A portable seismograph for recording artificial earthquakes

A portable seismograph for recording artificial earthquakes is described. The motion of the pendulum is magnified by means of an arrangement of two small magnets and a soft iron element suspended on a phosphor-bronze strip which is attached to the pendulum.The coupling of the magnifying system to the pendulum introduces a couple which opposes the restoring moment of the pendulum and lengthens the periodic time of the seismograph.Other important features of the instrument are the absence of friction from the magnification linkage and simple methods for the remote control of the "zero," the period and the sensitivity.An experimental investigation of the relation between the period and sensitivity is described.