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Of which we shall be the bet∣ter assured, after we un∣derstand that the Authours Rea∣sons in this Ninth Chapter for the ascent of steams or vapours from the Mercury it self, p. 139. l. 13. are not sufficient. For the two ways that he offers for the separating these steams or va∣pours from the body of the Mer∣cury
are, The first, expression or driving them out by the strong descent of the Mercury and com∣pression of the inferiour parts by the superiour. The other, is ex∣traction or straining out those parts that are more subtil and flu∣id, and capable of expansion, &c. To which I answer, that these two ways are in a manner one and the same, or at least the stress lies upon that one first, which if it fail the other will sig∣nifie nothing. And methinks it is apparent at least in such a case as this, that it will signifie no∣thing, namely, if the Tube filled with Mercury be immitted into the restagnant Mercury, very much inclining, and be raised to a perpendicular by degrees and leasurely, for then there being no such jolting of one part against another, but a gently bringing one part over another perpendi∣cularly, and being so posited,
they according to the law of Fluids not gravitating one part upon another in the Tube above the surface of the restagnant Mer∣cury, and having but little un∣der to gravitate upon, nor the restagnant Mercury (according to the same law of Fluids, even then when it was made some∣thing to ascend by the Mercury descending from the Tube) gra∣vitating one part upon another, it is manifest there was no com∣pression able to separate any par∣ticles from the Mercury and send them into the Tube.
The Authour himself raises a notable objection, p. 141. l. 26. against this opinion of Mercurial effluvia supplying the derelicted place of the Mercury in the Tube: Suppose, says he, the Tube were ten foot long, or the
upper end were a Bolts-head that should contain 4 pounds of Mer∣cury, this Mercury subsiding to 29 inches, where should there be effluvia to fill so great a space? His answer is, the more Mercury descends to 29 inches, the more effluvia there will be to fill the space; but I say if the Tube of Mercury be let down obliquely, as before, and be gently and lea∣surely raised to a perpendicular, according to the law of Fluids the compression will be even just nothing. From whence then can that vast empty space be supply∣ed but by the subtiler parts of the Air coming in through the pores of the Glass-Tube? which is that we aimed at.