Properties: As the same Air may at the same Time be said properly to be both Hot and Cold, or Dry and Moist, as it is compared with another Air, either Hotter or Colder, Dryer, or Moister; for with Regard to a hotter Air, it will be termed cold, when at the same Time if it be compared to a colder Air, it would be accounted hot: And so of the rest. To which Distinction, it is very necessary to have constant Regard to avoid Confusion.
THOSE Countries where the Air is hot and dry for the greatest Part, are related to be healthful, and free from Pestilential Diseases, except where there are great Swamps and stagnant Waters, or by any accidental Causes Bodies are exposed there to Putrefaction, the Steams of which render Persons Diseased. In such Countries, for the most Part of the Year, there is but very little Rain, and the Nights are comparatively colder than elsewhere, from the great Dews which then fall. As Piso[25] informs us, that the colder the Nights are in Brasil, and the more plentifully the Dews
fall, the Inhabitants account it most agreeable to their Soil, and conducive to Vegetation; and Physicians reckon it much the most healthful for the Inhabitants.
THE Heat of the Air alone, where it is constant and uniform, does not appear to render Persons born in it, or long accustomed to it, any more unhealthful, than that which is more temperate. Aristotle[26] indeed says, a hot and dry Southerly Wind will bring a Pestilence; but of such we have very few Instances, especially on this Part of the Globe. There is in Livy[27] an Account of a Plague at Rome, from a great Drought; and Nicephorus[28] relates such another: But these generally come from some other manifest Causes besides Heat, and in Places not accustomed to a dry Air.
BUT a hot and moist Air is very different. By Moist, is meant what arises from sudden or long Rains. This is the Constitution of Air that most Authors charge with being the greatest Instrument in Pestilential
Distempers. Hippocrates[29] ascribes a great deal to such an Air, and relates a Pestilence that had its Rise from great Heat, joined with Southerly Winds and much Rain. Galen is of the same Mind, as appears from several of his Writings[30], with many others too tedious to mention. The Truth of this is likewise manifest from the Histories of those Countries, where there are long settled Heats, and afterwards much Rain, as in several Parts of the East-Indies, which are known at such Times to be most grievously afflicted with Fevers and Diseases of a very malignant Kind. The same we are informed of from some Places in Africa,[31], viz. That if Showers fall soon upon the sultry Heats of July and August, pestilential Distempers certainly ensue. It may be generally observed here too in our own Climate, that the most unhealthful Times are after warm Rains, and the more if the Air is then agitated but little with Winds.
FROM a cold and moist Air, we have little complained of, as to their occasioning these Diseases, unless such a Constitution sets in immediately upon a contrary Extream; for all sudden Changes of Weather are more or less unhealthful, as well as in other Respects of living; for which Reason particularly, Corn. Celsus advises to be very slow in all Alterations of Moment: And Sanctorius frequently inculcates the same in his Aphorisms, and tells us[32] how it is hurtful, both to go suddenly out of a hot Air into a cold one, and out of a cold Air into a hot one; and is also very particular[33] in the Inconveniencies of such a Constitution of Air we are now speaking of, setting in after the Heat of Summer. Hippocrates[34] does tell us of a Pestilence from long continued cold Rains, as likewise does Fernelius[35], but such Instances are not common.
THE last Constitution of Air we are to take Notice of, is that which is cold and dry, against which there are a great
many very heavy Complaints. Galen writes of a most Raging Pestilence about Aquileia in Italy, that began in the very Middle of Winter, and had its manifest Cause in extream Cold. Fernelius[36] asserts the Rise of several Pestilences from the same Causes: As also does Morellus[37] observe great Malignities to proceed from some Northerly cold Winds. Titus Livy[38] likewise mentions a Pestilential Constitution arising from intense Cold, but Physical Histories abound with such Relations.
OF the strange and sudden Effects of intense Cold and dry Winds, we have very surprizing Accounts from those who have travelled into Countries where they are the most frequent. Dr. Bernard Connor[39] beforementioned, relates, That when he was in Poland, it was asserted to him by very creditable Testimonies, that it frequently happens in Lithuania, and some of the Northern Tracts of Muscovy and Tartary; that if sometimes, through the Neglect of the Shepherds, their small Cattle, as Sheep, Goats, and the