An extract of some physico-mathematical discourses contained in Mr. Cotes's Hydrostatical and pneumatical lectures : printed for the use of those that go the course of experiments.

  • Cotes, Roger, 1682-1716.
Date:
[1740?]
Catalogue details

Licence: Public Domain Mark

Credit: An extract of some physico-mathematical discourses contained in Mr. Cotes's Hydrostatical and pneumatical lectures : printed for the use of those that go the course of experiments. Source: Wellcome Collection.

    10/28 (page 10)
    Dr. Halley fays that he himfelf has feen the Air comp refs’d fo as to be 60 times denier than it is as we commonly breath it; and Monfieur Papin relates that he was a Witnefs that Monfieur Havens did once in a Glafs' o Veffel comprefs the Air to the fame degree before the Glafs was broken, yet never could any Experimenter determin how much further the Air might poffibly be rarefied or condens’d. However it’s certain that there are in Nature fome Limits which cannot be exceeded. No con- denfation can reach fo far as to caufe a penetration of Parts, and if the Rarefaction of the Air be {till greater, as its difiance from the Surface of the Earth increafeth, its Spring will at length be fo weakn’d that the force, with which every Particle of it endeavours to tend upwards from the Particles which are next below it, will be weaker than the force of its own gravity which endeavours conftantly to detain it. The Rarefa&ion of the Air mud therefore be bounded of necefiity when thefe two oppofite forces come to ballance each other. Though this be certainly true that the Air can’t poffibly expand it felf beyond a certain meafure upon ac¬ count of its Gravity, yet fince Men have not hitherto been able to fet any bounds to its utmoft expanfion, it is equally certain, that we cannot poffibly define the Limits of the Atmofphere. For as the Air may be more and more rarefied, lo will the fame Quantity of it (which equals the weight of about 3 0 Inches of Quickfilver) be contain’d in a greater Space, and thereby thofe Limits be fo much the wider. Notwithfianding this feeming difficulty we may ftill collect how much the Air is ratified at any propos’d Altitude from the Surface of the Earth after the follow¬ ing manner. Let XAclPX (Fig. 14.) reprefenta Veffiel reaching from the Surface of the Earth Acl to the top of the Atmofphere X. Let us imagin the fide AX divided into Inches AB, BC, CD &c. and let the Lines BK, CL, DM, EN &c be drawn parallel to Acl. ’Tis evident that the Air con- ] tam’d between BK and CL is rarer than the Air contain’d between Acl and BK; the former having a leffer Column of Air XCLX incumbent tipon it, than the Column XBKX which preffes upon the latter. Upon the fame account the Air between CL and DM is rarer than that be¬ tween BK and CL, and that between DM and EN rarer than that be¬ tween CL and DM. And thus is every fuperior Inch of Air rarer than that below it. Let us now fuppofe, that every Inch of Air is in all parts of it of an equal Denfity, or that the Air AK is every where uni¬ form, but denfer than the Air BL ; which is alfo fuppos’d to be every where uniform, but denfer than CM; and that to be uniform it felf, but denfer than DN, and fo onwards. Again let us fuppofe that the Air BL is reduc’d to a lelfer Space BO, fo as to become equally denfe with the Air AK, which is done by making the Space B (7 leffer than BL, in the fame proportion that the Air BL is lefs denfe than the Air AK; after the fame manner let the Air CM be reduc’d to the Space CR, and the Air DAT