PER 



PER 



PERCH. 1. In ichthyology, see PERCA. 

 2. A measure of length equal to 5j 

 yards : a rod or pole. 



PERCHLOR'ATE. A salt formed by the 

 union of the perchloric acid with a base. 



PERCHLOR'IC ACID. Oxychloric Acid. 

 An acid consisting of 1 equivalent of chlo- 

 rine and 7 equivalents of oxygen, con- 

 densed into a colourless liquid of sp. gr. 

 16. It is obtained by distilling perchlor- 

 ate of potash with an equal weight of 

 sulphuric acid, diluted with a fourth of 

 water. By redistillation with concen- 

 trated sulphuric acid, the perchloric acid 

 may be obtained in a solid form, and 

 crystallised. The discovery of this acid 

 is due to Count Stadion. 



PERCUS'SION, from percutio, to strike. 

 The striking of one body against another. 

 The centre of percussion, in any body, or 

 system of bodies revolving about a point 

 or axis, is that point which, striking an 

 immoveable object, the whole mass is 

 brought to rest in equilibrio, without 

 acting upon the centre of suspension. In 

 a straight stick, of uniform thickness, 

 the centre of percussion is two-thirds 

 of the length of the stick from the axis 

 of motion. Percussion caps are little caps 

 containing minute portions of fulminating 

 powder, to be fixed on the nipple of a 

 percussion lock, to ignite the powder in the 

 barrel of the musket, when exploded by 

 the stroke of the hammer or dog-head. 

 Locks adapted to explode fire arms, &c. 

 by these caps are called permission locks. 



PERE LA CHAISE. The name of a cele- 

 brated cemetery, in Paris, laid out in 1804. 

 It was formerly the chief seat of the 

 Jesuits' establishment in France, and was 

 presided over by Pere La Chaise, Con- 

 fessor of Louis XIV. 



PEREn'NiAL.Lat. jHrennis. from per, and 

 annus, & year. Lasting naturally more 

 than two years. Applied to plants, the 

 stems of which perish annually ; but the 

 roots last more than two years. The term 

 is sometimes used in the sense of per- 

 petual, or never ceasing, as a perennial 

 stream, spring, &c. 



PER'FECT NUMBER, is a number equal to 

 the sum of all its divisors. 



PERTO'LIATE, Lat. perfoliatus, from per, 

 and folium, a leaf. Applied to plants, the 

 leaves of which surround the stem at 

 their base. 



PERFORATE*. One of Linnaeus' natural 

 orders of plants, comprehending such as 

 have their leaves perforated with small 

 holes. 



PER'FORATE, Lat.per/or<, penetrated. 

 Applied to leaves through which the 

 stems pass, and also to those penetrated 

 with small holes. 



PEROAME'NEot's,Lat. pergamena, parch- 

 ment. In entomology, when a part resem- 

 bles parchment. 



PERGXJN'NAH. In the East Indies, A 

 subdivision of a district answering tj 

 the English hundred. 



PE'RI. In Persian mythology, the pei-.s 

 are the descendants of fallen spirits, ex- 

 cluded from Paradise until their penancs 

 is completed. 



PER'IANTH, Lat. perianthium. Th 

 calyx properly and commonly so caliM 

 when it is contiguous to, and makes pur; 

 of, a flower, from JTSJ/, about, and otvBof, 

 a flower. It has many forms. 



PERI'BOLOS, xtgi, and aiXXiu, I cast. In. 

 architecture, an inclosure entirely round 

 a temple, surrounded by a wall. 



PERICAR'DIUM, from tr^t, around, and 

 xxfita, the heart. The membranous baj? 

 which surrounds the heart, and the arte- 

 rial and venous trunks connected with 

 it. It contains a liquid which lubricates 

 the heart. 



PER'ICARP, ~La.t. pericarpiitm. The seed- 

 vessel of a plant. From xiy , about, and 

 xot%vos, seed. 



PERICH^'TIUJT, from frtgt, about, and 

 Xour/i, a hair. A scaly sheath investing 

 the fertile flower, and consequently tho 

 base of the fruit-stalk, of some mosses. 



PERICHOS'DRICM, from ^rtai, about, and 

 %ovSgof, a cartilage. The membrane 

 that covers a cartilage. 



PERICRA'MUM, from xty, about, and 

 xgetvior, the cranium. A membrane 

 covering the outside of the cranium, and 

 corresponding to the periosteum of other 

 bones. 



PEK'IDROME, from $/, around, and 

 SgOjttoj, a course. That part of a temple, 

 or other like edifice, between the perip- 

 tere and the wall, and which served 

 among the Greeks as a promenade. 



PER'IOEE, from tnot, near, and yn, the 

 earth. A term in the ancient astronomy, 

 opposed to apogee, and signifying the 

 nearest approach of the sun, or any of 

 the planets, to the earth. In modern 

 astronomy, the term perihelion is used, 

 because it is not the sun but the earth 

 which is in motion. 



PERIGY'NIUM, -reg/, and yaw,, female. 

 The arceolate body formed in the genui 

 carex by two bracteae. 



PERIG'TNOUS, from xsgi, around, and 

 yvv/1, a female. Applied to the stamens 

 of flowers, when they grow out of the 

 corolla, calyx, or perianth, or are not in 

 any way joined to the seed-vessel. 



PERIHE'LION, 1 from a-tfi, near, and 



PERIHE'LICM, J t^oj, the sun. That 

 point of the orbit of a planet or comet 

 wherein it is nearest to the sun, being 

 the extreme of the transverse axis neareM 



