[ 492 ] 
evaporation. The pure water never came near the boil- 
ing point, blit continued ftationary above an hour at a 
much lower degree; a fmall quantity of oil was then 
dropped into it, as had before been done to that with the 
wax; in confequence of which, the v/ater in both the 
veffels came at length to boil very brifkly. A faturated 
folution of fait in water put into the room, was found to 
heat more quickly, and to an higher degree, than pure wa- 
ter, probably becaufe it evaporated lefs ; but it could not 
be brought to boil till oil was added, by means of which 
it came toward evening into brifk ebullition, and confe- 
quently had acquired an heat of 230°. Some rectified fpi- 
ritof wine in a bottle flightly corked, which had been im- 
merfed into this folution of fait whilft cold, began to boil 
in about two hours, and foon afterwards was totally eva- 
porated. Perhaps no experiments hitherto made fur-, 
nifh more remarkable inifances of the cooling elfe6l of 
evaporation than thefe lalf fadls ; a power which appears 
to be much greater than hath commonly been fufpe6ted. 
The evaporation itfelf, however, was more conliderable 
in our experiments than it can be in almoft any other lltu- 
iiation, becaufe the air applied to the evaporating furface 
was uncommonly hot, and at the fame time not more 
charged with moifture than in its ordinary ftate. A pow- 
erful afliftant evaporation muft undoubtedly prove, in 
keeping the living body properly cool, when expofed to 
great heats ; but it can a6t only in a grofs way, and by no 
means in fuch a nice proportion to the momentary exi*» 
gencies of the animal as would be requihte for the exacfl: 
prefervation of its temperature : that other provilion of 
nature 
