[ 54 ] 



accelerates the ifTu'ing plate, is the prefTure of the ambient water, 

 which furrounds the cylinder immediately over the aperture ; 

 and this lateral preffure being communicated to the upper furface 

 of the plate, muft be as much cncreafed by the velocity of the 

 fuperior defcending plate, as it is diminifhed by that of the 

 inferior ifluing plate, fo as to remain conftantly of the fame 

 magnitude. 



On this principle it can be eafily demonftrated, that the 

 velocity with which water fpouts from an aperture in the 

 bottom or fide of a veflel, is equal to that which a heavy body 

 would acquire in falling through the height of the fluid above 

 the orifice. 



This uemonftration, however, as Mr. Atwood obferves, is true 

 only on hypothefis that the water fufFers no refifhance, but iflvies in 

 a cylindrical or p ifmatlc form correfponding to the hole. But, in 

 fadl, the velocity of the water according to theory will be dimi- 

 nlflied by the fridion of the particles againft the edges of the 

 orifice ; from their mutual attradlion, by which the ifluing particles 

 are retarded by thofe which are ftill in the veflel, and have not 

 acquired the velocity of thofe which precede them ; but prin- 

 cipally from the obliquity of their motions. 



For, as Chev. Cu Euat obferves, when water iflucs from an 

 orifice, the particles will flow from all fides, towa'ds the orifice, 



with 



