The works of the Honourable Robert Boyle, Esq., epitomiz'd by Richard Boulton ... ; illustrated with copper plates.

CHAP. XVIII. A Consideration concerning some Tryals of the Torrecellian and other Experiments' at the Tops and Feet of a Hill.

FOr a further Proof against Our Adversaries Doctrin, and for a Confirmation of ours, I shall add the following Experiments.

And First: The Famous Pecquet mentions an Experiment, made by Monsieur Pascal, at the Foot of a Mountain 3000 Foot high; where when he ascended, 150 Fathom, the Mercury in the Cy∣linder was not buoy'd up so high, as at the Bot∣tom, by two Inches and a Quarter; and at the Top of the Hill, it wanted 3 Inches of that Sta∣tion, which it was suspended at, at the Foot of the Hill; which is a strong Argument against our Adversary; the Difference plainly appear∣ing to depend on the different Length of the At∣mospherical Cylinder, which was abler to weigh up the Mercury at the Bottom, than the Top of the Hill.

And Gassendus, Tom. 1. P. 211. relates, that the like was observ'd 5 times on the Hills at Auvergne. And a very Noted Virtuoso, Mr. J. Ball, as well as that Ingenious Gentleman Mr. Townley, have observ'd the like in England. And it was by the last nam'd, likewise observ'd, that the Mercury included in the Top of the Cylinder, was not able to depress the Mercury, near so much at the Bottom, as at the Top of the Hill.

But to discover the weight of the Air, and it's Spring, without going up to the Top of such high Mountains, we made use of the following Weather Glass, suspending Water in the Pipe, instead of Mercury. The Instrument was a Glass with a broad Foot, and a narrow Neck (A B), and a slender Pipe of Glass (C D), which was open at both Ends; and so plac'd, that the lower End was not far from the Bottom (A B), and was so closely cemented at the Neck (A), as to prevent the Internal Air (I I) from communicating with External (K K), unless it were through the Pipe (C D). And having conveig'd Water (H H) into the Glass (AB), which was pretty large, and having blown so much Air into the Bottle, as to raise the Water in the Tube above the Vessel, upon the Leads of Westminster Abby. When the Air was thought to be equally Cold and Con∣dens'd within the Bottle, as without; we mark'd the Station of the Water (F), and letting it down by a String to the Ground, the Water subsided an Inch, where it's Station (E), being mark'd, and the Vessel drawn up again, the Water was rais'd to the Mark (F) again. Which Experiment being again try'd, had the like success. And af∣terwards the Top of the Tube being broke, we let it down within the Church, the Surface of the Water in the Pipe being at (G) an Inch above the Water in the Glass; where I observ'd, that the Air so depress'd it, when it came to the Bottom, as to force the Water out of the Pipe into the Glass, several Bubbles breaking through into the Capa∣city of the Glass, and this Glass being drawn up to the Top of the Church again, the Water was manifestly rais'd in the Tube again; from whence

it appears, that the Atmosphere gravitates more; Caeteris paribus, the nearer the Surface of the Earth; for the Experiment being repeated, we found that as the Height, at which it was try'd, vary'd; so the Elevation or Depression did.

Another Particular which may be a further Confirmation of our Hypothesis, is, That which is mention'd by Monsieur Paschal, viz. That a Foot-Ball being weakly blown, and carry'd to the Top of a Hill, swell'd more and more, as it was carry'd higher; and as gradually grew lank, when it was carry'd down the Hill again: From whence it appears, That as the Atmosphere is lon∣ger or shorter, it makes a greater Gravitation and Pressure upon the Bladder.

To this I shall add an Experiment, sent to Dr. Croon, by a Learned Professor of Gresham Col∣ledge, which is the following: Having Observ'd that in the Weather-Glass (A B), represented by the Second Figure, which was about two Foot long; the Water was suspended in the Pipe, about thirteen Inches above the Superficies of the External Water, at the Bottom of Hallifax Hill; but being carry'd to the Top of the Hill, it sub∣sided an Inch and a Quarter, to the Point (D). The Internal Air (A C), which was taken in at the Bottom, dilating it self at the Top further by (C D). In which Experiment, the Descent being much more considerable than what it ought to be in such a small Ascent, by the bare Pressure of the Atmosphere diminish'd, the Reason appears to be, the Expansion of that Air included in the Top of the Weather-Glass; as well as the Short∣ning of the Atmospherical Cylinder.

Notes

• The Height of Mercury suspended at the Top of a Hill.
• See Fig. the First, Plate the Second.
• See Fig. the Sec. Plate the Second.