the Variation of Local Heat. — 43% 
from below 30° they feldom rofe to 40°, the local variation im 
the day-time nearly ceafed, or was found in very fmall degrees 
inclining fometimes one way, fometimes the other. 
That the clearnefs of the tky fhould contribute to the cool- 
nefs of the air in the night, is not at all furprifing; but that, 
whenever the {ky becomes clear, the cold fhould feem to arife from 
the earth, and be found in the greateft degree, as long as itcon- 
tinues clear, in the loweft fituation, feemsa little extraordinary : 
this, however, appeared to be the cafe, both in the warmer as well » 
as in the colder weather, during the whole time thefe obfervations 
were taken, and remarkably fo on the following days. On the 
firft of January the weatner was cold, the {ky cloudy, the glafies 
in the night were at 20°, and in the day at 34°: the wind 
which had been at S.E. the day before, changed in the evening 
to S. and brought on a thaw. On the fecond of January 
clouds and mifty rain darkened the fky all day; the wind 
blew brifkly atS.W.; the glaffes in the night were at 32°%, in 
the day at 40°. On the third of January the clouds and rain 
continued, the weather growing ftill warmer; wind at S.W. 
by S.; the glaffes in the night were at 36°, in the day at 45°. 
‘Thefe three days. the weather gradually became warmer ; and, 
while the fky remained darkened by clouds, all the glafles in 
their feveral flations nearly agreed with each other. About 
noon, on the third of January, the fky becoming clear, the 
air grew cooler; and going into my garden, about eight o’clock 
in the evening, I perceived the furface of the ground, which 
had been wet by the rain in the forenoon, began to be frozen. 
Looking immediately at the thermometer, I faw the mercury at 
33°23 and obferving a piece of wet linen hanging near the 
—— 
a 
glafs, not five feet from the ground, I took it into my hand, 
and found it not in the leaft frozen; by which it appeared, 
that 
