[ 248 3 
fedlion of it, is precifelv equal to the preflure acting 
perpendicularly upon the fame furface, in an oppo- 
fite direction. And in the particular degree of den- 
fity, determined by that diftance of the adjacent 
particles, the fluid will remain, while the fame de- 
gree of preflure is continued. Imagine therefore 
the denfities of the two maflfes, A and B, to be the 
fame; then, from the fuppofed fimilarity of the fluids, 
it follows, that the number of particles, exerting their 
elaflicities upon any equal and fimilar fe&ions of A 
and B, mufl be equal ; and that the diftances of the 
correfponding particles, from each other, in the two 
mafles, mufl; be the fame: confequently the whole 
elaflicities, exerted upon equal and fimilar fedtions 
of the two mafles, will be as the abfolute elaftici- 
ties of which they are compoled. Therefore the 
compreflive forces are, in this cafe, as the abfolute 
elaflicities. Call the common denfity of the fluids 
D ; the compreflive force upon A, P ; upon B, n ; 
the abfolute elaflicities a , b, refpedlivdy. Let d 
denote fome other denfity of the mafs A, and p the 
compreflive force correfponding to that denfity. 
Now D and d are different denfities of the fame 
fluid A, under different compreflive forces P, p. 
Therefore, p : P = d: D (by hypoth.) 
But P : n — a \b. (as hath been proved.) 
Therefore, piU — dxa'.'Dxb', that is, the com- 
preflive forces upon the different fluids A and B, when 
the denfities are unequal, are as the denfities and abfo- 
lute elafliciiies jointly. Q. E. D. This demon- 
ffration is independent of any more particular hypo- 
thefis, concerning the law of the elafticity, than barely 
that it is the fame in both mafles ; and fuch, in both, 
as to make the denfities of either always proportional 
to 
