Vertical Galitzin-Wilup seismometer and recording drum at the Florissant, Missouri vault.
(J. B. Macelwane Archives, Saint Louis University)
The Florissant Station was established in 1928, at the Saint Stanislaus Seminary. The site was outside the city limits, far from any source of vibrations due to traffic in and around the Saint Louis University Campus.
The recording drum worked from a wind-up spring, in the manner of an old alarm clock. A rotating spherical pendulum acted as a governor. This was necessary before the advent of stabilized 60 Hz AC mains in the US and the use of synchronous motors.
The galvanometer is to the right and behind the seismometer. The light source is on the pier in front of the recording drum. Obviously, the photographic paper was removed when this picture was taken. The tripod in the rear could hold a scale, used for sensor calibration.
The Florissant station was upgraded to WWSSN in 1961 and continued operations through 1971.
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