OCR Text |
Show SU 5 U asin Peru, Mexico, the Alps, Sc. And to the fame Caufe it is owing, that the Nights in Arme are fhivering cold. . In the mountainous Places in thefe Countries, we are told, there is no fuch thing as pure Water, but all Ice. : Plants make a Shift to grow about the Feet of the Mountains, but higher up no Vegetable can live; not for want of Food, but through the Intenfeneds of the Cold; Men ftaying there but a little Time catch violent Agues, which with a longer Stay grow incurable. ; Heat then depends not upon the Fire’s be- ing fent or determined toward us, but only by its being reflected, either by Mountains or Clouds. ie If Fire be propagated through an uniform Medium, it will never produce any confide- rable Heats. : And hence it is that the Degree of Heat is not fo very intenfe in the Torrid Zone, as one would otherwife expect; but that in the Ifland of Ormus ’tis perfeétly fcorching, and not endurable by any Mortal, unlefs they were to fcreen themfelves under Water. SU Now this is owing to the Atmofphere, which being replete with an infinite Number of Corpuicles, reflects more of the Sun’s Rays to the Earth, when they fall perpendicularly, than would otherwife arrive there. For whereas falling obliquely, they would be reflected, and thus be thrown off, anddif- pers’d into other Parts; nowthat their Incidence is perpendicular they they will pafs directly through. And hence arifes what is frequently obferv’d by Sailors, viz. That when the Sux radiates obliquely upon the Sea, as in the Evening, there is no enduring his Rays; by reafon they are all reflected trom the Water, and fcarce any loft therein: So that the Rectitude or Obliquity of the Rays contribute very confiderably to the Collecting of Fire. Andthis Obliquity, &c. is to be confider’d in a two-fold refpect, both with refpect to the Matters in the Atmofphere, and to’ the Surface of the Earth. Now Heat maybe varied two Ways. 1. By Means of the Atmofphere; forthis does not always remain tite fame. Thus, «.g. Water is naturally tranfparent, and if you with only the Head out, warm it, it ftill retains its Tranfparency ; but if you make it boil, the Vapouriffuing from it, though perhaps a Million of Times rarer which is kept fufpended by a Contrivance for that Purpofe: The Cafe is, that the faid Ifand is full of Salt Rocks, which act like than the the primitive Water, will not be tranfparent, but opake, by reafon its Parts noware in a different Arrangement. The Heat here is faid to be fo vehement, that People, like Fifhes, are forced to fleepin Cifterns of Water, fo many Spicula, and reflethe Light in great abundance; fo that the Ifand at a Diftance appearslike one continuedFire. Another Caufe which fome alledge for this exceflive Heat, is, that the Ifland was anciently full of white Mountains, which having in Time beenall laid level, the whole Surface of the Ifland is white, and thus difpos’d to reflect abundance ofLight. Heat therefore does not immediately depend an the Su, but on Bodies that refle&t. Hence, in high Places, and where the Atmofphere is very rare, the Heat is extremely feeble, and Thefe cloudy Mirrors are fometimes round, fometimes concave, polygonous, &c. When the Face of Heaven is covered with fuch white Clouds, the Suz fhining among them muft of Neceffity create a vehement Heat, duced. they will be perfeét Burning-glaffes. hence the Pheenomena of Thunder, &&c. 1. A Body ftriking perpendicularly on ano2. A Body ftriking obliquely againft ano- ther, aéts with the lefs Force, deviates from the Perpendicular. the more it Lines, muft obferve the fame mechanical Law as other Bodies, and confequently its Action muft be meafured by the Sine ofthe Angle of Incidence. And hence Fire ftriking on any Obftacle in a Direétion parallel thereto has no and the Clouds on the oppofite one, fenfible Effect, by reafon the Proportion is almoftinfiNite, i.e. nothing. Accordingly Dr. Halley obferves, that the Sun radiating on the Earth in the Morning has but little Effeét, but that when rais’d to the Meridian he aéts withall his Force. And _ Ihave, fays Dr. Boerhaave, obferv’d a kind of hollow Clouds full of Hail and Snows during the Continuance of which the Heat was extreme; Now Fire direéted by the Sainto Right in effect, are a fort of wandering Fire, vifible by Night, and which determine the Fire over and upon the Farth. 2, It is varied by means of the Earth: For as the Surface of the Earth varies, fo muft the Heat. Thus fandy Places reflecting more Rays than others, muft excite a greater Degree of Heat. Onthe higheft Mountains we always find the moft Cold, Snow, and Hail. In the fultry Region of Peru, the Mountainsare all Summer long cover’d with Snow, by reafon they only receive direct, and but little refracted Fire; and the Effect ofFire arifing merely from being determin’d by the Sum into a Parallelifm, is found, by Computation to be very inconfiderable. For this Effect, as already obferv’d, is greater in Winter than in Summer. Though the Suz be in his Apogee in the Summer, and in his Perigee in Winter, yet will a Night’s Ice bear its fhining uponit five or fix Hours ere it be thaw’d. Andifas the Sum rifes nearear toward the Zenith, the Ice and Snow at length begin to, run, this is not owning to the greater Forceof Thus far the Learned Boe , The Sun (fays a certain Author) may be accounted the Parens Nature, or the Primum Mobile of all vegetative Motion. The Sun’s attractive Virtue is very confpi- cuous, in the Exhalation of thofe crude and unwholfome Vapou with which the Earth is often infefted; which, if they were fuffer’d to continue long upon the Face of the Earth, would renderita miferable Defart. The Sun, by fubliming thofe crude and hurtful Vapours, andtheir being rarefied before their Defcenfion and Diftribution, forms theminto Rain, which is of great Confequence in Vegetation. To this he adds, the Attra@tion of Plants themfelves, which creates a kind of Emula- tion in them, which fhall growthe talleft. But that which the Antients did ufe to attribute to Attraction, well folved by Pulfion. may now be very To apply which to Surface of the Matter in Hand: When the Sea, &. is divided by the Heat of the Sun, and the Power ofthe Air, their Afcenfion through the Atmofphere, either by the Rarefaction of the Air by the Suz, or otherwife by the Refpiration of the Globe, which in this Cafe may to act like the Body Natural; the Air being rarefied by the Terraqueous from Snow; the Reafon whereofis, that Water, Side, ther, aéts on it withall its Force. The Meteors in the Atmofphere havelikewife their Share in reflecting of Fire. Thefe, Add, that thofe white Clouds which appear in Summer-time, are, as it were, fo many Mirrors, and occafion exceffive Heat. is greater or lefs, greater or lefs Heat is proFor, Farth, liquify anddiftil in Drops. moreFire it contains; whenceit it, that Wa- ter depriv’dofall its Fire, fixes into Ice, and when expos’d afrefh to the Fire, refolves into Water; and all Fluids whatever, if deftitute of Fire, would do the fame. be fuppos’d the Sun, but to the greater Reflection and orelfe that Collection of his Rays from the CircumSum Beams, ftances and Pofition of the Atmofphere and does, by the Gravitation of his own Body in Earth. b But the higheft Topsof Hills are always free general, force thofe humid Vapours by Pulfion fince many of his Rays, which would otherwife perhaps never touch our Earth, are hereby reflected to us; thus if the Sum be on one But it remains here to be obferved, that All Clouds, ’tis probable, contain Snow and Ice, but thefe in their Fall through the warmer Regions of the Atmofphere nearer the And hence thofe Legions of Corputcles every where floating in the vaft Receptacle of the Atmofphere, whenever they acquire a different Difpofition, which they frequently do, alter the Colleétion of the Rays on the Earth. according as the Direction of the Sun’s Rays vice vErfa. Ste) they were fince by fuch Condenfation enabled to reflect much more ftrongly : After this came a fharp Cold, and then the Clouds difcharged their Hail in great Quantity ; to which fucceeded a moderate Warmth. Frozen, concave Clouds therefore, by their great Reflections, produce a vigorous Heat; and the fame whenrefolv’d, excellive Cold. i Henceit is probable, that Thunderis only produc’d when fuch concave Clouds, before convolved into fpherical Figures, are — with oppofite Motions againft each other 5 on the Rays tranfmitted through thofe Spheres from burning Foci. All i.e. the Vapours and Exhalations emitted therefrom, never rife by the Swn’s Action above a Mile high. But there are Mountains a Mile and ahalf high ; to the Topsofthefe therefore, Vapour, and confequently Clouds, can never mount. And hence it is, that in very high Mountains, asthe Pico de Theide in Bohemia, tho’ the middle Part be eternally invefted with Ice and Snow, and the Bottom fcorch’d with intolerable Heat, yet on the Top you find yourfelf in a pure, thin, ferene Air, and view the Clouds hovering at a confiderable Diftance below you. Hencealfo it is, that all Phun- der is confined within lefs than a Mile’s Height. Add, that in Caverns, andthe hollow Parts under-ground, the Heat is found very greats fo that the Air is coldeft in the higheft Places, and hotteft in the loweft ; but in the intermediate Atmofphere very unequal. Heat therefore depends on Clouds, Mountains, €%c. which refleét the Light varioufly, and on the Direction of the Sun’s Rays, or the Pofition of his Body withrefpect tous, Hence again we gather, that Fire is the univerfal Caufe of all the Motions about our Earth ; for all Fluidity depends on Fire; and accordingly in the large Burning-glaffes the firmeft Bodies become fluid, and evaporate in Fume: And the more fluid any Body is, the upwards, through thofe Beams or Rays of Light, which are, as it were, fo many Pipes or Tubes for their ready Paflage, Aicenfion, and Conveyance. Or if thofe Vapours are convey’d by the Undulation of the Air in a perpendicular Manner, rather than a radiant one, through the Rays and Beams of Light, which foever of thefe Ways it is, the Sym is the principal Agent in this Bufinefs; and the whole Procefs is either Attraction, Pulfion, or Refpiration, forwarded by the virtual Power of it. That the Rarefaétion of the Air by Heat is a great Help to Attraction or Pulfion, may be difcovered by the Fire Engine made by Mr. Savoury; we cannot fay that the Water is either forced or attraéted by the Heat, but that the Air that is in the Pipe is lighten’d by its rarefying Quality to fuch a Degree, that the 4quilibriumis loft, and the Impulfe and Preffure of the Air, which is without, forces the Water to that great Height that is feen in the Operation. Andfo, ifa little Scrip of Paper burning and fuming be put intoa common Drinking-glafs, andit be turn’d up immediately, and put upon a Plate of Water, it feems as tho’ it would fuck it up into the Glafs; when indeed, the Truth of the Expe riment is, that itis only the outward Preflure and the inward Weaknefs of the Air to refift, being purified by Heat: Forif the fame Glafs fhould be plung’d into a Bafon of |