PER 



PER 



cup, properly so called, the most common 

 species of calyx, placed immediately un- 

 der the flower, which is contained in it as 

 a cup. The flower-cup differs in point, 

 number, figure, proportion and situation. 

 PERICARP1UM. See BOTANY. 

 PERICRANIUM, in anatomy, a thick 

 solid coat, or membrane, covering the 

 outside of the cranium or skull. 



PERIGEE, in astronomy, that point of 

 the sun's or moon's orbit, wherein they 

 are at their least distance from the earth, 

 in which sense it stands opposed to 

 apogee. 



PERIHELIUM, in astronomy, that 

 point of a planet's or comet's orbit, 

 wherein it is in its least distance from the 

 sun; in which sense it stands in opposi- 

 tion to aphelium. 



PERILLA, in botany, a genus of the 

 Diclynamia Gymnospermia class and or- 

 der. Natural order of Verticellatas. La- 

 biatae, Jussieu. Essential character : calyx, 

 uppermost segment very short; stamens 

 distant ; styles two, connected. There is 

 but one species ; viz. P. ocymoides, an 

 annual plant, and a native of the East 

 Indies. 



PERIMETER, in geometry, the bounds 

 or limits of any figure or body. The pe- 

 rimeter of surfaces or figures are lines, 

 those of bodies are surfaces. In circular 

 figures, instead of perimeter, we say cir- 

 cumference, or periphery. 



PERINEUM, or PERINEUM. See 

 ANATOMY. 



PERIOD, in astronomy, the time taken 

 up by a star or planet in making a revo- 

 lution round the sun ; or the duration of 

 its course till it return to the same point 

 of its orbit. See ASTRONOMY. There 

 is a wonderful harmony between the dis- 

 tances of the planets from the sun, and 

 their periods round him ; the great law 

 whereof is, that the squares of the pe- 

 riodical times of the primary planets, are 

 to each other as the cubes of their dis- 

 tances from the sun; and likewise, the 

 squares of the periodical times of the se- 

 condaries of any planet, are to each other 

 as the cubes of their distances from that 

 primary. This harmony among the planets 

 is one of the greatest confirmations of the 

 Copernican hypothesis. 



PERIOD, in chronology, denotes a re- 

 volution of a certain number of years, or 

 a series of years, whereby, in different na- 

 tions, and on different occasions, time is 

 measured; such are the following. 



PERIOD, Calippic, a system of seventy- 

 six years. The calippic period compre- 

 hends 48 common years, and 28 inter- 



calary ones, 940 lunations, and 22,759 

 days. See CHHONOLOOY. 



PERIOD, Dionysian, or Victorian PE- 

 RIOD, a system of 532 lunx-solur and 

 Julian years, which being elapsed, the 

 characters of the moon fall again upon 

 the same day and feria, and revolve in 

 the same order, according to the opinion 

 of the ancients- This period is otherwise 

 called the great paschal cycle, because 

 the Christian church first used it, to find 

 the true time of the pascha, or easier. 

 The sum of these years arise by multiply- 

 ing together the cycles of the sun and 

 moon. See EASTER. 



PERIOD, Hipparclms's, a system of 304 

 years, both lunar and solar, which being 

 elapsed, Hipparchus thought lhat the 

 reckoning by the lunar motion would 

 coincide again with the solar measures. 

 This period comprehends 3760 lunar 

 months, or 111,039 days; the sum of 

 which arises from the multiplication of 

 the calippic period by 4, subtracting unity 

 from the product. 



PERIOD, in grammar, denotes a small 

 compass of discourse, containing a per- 

 fect sentence, and distinguished tu the 

 end by a point, or full stop, thus (.); and 

 its members or divisions marked by com- 

 mas, colons, &c. 



PERIOD is also used for the character 

 (.) wherewith the periods of discourse 

 are terminated, or expressed, being com- 

 monly called a full stop or point. See 

 PUNCTUATION. 



PERIOD, in numbers, a distinction 

 made by a point, or comma, after every 

 sixth place or figure ; and is used in nu- 

 meration for the readier distinguishing 

 and naming the several figures or places, 

 which see under ARITHMETIC. 



PERIOECI, in geography, such inhabi- 

 tants of the earth as have the same lati- 

 tudes, but opposite longitudes ; or live 

 under the same parallel and the same 

 meridian, but in different semicircles of 

 that meridian, or in opposite points of the 

 parallel. These have the same common 

 seasons throughout the year, and the 

 same phenomena of the heavenly bodies ; 

 but when it is noon-day with the one it is 

 midnight with the other, there being- 

 twelve hours between them in an east or 

 west direction. These are found on the 

 globe, by the hour-index, or by turning 

 the globe half round, that is 180 degrees 

 either way. 



PERIOSTEUM, or PERIOSTIUM, in 

 anatomy, a nervous vascuious mem- 

 brane, endued with a very quick sense, 

 immediately surrounding in every part 



