Experiments upon Heat* 29^ 
fmall, yet the difference of the times taken up by the firft 
twenty or thirty degrees from the boiling point is very re- 
markable, and ihows with how much greater facility heat 
paffes in moift air than in dry air. Even the flownefs with 
which the mercury in the thermometer N° 4. defcended in 
this experiment from the 30th to the 2cth, and from the 20th 
to the 10th degree, I attribute in fome meafure to the great 
conducting power of the moift air with which it was fur- 
rounded ; for the cylinder containing the thermometer and the 
moift air, being not wholly fubmerged in the freezing water, 
that part of it which remained out of the water was neceffarily 
furrounded by the air of the atmofphere ; which being much 
warmer than the water, communicated of its heat to the glafs ; 
which, paffing from thence into the contained moift air as 
foon as that air became colder than the external air, was, 
through that medium, communicated to the bulb of the in- 
clofed thermometer, which prevented its cooling fo faft as it 
would otherwife have done. But when the weather becomes 
cold, 1 propofe to repeat this experiment with variations, in 
fuch a manner as to put the matter beyond all doubt. In the 
mean time I cannot help obferving, with what infinite wifdom 
and goodnefs Divine Providence appears to have guarded us 
againft the evil effeCts of exceffive heat and cold in the atmo- 
fphere y for if it were poffible for the air to be equally damp 
during the fevere cold of the winter months as it fometimes is 
in fummer, its conducting power, and confequently its apparent 
coldnefs, when applied to our bodies, would be fo much in- 
creafed, by fuch an additional degree of moifture, that it 
would become quite intolerable ; but, happily for us, its 
power to hold water in folution is diminifhed, and with it its 
power to rob us of our animal heat, in proportion as its 
Vol. LXXVI. R r coldnefs 
