THAT from the several Constitutions of Air, our Bodies are differently affected; and that most Diseases are in some Measure more or less influenced thereby, is quite out of Dispute. _Hippocrates_, in a great many Places declares himself of this Mind: His whole third section of _Aphorisms_ is a Proof of it; and in several Places[23] he discovers his Opinion, that _Pestilential Diseases_ have their Rise from hence. _Galen_, his best Interpreter, understood his το θειον, which some will have to be meant of somewhat Divine, or the immediate Hand of God, to be nothing else but a particular Constitution of Air arising from natural Causes; and that he was of the same Mind himself, is very plain from his own Writings[24]. IT is almost endless, as well as altogether needless, to cite all the Authorities for this Opinion, that might be collected from the most remote Antiquity down to the present Age. We shall therefore proceed to consider the different Constitutions of Air, according to the forementioned Distinction; premising only, that the Terms _Hot_, _Cold_, &c. are used in a twofold Sense, the one is _Absolute_, and the other _Relative_; by the former, _viz._ _Absolute Heat_, _Cold_, &c. is understood one simple Property of the Air only, as it is different not in Degree, but in Quality from others: By the latter, that is, _Relative Heat_, &c. is meant certain Degrees of those 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.