404 Particles of Fluids aft independently [Book Vlt. 



I. In purfuing the firft object of this inquiry, it may 

 be eftablifhed as an axiom : 



i ft, That the parts of the fame fluid aft with re- 

 fpect to their weight or prefiiire, independently of each 

 other. 



This property arifes from their having fcarcely any 

 cohcfion among themfelves. It is otherwife with 

 folid bodies; their feveral parts adhering together, 

 they prefs in one common mafs; hence the falling of 

 folid bodies is productive of a different effect from 

 that of liquids. We dread the falling of a pound of 

 ice upon our heads, while we are much more indif- 

 ferent concerning that of a pound of water. The 

 latter, in its defcent, is divided by the refinance of the 

 air, by which fome of its parts are retarded more than 

 others i and the fwiftnefs of the whole mafs is ftill 

 more retarded by this divifion than it otherwHe would 

 be; for by being thus divided it acquires a larger fur- 

 face, which abates its effect. On the contrary, a folid 

 body falls upon a fmall fpace, which receives its whole 

 force. Hence it follows, that angular bodies falling 

 upon any part of the human frame are more dangerous 

 than flat or plane ones of the fame weight, and de- 

 fcending from the fame height. 



It follows from this principle, that if an aperture is 

 made at the bottom of a veffel full of any fluid, in order 

 to prevent the flowing out of the liquor, it is only 

 neceflfary to counteract the weight of that column of 

 fluid which has the aperture for its bafe, and that to 

 counteract thr.t weight it is the fame whether the vcffel 

 is full of liquor or whether it contains only a column, 

 the bafe of which fliall be equal to the aperture at the 

 bottom. 



Let the cylindrical vefiel of glafs A B (plate V. 

 fig. i.) have a hole in the bottom at C, furnifhed 



with 



