ces between the tropics, is esteemed so violent and
insufferable, when it appears, by these instances, that it is
sometimes rivalled, and even exceeded, in very high latitudes, not far
from the polar circle? I shall answer, That the estimation of heat,
in any particular place, ought not to be founded upon that particular
degree of it which may now and then obtain there; but is rather to be
deduced from the medium observed during a whole season, or perhaps in
a whole year; and in this light, it will easily appear how much more
intense the same degree of heat may prove, by being long continued
without remarkable variation. For instance, in comparing together St
Catharines and St Petersburg, we shall suppose the summer heat at St
Catharines to be 76 deg., and the winter heat to be only 56 deg.. I do not
make this last supposition upon sufficient authority, but am apt to
suspect the allowance is full large. Upon this supposition, therefore,
the medium heat all the year round will be 66 deg.; and this perhaps by
night as well as by day, with no great variation. Now, those who have
attended to thermometrical observation will readily allow, that a
continuance of this degree of heat for a length of time, would be
found violent and suffocating by the generality of mankind. But at
Petersburg, though the heat, as measured by the thermometer, may
happen to be a few times in the year considerably higher than at St
Catharines, yet, at other times, the cold is intensely sharper, and
the medium for a year, or even for one season only, would be far
short of 60 deg.. For I find, that the variation of the thermometer at
Petersburgh, is at least five times greater, from its highest to its
lowest point, than I have supposed it to be at St Catherines.[2]

[Footnote 2: On his own principles, the lowest heat of Petersburg
ought to be -2 deg., and the medium temperature of the year 48 deg.; but the
data are loosely expressed and quite unsatisfactory, as indeed is the
whole reasoning on the subject.--E.]

Besides this estimation of the heat of a place, by taking the medium
for a considerable time together, there is another circumstance which
will still farther augment the apparent heat of the warmer climates,
and diminish that of the colder, though I do not remember to have seen
it remarked by any author. To explain myself more distinctly upon this
head, I must observe, that the measure of absolute heat, marked by
the thermometer, is not the ce