is continued; but when that is at an End, the accumulation leffens, and the fides of the Triangle contract, gently and gradually, till the Corks meet. Balls of Lead, if fufpended to fuch Threads, will when electris'd repel each other in the fame manner, and to as great a Distance, if their Threads are fufficiently lengthened.

120. Fourthly. That the primary and fecondary Air mutually repel each other.

This is put paft difpute from the effects of the following

EXPERIMENT.

121. If a piece of Wire of about Six Inches in length be pointed at each end, and those ends turn'd different ways, as in Pl. II. fig. 2. and that wire be fufpended on the point of a Needle, erected for that purpose on the prime Conductor of the Machine, in the manner a magnetic Needle is fufpended; this pois'd Wire is no fooner electris'd, than the fiery Particles begin to be hurried off as ufual at the Points; thofe

έ Every particle of Matter electrified is mutually repelled by every other neighbouring particle equally electrified. Thus, the ftream of a fountain; naturally denfe and continual, when electrified, will separate and spread in the form of a Brush, every drop (or particle of the Water thus electrified) ⚫ endeavouring to recede from every other particle. But on taking away that electrical Fire, they clofe again,' like the cork Balls. See Mr. Franklin's Letters on Electricity. p. 37. 2d. Edition.

elaftic

elaftic Particles ftriking the elaftic Air mutu ally repel, and confequently the repell'd points of the Wire will give way, and fly back; which Motion of the Wire will increafe, till it becomes as rapid as the Flyers of a Jack, so that when the Room is darken'd, à circle of Fire is formed *.

Since then the primary and fecondary airfo manifeftly repel each other, can it be reafonably doubted, whether the retenfion of the former, in the experiments, which accumulates on grofs bodies (inftead of difperfing) be from the effect of the repelling fpring of the latter furrounding it? for otherwife, by means of its great Elafticity and Subtilty, it muft neceffarily escape, as foon and as faft as collected. But the elafticity of the ætherial particles contain'd in it, fuffers not the includ

The fiery particles, iffuing from pointed bodies when electris'd, have an exceeding lively refemblance of the fiery particles iffuing from the mouth of a fquib or ferpent, when kindled; which diverge and recede from each other, in the fame manner with thofe of the artificial fire-work, (particularly when they are faften'd to the circumference of a wheel,) and each of thofe appears to act from the very fame principle; tho' it must indeed be allow'd, that the fmallness of the aperture of a ferpent, thro-which the fiery particles force their way, very much accelerates the motion on the wheel. The elastic particles of each one, ftriking against the elaftic air, recoil, and are repell'd back.

ed primary air to efcape freely to gain its enlargement. Freely I fay, for it feems perpetually, tho' infenfibly efcaping; becaufe, a conftant Attrition of the revolving glafs is abfolutely neceffary to keep it to its full height: When once that attrition is difcontinued, the accumulation on the prime conductor, &c. is almost inftantly at an end; confequently it was before that, conftantly efcaping.

This doctrine concerning its retention when accumulated feems likewife to be confirmed, by obferving, that when the barometer is higheft, and the air confequently moft elaftic, the accumulation is then greateft, and continues the longest after the attrition is over. -But although these confiderations alone fufficiently evince, that the elafticity of the circumjacent air is tha only reafon why the electrical æther in thofe experiments is fo retained, as to accumulate on the included bodies; yet many others might be produc'd to prove it were it neceffary, and were it poffible to conceive any other agent fo ready at hand, and fo capable of confining it down to the electris'd body."

122. But as Mr. Haukfbee, obferves on another occafion, the. beft proof that can be given of the truth of any hypothefis, is, that the experiments made for that end do all of them and every way agree: That trying Nature on one fide, and on the other, yet every way (if the hypothefis be right) the ftill confefies the fame thing. Thus with • refpect

refpect to the nature of founds; it is demonftrable, that the air is a proper vehicle or me dium for the propagation of them; because founds do not only leffen and grow weaker, according to the degrees of the Air's rare faction; but alfo become more intenfe and Strong, according to the degrees of its con→ denfation.' Mr. Haukfbee's Exp. p. 88. 2d. Edition.

ra

By way of illuftration therefore, or ther to put it beyond difpute, I fhall proceed to fhew that the former arguments are juft, concerning the retenfion of the electrical fluid by means of the repelling fpring of the furrounding air; and that the fame thing is confirmed by the removal of it.

123. Provide a proper conductor to the infide of a glafs veffel, and exhaust the air, then electrife that conductor, and immediately a light appears in the vacuum,'

124. On the bottom of a tall frame of wood are two cups of glafs placed, partly fill'd with mercury, in which are immerfed the two ends of a long incurvated glass tube, in each part whereof, the quickfilver rifes above that in the bafon, to the height of a• bout 30 Inches; and all the internal part of the tube above the quickfilver, is a vacuum, or a space, as void of air, as can be made, perhaps, by art. -I lay a wire from the barrel (or prime conductor of the machine,) to the mercury in one of the glaffes, which conducts

I 2

conducts the electricity to the tube.-The globe is whirl'd round, and behold! How quick the lightning flies from the mercury. into the vacuum of the tube?-In that, how ftrong, how vivid, how fenfibly, and how quick it moves thro' that long space of the tube!Afcending in one part, running over the top, and down the other leg of the tube, in an apparent rivulet of fire.

• When I put my finger on the barrel, to intercept the fluid, it flows no longer in the tube.My finger removed, the torrent of fire rushes on, as before, with an unequal, undulating kind of motion. In that experiment, the conductor to the vacuum, was the column of quickfilver.

125. An experiment of this kind may be commodioufly made with the exhaufted glafs receiver, on the air-pump, where the conductor to the vacuum may be the wire, which is made ufe of to drop the guinea and feather both at once. And though art may double or triple the quantity and power of electricity, by combining together the action of feveral globes under attrition, at once, in the fame machine; yet, to what degree foever it be increased, 'twill be in vain to attempt to turn fuch ftreams of light into a vessel that is already filled with air.

+ See Mr. Martin's Gent, and Ladies Philofophy, Vol. ft. p. 321.