[ 648 ] _ 
in this ratio ; and extended indefinitely to all 
didaticcSj they would compofe a fluid extremely 
different from common air. If the repulfion of the 
particles was inverfely as the diflance, but extended 
only to a given very fmall diflance from their centers, 
they would compofe a fluid of the fame kind as air, 
in rcfpedl: of elaflicity, except that its denfity would 
not be in proportion to its compreflion : if the diflance 
to ‘which the repulfion extends, though very fmall, is 
yet many times greater than the diflance of the 
particles from each other, it might be fliewn, that the 
denfity of the fluid would be nearly as the fquare 
root of the compreflion. If the repulfion of the 
particles extended indefinitely, and was inverfely as 
fbme higher power of the diflance tlian the cube, the 
denfity of the fluid would be as fome power of the 
compreflion lefs than . The only law of repulfion, 
I can think of, which will agree with experiment, is 
one which ftems not very likely ; namely, that the 
particles repel each other with a force inverfely as the 
diflance ; but that, whether the denfity of the fluid is 
great or fmall, the repulfion extends only to the 
nearefl particles: or, what comes to the fame thing, 
that the diflance to which the repulfion extends, is 
very fmall, and alfo is not fixed, but varies in pro- 
portion to the diflance of the particles. 
p A R r 
