Page images
PDF

And not only Animals themselves, but even Trees and Plants, and the whole vegetable Race, owe their Vegetation and Life to tbis useful Element; as will appear when I come to speak of them, and is manifest from their Glory and Verdure in a free Air, and their becoming Pale and Sickly, and Languishing and Dying, when by any means excluded from it (g).

. Thus useful, thus necessary, is the Air to the Life of the animated Creatures; and no less is it to the Motion and Conveyance of many of them. All the winged Tribes owe their Flight and Buoyancy (b) to ir, as shall be shewn in proper place: And even the watery Inhabitants themselves cannot

ascend

(g) That the Air is the principal Cause of the Vegetation of Plants, Borelli proves in his excellent Book De plot. Animal. Vol. 2. Prop. 181. And in the next Proposition, he assureth, In Plantis quoque peraghAeris rtfpirationem quandam imperfe61am, a qua carum vita pendet, <y conjervatur. But of this more when I come to survey Vegetables.

Same Lettice-Seed being sown upon some Earth in' the open Air, and. some of the same Seed at the same time upon other Earth in a Glajs-P.ecetver of the Pneumatick Engine, aftenvards exhausted of Air: The Seed exposed to the Air was grown up an Inch and half high within Eight Days; but that in the exhausted Receiver not at all. And Air being again admitted into the fame emptied Receiver, to fee whether any of the Seed ■would then come up, it was found, that in the Space of ont Week it was grown up to the Height of two or three Inches. Vid. Phil. Trans. No. 13. Lowth. Abridg. Vol. z. p. 206.

(h) In volucribus pulmones perforati aerem inspiratum in tot am •ventris cavitatem admittunt. Hujiis ratio, ut propter corporis truncum Aere repletum w quasi extensum, ipfa magis volatilia evadant, faeiitusque ab aere externo, propter intimi penum, sustententur. Equidem pisces, quoleviusin aquis natent, in Ab domine vesicas Aere inflatas gestant: pariter v volucres, propter corporis truncum Aere impletum cr quasi insiatum, nudo Aeri i»»mbentes, minus gravantur, proindeque levins e? expeditiks volant. Willis de Anim. Brut. p. 1. c. 3.

[graphic]

ascend and descend into their Element, well without it (/').

But

(i) Fishes by reason of'the Bladder os Air within them, can sustain^ or keep themselves in any Depth of Wa:er: For the Air in that Bladder being more or less compressed, according to the Depth the Fish swims at, takes up more or less Space; and consequently, the Body of the FiJIi, part of whose bulk this Bladder is, is greater or less according to the several Depths, and yet retains the fame Weight. Now the Rule de Infidentibus humido is, that a Body, that is heavier than Jo much Water, as is equal in Quantity to the Bulk of it, will fink, a Body that is lighter will Jwim; a Body of equal Weight will rest in any part of the Water. By this Rule, if the Fish, in the middle Region of the Water, be of equal Weight to the Water, that is commensurate to the Bulk of it, the Fish will rest there, without any Tendency upwards or downwards: And if the Fish be deeper in the Water, the Bulk of the Fish becoming less by the Compression of the Bladder, and yet retaining the same Weight, it ivill fink, and rest at the Bottom. And on the other side, if the Fijh be higher than the middle Region, the Air dilating it self, and the Bulkos the Fish consequently increasing, but not the Weight, the Fijh will rise upwards and rest at the top of the Water. Perhaps the

fish by some Atticn can emit Air out of its Bladder , and,

when not enough, take in Air, and then it zvill not be won

dred, that there should be always a fit Proportion of Air in all ■fishes to serve their Use, &c. Then follows a Method of Mr. Boyl to experiment the Truth of this. After which, in Mr. Lozvthorp's Abridgment, follow Mr. Ray's Observations. / think tltat —■ hath hit upon the true Use of the SwimmingBladders in Fifties. For, I. It hath been observed, that if the Swimming- Bladder of any Fish be pricked or broken, such a Fist) sinks presently to the Bottom, and can neither support or raise it self up in the Water, z. Flat Fijhes, as Soles, Plaise,Scc. which lie always grovelling at the Bottom, have no Swimming-Bladders that ever I could find. 3. In most Fifties there is a manifest

Chanel leading from the Gullet to the said Bladder,

■which without doubt serves for the conveying Air thereunto.In the Coat of this Bladder is a musculous Power to contrail it ivhen the Fijh lists. See more very curious Observations relating to this Matter, of the late great Mr. Ray, as also of the curious anonymous Gentleman in the ingenious Mr. Lowthorp's Abridgment, before cited, f. 84s- from Phil. Tra\s. N. H4> 115

(4) Ampng

But ic would be tedious to descend too for into Particulars, to reckon up the many Benefits of this noble Appendage of our Globe in many useful Engines (k) > in many of the Functions and Operations of Nature (/) in the Conveyance of Sounds; and a Thousand Things besides. And I shall but

just

(*) Among the Engines in which the Air is useful, Pumps may be accounted not contemptible ones, and diveis other Hydraulical Engines, which need not to be particularly insisted on. In these the Water was imagined to rile by the power of Suction, to avoid a Vacuum, and such unintelligible Stuff; but the justly famous tAr.Boyl was the first that solved these Phenomena by the Weight of the Atmosphere. His ingenious and curious Observations and Experiments relating hereto, maybe seen in his little Tract, Of the Cause of Attraction by Sutfion, and divers others of his Tracts.

(/) It would be endless to specify the Uses of the Air in Nature's Operations: I (hall therefore, for a Sample only, name its great Use to the World in conserving animated Bodies, whether endowed with animal or vegetative Life, and its contrary Quality of dissolving other Bodies; by which means many Bodies that would prove Nuisances to the World, are put out of the Way, by being reduced into their first Principles, (as we fay), and so embodied with the Earth again. Of its Faculty as a Menstruum, or its Power to dissolve Bodies; I may instance in Crystal Glasses, which, with long keeping, especially if not used, will in Time be reduced to a Powder, as I have seen. So divers Minerals, Earths, Stones, FoflilShells, Wood, we. which from Noah's Flood, at least for many Ages, have lain under Ground, so secure from Corruption, that, on the contrary, they have been thereby made much the stronger, have in the open Air soon mouldered away. Of whrch last, Mr. Boyl gives an Instance (from the Dissertation de admirandis Hungar. Aquis) of a great Oak, like a huge Beam, dugout of a Salt Mine-in Transylvania, so hard, that it would not easily be wrought upon by Iron Tools, yet, being exposed to the Air out of the Mine, it became so rotten that in four Days it was easy to be broken, and crumbled between one's Fingers. Boyl'j Suspic. about some hid. Qual. in the Air, /.|Z8. So the Trees turned out of the Earth by the Breaches at West-Thurrock and Dagenham, near me, although probably no other than Alder, and interred many Ages ago in a rotten oaiy Mold, were so escsedingly tough, hard, and sound at iA. "first,

just mention the admirable use os our Atmosphere in ministring to the enlightening of the World, by its reflecting the Light of the heavenly Bodies to us (m); and refracting the Sun-beams to our Eye, before it ever surmounteth our Horizon (»); by which means the Day is protracted throughout the whole Globe $ and the long and dismal Nights are fhorten'd in the frigid Zones, and Day sooner approaches

first, that I could make but little Impressions on them with the Strokes of an Ax; but being exposed to the Air and Water, soon became so rotten as to be crumbled between the Fingers. See my Observations in Pbilos. Transact. N° 335.

(m) By reflecling the Light of the heavenly Bodies to us, I mean that Whiteness or Lightness which is in the Air in the Day-time, caused by the Rays of Light striking upon the Particles of the Atmosphere, as well as upon the Clouds above, and the other Objects beneath upon the Earth. To the fame Cause , *lso we owe the Twilight, viz. to the Sun-beams touching the uppermost Particles of our Atmosphere, which they da when the Sun is about eighteen Degrees beneath the Horizon. And as the Beams reach more and more of the airy Particles, so Darkness goes off, and Day light comes on and encreaseth. For an Exemplification of this, the Experiment may serve of transmitting a few Rays of the Sun through a small Hole into a dark Room: By which means the Rays which meet with Dust, and other Particles flying in the Air, are render'd visible; or (which amounts to the fame) those swimming small Bodies are rendered viflblf, by their reflecting the Light of the Sunbeams to the Eye, which, without such Reflection, would it self be invisible.

The Azure Colour of the Sky Sir Isaac Neivton attributes to Vapours beginning to condense, and that are not able to reflect the other Colours. V. Optic. 1.1. Par. 3. Prop. 7.

(») By the Refractive Power of the Air, the Sun, and the other heavenly Bodies seem higher than really they are, especially near the Horizon. What the Refractions amount unto, what Variations they have, and what Alterations in time they cause, may be briefly seen in a little Book called, The Artificial Clock-Maker, Chap. 11.

Although this infiebVtve Quality of the Air be a great Incutnhrance and Confusion of Astronomical Observations ; —— yet it is not without some considerable Benefit to Navigation; and indeed in some Cases, the Benefit thereby obtained is much greater

thm

proacheth them i yea the Sun it self riseth in Appearance (when really it is absent from themj to the great Comfort of those forlorn Places (0).

But passing by all these Things with only a bare mention, and wholly omitting others that might have been named, I shall only insist upon the excellent Use of this noble circumambient Companion of our Globe, in respect of two of its Meteors, the Winds, and the Clouds and Rain (f).

■—

than would be the Benefit of having the Ray proceed in an ex ail straight Line. [Then he mentions the Benefit hereof to the Polar Parts of the World] But this by the by (faith he.) The great Advantage I consider therein, it the first Discovery os Land upon the Sea; for by means hereof, the tops of Hills and Lands are raised up into the Air, so as to be discoverable several Leagues farther off on the Sea than they would be, were there no fitch Refrattton, which is of great Benefit to Navigation for steering their Course in the Night, when they approach near Land; and likewise for directing them in the Day-time, much more certainly than the most exaH Celestial Observations could do by the Help of an uninfiecled Ray, especially in such Places as they httve no Soundings. [Then he proposes a Method to find by these means the Distance of Objects at Sea.] V. Dr. Hook's Post. Works. Lect of Navig. p. 466.

(0) Cum Belg£ in nov& Zembla. hybernarent, Sol Mis apparuit \6diebus citiits, quam revera in Horizonte existeret, hoc est, cum adhuc infra Hortzontem deprejfuj effet quatuor circiter gradibus ejrquidem acre sereno. Varen. Geog. c 19. Prop. it.

[These Hollanders] found, that the Niqht in that place shortened no less than a whole Month; which must needs be a very great Comfort to all such Places as live very far towards the North and South Poles, where length of Night, and want of seeing the Sun, cannot chuse but be very tedious and irksome. Hook Ibid.

[By means of the Refractions] we sound the Sun to rise twenty Minutes before it fliould; and in the Evening to remain above the Horizon twenty Minutes ( or thereabouts) longer than it should. Captajn James's Journ. in Boyl of Cold. Tit. 18. p. 190.

(p)'Aerin Nubes cogitur: humoremque colligens terram auget imbribus: turn effiuens hue cr illuc, ventos efficit. Idem annuas frigorum e? calorum facit varietates: idemque vvolatus Alitum fufiinet, ey fpiritu duttus alit &• susttntat animantes. Cic. de Nat. Deor. \.x. c. 39.

CHAP.

« PreviousContinue »