It has been the constant Observation of Physicians, as well ancient as modern, and confirm'd by numerous Instances, that a hot and moist Constitution of the Air, joyn'd with southerly Winds, was generally a Fore-runner of malignant and Pestilential Fevers. Thus _Hippocrates_ observes, that the Constitution of the Air preceeding that malignant Fever describ'd in the 3d Book of his Epidemics, 'was calm, moist, and southerly, and succeeded a hot, and dry Season; the Winter, calm, cloudy, rainy, warm, southerly; some Showers, and Northerly Winds about the Equinox; the Spring, calm and southerly, with great Rains; the Summer very hot, with little Wind, and much Rain about the Dog-days[a]. Some Authors led by the Title of this Book of his Epidemics, _viz._ [Greek: Katastasis Loimôdês], or the Pestilential Constitution, have imagin'd the Diseases here spoken of, to be the same with that terrible Plague describ'd by _Thucydides_, which taking its Rise in _Æthiopia_, and passing thence thro' _Lybia_ and _Ægypt_, miserably harass'd all _Persia_, _Phoenicia_, _Judea_, _Greece_, and _Coele Syria_, and was one of the most dreadful Calamities of this kind that ever appeared in the World. But whosoever will give himself the Trouble to compare the Symptoms of the Fevers here described by _Hippocrates_, with those related by that accurate Historian[b], who both had it himself, and visited many others in it, will find that there is not the least Similitude between them. The one being highly infectious, and not the least Appearance of Contagion in the other: _Galen_ also the best Interpreter of _Hippocrates_, in his Comment on this Book of his Epidemic's suspects, this Title to be spurious, tho' both he and others observe much the same Constitution of the Air to be the Fore-runner of these Diseases. [a] _Hippoc._ Epidem. lib. 3. sect. 3. _Galeni_ Com. in hunc Loc. _Titi Lucret_, lib. 6. [b] _Thucydides_ lib. 2. [Sidenote: _What Places most Subject._] Pestilential and Malignant Fevers, are likewise observ'd to be the most frequent in those Places where the Climate is hot and scorching, and especially when Rains fall in such Seasons of the Year. Thus in _Ægypt_ and some other Parts of _Africa_, if Rains fall during the Months of _July_ and _August_, the Plague usually breaks out the _September_ following[c]. [c] _Joan. Leon._ Hist. _Afric._ lib. 1. cap. 10. _Purchas_ Pilgrim. lib. 6. cap. 17. _Athan._ _Kircheri Scrutin. Pestis_, pag. 179.