To make this Conjecture the more easily apprehended, I will suppose, that the Nature of Fire is as similar to its Parts, and they have as great a Propensity to adhere to one another, as we find the different Arrangements in all natural Bodies have; as may be seen in Gems, in Water, and in the various _Strata_ of the Earth, and the like. Do but force or invite these fiery Particles to a closer Contact than they have been supposed to be in, when uniformly dispersed through all Nature, and they are Lightning, or a Fire of less Force, as more or less Parts of that Fire are got together. To illustrate this, wax a small Thread, or slide a Rope swiftly thro’ your Fingers, and you are liable to burn them: Which probably arises from their grinding in, betwixt your Fingers and the Rope, so many more Particles of Fire than naturally come together when left to float in the Air. If this Reasoning be allow’d to be just (which it must be, till it is overturn’d by stronger Reasoning), then it follows, that the Air, which is violently ground or rubb’d betwixt your Hand and a glass Tube, or betwixt a glass Ball whirl’d briskly, and rubb’d with a Piece of Leather, as they are used in electrical Experiments, I say, the Air, so rubb’d, may leave behind it that Quantity of agitated Fire which causes Electricity. For, suppose the Ball or Tube inveloped with a Quantity of this Fire moving spirally round them, with the utmost Velocity; and it can no more depart from its Company than you find Sparks of Fire which fly from Steel on a Knife-grinder’s Wheel are liable to do. Every body almost can remember to have seen them adhere to the Wheel, and frequently pursue each other quite round it. Those who try these Experiments, find, that in moist Weather this Power is less attainable than in a more clear Day; and therefore some may be liable to attribute that to the _Apparatus_, which may be better accounted for by the watry Particles in the Air; which may be liable to hinder the lambent Flame, by me supposed to be universally scatter’d, from uniting, by the Friction before-mention’d. As I have mention’d Friction, I cannot help observing how unphilosophical and unmeaning it is, for any one to advance, that Fire is caused by Friction; when I think he may as well say, that Water is caused by Pumping. We know, that a Cart or Coach-Wheel, for Want of Grease, by Friction will be set on Fire; and Fire-Canes, rubbed together smartly, will take Fire; but neither of these, I believe, nor any thing else, will beget or generate the Element of Fire. They must either collect it out of the Air, or else it must be lodged within them, as we find it to be in Steel in an eminent Degree: For, if you drop the Filings of Steel through the Flame of a Candle, it sends out the most fierce Fire of any thing in Nature.