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and intelligible.

It must be confess'd that for a medium to be so much rarer than the air, and at the same time as much more elastic, appears like the greatest paradox, especially when we confider the method of rarifying the air with the Pneumatic Engine, which is, to exhaust the receiver of the main body of the air ; for then, tho' the remaining part must be own'd to be much rarified, yet the elasticity must, for that reason, be weaken'd in the same proportion.

At first sight therefore I fay, and before it is duly confider'd, such properties in the same medium


seem almost impossible ; yet we shall find by the following experiment, that both may be much heighten'd, even in com+ mon air, by means of heat. Let a blown blad der, for instance, when well dried, be untied and press’d with the hand till the air seems all excluded ; then if the neck of it be tied again, and the bladder put into a very warm place, the remaining part of the air, which is conceal'd between the folds of it, will be so extended, that the bladder will very soon be as tight and turgid as if new blown : Here therefore is an increase of the elasticity as well as of the rarity ; the former is evident by the expansion of the bladder, and the latter by its occupying more space.

The same experiment will succeed, if instead of heating the bladder, it be put under the receiver of an air- pump and the air exhausted, for then the in



ternal air, conceal'd in the folds, will expand till it fills it, as before.

N B. If it be objected that the foremention'd reasoning of Sir Haac being deliver'd only as Quæries, no great stress ought therefore to be laid on it. It may be answer'd, that the making of the experiment I, and the reasoning deduc'd from its; clearly prove it was then his opinion, that such a fubtile medium not only existed, but also that it was universal, His 2d. Advertisement also at the beginning of his Optics shews that the principal réafon for his putting them as Quæries was the want of experiments to prove them, and he expreffes not the least doubt or hesitation concerning the truth of the doctrine he had been discussing. However had he made any doubt, the modern experiments have so verified the truth of his conjectures (if they were no more) as to put it paft all future dispute.

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ژرژ 153


Lord Verulam's Conjectures concerning

a subtile Fluid, with the Author's
nezer Account of a more rare and ac,
tive Part of ther, to which he gives
the Name of PNEUMA, or SPIRIT of

ir condi od

toisi! *HAT worthily esteemid and renown'd T Philosopher Lord Bacon, as well as

Sir Ifaac Newton, was of opinion that

à fluid, extremely subtile and active, existed in the pores of gross bodies. 154.

• The Spirits and Pneumaticals' (he fays) that are in all tangible bodies are searcé $ known.' And then instances in a variety of circumftaices wherein the world had been grossly mistaken about them *: Which obserà vations, tho' now they appeät strictly just, yet could at that time be consider'd, but as merely conjectural, having no sufficient evidence to support them, no proper experiments being

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produced to countenance such an opinion ; it was therefore rejected : Nor was it capable of fufficient proof before the furprising accidental discovery made by professor Muschenbroek.But since that, and other subsequent ones, we are furnish'd with evidences which sufficiently prove, that thofe assertions were not mere conjectures, but rather like predictions, which are now clearly verified and realized by the plainest facts.

155. Those invisible things,' that noble Lord tells us, were but little enquir'd into;

altho' they were the things, which GOVERN * NATURE principally:' Those spirits or pneumaticals were scarce known: Yet without the help of these, he assures us we can make no true analyfis and indications (as he expresses himself) of the proceedings of nature. This, we are now convinc'd, proves literally true; , not only that such spirits, or pneumaticals merely exist, but we have the highest evidence, even that of our senses, pointing out to

very identical agent it lelf, in a more conspicuous manner, and rendering it much more familiar and plain than ever we were able to do even the common air.

156. No doubt but that noble' author and Sir Isaac Newton meant one and the same agent or medium, tho' the former varies a little from the latter in his term, and makes use of the plural number || whereas Sir Ifaac always speaks Pneumaticals.

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courle of our experiments we frequently disco ver a much more rare, subtile, active part of æther, which has not yet been confider'd, tho its effects are obvious, and the neglect of attending to them has been the occasion of various ambiguities. This superior part of it, (for so I must call it) tha' it seems inseparable from the fubtile medium, discoverable by electrical experiments, is yet remarkably evident in many other Phænomena of nature. For this more active part therefore, I am at a loss for an adequate Term: Should I call it ESSENCE OF ÆTHER, some would perhaps ask what I mean by such an essence, or else call it an unmean

ing Term. I lhall therefore, for distinction's sake, take the hint from that great Author's Pneumaticals, and call it in brief, by its more original appellation, PNEUMA, or else, Spirit of a Æther; and shall crave the liberty of the

promitcuous use of those Terms : For I find I Ihall be constrain'd either to make use of them, or others fimilar to them ; since, as I shall Thew, some other agent exists much more subtile and active than even the electrical medium itself. As no satisfactory method appears to solve the Phænomena of Nature without such a Pneuma or Spirit, I Mall in the first place produce my evidence to prove its existence ; and though

§ Spirit, Subtile Medium, or Æther.


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