Chap. 2.] Particles in Equilibrium. 409 



brium with each other, whether they are contained 

 in one vefiel or many, provided they communicate 

 with each other j and their furfaces alib are always in a 

 plane parallel to the horizon. 



This is a confequence of the principle which has 

 been before eftablimed : for, fince the particle h 

 (fig. 3.) would be raifed from the bafe towards the 

 top, unlefs a column equal to the column / k, prefTed 

 upon it to retain it in its place ; it follows that to be in 

 equilibrium, the upper extremities of the two columns 

 mould be in the fame horizontal plane, or in points 

 equally diftant from the center of the earth j which 

 points, however, cannot be found by a right line ; for 

 in the diftance of a thoufand fathoms there is about 

 one foot difference in the perpendicular height. From 

 this property of fluids it follows, that water conducted 

 by pipes placed in the earth, will remount as high as 

 the place whence it flowed, whatever the depth under 

 ground through which it may have been conducted 

 by the pipes. It is cuftomary to allow half an inch of 

 inclination in the length of fix feet, to counteract the 

 refinance produced by friction ; but it is clear from 

 what has been faid, that this is not abfolutely necef- 

 fary, for however long the pafTage might be, the water 

 would fti!l afcend as high as the place whence it 

 came, but it would require a little longer time to 

 accomplifh the afcent. We are enabled, upon this 

 principle, to account for the fprings which are fome- 

 times found on the tops of mountains. Such waters flow 

 from mountains dill more elevated (whether they are 

 far or nenr) by fubterraneous canals. It follows from 

 this principle, that if there are many refervoirs which 

 communicate together, it is neceflary only to fee one 

 of them to know the height of the water in the others ; 



for 



