HYDROSTATICS. 



ever different their width may be, a 

 fluid poured into them will stand at the 



same level, and thus a portion of fluid, 

 however small, as B D, (Jig. 2.) will re- 



sist the pressure of a portion, however 

 large, as A C E, and balance it ; for if 

 the small did not balance the large por- 

 tion, it would be forced upwards and 

 rise above B, so as to run over the 

 mouth of the tube, and be higher than 

 the level, A B. Neither the shape nor 



the size of the two portions make any 

 difference ; the mass 1 , A E C, will be 

 supported by the mass, B D, however 

 unequal in bulk, and however unlike 

 in form, the line A E B being the level. 

 Thus, if A B, (Jig. 3.) a small upright 

 tube, CD, a large one also upright, 



E F, a slanting one, G H, a crooked 

 one, and a globular one, I K, are all 

 fixed in the vessel W P, so as to com- 

 municate with it, and by means of it, 

 with each other, water or any other 

 liquid, being poured into them, will 

 stand at the same height in them all, 

 or have the same level line, S T U V. 



From these considerations two most 

 important conclusions follow, derived 

 both from reasoning, and from innume- 

 rable facts of daily occurrence. The 

 one is, that water, though, whenuncon- 

 fined, it never can rise above its level 

 at any point, and never can move up- 

 wards, will yet, by being: confined in pipes 

 or close channels of any kind, rise to the 

 height from which it came, that is, as 

 hisrh as its source : and upon this prin- 

 ciple depend all the useful contrivances 

 for conveying water by pipes, in a way 

 far more" easy, cheap, and effectual 

 than those vast buildings, called aque- 

 ducts, by which the ancients earned 

 their supplies of water in artificial 

 livers over arches for many miles. It 



is evident that the stream must have 

 been running down all the way, and 

 consequently that a fountain could in 

 this manner never supply any place 

 at the same or nearly the same height 

 with itself. The other conclusion is 

 not less true, but far more extraordi- 

 nary, and indeed startling to our be- 

 lief, if we did not consider the reason- 

 ing upon which it is founded: it is, 

 that the pressure of the water upon 

 any object against which it comes, any 

 vessel which' contains it, or any space 

 upon which it rests, is not at all in 

 proportion to the body or bulk of the 

 water, but only to the size of the 

 surface on or against which it presses, 

 and its own height above that sur- 

 face. 



This follows immediately from the 

 foregoing explanation and reasoning. 

 For, suppose the communication be- 

 tween the two limbs of the tube, GDI, 

 is cut off at F (fig. 4.), the body of 

 water may be raised to G H in the limb 

 G K, while it remains at B in the other 

 B2 



