"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.
On these occasions the mercury _sometimes_ descends to 10 or 12 degrees
below 0. Rivers a mile broad are frozen over in one night, and the bay of
Chesapeak traversed in waggons and sleighs!
Though this climate, compared with that of England, is not in my opinion
on the whole so good, yet it possesses many advantages, such as the
clearness of the atmosphere, greater equality of the length of the days,
and _certainty_ of settled weather; for though the transitions are more
_violent_, they are by no means so _frequent_ as in England; where you
have the wind from every point of the compass, and experience all the
seasons of the year in twenty-four hours!
Recollect these observations on the climate of America are confined to the
_middle states_, including Virginia in this description. Those of the
north, and south, are _somewhat_ different; but I am informed
the country to the S.W. of the Allegany Mountains is _materially
different_. The distance the N.W. wind has to travel to this country,
and the opposition it meets with from those mountains, in a great measure
meliorates and destroys those penetrating qualities, which make this wind
so formidable to the Atlantic States. I have heard so many extraordinary
accounts of the South-western territory, that I have long made up my mind
to visit that country: two _trifling_ reasons alone prevented me;
viz. want of _time_ and _money_; and from some disagreeable
intelligence I have lately received from _Wells_, instead of climbing
the _Allegany,_ I apprehend I shall soon be obliged to cross the
_Atlantic;_ in which case, I shall have the pleasure of returning you
thanks in person for your obliging attention to my order concerning
the........... which I received by the Peggy.