Part 9

The Perimeter of a polygon is its boundary considered as a whole.

The Base of a polygon is the side upon which the polygon is supposed to stand.

The Altitude of a polygon is the perpendicular distance between the base and a side or angle opposite the base.

A Quadrilateral is a polygon having four sides and four angles.

A Parallelogram is a quadrilateral which has its opposite sides parallel.

The side upon which a parallelogram stands and the opposite side are called respectively its lower and upper bases.

A Rectangle is a parallelogram having its angles right angles.

A Square is an equilateral rectangle, fig. 41.

A Rhomboid is an oblique-angled parallelogram.

A Rhombus is an equilateral rhomboid, fig. 42.

A Trapezium is a quadrilateral having no two sides parallel, fig. 43.

A Trapezoid is a quadrilateral in which two opposite sides are parallel, and the other two oblique, fig. 44.

=A POLYHEDRON= is a solid bounded by planes. There are five regular solids which are shown in figs. 45, 46, 47, 48 and 49. A regular solid is bounded by similar and regular plane figures.

Fig. 45.--The tetrahedron, bounded by four equilateral triangles.

Fig. 46.--The hexahedron, or cube, bounded by six squares.

Fig. 47.--The octahedron, bounded by eight equilateral triangles.

Fig. 48.--The dodecahedron, bounded by twelve pentagons.

Fig. 49.--The icosahedron, bounded by twenty equilateral triangles.

=PRISM.=--A solid whose bases or ends are very similar plane figures, and whose sides are parallelograms; prisms are called triangular, square, etc., according as the bases are triangles, squares, etc.

=PRODUCE.=--To continue or extend.

=PROFILE.=--An outline or contour.

=PROJECTION.=--The view of an object obtained upon a plane by projecting lines perpendicular to the plane.

=QUADRANT.=--The fourth part; a quarter; the quarter of a circle.

=QUADRISECT.=--To divide into four equal parts.

=SECTION.=--A projection upon a plane parallel to a cutting plane which intersects any object. The section generally represents the part behind the cutting plane, and represents the cut surfaces by diagonal lines.

=SECTIONAL.=--Showing the section made by a plane.

=SHADOW.=--Shade and shadow have about the same meaning.

=SOLID.=--A solid has three dimensions--length, breadth and thickness.