury, and the surface of mercury in 

 a dense glass vessel becomes, therefore, convex and depressed ; the angle of 

 contact being about 140°, and the depression one 17th of an inch. Between 

 two .plates of glass, the depression of mercury is an inch when their distance 

 is ..j4t» and in a tube, when its diameter is-g^ of an inch. (Plate XXXIX. 

 Fig. 537, 538.) 



A liquid may also adhere to a horizontal surface which is gradually raised 

 from it, until the hydrostatical pressure becomes sufficient to overpower the 

 cohesion of its superficial parts; the internal part of the fluid being usually 

 raised, not immediately by the force of cohesion, but by the pressure of the 

 atmosphere. The solid bears the whole weight of the liquid which is elevated 

 above the surface; and when the surface is perfectly wetted, this weight is 

 equal, at the moment of separation, to the hydrostatical pressure, or rather 

 suction, corresponding to the height ; but in other cases the weight may be 

 somewhat greater than the hydrostatical pressure on the surface of the 

 solid, on account of the elevation which surrounds the body, and which 

 is not compensated by the excavation immediately under it. A surface thus 



