PLA Si 



JO inches ; the smoothing plnne, about 7J 

 inches : these are called bench planet, being 

 always laid on the work-bench. Besides 

 these , there is a straight block , for straight- 

 ening short edges ; the plotujh, a very 

 narrow plane, having an apparatus to 

 guide it in ploughing a groove at any 

 required distance from the edge of a 

 board ; a dado, for similar purposes ; a 

 toothing plane, with a toothed iron, for 

 roughening woods for veneering ; mould- 

 ing planes, with curved faces and cutting 

 edges, for forming various ornamental 

 mouldings, and known by the names of 

 snipes'-bills, beads, hollows, rounds,ovolos, 

 ogees, &c. ; rebating planes, for cutting out 

 rebates, or semi-grooves, on the edges of 

 boards, and sometimes also for ornamental 



mouldings, &c. 1. In crystallography, 



the flat surfaces are called planes, or faces 



of the crystal. 5. In botany, see PLATA- 



NUS. The tree known by the name of 

 Plane in England, is the Sycamore, or 

 Great Maple (Acer pseudo-platanus). Its 

 wood is valuable, being close and com- 

 pact, easily wrought, and not liable to 

 splinter or warp. It takes a fine polish. 



PLANE TABLE. A rectangular board 

 enclosed by a frame, graduated into de- 

 grees from the centre, for finding the 

 position and distance of points which are 

 situated in the same plane, taking angles, 

 and laying down the work of a survey. 



PLAN'ET, from ^\.tv,TY i , wandering. 1. 

 A wandering star, as distinguished from 

 the fixed stars, which always maintain 

 the same relative positions with relation 

 to each other. In this primary sense of 

 the term, comets and satellites are in- 

 cluded ; but modern astronomers restrict 

 the term to those bodies which revolve 

 about the sun, as a centre, with a mo- 

 derate degree of eccentricity, thus ex- 

 cluding comets, the eccentricity of whose 

 orbits is great, and satellites which re- 

 volve about their primaries, as these 

 primaries do about the sun. 'fha elements 

 of the planets are certain quantities, which 

 are necessary to be known in order to 

 determine the theory of their ecliptic 

 motions. These are seven : (1.) The du- 

 ration of the sidereal revolution. (2.) The 

 ?erni-axis major. (3.) The eccentricity. 

 (4 and 5.) The mean longitude of the 

 planet at any given epoch, and the long- 

 itude of the perihelion at the same epoch. 

 (6 and 7.) The longitude of the nodes of 

 the orbit with the ecliptic at a given 

 epoch, and the inclination of the orbit to 

 this plane. 



PLAN'ET WHEELS. Wheels by whose 

 mutual connexion a variable angular 

 motion, such as that of the radius vector 

 of a planet in its orbit, may be exhibited 

 The common contrivance now in use for 

 this purpose consists of two elliptical 

 wheels, connected by teeth running into 



PLA 



each other : these wheels revolve on their 

 foci, and, while the driving ellipses more 

 uniformly, the radius vector of the other 

 has the required motion. 



PLANETA'RIUM. See ORRERY. 



PLANETOIDS. See ASTRONOMY. 



PLA'NI. A family of the order Malaco- 

 pterygii subrachiali, commonly called flat- 

 fishes, comprising the great genus Pleu- 

 ronectes, Lin. 



PLANIPET'ALOUS, from planus, flat, and 

 5TraA.ov, a petal ; flat-leaved. A flower is 

 planipetalous, or planifolious, when made 

 up of plain leaves set round the centre. 



PLAN'ISPHERE, from plamts, plain, and 

 sphere. 1. A projection of the sphere and 

 its circles upon a plane. 2. An astrono- 

 mical instrument used in observing 1 the 

 motions of the heavenly bodies, being a 

 projection of the celestial sphere upon a 

 plane, representing the stars, constella- 

 tions, &c., in their proper situations, dis- 

 tances, &c., as the astrolabe, which is a 

 common name for all such projections. 



PLANK, Sax. plane, or plank. A name 

 given generally to all timber, except fir, 

 which is not more than four inches thick, 

 and thicker than a board, which is an 

 inch and a half downwards. 



PLA'NO. A prefix to several words, as 

 plano-concave, plane on one side and con- 

 cave on the other ; plano-com-ex, plane on 

 one side and convex on the other ( 

 LENS) ; piano-horizontal, having a level 

 horizontal surface ; piano-subulate, smooth 

 and awl-shaped. 



PLAN'TAIN. The hcrbaceotis plantains 

 form the genus Plantago (q. v.) ; the water- 

 plantain is a species of Alisma; and th 

 Plantain-tree of South America, &c. be- 

 longs to the genus Musa. The t'ru i t of thi 

 perennial tree is highly valued by the 

 Indians as an article of subsistence. 



PLANT-CANB. A name in the West In- 

 dies for sugar-canes of the first growth, in 

 distinction from the ratoons, or sprouts 

 from roots of canes which have been cut. 



PLANTIG'RADA. Plantigrade animals : 

 from planta, the sole of the foot, and gra- 

 dior, to walk. A tribe of Mammiferous 

 quadrupeds, in which the whole sole of 

 the foot is placed upon the ground in 

 walking; distinct from the Di^itigrada 

 which walk on the extremities of the toes. 

 The bear and badger are plantigrade ani- 

 mals ; the cat aud dog belong to the Digi- 

 tigrade tribe. 



PLASH'INO. A mode of modifying a 

 hedge , by bending dow ti some of the shoou 

 and twisting them among the stems. 



PLAS'MA. A grass-green variety of 

 rhombohedral quartz, occurring in bedi 

 with common chalcedony. It was for- 

 merly in repute for ornamental purposet. 

 PLAS'TER. A composition of lime, sand, 

 and water, for coating the walls of buil-1- 

 ings. Th composition still retains tht 



