THERE is hardly any one Subject more largely treated of by Physical Writers, than that of _Pestilential Diseases_; and the Reason of it I take to be, the Frequency in all Ages and Countries, of Alarms from such dreadful Destroyers; and the uncommon Impressions they are apt to make upon the Minds of those, whose Profession naturally leads them to enquire into their Causes. But in this it has fared as with all the other Branches of that noble Science. The Conjectures and Opinions of Persons have at all Times been too much influenced by the Philosophy in Vogue, insomuch that it is almost an endless as well as an unprofitable Task, to examine into them all: And as such an Enquiry is not consistent with the intended Brevity of these Pages, I shall pass them by, only just taking Notice of the most considerable Opinions, under which, most that has been advanced to any Purpose may be reduced. ALL Authors upon this Subject, may be reduced under these two Sorts: Such as ascribe them to the immediate Wrath of Heaven, and account them as Punishments inflicted by the immediate Exertion of a Supernatural Power; and such as assign for their Origin some natural Cause. ALTHOUGH too great a Regard cannot be had to the Author of our Beings, yet Care should likewise be taken, not to ascribe every Calamity to the immediate Exertion of the Almighty Power; for it seems much more worthy of the Divine Being so to order it, that from the Course of second or natural Causes, Punishments shall pursue Offenders, than to imagine the frequent Exertion of his Power in a Way supernatural to inflict such Punishments. But there is a great deal of Reason to suspect, that the Number of this Sect was very much increased by such, as either out of Ignorance in other Causes, or out of an affected Devotion, thought it their Interest to come into this Opinion, and pretend to do greater Cures by certain religious Performances, and their Intercession with Heaven, than was in the Power of Medicine, of which they knew but very little. OF those that assign some natural Cause, there are several Opinions: Some ascribe them to astral Influences, to malign Conjunctions and Radiations of the Heavenly Bodies. We find, from the most remote Antiquity, not only _Pestilential Diseases_, but likewise a great many others, ascribed to the same Causes: But all the Reasonings about this Conjecture have been very obscure and perplexed until the present Age, when Sir _Isaac Newton_ first taught Men to think justly, and talk intelligibly about the Motions and Influences of those remote Bodies upon our _Atmosphere_: And upon his Theory Dr. _Mead_ has since further proceeded to determine their Efficacies upon humane Bodies. By which, as it does appear that they affect us no otherwise than as they occasion the several Variations of the Seasons, and different Constitutions of the Air, the Reader must be left to the Consideration of such Causes.