Abstract A steady state shaking table utilizing the principle of reaction has been constructed for the measurement of the response of seismometers and the over-all response of seismograph apparatus. A mass of 500 pounds is driven at amplitudes of the order of 10 (super -4) inches by a small eccentric mass which is rotated at the center of percussion of a bar, the upper end of which is pivoted to the bottom of the heavy mass. The amplitude of motion of the table top is independent of frequency between 10 cycles per second and an undetermined upper limit higher than 150 cycles per second.