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

EXPERIMENT XXV. What Height the Mercury in Barometers will be suspended at, at the Top of Hills. Some Obser∣vations of the Height of Mountains, especially, the Pic of Teneriff.

HAVING observ'd the Height at which Mercury was suspended at the Bottom of a Hill, and compar'd it with a Barometer made the ordinary ways; it was observ'd, that the Height it was suspended at, at the Top of the Hill, was ¼ part of an Inch below the Mark it reach'd at the Latter; and as the Barometer was brought lower, the Mercury in the Pipe rose higher and higher: But if such Observations could be made at the Top and Bottom of the Mountain Teneriff, the Experiment would afford further Proof of our Hypothesis concerning the Air's Spring and Weight.

An Appendix about the Height of Mountains.

* 1.1NOtwithstanding some Ingenious Men have taught, that the Height of the Atmosphere is of stupendious, and others confine it to narrower Dimensions; yet, I shall add some Observations, which may confirm what we have taught concerning it; and tho', as Ricciolus takes notice, the Jesuit Rector Melensius says, that of all the Clouds, whose Height he measur'd, they did not exceed 5000 Paces, yet if we allow Me∣teors and Comets to arise from Terrene Exha∣lations, and that the Height of Clouds varies according to the different Degrees of the Air's Rarefaction, it will follow, that the Height of most of them exceeds what Carden and Kepler allow.

But to proceed to what I have to relate con∣cerning the Height of Mountains; I shall re∣late, what I have learn'd by Information. And first, the Ingenious Mr. Sydenham told me, that the Mountain Teneriff is so high, that the Top of it may be seen 60 Leagues off, and that he himself had discover'd it at 40 Leagues distance like a blew Pyramid above the Clouds; and he likewise told me, that the Island of Madera might be seen from it, tho' 70 Leagues distant; and that the Great Canary seem'd so near it, that one would think it possible to leap down upon it: And indeed, Ric••iolus observes, that it might be seen 4 Degrees distance; and Snellius also al∣lows the Height of it to be Ten Miles; tho' I believe, that the way he takes to calculate the Height of it, may be none of the truest; he

likewise by Refraction, judging the Mountain Caucasus to be 51 Bolonian Miles high, which is not believ'd probable; since the Mountain Teneriff hath been observ'd, by one who took it's Height in a Ship at Sea, not to be above 7 Miles high in a Perpendicular Line, yet it is esteem'd the highest Mountain in the World; tho' if what Aristotle and others report of Mount Caucasus, be true, there may be others much higher than those. For tho', if measur'd from the Foot, or Level of that piece of Ground, which they stand on, they may be lower, yet considering that the Ground they stand on, may be much more protuberant, from the Level Superficies of the whole Globe, they may be much higher upon that Account.

Notes

• * 1.1

  The Height of Moun∣tains.