BODY

, in Geometry, is a figure conceived to be extended in all directions, or what is usually said to consist of length, breadth, and thickness; being otherwise called a Solid. A body is conceived to be formed or generated by the motion of a surface; like as a surface by the motion of a line, and a line by the motion of a point.—Similar bodies, or solids, are in proportion to each other, as the cubes of their like sides, or linear dimensions.

, in Physics, or Natural Philosophy, a solid, extended, palpable substance; of itself merely passive, being indifferent either to motion or rest, and capable of any sort of motion or figure.

Body is composed, according to the Peripatetics, of matter, form, and privation; according to the Epicureans and Corpuscularians, of an assemblage of hooked, heavy atoms; according to the Cartesians, of a certain extension; and according to the Newtonians, of a system or association of solid, massy, hard, impenetrable, moveable particles, ranged or disposed in this or that manner; from which arise bodies of this or that form, and distinguished by this or that name. These elementary or component particles of bodies, they assert, must be perfectly hard, so as never to wear or break in pieces; which, Newton observes, is necessary, in order to the world's persisting in the same state, and bodies continuing of the same nature and texture in several ages.

Body of a piece of Ordnance, the part contained between the centre of the trunnions and the caseabel. This should always be more fortified or stronger than the rest. See Cannon.

Body of the Place, in Fortification, denotes either the buildings inclosed, or more generally the inclosure itself. Thus, to construct the body of the place, is to fortify or inclose the place with bastions and curtains.

Body of a Pump, the thickest part of the barrel or pipe of a pump, within which the piston moves.

, Regular or Platonic, are those which have all their sides, angles, and planes, similar and equal. Of these there are only 5; viz, the tetraedron, contained by 4 equilateral triangles; the hexaedron or cube, by 6 squares; the octaedron, by 8 triangles; the dodecaedron, by 12 pentagons; and the icosaedron, by 20 triangles.

Let the annexed sigures be exactly drawn on pasteboard, or stiff paper, and cut out from it by the extreme or bounding lines: then cut the others, or internal lines, only half through, so that the parts may be turned up by them, and then glued or otherwise fastened together with paste, sealing-wax, &c; so shall they form the respective body marked with the corresponding | number; viz, N° 1 the tetraedron, N° 2 the hexaedron or cube, N° 3 the octaedron, N° 4 the dodecaedron, and N° 5 the icosaedron.

1. Multiply the proper tabular area (taken from the following table) by the square of the linear edge of the solid, for the superficies.

2. Multiply the tabular solidity by the cube of the linear edge, for the solid content.

For more particular properties, see each respective word. See also my large Mensuration, pa. 248, edit. 2.

These bodies were called platonic, because they were said to have been invented, or first treated of, by Plato, who conceived certain mysteries annexed to them.