Page:Cyclopaedia, Chambers - Volume 2.djvu/468

 POR

times as much Porofity as Solidity : If five fuch Degrees, it w iU have thirty-one times as much Space as Solidity : And jf fix Degrees, then it will have fixty-three times as much Vacuity, as folic! Matter.

And perhaps in the wonderful Conformation and Fabric!: of natural Bodies, there may be other Proportions of Space to Matter, to us wholly unknown ; whence it is poffible, there may be yet farther great Quantities of interfpers'd Vacuity. See Vacuum.

Pores, in Anatomy, are certain permeable Spaces, be- tween the Parts of the Skin ; whereby we fweat, or perfpire gc. See Cutis and Perspiration.

The Tores are moft remarkable in the Hands and Feet : By viewing the Palm of the Hand with a moderate Glafs, after walhing it well, we perceive innumerable little Ridges, of equal Size and Diftance, running parallel to each other ; efpecially on the Tips and Joints of the Fin- gers, iSc. where they are regularly difpos'd into fpherical Triangles and Ellipfes.

On thefe Ridges Hand the Pores, in even Rows, big enough to be feen by a good Eye without a Glafs ; but with one, every Fore looks like a little Fountain ; and the Sweat may be feen to (land therein, clear as Rock- Water ; aud as often as it is wiped off, iprings up again. See Sweat.

The Fores are plac'd on the Ridges, not in the Furrows between them ; that they might be lefs liable to be flop- ped by Comprefiion : For the fame reafon, the Pores of the Hands and Feet are larger than the reft ; thofe Parts being more ufed and prefs'd than the reft : and hence a- gain, there are no Ridges on other Parrs.

Thefe Pores are a very convenient Out-let for the more noxious Parts of the Blood, which by the continual Ufe of the Hands, and Feet, are plentifully brought into them : Whence in Hypochondriac and Hyfteric People, there is a continual Burning in the Palms and Soles.

In the Stoppage or Conftriction of the Pores of the Skin, confills that Difeafe we popularly call a Cold. See Cold.

In rhe Fhilofophical Tranfiiflions, we have an Inllance of a Student near Leyden, much addicted to Aftronomy, who fpending many Nights in Star-gazing, had by the nocturnal Wet, and Cold, fo obftrufted the Fores of his Skin, that little or nothing exhaled from his Body ; as ap- pear'd hence, that the Shirt he had wore five or fix Weeks, was then as white as if it had only been wore one Day. In the mean while, a Water was collected under the Skin, v hereof he was afterwards cured.

FORIMA, in Geometry, a Theorem, or Proportion, fo eafily demonftrated, that it is almoft felf-evident. See Axiom.

Such, e.gr. is this, That a Chord is wholly within the Circle.

On the contrary, an Aporima, is a Propofition fo diffi- cult, as to be almoft impoffible to be demonftrated; as the Quadrature of the Circle is now, and as the Squaring of any affign'd Portion of Hippocrates' s Limes formerly was.

The Forima coincides nearly with the Lemma, or Af- fumption. See Lemma.

The Word is form'd from the Greek mfvu®-, a Thing eafy to conceive; and which opens the way to fomething more difficult.

POR1SMA, in Mathematicks, a general Theorem, or Canon, dedue'd from a local Problem. See Theorem.

Frochts derives it from the Greek mew, to eftablifli, and conclude, from fomething already done and demonftrated ; and accordingly defines Forifma, a Theorem drawn occa- fionally from fome other Theorem already demonftrated.

PORISTICK Method, in Mathematicks, is that which determines when, by what means, and how many diffe- rent ways, a Problem may be faired. See Problem and Resolution.

PORPHYRY, in Natural Hiflory, iic. a precious Kind of Marble, of a brownifh red Colour ; frequently inter- fpers'd with white Stains ; antiently brought from Egypt, and exceeding all others in Hardnefs. See Marble. _ The Art of cutting Porphyry, praflis'd among the An- tients, is loft. In effecf, 'tis hard to conceive what kind of Tools they muft have ufed for the fafhioning of thefe huge Columns, and other Forphyry-Viotks found in fome of the antique Buildings in Rome.

One of the moft considerable Pieces, now remaining en- ''"•', is a Tomb of Confantia, Daughter of the Emperor Ccnftantine, in the Church of St. Agnes without the Walls; ordinarily call'd, The Tomb of 'Bacchus, becaufe of fevcral Boys reprefented herein, playing among the Vine-Leaves. Add to this. Apollo's, and the Bulls of twelve Emperors, all in Porphyry, in the Palace of the Tui'deries.

Some of the antient Pieces appear to have been wrought with the Chiffel, others with the Saw, others with Wheels, •tid others ground by degrees with Emery. Yer the modern iools will fcarce touch Porphyry: either the Antients,

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therefore, had the Secret of tempering Steel better than we ; or, as fome incline to think, they had the Art of foftemng the Porphyry ; Tho', 'tis more probable, rhat

M a Slv r b "S c °" tribu 'ed to increafe its Hardnefs.

Mr Addlfon tells us, he faw a Workman at Rome em- ploy dm the cuttmg of Porphyry; but his Advances were exceedingly flow, and almoft infenfible

AH the way the Italian Sculptors have to work the T*l °X & Far t h yy Columns fiill remaining (for the Forfhyry Quarries are long fince loft) is wi,h a Brafs Saw without any Teeth. With this, together with Emery and Water, they rub and wear, with infinite patience. See E-

MERY.

Yet have many excellent Pcrfons endeavour'd to retrieve the antient Art. particularly Leon Baptifla Jlforti 1 who fearch.ng for the neceffary Temper, fays, he found Goats mood the beftofany : yet even this avaii'd but little 5 for in working with Chiffels temper'd herein, Sparks of Fire came much more plentifully, than Pieces of the Stone. By means hereof, the Sculptors were able to make a flat or oval Form; but could never attain to any thing like a Figure. See Temper.

'Tjs ,rue; in '555, Cofmo de Medici is faid to have di- ftilld a Water from certain Herbs, wherewith his Sculptor trancefco Tadda, gave his Tools fuch an admirable Hard- nels and Temper, as that he perform 'd fome fine Works with them ; particularly, our Saviour's Head in 'Demi- relievo, Cofmo's Head, and his Dutchefs's. Even the very Hair, and Beard, how difficult foever, are here well con- dufled; and there is nothing of the Kind, better in all the Works of the Antients : But the Secret feems to have died with him.

The French have lately found another Method of cut- ting Porphyry, viz. with an Iron Saw without Teeth, and Grez, or a kind of Free-Stone pulv-riz'd, and Water. The Authors of this Invention pretend, they could form the whole Contour of a Column hereby ; had they Matter to work on.

PORPHYRIANS, a Name given to the Arians, in the fourth Century; by Authority of Conflantinc. See Ari- ans.

That Prince publifliing an Edift againft Arius and his Writings, declares, That as Arius has imitated 'Porphyry in compofing Books againft Religion, he deferves to benoted with his Infamy ; and that as Porphvry is become the Reproach of Poflcrity, and his Writings fupprefs'd ; fo he wills, that Arius and his Followers be cM'd <Porphr- rians, Sec.

The Propriety of the Name feems to confift in this, that the Arians endeavour'd to reftore Idolatry : For in fayino that the Son, whom they call a begotten God, is a Crea". ture ; they put a Creature in the Rank of God : And only differ from the Heathens in this, that the one give the Quality of God to one Creature, the other to a oreat many. &

PORPHYROGENETES, in Antiquity, a Name given the Children of the Eaftern Emperors ; implying, bo'rnin the (Purple.

Cedrenus will have the Word to fignify born in the 'Pa- lace of Porphyry, a Palace fo call'd in Confantinople.

PORRETANS, a Religious Sefl, rhe Followers of Gil- bert de la Forree, Bifliop of Poicliers, condemn'd in the Xllth Century, for admitting a Phyfical Diftinflion be- tween God and his Attributes; or, as Marfiiam fays, for having wrote too curioufly on the Subjefl of the Trinity : For his real Sentiments, we are not over well acquainted withal.

However, he gave occafion for thofe Sufpicions, by maintaining that this Propofition, Dais eft bonitas, is not true ; unlefs redue'd to this, 2>eus eft bonus. And there are fome Paffages noted by St. "Bernard, who wrote warm- ly againft him, wherein he feems to admit a real Diftinaion between the Nature of God, and his Attribures.

The Forretans are fet in oppofition to the Nominals. See Nominal.

PORRIDGE, of Porreau, French, of Forrum, Latin, a Leek or Herb frequently put in Broth ; a liquid Food of Herbs, Flefh, He.

PORT, or Haven, a commodious Place fituate on the Sea-Coaft, or at the Mouth of a River, with depth of Water fufficient for Ships of Burthen, and convenient Bottom for Anchorage ; whereVeflels lie by, ro load or unload ; fcreen'd from the Wind, and fafe from any Enterprize of Enemies; either by the difpofition of the Place, or by means of a Mole, a Dike, or the like, with a Chain and Light-Houfe. 'Ports are either Natural or Artificial. Natural are thofe which Providence feems to have form'd, for the Communication of Commerce.

Artificial Torts are thofe form'd with Moles or Pro- jectures into the Sea. See Mole.

The Englifir Coafts are exceedingly thin of Ports. France

has the Advantage of all other Countries in the Number

10 F and