^ CHAPTER IV. 



OF THE EQUILIBRIUM OF FLUIDS, 



§ 17. [Introduction]. Generxd equations of this equili- 

 hrium. Application to the equilibrium of a homogeneous 

 fluid, of which the surface is at liberty, and which covers a 

 solid nucleus of any figure, P. 47. 



[310. Definition. " 367/' A fluid is a 

 collection of particles considered as infinitely 

 small spheres, moving freely on each other 

 without friction. 



311. Theorem. " 368.'^ The surface of 

 a gravitating fluid, at rest, is horizontal. 



If the surface were in the least inclined to the horizon, 

 the particles found in it could not remain in equilibrium, 

 but would descend, in virtue of -their power of perfect free- 

 dom of motion, until the level were restored. But it is 

 more satisfactory to consider the immediate action of the 

 particles concerned: and we may suppose two minute 

 straight tubes, differently inclined to the horizon, and joined 

 at the bottom by a curved portion, to be filled with eva- 

 nescent spherules: then the relative 

 force of gravity is inversely as the 

 length, when the height is the same 



