FOR further Illustration hereof it may be observed, that the nitrous Spirit which circulates through the subterraneous Caverns may, instead of Obtaining a further Purification, take along with it corrupt and poysonous Vapours from arsenical or other Minerals; and loaded therewith, break out into the open Air: And this we have confirmed from common Observation in the Western Climes of _Africa_, that lye under the _Equator_, wherein the very Showers seem to be endued with a Stiptick or Caustick Power, so as to taint the Cloaths and Skin of the Travellers, and burn, as it were, upon them pestilential Characters. From which Disposition it cannot be a Wonder to any, that the Plague should reign after Earthquakes; because a poysonous Spirit at such Times break out into the Air; as also that Nitre thus loaded with an impure Mixture, and sometimes too that which is deadly, should of it self, like the Occursion of an Acid, force out its Way wherever there is Room, and leave behind in its Passage many Marks of Malignity; so that subterraneous Animals, such as Moles, Mice, Serpents, Conies, Foxes, _&c._ as conscious of approaching Mischief, leave their Burrows, and lie open in the Air; which is also a certain Sign of a Pestilence at Hand: Hence also a sudden Death of Fish; and a Departure of the Birds of the Air, to secure their Safety in that which is more wholesome. AFTER these Observations, it remains to shew how the nitrous Spirit frequently receives a Change like to that which may be termed Corruption, although it is vulgarly accounted incorruptible in it self, and is serviceable in Preserving other Things from Putrefaction. TO the Solution of this uncommon Difficulty, it is to be taken Notice that Corruption here is not in that Sense strictly as when it is the Produce of Humidity, but somewhat more congruous to the peculiar Nature of a nitrous Spirit; which although it cannot, like some other Bodies, putrifie, yet if it can be changed from its Nature and Figure, so as not to be reducible into them again, it does not seem improperly said that such a Change is equivalent to Corruption, its Vitality or Essence being destroyed, and a new Texture being obtained. And this I shall further endeavour to illustrate by a double Argument.