“ An “oblique cone” is the solid or surface traced out by a line which passes through a fixed point and through the circumference of a circle, the fixed point not being on the line through the centre of the circle perpendicular to its plane. A “quadric cone” is a cone having any conic for its base. The plane containing the vertex, centre of the base, and perpendicular to the base is called the principal section; and the section of a cone by a plane containing the vertex is a triangle if the solid be considered, and two intersecting lines if the surface be considered. ”

“ Analytically, the equation to a right cone formed by the revolution of the line y = mx about the axis of x is z = m (x2+y2) . Obviously every tangent plane passes through the vertex; this is the characteristic property of conical surfaces. Conical surfaces are also “developable” surfaces, i.e. the surface can be applied to a plane without wrinkling or rending. Connected with quadric cones is the interesting curve termed the “spheroconic,” which is the curve of intersection of any quadric cone and a sphere having its centre at the vertex of the cone. ”