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nation of this electric and clastic Fluid, efpeci ally as it proves to be true Fire.

$288. The Discovery of a fubtile Medium, which we have fo happily made, fhews it to be the fame mechanical Agent that Sir Ifaac New ton fo much wished for when he wrote his Principia.

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In the Preface to that Treatife, after the Author had been informing us of the method he had taken to explain the celestial Phænomena, and had, by that means, pointed out the different Forces, as he called them, which were the causes of those appearances, he adds, From thefe Forces, by other Propofitions which are also mathematical, we deduce the motions, of the Planets, the Comets, the Moon, and the Sea. I wish we could derive the rest of the Phænomena of Nature by the fame kind of reasoning from mechanical Principles. For I am induced by many Reasons to fufpect that they may all depend upon certain Forces £ by which the particles of Bodies, by fome Caufes hitherto unknown, are either mutually impelled towards each other and cohere in regular Figures, or are repelled and recede from each other; which Forces being unf known, Philofophers have hitherto attempted the Search of Nature in vain. But I hope the Principles here laid down, will afford fome Light either to that, or fome truer method of Philofophy.'

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289. This Reafoning of Sir Isaac confirms

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the foremention'd obfcurities and perplexities attending natural Philofophy.The Force i. e. the active Agent difcoverable by means of the electrical Apparatus being unknown to Philofophers when he wrote his Principia, they had always attempted the fearch of Nature in vain. That great Naturalift, we find, was fo far from endeavouring to obtrude any Opinion on others, before he was throughly fatisfied of the truth of it himself, that notwithstanding he had been taking fuch indefatigable pains in writing that Treatife; yet his ardent defire of feeing true Philosophy establish'd caused him to exprefs fome diffidence. I hope the Prin

ciples here laid down,' &c.In Sir Isaac's Time no Medium more fubtile and elaftic than the Air had ever been actually discover'd, confequently all that could be faid of Æther was for the most part conjectural. It was then the current Opinion that there really was no Me dium more active than the common Air. But what was the confequence? We are inform'd that Philofophers, had always attempted the Search of Nature in vain.-Had Sir Ifaac liv'd to fee his fubtile elastic Medium evidently discover'd, we may be very certain his enter prifing Genius would never have fat for 20 Years fupinely, as if nothing had happen'd, or as if he had thought, as fome of his Difciples seem to do, that the grand Difcovery was not worth cultivating.

CHAP.

CHA P. XIV. PART I.

SECTION 290.

The Use of pointed Iron Rods to preferve High Buildings, Ships, &c. from Lightning. Dr. Franklin's Pafteboard Tube, and artificial Kite.

AVING from a Series of ExperiH ments in the former Chapters, I hope, fufficiently proved the truth of Sir Ifaac Newton's Opinion, concerning a fubtile Æther, existing in the pores of all grofs Bodies, i. e. in all minute Spaces, I fhall now proceed to try what Evidences I can produce, in fupport of what he has advanc'd concerning the univerfality of the fame Medium in all open Spaces. The principal of which, I procured from my intimate acquaintance with the Letters of the ingenious Dr. Franklin. The first of which contains a curious electrical Experiment, that leads on to others of a more phyfical Nature, which indubitably proves, that the electrical Fluid and the Fire of Lightning are identically the fame Subftance; fince they invariably affume each others Offices and Properties, as will more fully appear from the following Extract, which is a literal Tranfcript

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from that ingenious Gentleman's Letters on that most interesting fubject, viz, Prefervation from the direful Effects of Lightning.

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291. I have,' fays he, a large prime Conductor made of feveral thin fheets of Fuller's pasteboard, form'd into a Tube near 10 feet • long and a foot Diameter: It is cover'd with • Dutch embofs'd Paper, almost totally gilt. This large metallic Surface fupports a much greater electrical Atmosphere than a Rod of • Iron of 50 times the weight would do: It is fufpended by filk lines, and when charg'd, will ftrike at near two Inches distance, a pretty hard ftroke, fo as to make one's knuckle ach. Let a Perfon, ftanding on the floor, prefent the point of a needle at 12 or more Inches • diftance from it, and while the needle is fo prefented, the Conductor cannot be charged, the point drawing off the fire as faft as it is thrown on by the electrical Globe. Let it be. charged, and then prefent the point at the fame distance, and it will fuddenly be dif charged. In the dark you may fee a light on the point, when the Experiment is made: And if the Perfon, holding the point, ftands. upon wax, he will be electrified by receiving the fire at that distance. Attempt to draw off the Electricity with a blunt, Body, as a bolt of Iron, round at the end and fmooth, (a Silversmith's iron Punch, inch-thick, is what I ufe) and you must bring it within the * diftance of three Inches before you can do it,

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and then it is done with a stroke and crack. As the Pafteboard Tube hangs loofe on filk lines, when you approach it with the punch iron, it likewife would move towards the punch, being attracted while it is charg'd; but if at the fame inftant, a point be prefent ⚫ed as before, it retires again, for the point discharges it. Take a pair of large brafs • Scales, of two or more Feet beam, the cords of the Scales being filk Sufpend the beam by a packthread from the cieling, so that the • bottom of the Scales may be about a foot • from the floor: The Scales will move round in a circle by the untwisting of the packthread. Set the iron punch on the end upon the floor, in fuch a place as that the Scales may pafs over it in making their circle: Then electrify one Scale by applying the wire of a charged Phial to it. As they move round, you fee that Scale draw nigher to the floor, and dip more when it comes over the punch; ⚫ and if that be placed at a proper distance, the • Scale will snap and discharge its Fire into it.

But if a needle be ftuck on the end of the * punch, its point upwards, the Scale, instead of drawing nigh to the punch and snapping, discharges its Fire filently through the point, • and rifes higher from the punch: Nay, even if the needle be placed upon the floor near the punch, its point upwards, the end of the punch, tho' fo much higher than the needle, will not attract the Scale and receive its Fire, U • for

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