But it is an improper quadric curve; and in speaking of curves of the second or any other given order, we frequently imply that the curve is a.
Since they are essentially positive the quadric is an ellipsoid; it is called the momental ellipsoid at 0.
A curve of the second order is a conic, and is also called a quadric curve; and conversely every conic is a curve of the second order or quadric curve.
The moment of inertia about any radius of the quadric (39) therefore varies inversely as the square of the length of this radius.
The diameter of a quadric surface is a line at the extremities of which the tangent planes are parallel.