Like all other planets, the earth is a solid sphere that has undergone a
slight flattening at the opposite extremities or poles of the axis of
revolution. More accurately, it is an oblate spheroid generated by the
rotation of an ellipse about its minor axis. Such a figure would be
assumed by a sphere of liquid rotating about a diameter, centrifugal
force acting most vigorously at the equator, and tending to overcome the
internal forces that keep the molecules together.