[ ] 
XXIII. A Dijfertation on the Nature of Eva- 
poration and fever al Fhcenomena of Air^ 
Water ^ and boiling Liquors : In a Let- 
ter to the Rev, Charles Dodgfon, Z). D, 
F, R, S, from the Rev, Hugh Hamilton, 
D. D, F. R. S, Profejfor of Natia al 
Philofophy in the Univerfety ^Dublin. 
Dear Sir ; 
Read May 1 6 , 'W' Here fend you, according to promife, 
X thoughts on the nature of eva- 
poration, the afccnt of watery vapours, and fome 
other phaenomena of the atmofphere, in explaining 
which I have employed a principle that, as far as I 
can find, is different from what has been hitherto ufed 
on this occafion, hoping thereby to avoid thofe objec- 
ions, which fome late writers have made to the former 
accounts, that have been given us of thefe phaenome- 
na. For in all the accounts I have met with, fire or 
heat, and rarefa(ftion, by which watery vapours are 
fuppofed to become fpecifically lighter than air, are 
made to be the principal, if not, the only caufes of 
their afcent into the atmofphere. Dodlor Nieuwentyt, 
and fome others, fuppofed that the particles of fire, by 
adhering to thofe of water, make up molecula?, or 
fmall bodies, fpecifically lighter than air. And Dr. 
Halley thought, that by the adtion of heat, the par- 
ticles of water are formed into hollow fpherules filled 
with a finer air highly rarefied, fo as to become fpc- 
cifically lighter than the external air. This lafi: 
was 
