“ If the conic be a circle the conoid is a sphere (q.v.) ; if an ellipse a spheroid (q.v.) ; if a parabola a paraboloid; if a hyperbola the surface is a hyperboloid of either one or two sheets according as the revolution takes place about the conjugate or transverse axis, and the surface generated by the asymptotes is called the “asymptotic cone.” If two intersecting straight lines be regarded as a conic, then the principal axes are the bisectors of the angles between the lines ”