Primum MOBILE, in the ancient astronomy, was a ninth heaven or sphere, imagined to exist above those of the planets and fixed stars. This was supposed to be the first mover, and to carry round all the lower spheres along with it; communicating to them a motion by which they revolved in twenty-four hours. But the diurnal revolution of the planets is now accounted for without the assistance of any such primum mobile.
Perpetuum MOBILE. See PERPETUAL MOTION.