If it should be asked how it comes to pass, then, that the heat in many places between the tropics is esteemed so violent and insufferable, when it appears, by these instances, that it is sometimes rivalled or exceeded in very high latitudes not far from the polar circle? I should answer that the estimation of heat in any particular place ought not to be founded upon that degree of heat which may now and then obtain there, but is rather to be deduced from the medium observed in 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. Catherine's and Petersburgh, we will suppose the summer heat at St. Catherine's to be 76°, and the winter heat to be twenty divisions short of it. I do not make use of this last conjecture upon sufficient observation, but I am apt to suspect that the allowance is full large. Upon this supposition, then, the medium heat all the year round will be 66°, and this perhaps by night as well as day, with no great variation. Now those who have attended to thermometers will readily own that a continuation of this degree of heat for a length of time would, by the generality of mankind, be stiled violent and suffocating; but at Petersburgh, though a few times in the year the heat by the thermometer may be considerably greater than at St. Catherine's, yet, as at other times the cold is immensely sharper, the medium for a year, or even for one season only, would be far short of 66°. For I find that the thermometer at Petersburgh is at least five times greater, from its highest to its lowest point, than what I have supposed to take place at St. Catherine's.