EOST Jardin des Sciences
Université de Strasbourg
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5 - 19 tons


or "Big Pendulum"

19 tonnes

Construction began before World War I and was finished in 1925.
It was used in Strasbourg from 1925 to 1976.

  • made of a mass suspended from 4 springs and associated with two horizontal arms
    mass 19000 kg
    period 2 s
  • can record two horizontal components
  • cannot be used for vertical movements
  • damping by air pistons
  • mechanical amplification by lever
  • recording on smoked paper.

The mass is constituted mainly by metallic parts (12 tons of military truck axles, 2 tons of weapon parts....).
In 1970, two coils were installed allowing a galvanometric recording on paper. Since 1987, recording is in numeric form thanks to displacement transducers.

19 tonnes enregistrement

The construction of a big pendulum in Strasbourg seismological station was begun by the Germans before the war and completed by the French in 1925. The original project, in 1910, was to construct a large "17 tons" instrument, similar to those made by Wiechert in Goettingen (Germany) in 1906 and in Tacubaya (Mexico) en 1910. In 1918, after the armistice, Edmond Rothé, the new director of the station, decided to use the elements already prepared by the German physicists (tank, steel bars...) to make a big mass instrument similar to de Quervain and Piccards' one in Zurich (Switzerland) - a "21 tons "instrument.

19 tonnes schéma

The mass of 19 tons is suspended from 4 springs and is held under its centre of gravity by two holders. The mass can oscillate in all directions but it turned out that vertical recording was impossible, and so this apparatus allows only the recording of two perpendicular horizontal components. Damping is by air pistons similar to those in the Wiechert's seismometers. Amplification is achieved mechanically by levers, and the recording is on smoked paper.

This instrument is still in use. In 1970, two coils were installed, allowing galvanometric recording on paper, and the smoked paper was abandonned.
Since 1987, numerical recording is possible using displacement transducers, and a fibre optics liaison "brings" the signal to what is now the School and Observatory of the Sciences of the Earth (EOST).