Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/189

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off from them by the nails, they often are the occafion of malig- nant and very troublelbme ulcers, that are not eafily cured. Bontius, whofe long refidence in this part of the world gave him many opportunities of obferving thefe papules in all their ftages, advifes peop'e, to prevent danger and remove their troublefome itching, to foment all the parts where they appear ■with a mixture of vinegar, water, and faltpetre ; or if this he required yet more acrid, to add to it juice of lemons, and ufe it as before. The effect of this application is at firft an intenfe pain but this foon decreafes fo far, as to become lefs trouble- fome than the intolerable itching of the parts. He gives great caution alfo againft purging medicines, however mild; for by tbefe the matter which caufes the papula is often carried to the bowels, and produces dyfenteries. The cure is either to be wholly left to nature, or afiiltcd by fudorifics. Bontius de Med. Ind. VAR(Cyd) — Par acccflhriitm, in anatomy, See the article

Accessory, Cycl. PARABELE, in ichthyology, a name given by Marggrave to the flying fifh, the w'rfvus hirundo and cuculus of feveral authors. Thefe are names, however, fo little expreffive of the cha- racters of fifh, that they are applied by different authors to the different fpecies. Artedi is the only author who has reduced this part of natural hiftory to a regular fyftem ; he makes this fifh a fpecies of the trigiia, and diftinguifhes it by the name of the triglla with the head a little aculeated, and with a fin- gular fin placed near the pectoral fins. See the articles Mil- vusand Triglia. PARABOLIC (Cycl.) — Parabolic afymptote, in geometry, is ufed for a parabolic line approaching to a curve, fo that they never meet ; yet by producing both indefinitely, their diftance from each other becomes lefs than any given line. There may be as many different kinds of thefe afymptotes as there are parabolas of different orders. See Mac Laurin's Flux. B. i. ch. 10.

When a curve has a common parabola for its afymptote, the ratio of the fubtangent to the abfeifs approaches continually to the ratio of two to one, when the axis of the parabola coin- cides with the bafe; but this ratio of the fubtangent to the abfeifs approaches to that of one to two, when the axis is perpendicular to the bafe. And by obferving the limit to which the ratio of the fubtangent and abfeifs approaches, para- bolic afymptotes of various kinds may be difcovered. See Mac Lour. Flux. Art. 337. Par \bolic fpircd, in conies. See Helicoid parabola, Cycl. PARACENTESIS {Cycl.)— See Tapping. PARACOPE, a word ufed by Hippocrates to exprefs a flight de- lirium in fevers. PARACRUSIS, a word ufed by Hippocrates, and by many other writers, and exprefling the fame asparaape, a flight d< Jirium in a fever. PARADIGRAMMATICE, is ufed by fome for the art of making all forts of figures in plaifter. The artifts in this are called gypfocbi.

PARADIS^A, in zoology, a name ufed by fome authors for the bird manucodlata, or avis paradifaa, the bird of paradife, by- others. In the Linnzean fyftem this makes a diftinct genus of birds of the order of the pica, the diftinguifhing characters of which are, that they have two fingular and extremely long feathers, which are neither inferted in the wings nor rump. See Tab of Birds, N°, 6 and Linnai Syftem. Nat. p. 44. PARADISIACA, in botany, a name given by fome authors to

the arbor vita?, or thuya. Cbabraus, p. 73. PARADOX [Cycl.) — Geometricians have of late been accufed of maintaining paradoxes; and it muft be owned, that fome ufe very myfterious terms in exprefling themfelves about afymp- totes, the fums of infinite progreftions, the areas comprehend- ed between curves and their afymptotes, and the folids gene- rated from thefe areas, the length of fome fpirals, C5V. But all thefe paradoxes and myfteries amount to no more than this: that a line or number may be continually acquiring increments, and thofe increments may decrcafe in fuch a manner, that the whole line or number fhall never amount to a given line or number.

The neceflity of admitting this is obvious from the nature* of the molt common geometrical figures : thus, while the tangent of a circle increafes, the area of thecorrefpondingfector increafes, but never amounts to a quadrant. Neither is it difficult to conceive, that if a figure be concave towards a bafe, and have an afymp- tote parallel to the bafe, ay it happens when we take a parallel to the afymptote of the logarithmic curve, or of the hyperbola, for a bafe; it is not difficult to conceive, I fay, that the or- dinate in this cafe always increafes while the bafe is produced, but never amounts to the diftance between the afymptote and the bafe. In like manner, a curvilinear area may increafe while the bafe is produced, and approach continually to a cer- tain finite fpace, but never amount to it ; and a folid may in- creafe in the fame manner, and yet never amount to a given folid. See Logarithmic curve.

A fpiral may in like manner approach to a point continually, and yet in any number of revolutions never arrive at it; and there are progreflions of fractions which may be continued at pleafure, and yet the fum of the terms fhall be always lefs than a given number. See Mac Laurin\ Fluxions, B 1. ch,

10. feq. where various rules are demonftrated, and illuftrated by examples, for determining the afymptotes and limits of fi- gures and progreffions, without having recourfe to thofe myf- terious expreflions which have of late years crept into the writ- ings of mathematicians. For, as that excellent author ob- ferves elfewhere, tho' philofophy has, and probably a'ways - will have myfteries to us, geometry ought to have none.

PAR^EA, in zoology, the name of a fpecies of ferpent, called alfo anguis afculapii. It is a perfectly innocent and harmlefs creature, and is fo little dreaded by the inhabitants, that it is common about their hoilfes, and even fometimes gets into their beds. Its mouth is full of very fmall teeth, and when much provoked, it is fometimes known to bite, tho* without any bad fymptoms attending the wound, it is a very long kind, and is of a yellowifh green colour on the fides and blackifh on the back: it has two fmall eminences on the neck, and be- tween them two final] finews. It is very common in Spain, Italy, and molt other of the warm countries. Ray's Syn. Anim. p. 291.

PARAGAUD./TL, among the Romans, a fort of wreaths, either wholly of gold, or of filfc adorned with gold, which were in- terwoven in garments, and not fowed to them. The gar- ment was fometimes of one colour, in which was woven one partfgauda ; others were of two colours, and had two para- gauda ; and fome had three colours, and three paragauda. They were worn both by men and women.

PARAGOGE (Cycl.) a word ufed by medical writers to exprefs a reduction of luxated bones.

PARAGONE, in natural hiftory, the name o;iven by many to the bafaltes, a black marble, ufed as a touehitone. See the article Basaltes.

PARAGUA, in zoology, the name of a Brafilian parrot, of the fize of our common green parrot; but its back is all black, and its breaft and the forepart of its belly are of a beautiful red. Its eyes are black, with a red circle round them ; its beak brown, or a very dufky grey, and legs and feet grey. Marg- grave, Hift. of Brafi!.

PARALAMPSIS, a word ufed by medical writers to exprefs a cicatrix in the tranfparent part of the cornea of the eye.

PARALIA, na-a^ia, in antiquity, a day kept in memory of an antient hero, called Faralus. Potter-, ArchseoJ. Grsec. 1.2. c. 20. • T. 1. p. 424.

Paralia was alfo the name of one of the Athenian tribes. Potter, ibid. T. 1. p. 49.

PARALLAXIS, in the medical writers, exprefTes a mutual change in the fituation of the parts of a broken bone, as when the two fragments flip to the fides of one another.

PARALLEL (Cycl.) — Parallels of declination, in aftronomy, are circles parallel to the equinoctial, imagined to pafs through every degree and minute of the meridians, between the equi- noctial and each pole of the world.

PARALLELA, a word ufed by medical writers to exprefs a fort of fcurf or leprous appearance, affecting only the palms of the hands. It is a fymptom of the pox.

PARALLELOGRAM (Cycl.) -Parallelogram of the by perbola, in geometry, is ufed for the parallelogram formed by the two afymptotes of an hyperbola, and the parallels to them* drawn from any point of the curve. A parallelogram thus formed, is of an invariable magnitude in the fame hyperpola ; and the rectangle of its fides is equal to the power of the hy- perbola. U Hopital, SccT Coniq. Art. 99 — 101. See the article Power, Cycl.

This parallelogram is the modulus of the logarithmic fyftem; and if we take it as unity, the hyperbolic fectors and feg- ments will correfpond to Napier's or the natural logarithms. If the parallelogram be taken = 0. 43459, Wc. thefe feflorS and fegmcntswill reprefentBriggs's logarithms. See the article Logarithm.

Huygens has made ufe of this term, De cauf. gravitat. in fin. See LoGARiTHMic-cars^?.

pARALLEL0CRAM-/»rsrmJ7w*, a mathematical inftrumenr, con- futing of a femicircle of brafs, with four rulers in form of a parallelogram-, made to move to any angle : one of thefe ru- lers is an index, which ihews on the femicircle the quantity of any inward or outward angle.

PARALLELLOPIPED (Cycl)— The paral'clkpiped with ob- lique angles, is a figure very common to many kinds of ftones, efpecially of the fofter fort. The common cryftalizations of grottos break naturally into fragments of this fhape ; and the iialadtits which hang down from their roofs in form of icicles, are originally fmall hollow pipes formed by the water which continually trickles down drop by drop ; and wbofe outer fur- faces, fixing themfelves by their fmall bafes., form by degrees a fort of blunted pyramids, which, like fo many rays front the axis, which is the hollow pipe, grow hollow at laft. This axis feems to be compofed of plates, almoft cylindrical, laid one over another ; but if broken, the whole divides into frag- ments of a parallelepiped figure : the blunted pyramids that are about the axis divide themfelves at firft into other blunted py- ramids; but afterwards almoft all thefe fragments divide of themfelves into other fragments of a pa> aUellopiped figure, this feeming* every where the ultimate fhape of the particles. In the mountain of Barege there is found a vaft quantity of afbeltus ; the ftone upon which this grows, tho' in itfelf of