[ 26 5 ] 
iuppofed to a£t upon the fluids in the columns EF, 
CD, being equal, and the heights of the columns 
being, reciprocally, as the denfities of the fluids, the 
compreflive forces of the columns will be equal. 
B-ut GH is the perpendicular height of a column of 
an inelaftic fluid, of the fame denfity with the air at A, 
the level of the fea, which, if the whole were 
urged with an accelerative force equal to that of 
gravity at A, would fuftain the mercurial column 
KL (by fe<ft. 4 ). Suppofe MN equal to the per- 
pendicular height of a column of an inelaflic fluid, of 
the fame denfity with the air at B, which, if the 
whole were urged with an accelerative force, every 
where equal to that of gravity at A, would fuftain 
the mercurial column CD. It is evident that EF is 
to MN as the accelerative force of gravity at A to the 
accelerative force of gravity at B; for EF and 
MN are columns of fluids, of the fame denfity, 
exerting equal compreflive forces. Therefore, 
the heights of the columns muft be reciprocally 
as the accelerative forces by which the compreflive 
force is produced. But gravity at A is to gravity at B 
as the fquare of TB to the fquare of T A. There- 
fore, EF : MN = TB 1 : T A\ Again, GH and 
MN are columns of fluids of different denfities, 
afted upon by equal accelerative forces j therefore, 
the compreflive forces which they exert, that is, 
which they fuftain, will be as their heights and the 
denfities of the fluids jointly ; that is, if P, Q^be as 
the compreflive forces of thofe fluids, and R, S as 
their denfities, then PiQ^GHxRiMNxS. 
But the compreflive forces fuftained by thefe co- 
lumns are the preffurea of the air at A and B; alfo 
Vol, LX1V. M m the 
