( i8 ) 
Steam is made toprefs immediately on th'e Water) that 
Steam will drive away Air, and that in Proportion 
to its Heat ; chough in the open Air it floats and 
riles in it like Sinoak. 
Now if the Particles of Water turn’d into Steam 
or Vapour repel each other ftrongly, and repel Air 
more than they repel each other ; Aggregates of 
fuch Particles made up of Vapour and Vacuity rhay 
rile in Air of different Denfities, according to their 
own Denfity dependant on their Degree of Heat, 
without having Recourle to imaginary Bubbles 
form’d in a Manner only luppoled, and not proved, 
as we have already Ihewn. I own indeed^ that if 
the watry Particles had no refellent Force^ they 
muji frecifitate in the fame Manner that F)uft 
will do after it has been raifed uf ; but we have 
too 7nany Obfervations and Experiments to leave 
any ‘Doubt of the Exijlence of the repellent Force 
above-mentioned. Neither can 1 Jhew by any Ex^ 
periment^ how big the Moleculae of Vapour muft be 
which exclude Air from their htterfices, and whe- 
ther thofe Moleculse do vary in ^Proportion to the 
Degree of Heat by an Increafe of repellent •Force 
in each watry Particle^ or by a farther Divifon 
of the Particles into other Particles fill lefs ; 
but in general we may reafonably affirm^ that the 
Rarity of the Vapour is proportionable to the 
Degree of its Heat, as it happens in other Fluids 
( See Phil. Tranfadf. Numb. xjo . ) and that, though 
the different Degrees of the Air*s Rarefabf ion are 
alfo proportionable to the Heat ; the fame Degree 
of Heat rarefies Vapour much more than Air. 
Now to lliew, that what has been Paid will ac- 
count for the Rife of Vapours and Formation of 
Clouds, 
