Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/327

 fYR

The diftingiufhing characters of the fyricnlia are thefc : they are compound, inflammable, metallic bodies, of a cubic figure, or refembling a die, being compofed of fix fides. Of this genus there are only two known fpecies : i. The great pyrkubium, of a fohaceous ftru&ure ; and, 2. The fmaller folid pyrkubium. See Tab. of Foil*. Clafs 5. The firft of thefe is a very elegant foflil, and is fo regularly Ihaped, and fo highly polifhed by nature, that it has been often fuppofed to be wrought by art. It is but moderately hard, but is very heavy, and is of a foliaceous ftru&ure. It is exactly of the figure of a die, being compofed of fix regular fides, placed at right angles ; but tho' ever thus regular in fhape, it is not at all fo in fize : the molt common fpecimens of it are about a third of an inch in diameter ; but it is found much larger, even to three inches, and fo fmall as to the tenth of an inch. It is perfectly polifhed and fmooth on all its fur- faces, and is of a very beautiful whitifh green, with a faint admixture of yellow. It is found in the German and Hunga- rian mines, and in the Eaft Indies.

The fecond fort, or the fmall folid pyrkubium, is a foflil of much lefs beauty, tho' equally regular in its fhape and appear- ance. It is very heavy, and extremely firm and hard, and is not of a foliaceous or flaky ftrudture; but of one regular and uniform mafs, and when broken appears very bright and glofly. It is ever found in the regular form of a cube, or regular folid body, made up of fix flat fides placed at right angles. Its ufual fize is about the eighth of an inch diameter, but it is found fmaller than a pin's head, and fometimes fo large as to be near an inch. It is perfectly fmooth on all its furfaces, and is naturally of a pale yellowifh green, and as bright on the outfide as within ; but very often it is found of a ferrugi- neous or dufky furface, owing to a fort of ruffing, which is an accident to which the feveral fpecies of naturally bright py- ritse are moft of them alfo fubjecT:.

It is very common in Germany and Ttaly, and in fome parts of America, as alfo in our own country. With us it is com- monly found immerfed in flate, fuch as we cover houfes with ; but in Germany and other places it is ufually found loofe among the earth of mountains. With us it is ufually of a bright furface, in Germany it is more frequently dufky, Hill's

Hift. of Fofn p. 619.

PYRIFORMIS (Cyd.)— This is alfo called pyramidaih\ and is a fmall oblong mufcle, of the figure of a flat pear, or pyramid, whence it has its names.

It is fituated almoft tranfverfely between the os facrum and ifchium, being covered and hid by the firft: two glutsei. It is fixed to the interior lateral part of the os facrum by flefhy iibres, and to the neighbouring part of the anterior or concave fide of that bone, by three digitations lying between the an- terior holes. It is alfo fixed by a fmall infertion to the liga- mentum facro-fciatrcum, and edge of the great finus of the os ahum. From thence it runs tranfverfely toward the joint of the hip, its fibres contracting in breadth; it terminates in a fhort tendon, which is inferted in the middle of the internal Jabium of the upper edge of the great trochanter, by two or three branches. The upper part of this tendon receives fe- veral fibres from the glutseus medius, and its lower partis united to the gemellus fuperior, and tendon of the obturator internus. Sometimes there are two pyriformes, feparated only by the nervus fciaticus. JFinJlow's Anat. 209. PYRIPHLEGES, a word ufed by the old writers in medicine to exprefs a perfon labouring under an extreme degree of a febrile heat. PYR1PLACIS, in natural hiftory, the name of a genus of py- ritas, the characters of which are thefe : they are compound, inflammable, metallic bodies, found in loofe detached manes of afimple and uniform, not ftriated internal ftrudture, and are covered with an inveftient coat or cruft. Of this genus of foffils there are three known fpecies : 1. A flatted kind, with a fcabrous coat. 2. A globofe one, with cracked and furrowed coat. And 3. A flatted one, with a very thick, brownifh- white cruft. See Tab. of FofT. Clafs 5 The firft of thefe is a dufky brownifh-green mafs, furrounded and every way covered by a fenugineous coat, of the thick- nefs of a {billing or more, which is rendered very rough and fcabrous, by having received multitudes of fmall pebbles and particles of fand into its fubftance while yet moift, which are become firmly bedded in it, and make a part of its fubftance. This is common in the gravel-pits about London. The fecond is of an orbicular figure, and is of a very coarfe ftructure, being compofed of vifible granules, and is of a pale yet dufky green colour. It is covered with a brownifh yellow or fenugineous coat, of the thicknefs of half a crown, or fometimes much more. This is ufually fomewhat irregularly raifed in tubercles on the furface, which are divided by a fort of fine lines : thefe are truly fo many cracks in the fuperficies, all which, when the body has been fome time expofed to a damp air, fly more afunder at their edges, and become deeper, opening into the body of the mafs. This fpecies is found of all the intermediate fizes between an ounce and eight or ten pounds in weight. It is very common in the chalk-pits of Kent, and in many other parts of the kingdom; and tho' moft frequently found in chalk, yet is fometimes met with among gravel, or lying loofe upon the furface. Suppl. Vol. II.

P Y R

The third Is a very lingular fpecies, yet from its unpromifing appearance has been overlooked by all the enquirers into thefe fubjecls; having never been defcribed in the writings, nor preferved m the mufeums of the late collectors of foffils. It is very hard, and moderately heavy, and is ufually of a flatted orbicular, or oval figure; and its moft frequent fize is between two and three inches in diameter. It is of an irregular, un- even, and rough furface, full of fmall prominences, very harfh and rough to the touch, and looks merely like a lump of greyifh hard clay. When broken, it is found, however, to confift of a nucleus of the fame fhape with the whole body, and every way equally furrounded with a cruft of a thicknefs equal to its whole diameter, or nearly fo. The nucleus is of a deep and dufky brownifh-green colour, and of a plain fimple ftrudture ; being compofed of no vifible moleculae. The cruft is of a pale, greyifh-brown, earthy fubftance, appearing like an indurated earth, and flittering in fome few places with fmall glofly particles. This is found in great plenty in fome of the clay-pits about London. Hilt's Hift. of FofT. p. 613. PYRIPOLYGONIUM, in natural hiftory, the name of a ge- nus of foffils, the characters of which are, that they are com- pound metallic bodies, of a regular figure, confifting gf twelve planes. See Tab. of FofT. Clafs 5.

There is only one known fpecies of this genus, tho' fubject to great varieties in its appearance; and this has been by authors hitherto confounded, with many other bodies of very different nature and figure, under the general name pyrites The pyripolygonium, when perfect, is an extremely elegant and beautiful foflil ; but this is a ftate it is very rarely found in. It is moderately firm, of a compact texture, and very heavy; tho' its natural figure be a regular body, compofed of twelve planes, yet it is fubjedt to great imperfections and irregulari- ties. It often feems to want one or more .of its fides, and not unfrequently, from the accidental breaking of fome of its angles, to have more than its number; and very often has a great many other fmaller and lefs perfect bodies of its own kind, growing to its larger and lefs perfect fpecimens. it is found from the twentieth part of an inch, to four inches in diameter; but its moft common fize is about a third of an inch. It is naturally of a polifhed and fhining furface, and of a pale whitifh yellow; but fometimes it is brownifh, or of an iron colour.

It is not unfrequent in Cornwall and Devonfhire ; but is much more common in Germany. Bill's Hift. of FofT p. 621. PYRITES, (Cyd.) in natural hiftory, a name ufed by Dr. Hill as the claflicai term for the lefs regularly figured bodies of the number of thofe ufually called, too indeterminately, by that name. See Tab. of FofT Clafs 5.

According to this diftincVion/iyr/fcs are compound, inflammable, metallic bodies, found in detached mafles, but of no determi- nately angular figure. Of this clafs there are two general orders of bodies; the firft, thofe which are of a plain and fimple internal ftrudture; and the fecond, thofe which are regularly ftriated within : and of each of thefe there are two genera. Thofe of the firft are :

r. The pyriploces. Thefe are pyrites of a fimple internal ftrudture, and covered with an inveftient coat or cruft. 2. The gymnopyres. Thefe are pyrites of a fimple internal ftructure, and naked, or not covered by any inveftient coat or cruft.

The genera of the fecond order, or the ftriated pyrites, are, I, The pyriir'icha. Thefe are the pyrites of afimply filiated ftrudture.

And, 2. The pyritrhhiphylh. Thefe are the pyrites whofe furfaces are covered with foliaceous flakes, made by a conti- nuation and expanfion of the ends of the ftriae. Hill's Hift. of FofT. p. 612.

The feveral fpecies of each of thefe genera, fee under the fe- veral generical heads, Pyritrichum, £3V. Diofcorides mentions only one kind of pyrites, which is the common yellow fpecies. Avifenna and the other Arabians mention two yellow forts, a white one, and a ferrugineous one. None of thefe authors made any diftinction between the marcafites and pyrita, but this fort of matter, whether formed into fmall nodules, or continued ftrata, was called in- differently by one or other of thefe names. The four kinds of this ftone mentioned by the Arabians are called from their colours, the golden, the filver, the brafTy, and the ferrugineous pyrites. The oldefl authors are of the opinion of Diofcorides, and mention only one kind, deducing them all from the fame principles, and fuppofing their va- riety of colours to be only owing to accidents Ariftotle and Theophraftus thus mention the pyrites as one thing, under the name mylia, which having been tranflated molaris lapis, has • been underftood by fome to mean fome fort of mill-ftone, or other coarfe ftone fit for fuch purpofes ; and by that means the whole fenfe of the authors has been perverted and mif- underftood.

Pliny mentions two kinds of the pyrites, the gold and the filver kind : he tells us, there is a ftone, with fome refem- blance of brafs in its appearance, which is found in Cyprus, and about Acarnania ; and that it is of two kinds, yellow and white. It is clear from this, that this author had con- 3 I i fuited