can never be fuppofed to fteer clear of Extremes; but I obferve, you mentioned the Hand of Providence in the Cafe, which gives an easy Solution of this, otherwise, wonderful Event.

Cleon. There is no other Way of accounting for fuch an Oeconomy in the Clouds. Such a juft and neceffary Diftillation, and Diftribution of Waters, from the grand Alembic of the Atmosphere, could never proceed but from the Superintendence, Wisdom, and Direction, of that omnipotent Chymift, in whofe Hand are all the fecondary Powers of Nature, to vary their Operations as he fees confiftent with the general Good of the whole.

Euphrof. I am fatisfied of the Truth of what you have obferved; but may we not reckon the Winds another general Caufe of Rain, by driving the Clouds together, and forcing them to coalefce, condenfe, and become heavier, and therefore to fall in Rain?

Cleon. Most affuredly: You have expreffed this Matter as well as any Philofopher could have done. Those Winds that blow from the Ocean, as the South and Weft-winds, bring large Recruits of Vapours to the Clouds, and therefore are more inclined to produce Rain than others which come off the Land, as the North and North-Eaft-winds, which generally disperse the Vapours, and blow the Clouds away; as is thus elegantly expreffed by Ovid.

Fierce Boreas flies,

To puff away the Clouds, and purge the Skies:
Serenely while he blows, the Vapours driv'n,
Difcover Heav'n to Earth, and Earth to Heav'n.

DRYD. OVID. The fame Poet very philofophically introduces the South-wind, as bringing Fogs, Mifts, and Rain upon the Earth.

The South-wind Night and Horror brings,
And Fogs are fhaken from his flaggy Wings.
From his divided Beard two Streams he pours,
His Head and rheumy Eyes diftil in Show'rs:
With Rain his Robe and heavy Mantle flow,
And lazy Mifts are low'ring on his Brow.

DRYD. OVID.

Euphrof. You have pretty well fatisfied me, as to Wind and Rain; but how do you account for Fogs and Mifts, which oftentimes fo far obfcure the Body of the Atmosphere, that we can fcarcely fee any Thing at a Distance from us?

Cleon. Every Sort of Vapour of this Kind, that goes under the Name of Fogs and Mifts, is only a denfer Kind of Vapour, which is too heavy to be immediately raised up into the Air. The Condensation of this Vapour is either owing to a greater Degree of Warmth in the Surface of the Earth and Water, which throws it off in a greater Proportion than common, and faster than it can rife through the Atmosphere; or else, to the Want of a fufficient Degree of Heat in the Atmofphere to attenuate thofe Vapours, and increase their Elafticity, and confequently their Rarity: For Want of thefe Qualities they are detained in the lower Part of the Atmosphere in large and opake Particles, visible themselves to the Eye; but preventing Vifion of other Objects through them.

Euphrof. The Cafe then, I conceive, is fomewhat analogous to One's Breath in a cold Morning, which then, I can plainly perceive; whereas, in a warmer Air, the Particles of One's Breath become invifible, and therefore, infenfibly fly off, and mix with the Air. In like Manner, as I have often feen, after a foggy Morning, and the Sun has afcended high enough to warm the Atmosphere with its Beams, the Milt, or Fog has been, by Degrees, diffolved, and difpelled in the Form of Clouds; or, at other Times, totally vanished away. Agreeable to which, I remember the following Verfes of Milton.

Ye Mifts and Exhalations, that now rife,
From Hill or steamy Lake, dufky and grey,
'Till the Sun paint your flcecy Skirts with Gold:
Either to deck with Clouds th' uncolour'd Sky,
Or wet the thirsty Earth with falling Show'rs.

MILTON'S Paradife Left,

You have fatisfied my Curiofity with regard to Fogs and Mifts; but how am I to understand the Reason of that Phænomenon which we ufually call a Hoar-Froft? I know it proceeds from Cold; but fhould be glad to know the Manner how,

Cleon. Cold is only a comparative Term, and fignifies nothing more than that lefs Degree of Heat, which we ufually call a moderate Warmth. Now it is well known, that many Bodies will liquify with one Degree of Heat, and become fixed with another: This is the Cafe of all Metals, Salts, Oils, Water, &c. With one Degree of Warmth, Water will appear in a fluid State; with a lefs Degree, the Particles will be found to be fixed, congealed, or (as we ufually term it) frozen. Thus the Vapours, in a warm Air, are in a fluid State, and when condensed by the Coldness of the Evening, and defcend, they adhere to the Piles of Grafs in the liquid Form of pearly Drops, which, in that Cafe, we commonly call DEW; but thefe very Particles in a colder Air will be fixed, and while they are floating in the Air, they make what is called a Rimy-Fog, or frozen Mift. When these Particles defcend, they fall upon the Grass, and the Twigs of Shrubs and Trees, and make a beautiful Incruftation, which is called a Hoar, or White-Froft, in Contradiftinction to another Sort, which is called the Black-Froft, only because it does not appear white; and this Black-Froft differs from the other in nothing more than this, that it is not attended with a Mift or Fog,

Euphrof. The Account you have given of freezing, in the Parts of Water, feems, to me, very natural; but how am I to understand the Manner of thofe Particles becoming fixed, which I think you have not sufficiently explained?

Cleon. It is certain, from Experience, that Fluidity in the Parts of moft Bodies is promoted (I will not fay occafioned) by Heat; and Fixity (or freezing in Water) is the Effect of Cold, or a lefs Degree of Heat: But to defcribe the Mode of Action, or Procefs of Nature in this Refpect, I will not pretend to; for what I fhould naturally think was likely to account for freezing is inconfiftent with another Phænomenon of that Affair, viz. that all thefe Bodies, in a fixed State, have a larger Bulk than in a fluid one. This Water, fet to freezing in a cylindric Veffel, will be congealed into a larger Bulk of ICE, which is nothing but Water fixed. Ön the other Hand, a fixed Metal, as Lead, Tin, &c.

when

when melted, or liquified, runs into a leffer Space, or becomes of a lefs Bulk. These Appearances make it fomewhat difficult to account for the Nature of freezing, or Congealation, fo perfectly as one might wish; and therefore you will excufe my faying any Thing more than I know upon this Subject.

Euphrof. Very readily, dear Cleonicus; it is certainly over-doing the Thing, to load any Theory with Conjectures; nor was I ever fond of any Hypothetical Reafoning, tho' I fhould prefer your Opinion, if I chose to be inftructed in that fuperficial Way. -I am glad you have put me into fo good a Way of thinking about this cold, but very curious Subject, which is fo elegantly defcribed by the late ingenious Dr. Broome, in the following Lines.

When formy Winter, from the frozen North,
Borne on his icy Chariot, iffues forth,

The blafted Groves their verdant Pride refign,
And IVaters, harden'd into Crystal, fhine:
Sharp blows the Rigour of the piercing Winds,
And the broad Flood, as with a Breast-plate, binds:
Ev'n the proud Seas forget in Tides to roll,
Beneath the freezing of the northern Pole;
There Waves on Waves in folid Mountains rife,
And Alps of Ice invade the wond'ring Skies ;
But if warm Winds a warmer Air reflore,
And fofter Breezes bring a genial Show'r,
The genial Show'r revives the chearful Plain,
And the huge Hills flow down into the Main.

BROOME,

Cleon. The Doctor has expreffed the Thing very elegantly; and, at your Leifure, you may confult Mr. Thomson's poetical Philofophy at large, on this Head, in his Winter Seafon; and the next Opportunity that offers I fhall take to explain the Nature of other Meteors to you.

DIALOGUE V.

The Nature and Generation of METEORS, continued. Of SNOW, HAIL, LIGHTENING, THUNDER, Aurora Borealis, &c.

SIN

Euphrofyne.

INCE our laft Interview, the Weather, having been very cold, gave me an Opportunity of observing, more particularly, the various Phænomena of freezing, which you then explained to me; and among other Things, the Fleaks of Snow very much entertained me as they fell on the Leads before the Window. These I viewed with a magnifying Glass, and thought I perceived fomething very beautiful and regular in their Form. Pray, what Account do the Philofophers give of this ftriking Phenomenon we call SNow?

Cleon. It is a Subject every Way worthy of your Speculation, and one of the most curious Productions of Nature. This has been already intimated to you by your Glass, and will be farther evident, when you view them thro' a larger Magnifier. The Philofophy of Snow, in fhort, is this. -The Particles of all Salts have a natural Difpofition to run together, and conftitute fome particular, or fpecial Form; and as thofe Particles are originally, and, in themselves, transparent, and clear as Glafs, or Cryftal, this natural Action of fhooting into those peculiar Forms is what they call CRYSTALIZATION; and the Particles fo combined and configurated are called the Cryftals of fuch and fuch Salts, or Metals. On this head we fhall be much larger hereafter; it is fufficient, at prefent, that you confider Water as an infipid, fluid Salt; and that in the upper Region of the Air, where the Parts of nitrous Salts abound, this Difpofition to freezing or Congealation, is very great in the Winter-feafons, when the Atmosphere is much less heated by the Sun's Rays: The Aqueous Particles, therefore, mixing with Nitre, immediately fhoot into Crystals, and form the original Parts of Snow, whofe Figure is truly wonderful,