Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/289

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POWCHES, in a fhip. The feamen call by this name the fmall bulk-heads made in the hold, to flow corn, goods, or the like, that it may not fhoot from one fide to the other.

POVDER (Cycl.)— Gim-PowDER- See Gun.

Powder-Mj, in artillery, are moft commonly made of horn, of any convenient fize and figure, to carry powder for prun- ing f cannon : this is their chief ufe in armies. ' Sometimes they are fo made as to have a meafure for the charge of the piece at top, but this is of more ufe to gentle men in fowling, &c. than to foldiers, who have the charges of their piece put into cartridges, which they bite off, and firft prime, and then load.

PoWDER-ro^m, inafhip, that part of the hold wherein the pow- der is flowed.

POWER (Cycl.) — If any power of a quantity be divided by a greater power of the fame quantity, the quotient muff be ne- gative. For the rule for dividing any power of a quantity by another power of the fime, is to fuhtracf the exponent of the divifor from the exponent of the dividend, and make the dif- ference the exponent of the quotient.

For inlrance, ~ =z a = a and — - = a Pi Hence

a* a?

if p be greater than m 3 the exponent m — p muft be negative. Thus if d:=7/j-r-s, then — = — v— = a

Jt is obvious that —~a :

P R M

But*


 * I: and there-

fore a°

In like manner - :

a = a ; — - — a J —a jfo that the quantities*?,!, aaa *

-, — ,— j-r, &>V. may be exprefled thus, a, a ,a , dt a h a' a*

This change of expreflion is often of great ufe in the com- putation of fluxions and infinite feries.

When the quantity to be raifed to any power is pofitive, all its powers mufl: be pofitive. And when the radical quantity is negative, yet all its powers, whofe exponents are even num- bers, mufl; be pofitive. For — X — gives -f-. The power then can only be negative, when the exponent is

an odd number. Thus the powers of — a are ■ — a, 4- a- ■

a 3, + a * > — a ! ) &' c - Thofe whofe exponents are 2, 4,

6, c3V. are pofitive, but thofe whofe exponents are 1, 3 5

7, faff, are negative. Mac. Laur. Algebr. p. 37, 38. Hence if a power have a negative fign, no root of it deno- minated by an even number, can be affigned ; fince no quan- tity multiplied into itfelf an even number of times can give

a negative product. Thus the fquare root of — aa or -/

aa cannot be affigned, and is what mathematicians call an zmpofftble, or imaginary quantity or root. See Root. Obferve, that every power has as many roots, real and ima- ginary, as there are units in the exponent of the power. This holds true of unity itfelf. Mac. Laur. Ajgebr. p. 1 28. See the article Unity.

Imperfect Power, in algebra, is ufed for a power that has a

H. B. X 2

fractional exponent ; thus a * a ' s a i a J, &c. are imperfect powers. Mac. Laur. Algebr. p. 44.

Thefe are otherwife expreffed by placing the given power with- in the radical fign */, and placing above the radical fign the number that denominates what kind of root is required. Thus

■y- ^y-.-v^

Thefe imperfect jtawn are alfo called furds. See Surd, Cycl.

Negative. Power, in algebra. See Negative power.

POWTER, orEnglifiPowTZR, the name of a peculiar fpecles of pidgeon, called by Moore the columba gutturofa Anglica. It was firft bred in England, and is of a mixed breed, between what is called the horfeman and the cropper. It is a very beautiful fpecies, and is valued for its length of legs and body, neatnefs of crop, and flendernefs in girth, added to the beauty of its feathers. This fpecies is often eighteen, fometimes twenty inches long from the end of the bill to the extremity of the tail. Its legs, from the upper joint of the thigh to the toe-nail, is fometimes Ceven inches ; the crop is Ian*e and round, cfpecially toward the beak, filling alfo behind, and making almoft a perfectly orbicular figure. They are either blue-pied, black-pied, red-pied, or yellow-pied j the laft co- lour is moft valued. .Moor's Columbarium, p. 35.

Parifian Powter, a fpecies of pidgeon called by Moore colum- ba gutturofa Parijiorum.

It was firft bred at Paris, and thence fent to Brufiels, whence it was afterwards brought into England. It refembles the Englifli powter, but is fhort-bodied, ihort-Iegg'd, thick in the girth, and long-cropp'd. It is admired for The beauty of its feathers, which is peculiar to itfelf; it refembting in this a

t 'f! P n Ce ° f th " f ° rt ° f nee(Jle - work which the ladies call the Infh flitch, being chequered with various colours in every

feather, except the flight, which is white. It has generally a good deal of red intermixed with the other colours, and the more it has of this the more it is efteemed.

Horfeman POWT1NG, a name given to a mixed breed of pid- geons, produced between thofe two kinds known by the names of the cropper and the horfeman, according to the number of times that the young are bred over from the cropper* They are diftinguifhed by the names of the firft, fecond, or third breed.

Thefe are a very agile and nimble pidgeon ; and by their con- tinually flying up and down about the dove4ioufe, are apt to bring in other ftray pidgeons, which cannot find their houfes, They are obfened to breed often, and take great care of their young ones. Moore's Columbarium, p. 38.

POX (Cycl.) — Small Pox. Dr. Hahn endeavours to prove, that the fmall pox was defcribed by the old Greek phyficians under the name of carbuncle.

Dr. Hahifs treatifc on the antiquity of the fmall pox, has been criticized by Dr. WerlhofF, who endeavours to fhew, that Dr. Harm's quotations from the old Greek writers concerning the carbuncle, cannot be underftood of the fmall pox, which is a difeafe we have no account of tiil the Saracens difperfed it. Med. Eff.Edinb.

Dr. Hilfcher recommends cutting off the hair in the fmall~pox 9 by which perforation may be increafed. This method was pracfifed on the king ef Spain's Ton Don Carlos, and on a Saxon prince with fuccefs. Med EfK

Dr. Martin of Laufaunne, recommends bathing the face and body with cloths dipped in tepid water every four hours dur- ing the eruption of the fmall pox ; afliiring that it has excel- lent good effects. Hift. de 1'Acad. des Sciences, 1737. Dr. Haller tells us, that camphor affifts greatly to fill the puf- tules of the fmall pox of the confluent kind with petechia?. Commerc. Norimb. 1736. Hebd. re. § r. Dr. Lobb difapproves entirely of blood-letting in the fmall pox, and thinks the difeafe may be prevented, or cured, with* out any eruption, and that a fpecific may be found : he pro- pofes the /Ethiops mineral as fuch, and relates fome examples of the difeafe being, in his judgment, prevented by the time- ly ufe of it. The bifhop of Cloyne feems to afcribe the fame virtues to tar-water. See TAR-wder.

Dr. Wintringham fays, he never obferved antiphlogiftic me- dicines, which open the belly, diluting clyfters or fuch like, to have any bad effects in this diftemper ; but on the contrary, has always feen them ferviceable to young, vigorous, pletho- ric patients; whole too bound a belly frequently at laft pro- duces a dangerous diarrhoea. Hepropofesin urgent cafes of the confluent fmall pox, where from the reforption of the va- riolous matter there is great danger of increafing the fecondary fever, that the puftules fhould all be opened, and treated as fo many ulcers. See his Commentar. Nofologicum. Bloody urine is looked upon as a forerunner of death in the fmall pox ; but we have inftances of perfons recovering under fuch fymptoms. See Phil. Tranf. N° 470. Sect. 1 1.

Great Pox. For the cure of the lues venerea, Dr De Sault, in his treatife on this difeafe, recommendsfrequent frictions with large quantities of mercurial ointment made with one third of quick- filver ; to wit, from two or three drams to an ounce, or an ounce and an half every night, or every other night, taking care to keep the belly in a purging way, by clyfters, laxatives, or the ftronger purgatives, if the mercury begins to affect the mouth. He fays this method is fure, and altogether fafe, and he relates feveral hiftories of cures performed by it, not only in the lues venerea, but in many other difeafes, particularly jri obftru&ed hardned glands, the liver, teftes, £3V. Med. Eff. Edinb.

Mr. Douglas greatly commends De Sault's method, and it is faid that it has been praciifed with fuccefs in fome of the hofpi- tals in London. See A Letter on the cure of the venereal difeafe. Dr. WerlhofF prefers frequently repeated fmall dofes of mer- cury to a fahvation, for the cure of the lues venerea. Com- merc. Norimb. 1 2x5. Hebd. 13. § 4.

Mr. Macky, profefior of hiftory in the univerfity of Edin- burgh, fent the Royal Society a voucher for the grandgor (lues venerea) raging at Edinburgh in 1497. -^ 1S a ro y a l proclamation, ordering all who had the difeafe, or who had attended people under it, to repair forthwith to an ifland in the Frith of Forth. Phil. Tranf. N° 469. §5.

PRACTORES, npojclopij, among the Athenians, officers appoint- ed to receive the money due to the city from fines laid upon criminals. Potter, T. 1. p. 81.

PRjEBIUM, a name ufed by medical authors to exprefs a dofe of any thing, or the quantity of a medicine to be exhibited at one time.

PR/ECliE, among the Romans, the fame with praclamitatores ; which fee.

PRECIPE (Cycl.)— Precipe in capite, a writ iffuing out of the chancery, for a tenant holding of the king in capite; viz. in chief, as of his crown. Magn. Chart, c. 24. Reg. Orig. 4. Terms of law.

PR^ECLAMITATORES, among the Romans, officers that went along the ftr^Lis of Re me before the flymen dialis, to oblige all people to cive over their work on public holydays ;