Revd. Mr. Stiles

Dear Sir,

Philadelphia May 29 1763

I have now before me your Favours of Jany. 31.
& March 1. the Receipt of which I ought sooner to have
acknowledged. Your kind Congratulations on my Arrival
& the Advancement of my Son, are extremely obliging.

I think I have read somewhere that Fahrenheit's
0 was what he understood to be the greatest cold of Sibe-
ria, Greenland or any inhabited Country. So he graduated
from thence upwards, & found the Degree of Cold in Water
just freezing happen'd to be the 32d on his Scale. Had
the Divisions of his first Scale been larger or smaller,
the freezing Point would have fallen on a different Degree,
and that would have been a Matter of little Importance;
but it was of some use to make all his subsequent Scales
alike.

I doubt with you, that Observations have not been
made with sufficient Accuracy, to ascertain the Truth of
the Common Opinion, that the Winters in America are grown
milder; and yet I cannot but think that in time they may
be so. Snow lying on the Earth must contribute to cool
& keep cold the Wind blowing over it. When a Country is
clear'd of Woods, the Sun acts more strongly on the Face
of the Earth. It warms the Earth more before Snows fall,
and small Snows may often be soon melted by that Warmth.
It melts great Snows sooner than they could be melted if
they were shaded by the Trees. And when the Snows are
gone, the Air moving over the Earth is not so much chill-
ed; &c. But whether enough of the Country is yet cleared
to produce any sensible Effect, may yet be a Question.
And I think it would require a regular and steady Course
of Observations on a Number of Winters in the different
Parts of the Country you mention, to obtain full Satis-
faction on the Point.

While I was at Cambridge in England, I assisted
at an Experiment made by Dr. Hadley, then Professor of
Chemistry there, at my Request, to find what Degree of
Cold might be produced by Evaporation. The Thermometer
was plung'd into a Vessel of that highly rectified Spirit
the Vitriolic Ether; which as it had long stood in the
Room with the Thermometer, & consequently was of the same
Temperament, did not in the least alter the Height of the
Mercury; but the Moment the Thermometer was taken out,