[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 certain criterion of the sensation of heat with which human bodies are affected; for, as the presence and perpetual succession of fresh air is necessary to our respiration, so there is a species of tainted or stagnated air often produced by the continuance of great heats, which, being less proper for respiration, never fails to excite in us an idea of sultriness and suffocating warmth, much beyond what the heat of the air alone would occasion, supposing it pure and agitated.  Hence it follows, that the mere inspection of the thermometer will never determine the heat which the human body feels from this cause; and hence also, the heat, in most places between the tropics, must be much more troublesome and uneasy, than the same degree of absolute heat in a high latitude.  For the equability and duration of the tropical heat contribute to impregnate the air with a multitude of steams and vapours from the soil and water; and many of these being of an impure and noxious kind, and being not easily removed, by reason of the regularity of the winds in those parts, which only shift the exhalations from place to place, without dispersing them, the atmosphere is by this means rendered less capable of supporting the animal functions, and mankind are consequently affected by what they call a most intense and stifling heat.  Whereas, in the higher latitudes, these vapours are probably raised in smaller quantities, and are frequently dispersed by the irregularity and violence of the winds; so that the air, being in general more pure and less stagnant, the same degree of absolute heat is not attended by that uneasy and suffocating sensation.

This may suffice, in general, with respect to the present speculation; but I cannot help wishing, as it is a subject in which mankind are very much interested, especially travellers of all sorts, that it were more thoroughly and accurately examined, and that all ships bound to the warmer climates were furnished with thermometers of a known fabric, and would observe them daily, and register their observations.  For, considering the turn to philosophical enquiries which has obtained in Europe since the beginning of the eighteenth century, it is incredible how very rarely any thing of this kind has been attended to.  For my own part, I do not remember to have ever seen any observations of the heat and cold, either in the East or West Indies, which were made by marines or officers of vessels, excepting those made by order of Commodore Anson on board the Centurion, and those by Captain Legg on board the Severn, another ship of our squadron.