A linear strain seismograph*

The response of hitherto known practical forms of seismographs depends the relative motion of a pendulum and the moving ground to which its structure is fastened. The various kinds of seismographs differ in type of pendulum used, such as gravity, spring, torsion, and/or they differ the type of magnifying and recording elements which they employ. They all or indicate the vibratory motion of the ground at a giver point. In contrast to these earlier forms, the strain seismograph is a nonpendular instrument. does not respond directly to vibratory movements Its operation depends variations in the distance between two points of the ground. Such or linear strains are set up by seismic waves. A schematic drawing the seismometer is shown in figure 1. A and B are two piers separated by a of 20 meters. One end of the rod R is rigidly fastened to the pier B. other end extends to within a short distance of pier A. Earth strains resulting from a seismic wave train produce variations in the separation of the piers, and these variations are observable as changes in the distance between free end of the rod and pier A. These small movements of the end of rod relative to the adjacent pier actuate an electromechanical transducer generates an e.m.f, proportional to the rate of change of the relative displacement. is accomplished by means of galvanometers. A photograph the seismometer is reproduced in figure 2.