The Duplex Pendulum Seismograph

Abstract

As the accuracy of the duplex pendulum seismograph has been impugned by a writer in NATURE, vol. xxxvii. p. 571, who at the same time adopts the instrument (with modifications which are, in my opinion, the reverse of improvements) I forward to you comparison diagrams. They show side by side the record given by the seismograph itself, and the real motion of the base of the instrument when that was artificially shaken in a manner that closely imitated an earthquake. The real motion was recorded by means of a multiplying lever hinged by a universal joint in a bracket fixed to a separate support. In both records the motion is magnified about six times. The agreement of the two demonstrates the accuracy of the instrument as an earthquake recorder, alike for large and for small motions. These are examples of tests which I have been in the habit of applying to seismographs since 1880 (see Proc. R. S., vol. xxxi. p. 440). In the present case the test was made with one of the duplex pendulum seismographs made and sold by the Cambridge Scientific Instrument Company, and described by me in NATURE, vol. xxxiv. p. 343.