An Explication of the Fourth Plate.

Figure 1. Is a compound Instrument, to shew, why in a Storm the Mercury in the Barometer vibrates so much, by a parallel Case in an Imitation of such a Storm. AA is a large hollow Brass Sphere, into which by the means of the Syringe in Fig.2. Air is crouded till it is 8 or 10 times as dense as usual. HF and LK are Two Barometers, with their Basons in the Boxes FF, KK, which Boxes communicate by a long hollow Tube II. EE is a Brass hollow Tube, to convey the crowded Air near the Surface of one of the Basons of Quicksilver, which Air passes out of that into a larger hollow Pipe GG, and so into the open Air. Upon the turning of the Stopcock C to give vent to the condensed Air, it rushes with great Force along the hollow Pipes EE, GG; and as it passes not far off the Surface of the Bason of Quicksilver FF, it causes the Mercury in both the Barometers HH, and LL, to descend and vibrate several Inches, as the great Storm made Barometers descend and vibrate in Chambers at a distance from it.

Fig.3. Is a Transferrer; containing one common hollow Stem I (here represented as screw'd to a square Piece of Wood, and thereby held upright) with its Stopcock I, and its Horizontal Hollow GH with which it communicates. Upon this Horizontal Piece two more hollow Stems are erected, and communicate therewith. These also have Stopcocks E and F, and to these are screw'd Two Brass Plates AB and CD, on which Two Recipients may be fix'd, and may communicate with the rest. By this means the whole Instrument may be apply'd to the Air Pump, and one or more of its Recipients exhausted; and afterward any Factitious or Natural Air may be transferr'd from one Receiver to another, as Occasion requires: Of which Instrument Mr. Boyle made great Use in his Second Continuation of Experiments.

Fig.4. Are very small or capillary Glass Tubes, of different Bores, let down into Tinged Water, in Vacuo, to shew, that by the Attraction of the Glass the Water will be elevated, contrary to the ordinary Law of Hydrostaticks, and that to a considerable Height; and what is chiefly remarkable, is, that the Altitude of the Liquid in the Tubes is the same in Vacuo as in the open Air, and is always in an exact reciprocal Proportion to the Diameters of their Bases.

Fig.5. Is the noble Improvement of the former Experiment by Mr. Hauksbee, Sen. upon which the Learned Mr. Ditton has written a small Treatise. It is done by two Glass Plains, ACB, ADB, meeting in an Axis at AB; and being about a Tenth of an Inch distant at the greatest Aperture DC. These Plains are Erected in Spirit of Wine, and are like a Series of Tubes of all different Diameters less than DC, which must therefore elevate the Fluid a little at DC, and higher all the way to B, where the Elevation ought to be Infinite; the Tops of the elevated Columns will form an Hyperbola, EFG, with its Two Asymptotes, the Surface of the Fluid DCB, and the Line BA. Note, That if the Angle at DC be altered, the Bigness of the Hyperbola will be alter'd, while its Species remains; but that if the Angle ABC be alter'd, the Species of the Hyperbola will be alter'd also, though it will still be a true Hyperbola, and that if the Glass be clean, to a surprizing Degree of Exactness.