PER
cate and moiftcn the Heart, and prevent any Inflammation that might probably arife from the dry Fricfion of the Heart and its Capi'ula. But this latter Ufe is controverted ; for fome take the Humour found in it to be unnatural, and will have it forcibly feparated by the convulftve Agonies fupervening in the Article of Death. In effect., Anatomifts are puzzled to find whenceit fhou'd come, or from what Veffels it is fecteted.
The word 'Pericardium is form'd from the Greek irifl about and aafJiu Heart.
Dr. Keil, in his Trcatife of Anira. Secretion fhews that the Liquor in the 'Pericardium muft be the mod Fluid of any feparated from the Blood, becaufe its Particles unite fitft, and are fecreted firft. For thofe Particles which unite firff, will have the greateft attractive Force, confequenfly their Par- ticles muft be the mod Spherical and moft Solid ; and there- fore their Contaft the leaft of any, therefore the moft Fluid.
In the Memoirs of the French Academy, M. ie Mortal oives an Inftance of a 'Pericardium, which being open'd, the Liquor contain'd therein, was found congeal'd into a Confif- tence fit to be cut with a Knife, and two fquare Fingers thick about the Heart
PERICARP1A, from irifi, circum, about, and Carpus the Wrift are Medicines that are applied to the Wrift.
PERI CARPUS, in Botany, a Pellicle, or thin Mem- brane, incompaffing the Fruit or Grain of a Plant. See Fkuit, Seep, £S>c. The Wordis form'd of the Greekirifl about and Httyirh Fruit.
PER1CHORUS, in Antiquity, a Name given by the Greek to their profane Games and Combats ; i. e. to fuch as were not confecrated to any of the Gods. See Games.
The Word in the Original, {lgni&cs near or neighbouring ; apparently becaufe none but the People of the Neighbour- hood attended at thefe obfeure Exercifes.
The Champions did not fight in Honour or any Ood or Heroc as in the others ; but only for the prize Sake.
The Word is form'd from the Greek r.tgi about and ;v/p«
°PERI CRANIUM, in Anatomy, a thick folid Coat or Membrane, covering the out Side of the Cranium or Skull.
Some tall it W the general Name of 'Periofteum, becaufe of its adhering to the Bone: others divide it into two Mem- branes the under whereof immediately mvefting the Skull, they call Periofteum ; and theupper the •Pericranium. But in effect, 'tis but one double Membrane, confifting, as moft others do of two Coats. 'Tis fuppofed to have its Origin from the dura Mater - which pafling thro' the Sutures of the Skull, by means of feveral Filaments forms this thick Membrane : At leaft 'tis ftill f° ur,d connected to the dura Mater by Fi- bres 'transmitted from it to the Membrane, thto' the Sutures. About the Origin of the temporal Mufcles, the two Coats of the 2>mOT»w/«°part; the Outer paffing over thofe Mufcles, and the Inner ftill adhering clofe to the Cranium. See Pe-
'■The Word is form'd from the Greek Mfi about and xf «r»»
Head
PERIDROME, PERIDROMUS, in the ancient Archi- teaure the Space, Gallery, Alley, or the like, in a Peripte- re between the Columns and the Wall. Sabmjim obferves that the 'peridromes ferved for Walks among the Greeks.
PERIOECI, in Geography, fuch Inhabitants of the Globe as have the fame Latitudes, but oppofite Longitudes ; or live under the fame Parallel, and the fame Meridian, but in dif- ferent Semi-circles of that Meridian. See Globe.
Thefe have the fame common Seafons throughout the Tear ■ and the fame Phajnomena of the heavenly Bodies; but their Hours, or times of the Day, are oppofite to each other. When v. g. with the one 'tis Mid-day ; with the other 'tis Mid- night. See Day and Season.
The Word is form'd from the Greek mfi about and omso
'pERIEGETES, a Greek Term, fignifying a Perfon who conduits anothet about a Thing, to fliow it him, fgc.
It is applied in Antiquity to Geographers ; efpecially to thofe who deicribed the Sea-Coaffs : Thus Diovyjins is ftiled •Periegetes, for publishing a Geography in Hexameter Verfes ; which EuStU&f® has commented on, both, 'm Greek.
The Name 'Periegetes was alfo given to thofe who con- ducted Strangers about in Cities, to fhew 'em the Antiqui- ties Monuments, Curiofities, pc. thereof.
Thefe 'Periegetes were the fame with what they now call Antiquaries in Italy. See Antiquary.
PERIG/EUM, PERIGEE, in Aftronomy, that point of the Heavens, wherein the Sun and Planets are at their leaft Diftancefrom the Eatth. See Excentric.
The Moon in her 'Perigee is 53 or 54 Semi-dameters of the Earth diftant from us. See moon. _
The Term is but little ufed, except in the Ptolomaic Syftem ; where the Earth is placed in the Centre of the World and the Diftances of the Planets chiefly confider'd with regard thereto; being form'd of the Greek artf/, about and yii 'Jerra, Earth.
(780
PER
The Copernicans ufe the Word Perihel'w.m in lieu of 3> e . rigeum ; becaufe they place the Sun in the Centre. See Pe.
R1HELIUM.
PERIHELIUM, in Aftronomy, that point of the Orbit of a Planet, or Comet, wherein it is at its leaft Diftance from the Sun. See Planet, Comet, Son, igc.
The Word is form'd from the Greek %i f i, and a/©», Sol, Sun.
The ancient Aftronomers, in lieu hereof ufed 'Perig&ttm ; becaufe they placed the Earth in the Centre. See Peri-
GiEUM.
PEREGRINART, PEREGRINARIUS.in the ancient Monafteries, a Monk to whom was committed the Care of receiving, and entertaining Strangers, or Vifitors.
PERIMETER, in Geometry, the Ambit, or extent, that bounds a Figure or Body. See Figure.
The Perimeters of Surfaces, or Figures, ate Lines ; thofe of Bodies are Surfaces. See Superficies.
In circular Figures, i$c. inftead of Perimeter we fay Cir- cumference ox 'Periphery. See Periphery.
The Word is form'd from the Greek -as/i and ^i T! a Mea- fure.
PERINEUM, in Anatomy, the Space between the 'Pe- nis or Scrotum, and the Fundament ; properly the Ligamen- tous Seam ; cali'd by the Latins, Femen, and Interefemineum.
The Word 'Perinigum is form'd from the Oreek m/l and vamii to inhabit.
PERINDE Valere, in the Canon Law, a Difpenfation granted a Clerk, who being legally incapable of a Benefice, or other ecclefiaftical Function, is, dejatlo, admitted to it. Sec Dispensation.
The 'Perinde Valere, is a kind of Writ ; thus cali'd from two Words therein, fignifying the Difpenfation to be equiva- lent or tantamount to a legal Capacity.
PERIOCHA, an Argument containing the Sum of a Dif- courfe.
PERIOD, in Aftronomy, the Time taken up by a Star or Planet, in making a Revolution; or the Duration of its Courfe, till it return to the fame Point of the Heavens. See Revolution.
The Sun's, or rather the Earth's 'Period, is 31? 5 Days, five Hours, 4<. Min. That of the Moon 27 Days, 13 Hours, 9 Min. (gc See Sun, Moon, ($c.
The 'Periods of the Comets are now many of 'em pretty well afcertain'd. See Comet.
There is a wonderful Harmony between the Diftances of the Planets from the Sun, and their Periods round him ; the great Law whereof is, that the Squares of the 'Periodic Times are ever proportional to the Cubes of their meaniDifiances from the Sun. See Planet.
The feveral 'Periods and mean Diftances of the feveral Planets are as follow.
PERIODS.
Days h. 1 11
mean Dift.
Saturn
10570 6" 3<J 2(f
953800
Jupiter
4332 12 20 35
520110
Mars
(S8<S 23 27 30
152569
Earth
3<f5 6 9 S°
IOOOOO
Venus
224 16 49 24
72333
Mercury
87 23 15 53
38710
Period, in Chronology, an Epocha or interval of Time, by which the Years are accounted; or a Series of Years, whereby, in different Nations, and on different Occafions Time is meafur'd. See Time.
Such are the Callipic, and Metonic Periods, two different Corre&ions of the Greek Calendar ; the Julian Period, in- vented by jfof. Scaliger$ the Vitlorian Period^ Sfa
Metonic Period, or Cycle, cali'd alfo the Cycle of the Moon, is a Series of 19 Years, which elaps'd the new and full Moons, are fuppofed to return to the fame Day of the folar Year : It was thus cali'd from its Inventor Meton. See Me- tonic. See alfo Cycle.
Callipic Period, is a Series of 76 Years, returning in a perpetual Circle 5 which elaps'd the new and full Moons, are fuppofed to return to the fame Day of the folar Year. The Collipic Period is an improvement on the Metonic of 19 Years, which proving inaccurate, Calippus the Athenian multiplied it by 4, and thus arofe the Calippic Period. See Calippic.
Hipparchiis's Period, is a Series of 304. folar Years, re- turning in a conflant round ; and reftoring the new and full Moons to the fame Day of the folar Year 5 according to the Sentiment of Hipp 'archils.
This Period arifes by multiplying the Calif pic period by 4* Bipparchm affumed the Quantity of the folar Year to be 3<?5 Days, 5 Hours, 55' 12". And hence concluded that in 1 04 Years, Callippits's Period wou'd Err a whole Day. He therefore multiplied the period by 4, and from the Product* call away an entire Day. But even this does not reflore the new and full Moons to the fame Day throughout the whole
