Earthquakes and other Earth-Movements

Abstract

THE object of this work is “to give a systematic account of various earth-movements”: these are classified as (1) Earth-quakes, (2) -Tremors, (3) -Pulsations, and (4) -Oscillations, which are severally defined as (1) sudden or violent, (2) minute, (3) slow, (4) secular movements of the ground. The earthquakes occupy 305 pp., whilst only 43 pp. are given up to the other three motions. After an introduction follows a description (22 pp.) of about twenty different kinds of instruments for recording earth-movements (seismo-scopes, -meters, and -graphs), beginning with an ancient Chinese seismoscope (A.D. 136). The construction of a proper seismograph which shall record period, amplitude, and direction of movements is difficult, the inertia of the moving parts masking the earth-movement. A set of tipping columns seems to be the simplest seismoscope, and some form of pendulum the simplest seismograph: these can be made “astatic,” so as to retain any deflected position. Of recorders of motion a smoked-glass plate seems the simplest. The “Gray and Milne seismograph” is an elaborate instrument, recording continuously and simultaneously the times, and also the three rectangular components, of any displacement.

Earthquakes and other Earth-Movements.

By J. Milne. "International Scientific Series," Vol. LVI. (London: Kegan Paul, Trench, and Co., 1886.)