ESSAY To Shew From what CAUSES Electricity is Produced, _&c._ _Kind Sir_, When I reflect on the great Ingenuity you have shewn, in your _Apparatus_ for the Improvement of the Knowlege of Electricity, and how industrious and kind you have been in communicating the many Experiments you have made to your Friends and Acquaintance relating thereto, I was in hopes, from you or some of them, an Essay would be made ere this, not only to go farther with these Experiments, but to give some tolerable Conjecture from whence this Fire, and astonishing Effect, is produced. I was going to give you my Thoughts concerning it, when I last saw you at _Child_’s Coffee-house; but, on Reflection, I chose rather to do it in Writing: For, in all Novelty, till the Relater is quite understood, Words are forgotten easily; but Things of this sort in Writing may again and again be consider’d. To begin then: In order to shew whence this electrical Fire and Force is produc’d, I will first endeavour to prove, that it arises not from any of the _Apparatus_ itself; not either from the glass Ball, nor the Leather, nor from the Tube, or Hand that rubs it: Because nothing we know of can send out of it a Quantity of Matter, but there must be less of that Matter remaining, after it has been so discharged; whereas it cannot be shewn, but that the Ball of Glass, after ever so many Times using, remains as fit for the same Use as at first. Having, from Probability, I think, shewn, that the Fire and Force, here treated of, come not from the _Apparatus_, it is natural for me to suppose they are produced from the Air they are mov’d in. And I believe this Notion will not appear trifling, when we consider, that the most ancient and ablest Philosophers have look’d upon the Animal and Vegetable World as actuated by Fire; and that they are nourish’d by Water, and what it contains. If this be allow’d, then the Air, which is esteem’d the _Pabulum Vitæ_, from its rubefying the Blood of all Animals in Respiration, seems to be universally impregnated with this Fire. And tho’ there is not enough of it so dispersed as to hurt the Animals in Respiration, yet I can suppose it as universally dispersed, as I can a small Quantity of any Liquor dropp’d in Water, which, when so dispersed, is of no Harm to a Patient, though a few Drops of it by themselves would have been certain Death. And yet, if you farther consider it so dispersed, you cannot consider one Particle of the Water without a Particle of the Medicine: Just so it may be with the Fire of this lower Region, or, what I chuse rather to call it, this _Flamma Vitalis_. I proceed now to consider, how this Fire, so dispersed, may be collected; and have given to it, in electrical Experiments, a Force equal to, and of the same Nature with, Lightning.