A correction necessary in pendulum observations of gravity. The vibrating pendulum produces oscillations of the receiver case, of the pillar, and of the surface soil. Rather complex, coupled vibration phenomena arise and the period of the pendulum itself changes. Numerous methods have been suggested to correct for this influence or to eliminate it. Since the correction is of the order of 10 x 10_-7to 40 x 10_-7s on solid rock or cement and may increase to as much as 500 x 10_-7s on marshy ground, it must be determined accurately.