[ 2+6 ] 
do this to a very great degree, I apprehend none of 
thofe objedlions will take place againd us, with which 
Mr. Eeles has fo fenfibly confuted the former received 
theories on this fubjedt. 
If we are afked, how clouds come to be fupported 
in the abfence of the fun ? it mud; be remembered, 
that large mafi'es of vapour mud; for a condderable 
time retain much of the heat they have acquired in 
the day ; at the fame time reflecting, how fmall a 
quantity of heat was necedary to raife them ; and 
that doubtlefs even a lefs will be fufficient to fupport 
them, as from the diminiflied preflure of the atmo- 
fphere at a given height, a lcfs power may be able to 
continue them in their prefent date of rarefaction ; 
and, ladly, that clouds of particular drapes will be 
fudained or elevated by the motion they acquire from 
winds. 
I ffiould here have concluded this paper, perhaps 
already too long j but upon revidng it, I dnd, where 
the affinity of fome bodies with heat is mentioned, 
that the deductions made from thence are not diffi- 
dently explained to be intelligible. Fird then, If 
the power of expanfion of any two bodies, by heat, 
be in a greater proportion than their fpecidc gravities, 
then will there be a certain degree of heat, in which 
their fpecidc gravities will be equal j and another, in 
which the gravity of that, which was lighter when 
cold, will exceed the gravity of that, which was 
heavier when cold. Hence zinc and bifmuth alter 
their fpecidc gravities in fudon ; fome urine, and 
many folutions of folids, grow turbid as they cool ; 
others alter their colours. Secondly, If (the power 
of expanfion by heat being equal) the power of re- 
