and yet fo potent, as by its emiffion to caufe no fenfible diminution of the weight of the electric body, and to be expanded through a fphere, whofe diameter is above two feet, and yet to be able to agitate and carry up leaf copper or leaf gold, at the distance of ⚫ above a foot from the electric body? And how the effluvia of a magnet can be fo rare ⚫ and fubtile, as to pass through a plate of glafs " without any refiftance or diminution of their 'force, and yet fo potent, as to turn a magne tic needle beyond the glass?' And may not I add? Let him tell him how the electrical effluvia can be fo rare and subtile, as to pass freely through a glafs receiver, and yet fo potent, as to act on a downy feather, with no less force and activity, than what we perceive to be acquired by the magnetic needle, from the best of loaditones?The experi ment may be made thus.... 148. Let a downy feather be faften'd to the top of a small wire or ftick, on a foot or stand, and cover'd with a tall glafs receiver; then if a glafs tube be rubbed within a foot of the receiver, the feather (notwithstanding the interpofition of the glass) will follow the motion of the hand rubbing the tube. 149. In all human probability no expedient could have been thought of, nor any experi ment invented to have proved the exceeding rarity and elasticity of æther, befides thofe principles on which that fagacious enquirer so happi ly ly proceeded: Poffibly they might for ever have remain'd in oblivion. For altho' the general Phænomena arifing from the natural effects have been obferv'd by many; yet we do not hear of any who ever represented it as poffefs'd of those properties in fuch an eminent degree, or that ever thought of any expedient whereby to compare it with the common air, and compute the proportion of the difference between thofe properties in æther and the fame proper ties in air. 150. From the effects then which Sir Isaac had been mentioning, his conclufions were (as) before obferv'd) that æther muft neceffarily be at leaft 700000 times more rare than the common air, and yet 700000 times more elastic. Properties, which altho' they feem incompatible with each other, are yet verified by the electrical fluid, in which thofe properties are obferv'd to exist in a very furprifing degree, although the precifenefs of the proportion may not be eafily determin'd: Probably, as before obferved, there is no other means of making any tolerable computation than those which are there laid down. 151. If thofe natural properties fo obvious in the electrical fluid are heedlefly pafs'd over and difregarded, the experiments feem irreconcileable with each other, and confequently inexplicable; but when thofe properties are duly examin'd and confider'd, they become fuch a key as to render the most abftrufe of them plain and and intelligible. 152. It must be confefs'd that for a medium to be fo much rarer than the air, and at the fame time as much more elaftic, appears like the greatest paradox, efpecially 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 fame proportion. At first fight therefore I fay, and before it is duly confider'd, fuch properties in the fame medium may feem almost impoffible; yet we fhall find by the following experiment, that both may be much heighten'd, even in common air, by means of heat.-Let a blown bladder, for instance, when well dried, be untied and prefs'd with the hand till the air feems 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 fo extended, that the bladder will very foon be as tight and turgid as if new blown : Here therefore is an increase of the elafticity 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 fame experiment will fucceed, if inftead of heating the bladder, it be put under the receiver of an airpump and the air exhaufted, for then the in L ternal 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 reafoning of Sir Ifaac 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, and the reasoning deduc'd from it,: clearly prove it was then his opinion, that fuch a fubtile medium not only existed, but also that it was univerfal. His 2d. Advertisement alfo at the beginning of his Optics fhews that the principal reason for his putting them as Queries was the want of experiments to prove them, and he expreffes not the leaft doubt or hesitation concerning the truth of the doctrine he had been difcuffing. 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 difpute. Optics. Quære 18. would e **** СНАР. Lord Verulam's Conjectures concerning a fubtile Fluid, with the Author's new Account of a more rare and active Part of Æther, to which he gives the Name of PNEUMA, OF SPIRIT of ÆTHEN. THAT worthily efteem'd and renown'd Philofopher Lord Bacon, as well as T 業 Sir Ifaac Newton, was of opinion that a fluid, extremely fubtile and active, exifted in the pores of grofs bodies.is. 154. The Spirits and Pneumaticals (he fays) that are in all tangible bodies are fearce known. And then inftances in a variety of circumstances wherein the world had been groffly mistaken about them*: Which obfervations, tho' now they appear ftrictly juft, yet could at that time be confider'd, but as merely conjectural, having no fufficient evidence to fupport them, no proper experiments being |