A cone is a solid bounded by a conical surface and a plane which cuts the conical surface. It may be considered as a pyramid with an infinite number of sides, Fig. SO.

The conical surface is called the lateral area and it tapers to a point called the vertex; the plane is called the base.

The altitude of a cone is the perpendicular distance from the vertex to the base.

An element of the cone is any straight line from the vertex to the circumference of the base.

A circular cone is a cone whose base is a circle

A right circular cone, or cone of revolution, Fig. 81, is a cone whose axis is perpendicular to the base. It may be generated by the revolution of a right triangle about one of the legs as an axis. A frustum of a cone, Fig. 82, is the portion of the cone included between the base and a plane parallel to the base; its altitude is the perpendicular distance between the bases.

Fig. 80. Cone

Fig. 80. Cone.

Fig. 81. Right Circular Cone

Fig. 81. Right Circular Cone.

Fig. 82. Frustum of Cone

Fig. 82. Frustum of Cone.