Duplex Pendulum Seismograph

A paper label on this seismograph reads “Made from the Designs of Professor Ewing of Dundee, by the California Electric Works, 35 Market street, San Francisco; and recommended for use in California by Professor LeConte of Berkeley and by Professor Holden, Director of the Lick Observatory.”

James Alfred Ewing was a young Scottish physicist/engineer who, while teaching in Tokyo in the years between 1878 and 1883, designed several seismographs. Among these was a duplex pendulum instrument that recorded the two horizontal components of earthquakes. It was, he claimed, “comparatively cheap and simple” and was “employed by many private observers in Japan.”

The Cambridge Scientific Instrument Company in England began manufacturing Ewing’s several seismographs in 1886. The first examples in the United States were installed in the Lick Observatory on Mount Hamilton and in the University of California at Berkeley. Edward Holden was then director of the former and president of the latter, and Joseph LeConte was professor of geology at Berkeley.

Enthusiastic about the new science of seismology, Holden and LeConte convinced Paul Seiler, head of an electrical apparatus supply firm in San Francisco, to manufacture duplex pendulum seismographs that would sell for $15 apiece (rather than the $75 charged by the English firm). Over a dozen examples are known to have been distributed across the country and around the world, some recording earthquakes as early as 1889. This one came to the Smithsonian in 1964, a gift of Case Institute of Technology in Cleveland, Ohio.

Ref: Edward S. Holden, Handbook of the Lick Observatory (San Francisco, 1888), pp. 54-56.

Edward S. Holden and Joseph LeConte, “Use of the Ewing Duplex Seismometer” (1887), reprinted in Holden, “Earthquakes on the Pacific Coast,” Smithsonian Miscellaneous Collections 1087 (1898).

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