PET 



553 



PET 



in Linna'us's natural method, character- 

 ised by being fetid, poisonous, and aro- 

 matic, with personate corollae. 



PEB'SONATE, Lat. personaius, from per- 

 ona, a mask. A term applied to mono- 

 petalous flowers of an irregular form, the 

 corolla having an oval appearance, with 

 the labia closed. 



PERSPECTIVE, from perspicio, to see 

 through. 1. A term, in drawing and paint- 

 ing, lor the science by which objects are 

 ranged upon a plane surface, as in a pic- 

 ture, according to their appearance in 

 their real situation. This embraces three 

 subjects: lines, which determine the out- 

 line ; the chiaro-'scuro, which shows the 

 relief; and the color, which gives the 

 true appearance. The lines form what 

 we call the design, and the colouring, in 

 conjunction with the design, constitutes 

 the art of painting; consequently we may 

 i' vide perspective into linear and atrial. 

 The first is a branch of mathematics, and, 

 as such, is subject to principles which are 

 rigorously demonstrated : it shows how 

 lines which define figures appear to the 

 eye of tlie spectator, according to the 

 point on which the eye is fixed, and the 

 distance of the objects. Aerial perspective 

 is o named because it is the effect of the 

 vaporous air which is interposed between 

 the different objects, diminishing by its 

 colour the tones in proportion to its 

 greater or less quantity, and the distance 

 of the planes of the picture in relation to 

 the eye. Perspective, generally, divides 

 itself into projection, ichnography, ortho- 

 grcivhy, scenography, and stereography 

 (q. v.). 2. A terrestrial telescope. 



PEB.SFIBA'TION, fromperspiro, to breathe 

 through. The vapour secreted by the 

 extremities of the cutaneous arteries from 

 the external surface of the body. It is 

 called sensible when it becomes visible in 

 the form of very small drops (sweat) ad- 

 hering to the skin; and insensible, when 

 it passes off in the form of invisible 

 vapour. 



PEBTURBA'TION. In astronomy, the de- 

 viation of a celestial body from its theo- 

 retical elliptical orbit, caused by the at- 

 traction of other bodies. 



PEBB'VIAN BALSAM is the produce of the 

 Nyroxylon Peruiferum. a tree of Peru, &c. 

 Set BALSAM. 



PEBB'VIAN BABX. Cortex Peruvian. 

 See BARK and CINCHONA. 



PE'SADE. Fr. pessade. The motion of a 

 horse when he raises his fore quarters, 

 and keeps his hind feet on the ground, 

 without advancing. 



PIS'SARI, from xuriru, to soften. A sur- 

 gical instrument or application of many 

 forms, for introducing into the vagina, to 

 support the uterus. 



PET'AI., Lat. petalum, and Gr. 



from xtTte.*, to expand. The name of 

 each of the coloured leaflets of the corolla 

 of a flower. In monopetalous flowers the 

 corolla and petal are the same. 



PETALOI'DEUE, xiTot\ot and iioof Any 

 organ like a petal in texture or colour 



PET'ARD (French). A warlike engine, 

 made of metal, and shaped like a sugar- 

 loaf. It is loaded with powder, and fixed 

 on a madrier or plank, and exploded 

 against gates, barricades, &c., to break 

 them open. 



PETAU'RVS. A genus of Marsupialia, 

 established by Shaw, to receive fhejiyiny 

 phalangers of New Holland. Name from 

 trSTwAon, a leaf, and &$, a tail ; the skin 

 of the flanks being more or less extended, 

 which enables them to sustain themselves 

 momentarily in the air, and make great 

 leaps, like the flying squirrels among the 

 Rodentia. 



PETE'CIIIA. An Italian word, commonly 

 used in the Latin plural from petechiat, to 

 denote the purple spots which appear on 

 the skin in some malignant fevers. 



PET'IOLAR, Lat. petiolaris. Fixed to the 

 petiole or leaf-stalk. 



PETI'OLATE, Lat. petiolatus. Having pe- 

 tioles or leaf-stalks. 



PE'TIOLE, Lat. petiolus. The footstalk 

 or leafstalk of a plant. 



PETI'TIO PRINCIPII. In logic, the tak- 

 ing of a thing for true, and drawing con- 

 clusions from it as such. This is what is 

 termed, in common parlance, " begging 

 the question." 



PET'REL. A name for all those storm 

 birds forming the extensive genus Procel- 

 laria, Lin. Set PROCELLA.RIA and PELECA- 

 NOIDES. 



PETRIFAC'TIONS, Lat. petra, stone, and, 

 facio, I make. Otherwise called organ- 

 ised fossils, organic remains. The con- 

 version of vegetable and animal matter 

 into a stony substance. 



PETROBHU'SIANS. The followers of 

 Peter de Bruys, a heretic of the 12th 

 century. 



PETROLE'NE, from petra, stone , and ol-eum , 

 oil. An oily liquid, of a pale-yellow co- 

 lour, and Sp. gr. 0'891, obtained by distil- 

 ling about 151bs. of the bitumen of Beche- 

 broun, in the department of Bas-Rhin, 

 with about 22 imperial gallons of water. 

 The bitumen itself is viscid, has a deep 

 brown colour, and is employed, around the 

 locality where it is found, as grease for 

 machinery, under the name of stone oil. 



PETRO'LECTM, from petra, rock, and 

 oleum, oil. A mineral oily substance, 

 which flows from the clefts of rocks, and 

 in different places at the surface of the 

 earth. It is usually, at the temperature 

 of this country, about the consistency of 

 tar, has a reddish -bro*rn colour, but bs- 



