BUT both the Ancients and Moderns have taken the utmost Pains in contriving to purge the Air, on a Supposition that, in a pestilential Contagion, that is _substantially_ infected: But as the Air, as before demonstrated, is only the Lodgment or Vehicle to the pestilential _Miasmata_, which are every Way agitated in it, it does not seem so much to want Depuration on its own Account, as that poisonous Mixture which is joined with it. Indeed the pestilential Particles residing in the Porosities of the Air, may often, without any Change of Figure, for Want of due Agitation, remain and stagnate in it a long Time, so as to be drawn in by the Lungs in Inspiration, and hence from the intimate Mixture and Confusion as it were of both, a Suspicion may be entertained of the Taint coming from a Corruption of Air; but of this we have said enough already; and as howsoever this Matter is, a Purgation of the Air is by common Consent called for on all Sides in these Cases, we shall consider this Matter, chiefly in these two Respects. _FIRST_, That the pestilential _Seminium_ be dislodged; and to this Purpose contribute brisk Winds, especially from the _North_, and the frequent Explosions of great Guns, in the Morning and Evening chiefly; because such Concussions agitate the poisonous _Miasmata_, and not only help to dissipate them; but to change and alter them in those particular Configurations whereby they become so noxious; and it hath been attested by Experience, that an intimate Combination of _Nitre_ and _Sulphur_ greatly alters the saline Qualities of the pestilential Taint. _SECONDLY_, The utmost Diligence is to be used to prevent the pestilential Particles from taking Effect; which is succesfully done by proper Fumigations. _Hippocrates_, the Oracle in Physick, hath left it to Posterity, to kindle Fires in the publick Streets; and these sometimes I conceive may do good; but not as some will have it, by absorbing the pestiferous Humidities, but by diffusing on all Sides a great deal of _Nitre_, which gives a considerable Change to the venomous _Miasmata_; I judge it best therefore that such Fires should be made of resinous Woods, which throw out a clear and unctious Smell, such as _Juniper_, _Fir_, _Oak_, _Ash_, _Elm_, _Chesnut_, &c. but by no Means Coals, which exhale an impure, fetid, and suffocating Sulphur. BY the Care of the Magistrate also the Streets, Sinks, and Canals, should daily be cleared of all Filth; because Stench and Nastiness are justly reckoned the Entertainers of Infection, and we find the Air to be corrupted frequently from noisome Smells; so that the pestilential Venom cannot but receive additional Strength from such Means.