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Observations on n the Theory v Rain. 
Tey ‘one ‘wust have noticed an abxiots 
connection between heat and the vapour in 
the atmosphere. Heat promotes evaporation, 
and contributes to retain the vapour when in 
the atmosphere, and cold precipitates or con- 
denses the vapour. But.these facts do not 
explain the phenomenon of rdin, which is as 
frequently attended with an increase as with 
a diminution of the temperature of the at- 
mosphere. 
The late Dr. Hutton, of Edinborgh,. ‘was, 
1 conceive, the first person who published a 
correct notion of the cause of rain. (See 
Edin. Trans. Vol. 1 and 2, and Hutton’s 
Dissertations, &c). . Without deciding whe- . 
ther vapour be simply expanded by heat, and 
_ diffused through the atmosphere, or chemi-.. 
cally combined with it, he maintained from 
the phenomena, that the quantity of vapour 
capable of entering into the air, increases in 
a greater ratio than the temperature; and 
hence he fairly infers, that whenever two vo- 
lumes of air of different temperatures, are 
mixed together, each being previously satu- 
rated with vapour, a precipitation of a por- 
tion of vapour must ensue, in consequence 
