Small steel rotors have been suspended by an axial magnetic suspension using inductance control to effect vertical stabilization. They have been spun in vacuum by means of a rotating magnetic field having a frequency of the order of 100 kilocycles. Rod rotors tended to precess in the absence of horizontal damping. This was remedied by placing a copper block just above the upper end of the rod. A tapered length of drill rod ⅞″ long (max. diam. ′′
) reached 36,000 r.p.s. before bending double due to the effect of centrifugal force. Steel balls have the advantage of no precession; however, on starting to spin they soon built up a circular orbital motion of increasing amplitude. A damping needle situated outside the vacuum system and immersed in oil was found to eliminate this motion satisfactorily. A ′′
diam. ball has been spun to 110,000 r.p.s. This corresponds to a centripetal acceleration at the periphery of 58×106
gravity. The rate of free deceleration at 106,000 r.p.s. was about 1 percent per hour. Rotational speed was measured by observing the rotor in stroboscopic light whose frequency could be matched with the speed of the rotor.