“Yours, &c.”

* * * * *

Philadelphia June 27th, 1796.

DEAR FRIEND,

“In some part of the middle states, a climate similar to that of England may easily be found.”

Inform our old acquaintance H——­, that if he emigrates to America on the strength of this assertion of Cooper, (on which, you tell me he so much depends), he will, on his arrival, find himself egregiously mistaken.  The sameness of latitude does not always indicate similarity of temperature:  there are many other causes, which contribute to make this a very different climate from that of Great Britain.

The middle states of North America are hotter and colder at intervals, not only than England, but than any part of the Old Continent, under the same parallel of latitude.

Jefferson says, “Our changes from heat to cold are sudden and great.  The mercury in Fahrenheit’s thermometer has been known to descend from 92 to 47, in thirteen hours.”

And I copied the following from a New York paper:—­

“Wednesday, the 14th of May, the mercury in Fahrenheit rose to 91 degrees, The Saturday night following, there was a severe frost.  The next Tuesday and Wednesday, the mercury rose to 85 degrees; from the 20th to the 26th, it has been nearly stationary, varying only from 60 to 64.:  Easterly wind, and rain.”

These violent transitions from heat to cold, are produced by means of the N.W. wind, which in this country is the most keen and severe of any that is to be met with on the face of the globe.  It is much the most prevalent wind we have, and seldom fails to blow four or five days with great uniformity.  This wind is perfectly dry, and so uncommonly penetrating, that I am convinced it would destroy all the plagues of Egypt in a very short time.  You may recollect, I informed you of the astonishing effect of this powerful agent in stopping the yellow fever in a few hours, last year, at Baltimore.

Neither the prevalence, nor uncommon severity of this wind has been properly accounted for; but we may now expect something more satisfactory on this subject, from the celebrated Volney; who is here endeavouring to investigate the causes of this, and other phenomena, relative to the winds of this continent.

Our heats in summer are sometimes very great; but the excess seldom exceeds three days; the rotation is generally as follows; the first day perhaps the mercury rises to 86, the next to 90, and the 3rd to 97, and sometimes, though very rarely, to upward of 100 then comes a thunder gust, which restores the air to it’s usual summer temperature, till another three days period of excessive heat begins and ends in the same manner, at intervals, through the season.  The succession of the degree of cold in winter is exactly the same:  I never knew the excess exceed three days; not that we have then a thaw but that the weather is moderate, till another excess commences of three days.