SECTION

, in Geometry, denotes a side or surface appearing of a body, or figure, cut by another; or the place where lines, planes, &c, cut each other.

The common Section of two planes is always a right line; being the line supposed to be drawn by one plane in its cutting or entering the other. If a sphere be cut in any manner by a plane, the figure of the Section will be a circle; also the common intersection of the surfaces of two spheres, is the circumference of a circle; and the two common Sections of the surfaces of a right cone and a sphere, are the circumferences of circles if the axis of the cone pass through the centre of the sphere, otherwise not; moreover, of the two common Sections of a sphere and a cone, whether right or oblique, if the one be a circle the other will be a circle also, otherwise not. See my Tracts, tract 7, prop. 7, 8, 9.

The Sections of a cone by a plane, are five; viz, a triangle, circle, ellipse, hyperbola, and parabola. See each of these terms, as also Conic Section.

Sections of Buildings and Bodies, &c, are either vertical, or horizontal, &c. The

Vertical Section, or simply the Section, of a building, denotes its profile, or a delineation of its heights and depths raised on the plan; as if the fabric had been cut asunder by a vertical plane, to discover the inside. And

Horizontal Section is the ichnography or ground plan, or a Section parallel to the horizon.