the Annual Evaporation at Liverpool, Sec. 257 
From this experiment it appears, that air is a chemi- 
cal folvent of water, and as fuch is undoubtedly to be 
confidered as one caufe of the evaporation of water. 
Heat is another caufe of evaporation, and when raifed 
to a fufficient degree may produce this effect with- 
out the intervention of air, and the evaporation confe- 
quently go on copioufly in an exhaufted receiver, agree- 
ably to the experiments of the ingenious Dr. irving^. 
The following obfervations are added as a farther il- 
luftration of this fubjed. W ater may exift in air in three 
different ftates. 1. In a ftate of perfect folution. 2. In 
a ftate of beginning precipitation. Or, 3. Completely 
precipitated, and falling in drops of rain. 
In the firft inftance, where the water is in a ftate of 
perfed folution, the air is clear, dry, heavy, and its 
powers of folution ftill adive, though it already contains a 
confiderable proportion of water. In the fecond, the air 
becomes moift, foggy, its powers of folution are dimi- 
nifhed, and it becomes lighter in proportion as its water 
is depofited. It is a Angular and well-attefted fad, that it 
never rains in the kingdom of Peru ; but that during part 
of the year the atmofphere is conftantly obfcured with 
(i) Phipps’s Voyage to the North Pole, p, 21 1. 
Vol. LXVII. L 1 vapours, 
