An Explication of the Second Plate.

Figure 1. Is the Air-Pump, with its Receiver and Gage, as ready for Use; aa, aa are two strong hollow Cylindrical Barrels, in which are suppos'd to be Suckers, with their Handles cc, cc notched; into which Notches a Cog-wheel falls, which Cog-wheel moves upon the Axis f, when the Engine is put into Motion by the Winch bb. gg, gg are two Cylinders of Wood, fixed to the Frame of the Air-Pump, with Screws at the Top, on which the Nuts e, ee do run, and press down the upper Piece ff upon the Tops of the Brass Barrels, to fix them both at Top and Bottom. hh is a Swan-neck'd, or small bended hollow Brass Pipe, leading from the Top-Plate iiii, or rather from the Brass hollow Piece above nn, which communicates through that Top-Plate with the Cavity of the Receiver. This Pipe is screwed to a bottom Brass Piece, included in the Box dd; which is perforated not only lengthways, but also upwards, in three Places: The Middle one for a Communication with this Swan-neck'd Pipe, and at the two Ends through small Cylinders; inserted into the two Brass Barrels aaaa; and 'tis by this Threefold Communication, that the Air is pump'd out of the Receiver. lll is the Gage; which is no other than a common Barometer, or Weather-Glass; with its Bason of Mercury mm, fix'd to the Engine by a particular Contrivance, and its Index or Boxen Receptacle, with Inches, and its Cork to support that Index upon the Surface of the Mercury, and to rise and fall with it; for the Exactness of measuring the Height of the Mercury from that Surface. Only this Barometer is open at the Top, and communicates, as does the Swan-neck'd Pipe, with the Cavity of the Receiver. nn is a Stop-cock, that communicates also with the Cavity of the Receiver, and either excludes or readmits the Air, as you see convenient. k is the Bottom of the Receiver, ground true to fit the Brass Circle below it; to which it is affixed by the Hand at first, and afterward by the Pressure of the Air, with wet Leather instead of Cement.

Fig.2. Is a Barometer Tube, open at the Top H, and included in such a Receiver GB, as gives room for it to stand upright, and yet permits the Air to go backward or forward on its Surface, according as you pump the same out of or readmit the same into that Receiver. And this is done so, that the included Air CD, which supports the Mercury, by pressing on the Surface of that in its Bason ED, is confin'd within. This small Quantity of Air, on the Extraction of that in the Receiver, will, by its Elasticity, raise the Mercury almost as high as the usual Standard: And thereby shews, that the Spring of any small Part of common Air presses equally with the whole correspondent Column of the Atmosphere.

Fig.3. Is a Contrivance to make an Explosion of Gunpowder in Vacuo: Where HD is a red hot Iron, standing on its Pedestal E, within a Receiver GC; and F is a Cock made above like a Dish, to contain the Gunpowder; which by the pulling up and thrusting down a strong Wire, with a Hole like the Eye of a Needle, is in a certain Quantity let fall every time upon the hot Iron; and on the Explosion produces Flame, and fictitious Air; but very little Sound, by reason of the Absence of the Air that should convey it.

Fig.4. Is a Syringe, which will suck up the Water in the Glass CD, when it is in the open Air; but will not do the same under the Exhausted Receiver EF, unless for so small an Altitude as the remaining Air can sustain.