Page:Cyclopaedia, Chambers - Volume 1.djvu/509

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Crystal Mineral, call'd alfo Mineral Anodyne \ and Sal (prunella, is Salt-petre prepar'd with Sulphur; thus: Put i If a Pound of Salt-petre in a Crucible, and fet that in a frnacc ; and when the Salt-perre is in Fufion, add, at fe- eral times, two Drachms of Flower of Sulphur. After 1L Flame is over, invert the Crucible in a fiat Pewter Ba-

fon thilt the Salt ma ^ ^ loor -

This is efteem'd good agamft the Squinancy, whence its Kame of <SW 'Prunella 5 Truna, or Prunella, expreffing that Difeafe. See Prunella.

Crystals af Silver, or of Luna t is Silver, penetrated act reduced into the form of Salts, by the pointed Acids Vgpjrit of Nitre. Sec Silver.

"lis ufed for making Efchars, by applying it to any Part : 'tis alfo of ufe internally, in Dropfies, and Difeafes of the

Crvstals of Mars, call'd alfo Salt, or Vitriol of Mars ; j s Iron reduced into Salts by an acid Liquor ; ufed in Dif- eafes arifing from Obttructions. See Mars.

Crystals of Venus, call'd alfo Vitriol of Venus ; is Cop- per reduced into the form of Vitriol by the Spirit of Nitre ; very cauftick, and ufed to cut off proud Fleili. See Vitriol.

Jjland Crystal, is a tranfparent Affile Stone, brought from I/land; fofr, as Talc j clear, as Rock-Cryfial, and without Colour ; famous among optic Writers for its unufual H.efract' c;is ' See Refraction.

It bears a red heat without lofing its Tranfparency ; and, jn a very intenfe heat, calcines without Fufion: Siecp'd a day or two in Water, it lofes its natural polifli 5 rubb'd on Cloth it attracts Srraws, £j?c. like Amber. In effect, it ap- pears a kind of Talc; and is found in form of oblique Pa- rallelepipeds with fix parallelogram Sides, and eight lolid Angles. See Talc.

The Phenomena of this Stone are very remarkable, and have been examin'd with great accuracy by M. Huygcns and Sir I.Newton : For, firit, whereas in other pellucid Bodies there is only one Refraction, in this there are two 5 fo that Objects view'd thro' it appear double.

idly, Whereas in other tranfparent Bodies, a Ray falling perpendicularly on the Surface, paffes {trait thro', without fuffering any Refraction 5 and an oblique Ray is always di- vided : In Ifland Cryjial, every Ray, whether perpendicu- lar or oblique, becomes di-pided into two, by means of the double Refraction. One of thefe Refractions is, according to the ordinary Rule, the Sine of Incidence out of Air into Cryjial, being to the Sine of Refraction as five to three 5 but the other is perfectly new. The like double Refrac- tion is alfo obferv'd in Cryjial of the Rock, tho much lefs fenlibly.

When an incident Ray is thus divided, and each Moiety arrives at the further Surface ; that, refracted in the firlt Surface after the ufual manner, is refracted entirely after the ufual manner at the fecond 5 and that refracted in the unufual manner in the firit, is entirely refracted after the like manner in the fecond : So that each emerges out of the fecond Surface, parallel to the firlt incident Ray.

Again, if two pieces of this Cryjial be plac'd over each other, fo as the Surfaces of the one be parallel to the corre- fponding ones of the other 5 the Rays refracted in the ufual manner in the firit Surface of the firft, are refracted after the ufual manner in all the other Surfaces : And the fame Uniformity appears in the Rays refracted after the unufual manner 3 and this in any Inclination of the Surfaces 5 pro- vided their Planes of perpendicular Refraction be parallel.

From thefe Phenomena, Sir /. Newton gathers, That there is an original Difference in the Rays of Light 5 by means whereof fome are, here, constantly refracted after the umal manner 5 and others in the unufual manner. See Ray, and Light.

Were not the difference original, and did it arife from any new Modifications impreis'd on the Rays at their firit ■Refraction, it would be aiter'd by new Modifications in tfl e three following ones 5 whereas, in fact, it fuffers no Al- teration at all.

Again, he hence takes occafion to fufpect, that the Rays °t Light have fcveral Sides, endu'd with fevetal original Pro- perties : For, it appears from the Circumfiances, that there ar enottwo forts of Rays differing in their Nature from each oth er, one conttantly, and in all Pofitions, refracted in the ^ ua], and the other in the unufual manner 5 the difference

the Experiment mention'd, being only in the Pofitions R f A^^ es °*" t ^ ie -^ a )' s » t0 r ^ G ^ ane « of perpendicular ■ etTa( -"on. for one and the fame Ray is refracted Ibme- lmes a ^ ter the ufual, and fometimes after the unufual man-

th T> LCOrt1in § t0 the Pnfirion of its Sides to the Cryjial: ^e Kefraaion being alike in both, when the Sides of the diffi; 8 arC P°*" e d the fame way to both, but different when

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CRY

the Rays before their Incidence on the fecond, third, and fourtH Surfaces; and fuffering no Alterations, for what appears, in their pafiage thro 'em ; mull be original and cSnnare; oee Kay, and LkSht ; fee alio Refraction.

CRYSTALLI, among Phyficians, are Putlules difpe'rs'd all over the Body ; white, and of the bignefs of a Lupine.

CRYSTALLINE Humour', is a thick, compafl Humour of the Eye, in manner of a flattifK convex Lens, fituatc in the middle of the Eye • ferving to make'that Refradion of the Rays of Light, neceflary to have em meet in the Re- tina, and form an Image thereon, whereby Vifion may be perform'd. See Eye, Humour, Refraction, Vision, Re- tina, He

'Tis the Configuration of the Cryflalline that occalions ierlons to be either Myopes, or \Presiytg, i. e. to be

long

her

ftiort-fighted. See Myopes, and Presbytk. The Cryflalline being of two Confidences; outwardly* u C a 9 el ' y ' '"" toward the Centre as hard as Salt : Hence, fome Authors think that its Figure may be varied 5 which Variation they fuppole to be effefted by the Llga- mentum Ciliare. Hence Dr. Grew, and others, afefibe to the Ciliary Ligament a Power of making the Cryflalline- more convex, as well as of moving ir ro or (rom the Re- tina : Accordingly, by the Laws oY Opticks, fomething of this Kind is absolutely neceffary to diUinfl Virion : For, as the Rays from dittant Objects diverge lefs than thofe from nigh ones ; either the Cryflalline Humour mull be capable of being made more convex, or more flat ; or elle there muft be an Elongation of the Eye tween that and the Retina. and Sicht.

or of the Diftance be- See Ligamentum Ciliare*

Sides ^ r?^' tnere f° rc > "lay De confider'd as having four conltant : and fii difixif Cr, Qj arters 5 tw o of which, onpoiite to each other, J, th e Ray to be refrafted after 'the unufual manner; "«d toe other -■-••■

The Cryflalline Humour, when dried, appears to confifl: of a vaft Number of thin, fpherical Lamhue, or Scales* lying over one another : Leeni-enboeck reckons there may be 2000 of 'em in one Cry/laUine ; each of thefe, he fays* he has difcover'd to confilt of a fingle Fibre, or fine Thread wound up in a ftupendous manner, this way and that ; fo as to run feveral Courts, and meet in as many Centres : and yet not interfere nor crofs in any Place. c fbilof ■I'ranfaSi N° io'5 J and 293.

Crystalline Heavens, in the old Aftronomy, two Orbs imagined between the 'Priimtm Motile and the Firmamenr, in the ^Ptolemaic Syllem, where the Heavens were fuppos'd folid, and only fufceptible of a fingle Motion. See Heaven.

King Alphonflis of Arragon is faid to have introdue'd the Cryftallines, to explain what they call'd the Motion of -Tre- pidation, or Tituhation. See Ptolemaic System.

The firft Cryflalline, according to Rcgwmontanus, &c. ferves to account for the flow Motion of the fix'd Stars ; which makes 'em advance a Degree in 70 Years, according to the Order of the Signs, viz. to the Eaft ; which occalions the- Prccefllon of the Equinox. See Precession.

The fecond ferves to account for the Motion of Libration, or Trepidation ; whereby the Celeflial Sphere is carried (rom one Pole towards another, occafioning a difference in the Sun's greateft Declination. See Trepidation.

But the Moderns account for thefe Motions, in a much more natural and eafy manner. See Libration, iSc.

CRYSTALLIZATION, in Chymiltry, a Kind of Con- gelation, befalling Salts, both ejfential, fix'd, and volatile 5 when, being fet free from the greateft Part of theirHumidity, they arc left to harden, dry, and (hoot into Cryflals. See Salt.

The ordinary Merhod of Cryftallization, is perform'd by diffolving thefaline Body in Water, filrering it, and lc ting it evaporate, till a Film appears'at the top ; and laftly, letting it ftand to moot. See Dissolution, and Evaporation.

This Shooting is accounted for, on Sir /. Ne-wton's Prin- ciples, from that attractive Force which is in all Bodies, and particularly in Salt, by reafon of its Solidity ; whereby, when the Menftruum or Fluid in which fuch Particles floar, is fated enough, or evaporated, (which brings it' to the fame) fo that the faline Particles are within each other's attractive Powers, and can draw one another more than they are drawn by the Fluid, they will run into Cryflals. See Attraction,

This is peculiar to Salts, that let them be ever fo much divided, and redue'd into minute Panicles ; yet, when they are form'd into Cryflals, they each of them rcaffume their proper Shapes : fo rhat one might as eafily diveft and de- prive 'em of their Saltnefs, as their Figure.

This being an immutable and perpetual Law, by know- ing the Figure of the Cryflals, we may understand what the Texture of the Particles ought to be, which can form thofe Cryflals : and, on the other hand, by knowing the Texture of the Particles, may be determin'd the Figures of rhe Cryflals.

For, fince the Figures of the moft fimple Parts remain always the fame, it is evident that the Figures they run into, when compounded and united, muft be uniform, and ' the Force of Attraction may be ftronger

on one fide of a Particle than on another ; there will con-

, ftantly be a greater Accretion of Salts upon thofe Sides

two in the ufual. Thefe Difpofitions, being in which attract more ftrongly : From which it may eafily be

I y y Y demon-