FURTHER, as to the fatal Influences of a Plague, if the before recited Account is not sufficient to shew it, it would not be a Task of any Difficulty to produce many Instances of its Tyranny and Destruction: Hence the Plague by the _Hebrews_ was called לבד, or Perdition; as if it was ordained on Purpose to destroy Mankind: It is also called _Lues_, from λυω, to dissolve, a most certain Way of Destruction, and whose fatal Property in the Plague is most remarkable, whereby it does not so much prepare the Way, as immediately of its self destroy, and of whose certain Ruin, through whole Regions together, we have too many Testimonies upon Record, in the Writings both of Ancients and Moderns. AGAIN, the Pestilence is said to be contagious; because some are come to that Height of Boldness, (being blind with too much Light) to propagate strange Conjectures to the contrary, as if the late Plague was begun and continued by a foreign Influence; but to remove this Controversie, it may be convenient to explain the Nature of a Contagion, and its supposed Conditions of Exertion; but before I enter upon this, it will be necessary to dispatch the other Members of this Definition. IT is further added, that the Plague affects many Regions together at the same Time, in Order to distinguish it both from _Endemick_ Diseases, that is, such as are appropriate to one Place only; and also from _Sporadick_ Diseases, which although they rage amongst the Populace in this or that Country or Climate indifferently, according to the Influence of their procatarctick Causes, they are yet to be deemed particular, as well as they are pernicious: But enough of these Matters. AT length then it becomes necessary to change the Consideration, and enquire how it comes that the Plague hath its chief Origin from a Change or Corruption of the nitrous Spirits in the Air: This is the great Difficulty! This is our Task! It is therefore to be hoped that the Novelty of the Opinion will not occasion any one to receive it at first Sight amiss, until by due Examination he hath brought it to Trial; but in Order to erect this upon a sure Foundation, it is proper to premise some Considerations. AND first of all, the central nitrous Spirit does every where transpire and exhale towards the Surface, to recruit the Consumptions of Nature, and for other Purposes hereafter to be mentioned. From this saline Origin straining through the Bowels of the Earth, it is by every one understood Vegetation is carried on; and that the Light and vital Warmth of the Sun is impregnated by it through the whole Region of Air; and the mutual Intercourses or Operations upon one another between the Sun’s Rays, and these saline Exhalations, by a Kind of Magnetism between them, is too obvious in a Multitude of Instances to want any Comment.