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THe foregoing Experiments having sufficiently manifested the strength of the Airs Spring upon fluid Bodies, I next thought fit to try, whether the force of a little included Air would
also upon consistent and even Solid bodies emulate the Opera∣tions of the weight of the Atmosphere. In the prosecution of which Enquiry we thought fit to make two sorts of Tryals: the one, where the Air is included in the Bodies, on which its Spring does work; and the other, where tis External to them. Of the first sort are this 7th, and the two following Experiments; and of the second sort are some other Tryals, to be comprehended un∣der the 10th Experiment.
Having formerly mention'd to Your Lordship, that we were several times able (though sometimes not without much difficul∣ty) to make a blown Bladder break with the Spring of its own Air; I should not think it worth while to say any thing here about the same Phaenomenon, but that (besides that it seems odd enough, and is not unpleasant to many Spectators,) it may deserve not to be wholly neglected, because a Good way to break Bladders in the much Exhausted Receiver, may sometimes prove an useful Expedient, especially in such cases where the Experimenter (who sometimes either is not skilful enough, or well enough furnish'd with accommodations to regulate the ingress of the Air) would very suddainly supply the Receiver with fresh Air, when it has been much emptied, without danger of letting in too much Air from without. Not to mention, that the Air, included in the Bladder to be broken, may be so mingled with streams, or imbu'd with divers qualities, as to be much fitter than common Air for some particular Purposes.
We shall then for the affinities sake between this Tryal and the former, subjoyn now the way, by which we seldom fail'd of brea∣king Bladders in our emptied Receivers. For this purpose, the blown Bladder that was to be burst, having the neck very closely and strongly tyed, was kept a pretty while in the Receiver, whilst the Air was pumping out, and then taken out again, that, now the fibres were stretcht and relax'd, the Capacity being lessen'd by a new ligature that I order'd to be strongly made near the Neck, the Bladder might be lessen'd though the Air were but
the same, and the Membrance being not so capable of yielding as before, upon the second exhaustion of the Receiver the Bladder in it would break, far more easily then otherwise, and perhaps be oddly enough lacerated.
We sometimes also varied this way of disposing Bladders to be burst, by omitting the preparatory putting in of the Bladder into the Receiver, and onely taking it in a little near the Neck, that, the Bladder having not been blown very full at first, the tension of the included Air might be greater. But this last way is to be made use of, when the thing we desire is, that the Bladder by breaking at a certain time may part with its Air, and not when tis onely to give an instance of the force of the Spring of uncom∣press'd Air against the sides of the Vessel that contain it.