(Science: astronomy) In the ptolemaic system, the outermost of the revolving concentric spheres constituting the universe, the motion of which was supposed to carry with it all the inclosed spheres with their planets in a daily revolution from east to west. See crystalline heavens, under Crystalline. The motions of the greatest persons in a government ought to be, as the motions of the planets, under primum mobile. (bacon)
Origin: L, first cause of motion.