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Show VA VA That Rain is produced by the Separation of the Particles of Fire from thofe of Water, which laft being then reftored to their former fpecifick Gravity, can be no longer fuftained by the Air ; but muft fall in Drops. This, fays Dr. Defaguliers, is liable to feveral Objeétions. 1. It is built upon a Suppofition, that Fire is a particular Subftance, or diftiné Element, which has never yet been prov’d by convincing Experiments and fufficient Obfervations ; and which the Reverend Mr. Hales has fhewn to be an ill-grounded Opinion, in his late Book of Vegerable Staticks, and has made it VA by the blowing away fome of the fuperiot Air, that which is about the Cloud rarer, as it is lefs comprefs’d, or by becomes the Cloud being driven upwards ;) Rain muft neceflarily follow ; whereas one may often fee Clouds rife and fall without Rain, even when the Ba- rometer fhews the Weight of the Air to be altered. For that happens only, when by the great Diminution of the {pecifick Gravi ty of the Air about the Cloud, it has a great Wayto fall; in which Cafe the Refittance of the Air, which increafes as the Velocity ofthe defce nding Cloud, caufes the floating Particles of Water very plain, that thofe Bodies which had been. to come within the Power ofeach other’s Atthought to become heavier by Particles of traction, and form Fire adhering to them, have, by chymical {pecifically heavi fuch big Drops, as being er than any Air, muft fall in Operations, been prov’d to be only fo by the Rain. Adhefion of Particles of Air, €&¥c. which he No gentle Defcent of a Cloud ; but only has fhewn to be abjorbed in great Quantities, an accel erated Motion downwards, produces by fome Bodies, whilft it is generated (or re- Rain. duc’d from a fix’d to an elaftick State) by He explains himfelf, that by this he does others ; nay, that it may be abjorbed and ge- not mean, That the quick Dejcent of a Cloud nerated fucceffively by the fame Bodyunder is the only Caufe of Rain; becaufe the Shock different Circumftances, from a Elafo of Lightning, and-the Judden Re2dly, If the above-mentioned Suppofition turn ofthe Air, after the Vacuum made by the fhould be allow’d, the Difficulty will {till reFlafh, will condenfe the floating Vapour into main about the Rain which is produc’d by Water ; and the Fire's being feparated from the Water: free Air mightalfobethe fame Cloud which in the carried horizontally, with For Dr. Niewentyt afcribes this Effect to two out being turned into Rain, meeting with a high different Caufes, Firft, to Condenfation ; for he fays 5 «¢ That ** when contrary Winds blow againft the fame ** Cloud, and drive the watry Particles toge“ ther, “ce “ee the Fire that adher’d to them gets loofe, and they (becoming then fpecifically heavier) precipitate and fall down in Rain? And in the very next Seéfion he afcribes it to Rarefaétion ; in that he fays; ‘* When a ** Wind blowing obliquely upwards, caufes a «© Cloud to rife in a thinner Air, (i.e, fpecifically lighter than it felf) the Fire, which by fticking to the Particles of Water render’d themlighter, extricates it felf from them, and afcending by its Lightnefs, the Water will become too heavy, not only to remain in this thin andlight Air, but even in a thicker and heavier near the Earth, and fo will be turned into a defcending Dew, Mift, or Rain, or Snow@br the like, according as the watry Vapours are either rarefied or compreffed.” To this Dr. Defaguliers anfwers: That the firft of thefe Caufes of Rain is contrary to Experience; for when two contrary Winds blow againft each other, over any Place of the Earth, the Barometer always rifes, and we have fair Weather. For then (as Dr. Halley fays, in Pbilofopbical TranfaGtions, N° 183.) the Air being accumulated above, becomes fpecifically heavier about the Clouds, which (inftead of falling into Rain, as Dr. Niewentyt Hill in the Way, will be condensd, and falk in Drops; efpecially if in the Day-time it be driven by the Wind out of the Sun-Sbine, againft the foaded Side of a Mountain. Befides all this, if Particles of Fire were join’d with thofe of Water. to raife them up, thofe igneous Particles muft beat leaft a thoufand times greater in Bulk than the watry ones; fo that a Perfon, who at the Top of an Hill, has his Hands and Face in a Cloud , mutt feel a very fenfible Warmth, by touch- ing a muchgreater Surface of Fire than Water in the Cloud, and afterwards find the Rain produc’d by that Vapour fenfibly colder ; where as the contrary is proved by our Senfes; the Tops of Hills, though in the Clouds, being much colder than the Rain at the Bottom. There is another Opinion concerning the Rife of Vapours, namely ; That though Water VA For the Rife of Duft is owing to the Motion of Animals Feet in it, or to the Wind; whereas Vapéurs rife in cold Weather, as well as windy; neither do they, like the Dutt, always fall to the Ground, when the Wind ceafes to blow. The third Opinion, and whichis moft commonly receiv’d, is, that by the Aétion of the Sun on the Water, fmall Particles thereof are formed into hollow Spherules, filled with an dura, or finer Air highly rarefied, fo as to all over its Surface? will be fpecifically lighter than common Water, whoie fpecifick Gravity is to that of Air Air, to blow up the Bubbles (as Bubbles of foaped Water are blown up by warm Air as 851 to 13 then, if the Denfity ofthe Aura, er Spirit within the little Shell, be fuppofed 9 times lefs than that of Air, or as 50 to 850, that fpecifick Gravity of the Shell, and its Contents, will be co that of Air, as goo fo 10003 therefore fuch an aqueous Bubble He till come to an Aquilibrium in Denfity is to the Denfityofthat in n torife, as 850 to 945, or nearly. ars by Experiments, that Air rarefied by an Heat, which makes a Retort red hot, is only increafed in Bulk, ordilated i 2 . t of boiling Water only irdss; and by the Heat of human Body, (fuch as will raife Vapours plenufully) or ly 42, or about one Fourth. e s Objection may be anfwered, ing the Spherule of Water to be more increafed in Diameter; as for Example, times; becaufe then if it be filled with only 4 rather than commonAir, it will be ecifi lly lighter, and capable of rifing to a confiderable Height. : To give this Solution all its Force, let it be exprefs’d in Numbers. Let A and W(Fig. fent a Particle of Air, and one of r of equal Bulk, then will the Weight he Weight of Was 1. to 850, Iks- being equal. If the Particle of then every Time a Cloud is encompaffed with reafon of its great Refiftance to fo large 8 3 for the fame Reafon alfo hin- For that without them, fince the Sun’s Rays, which aé& upon the Water, are equally denfe Query 2. If it could be poffible for a rarer Air to be feparated from the denfer ambient from the Lungs, whilft the ambient Air is colder and denfer) what would hinder that cold Air, by its greater Preflure, from reducing the Bubbles to a lefs Bulk, and greater {pecifick Gravity than the Air, efpecially fince Cold can be communicated thro’ fuch thin Shells, and the Tenacity of common Water is very finall, when compared to that of fop’d Water, whofe Bubbles, notwithftanding that Tenacity, are foon deftroy’d by the Preffure of the outward Air, as the Air within them cools ? Quere 3. If we fhould grant all the reft of the Suppofition, yet this Difficulty will remain: If Clouds are made up of hollow Shells of Water filled with Air, why do not thofe Clouds always expand when the ambient Air is rarefied, andpreffés lefs than it did before, and alfo fuffer a Condenfation, as the ambient Air is condens’d by the Accumulation of the fuperior Air? *If this Condenfation and Rarefaétion fhould happento Clouds, they would always continue at the fame Height, contraryto Obfervation, and we fhould never have any Rain. Fromall this it follows, that the Condenfation and Rarefattion of the Vapours, which make Clouds, muft depend upon another Principle, than the Condenfation and Rarefattion of the wil there is fuch a Principle Air, and hereafter fh Lemma. Zhe Particles of all Fluids have a repellent Force, Fluids are elaftick or unelaftick: The elaftick Fluids have their Denfity proportionable to their Compreffion, and Sir I/aac Newton has demonftrated (Princip. Lib. 2. Sef. 5.) that they confift of Parts that repel each other from their refpeétive Centers. Unelaftick Fluids, like Mercury, Water, and tals diffoly’d, which are fpecifically heavier than the Men/truums. fpeci- Surface 5 it will fically lighter than it felf, (whether itAir be wher der the Afcent. Queries muft be anfwered. as it becomes a hollow Sphere, be only in. creafed ten times in Diameter, its Bulkwill be increas’d a thoufand times; therefore, it ter: That we fee this in the Duft in Summer, and in Menftruums that fuftain Me- Weight remaining the fame) will, in a great If the falling of Rain might be attributed meafure, hinder (or rather tetard) the De{cent of fmall Bodies, moving in the Air, by to the fecond of thefe Caufes, This is the ftrongeft Way of {tating the Hypothefis ; but to fupport it, the following Query 1. How comes the Aura or Air in the Bubbles to be fpecifically lighter than Air refifts, only as the Square Root of the Diame But this will nor explain the Phenomenon becaufe though the Increafe of Surface (the whofe Denfity is to that of the Air, next to the Surface of the exhaling Water, as 6850, to 8000, become fpecifically lighter than common Air, and confequently that they muftrife in it by Hydroftatical Laws, As for Example: If a Particle of Water, be fpecifically heavier than Air, yet ifits Surface be increas’d, by very much diminithing the Bulk of its Particles, when once rais’d, itcannot eafily fall; becaufe the Weight of each Particle diminithes, as the Cube Root of its Diameter, and the Surface to which the {uppofes) afcend up into fuch a Part of Atmofphere, as has the Air of the fame the fpecifick Gravity with themfelves, Number 60003 fo that the Shell of Water being in Bulk 8000, would be in Weight 850--6009=6850, whilft an equal Bulk of Air weighed 8000, and confequently the watry Bubble would rife *till it came to an Air, other Liquors, are, by Experiments, fouttd to Bignels, has its Weight | to 8000: Now, if an than common Air, be watry Bubble to keep it fame as if + of the Air into (W) and then the ould be increas’d by the be incompreffible; for Water, in the Florentine Experiment, could not, by any Force, be comprefs’d into lefs Room, but 002’dlike Dew through the Pores of the hollow golden Ball, in which it was confin’d, when a Force was apply’d to prefs the Ball out of its fpherical, into a lefs capacious Figure, 8 F Now |