Spheroid

Spheroid is a limiting case of the ellipsoid when the sections in one direction are circles instead of ellipses. It can be obtained by the revolution of an ellipse about one of its axes. If the major axis be taken as the axis of revolution, a prolate spheroid is obtained, while revolutions about the minor axis give an oblate spheroid. The earth is an example of the latter. As major and minor axes approach each other more and more in length, the two ellipsoids also become more alike, the limiting case being the sphere. [ELLIPSOID, QUADRIC SURFACE.]