Chap. l~\ Fluids prefs equally in all Directions. 407 



necefiary in this cafe is, to fupport the weight of the 

 column of water diredlly above the pifton, becaufc 

 this column can move independently of the remainder; 

 but if the whole mafs of water was converted into ice, 

 then the mafs ceafmg to be a liquid, and all its parts 

 adhering together, to raife up the pifton it would be 

 neceffary to fupport the weight of the whole mafs, 



2.dly, Fluids prefs equally in all directions. 



In other words, they not only prefs from the top to 

 the bottom like other bodies, but they alfo prefs, ac- 

 cording to their weight, upon all bodies that oppofe 

 them in a lateral direction, and even from the bottom 

 to the top. Hence, if a calk is filled with liquid oil, 

 the oil will run out if an aperture is made in the fide, 

 but when it is congealed it will not run out on account 

 of its having become a folid body, for folid bodies 

 prefs only from their vertex to their bafe, and not 

 laterally. 



To underftand properly this lateral prefTure of 

 fluids, and alfo that which they exert from their bafe 

 towards their vertex, it is neceffary to confider them 

 as a mafs of fmall globules depofited in a veffelj and 

 to remember that thefe minute globules are not ar- 

 ranged regularly as upon a cord, but that very fre- 

 quently one column exercifes its prefTure between two 

 others, and has a propenfity to difplace them, as may 

 be feen in plate V. (fig. 3.) where the perpendicular 

 preflure which is made oppofite to the point d, is 

 directed by the lateral columns towards the fides, ef, 

 of the veflel, in fuch a manner, that if the veifel was 

 open in thofe places the liquid would flow out, on 

 account of the great mobility of its parts. Jc is by 

 the fame mode of reafoning that the prefTuit of fluids, 

 from their bafe towards their vertex, is accounted 

 for: for example, when the column ^/(%- 3-) to* 

 D d 4 a ten- 



