[ H7 ] 
particles of A, and to vary, with the diftance, as any 
power or function of the diftance whatever. Ima- 
gine an elaftic force, varying according to the fame 
power or function of the diftance, exerted between 
every two particles of B. Thus the fluids are 
Jimilarly elaftic ; but they are to be fuppofed un- 
equally foj that is, the force exerted between two 
particles of the one, at any given diftance, is to be 
greater than the force between two particles of the 
other, at the fame diftance. Now, if the law by 
which the elaftic force varies, at different diftances, 
in one of thefe fluids, as A, be fuch, that the den- 
fities of A, under different compreflions, are to 
each other, as the compreffive forces j the denfities 
of B, compared with each other, under different com- 
preflions, will likewife be as the compreffive forces. 
But the proportion of the compreffive forces will 
not fubfift between the denfities of the two different 
fluids. The denfities will not be the fame, when 
the compreffive forces upon A and B are equal ; 
nor will they be as the compreffive forces, when 
thofe forces are unequal. The denfities will be as 
the compreffive forces direftly, and the abfolute 
elafticities inverfely ; that is, the compreffive forces 
will be as the denfities and abfolute elafticities jointly, 
which is eafily demonftrated. 
The compreffive force upon any fluid, is to be 
eftimated by the quantity of the preffure, adling 
perpendicularly upon a given furface, or plane flec- 
tion of it. Whatever degree of preffure afls upon 
the mals of an elaftic fluid, its particles will approach 
or recede, till the diftances of every two adjacent 
particles are fuch, that the whole elaftic force, 
exerted perpendicularly againft every furface or plane 
fe&icn 
