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131. Twas not a little surprising also, to observe, that after both glaffes had been in • motion for some time, and the hand applied
during that time to the surface of the outer one, that then, the motions of both ceasing, and no light appearing at all, if I did buc approach my hand again near the furface of the outward glass, there would be fashes of light (like lightning) produced in the inwand glass; just as if the effluvia froin the outer glass had been puthed with more force upon • it by means of the approaching hand' 110
132. From the effects of all these experiments and many others it indisputably appears, that the common air is a much stronger barrier for securing and confining the more pure air, than the glass of the tube
or globe, by finding how readily it pervades the latter, to efcape from the pressure of the former, when the air is exhauffed out of the glass.
133. Hence alfo it evidently appears, that the sole cause of the whole electrical Phanos menon depends on this principle, namely, tbat the primary air or æther is retained in the expera riments by means of the repeling Jpring of the circumambient secondary air, which confines it down on every fide to the gross body on whinta it is accumulated.
10:11 COROL'L A R Y. 134. Hence it appears, that Sir Ifaac Nedenis ton's position concerning the extreme rarity
and extreme elasticity of æther was just; lince it is so clearly confirm'd from the effects of the foregoing experiments, where we find fo great an elasticity in the electrical fluid accumulated on the prime conductor, &c. as to buoy up, and bear off the common air and by that means a vacuum is form'd in those limits, or what is equivalent to it, the æther which occupies that space, being according to Sir Isaac's calculation 700000 times more rate than the common air, which it has by means of its superior elasticity displac'd : But yet the fame surrounding air retains it there, so as not to suffer it to make a free escape.
The want of this knowledge render'd almost every thing else in electricity, dark and mysterious.
135. Tho' the rarity, elasticity, and subtilty of æther fo much exceeds the fame properties in common air, and must therefore appear most wonderful ; yet how much more so must it áppear when we consider the exceeding expansity and fubtilty of the common air, which fd freely insinuates and pervades the pores of various compacted bodies? By means of the spring and pressure of the atmosphere, water is protruded in a vacuum to a considerable height, as in a common pump, not only while the mouth of the well is open, but after it is com vered ever so firmly with boards and earth; for even then the artificer seldom finds it ne cessary to use any precaution, so as to leave a
fent-hole through such covering, for admission of the air. again,
138. The elastic spring and expansive force of the common air at the surface of the earth is almost incredible.-Sir Isaac Newton ina forms us, he had found by a calculation, • that if a sphere of our air, of but one Inch
in diameter, were equally rarified with the fame air at the height of one semi-diameter
of the earth, from the earth's surface, it i would fill all the regions of the planets, to
the orb of saturn, and far beyond it.' Princip. Lib. 3d. p. 366.
137. "Tis presum'd that the force of those evidences already produced is abundantly fufficient to serve as a specimen of the justness of Sir Isaac Newton's position, concerning t fubtile medium existing in the pores of gross bodies, though many more might be added to corroborate and confirm it were they necessary, I shall therefore (as there appear no material evidences to invalidate or set aside those already produced ) enquire yet more particularly what he has asserted concerning it.
138. In his optics we find him making an ingenious experiment to prove the existence of fuch a subtile and expansive medium in a space void of air, and then appeals to the candid and judicious reader, to determine, whether it must not be nécessarily universal, and expanded thro all the Heavens. See Quære. 18. 139. He next proceeds to investigate its nami
tural, or efsential properties, and makes fuch a notable discovery, which was scarce ever attempted before, at least with any success, name
ly, that the same æther which was so much like mair, was 700000 times more fine or rare, and
yet 700009 times more elastic than that. That I may not marr the sense of his reasoning, I shall cite the whole paffage, in the following chapter, and conclude the prefent with a few remarks on the most predominant accidental quality of æther, viz that of fubtilty.
140. Now subtilty is that property of æther which by means of the rarity, or exceeding fineness of its first elements or corpuscles, in conjunction with its elasticity, seems necef-- sarily as it were, to pervade or insinuate into the intersticial vacuities of gross bodies, to efcape from the incumbent pressure, and repelling spring of the surrounding atmosphere*; subtilty therefore, in strictness, is by no means fa properly a natural quality, or effential property, as either rarity or elasticity. As a conféquence then of this property of subtilty, &c. we find it in the pores of all gross bodies, par,
ticularly those term'd non-electrics, whether - of metals, water, or animals; or vegetables pro
To all minute vacuums (if the term be allow; ed)'i. e. the pores contained in the most dense and compacted bodies, provided they are non-electrics, and those whose pores are so small
. that the gross air is excluded, and where nothing but the same acher, or primary air can insinuate.
vided they are green and replete with Juices: Those being the only bodies to which it escapes' the most freely, since it is not repelld by them:. Any of those kinds of bodies, when perfectly insulated or cut off from all communication with the earth by means of filken strings, or other original electrics, are those to which it escapes and accumulates all the time the machine is in motion, if
of those insulated bodies are within the reach of it; accumulates I say, the pores seeming always so replete with the same electrical principle, as if incapable of receiving any addition, as will more fully appear farther on.
N. B. The pores of all other bodies even those that are the most perfect electrics per fe, appear as replete with this principle, as thote term'd non-electrics ; but in those bodies it is more firmly fix’d.
CH A P. V. Part I.
Come now to consider the Rarity, or Thinness, and the Elasticity, or Springness of Æther, with the Proportion observed by Sir Ifaac Newton between