This is one of the many measuring instruments that developed out of the cooperation between the engineer Marcel Deprez (1843-1918) and the biophysicist Jacques Arsène d'Arsonval (1885-1940) with the engineer who built them, Jules Adrien Carpentier (1851-1921), all French. The instrument presented here is a mobile coil galvanometer which, of the galvanometers of the same kind, was certainly the most common. It consists of a coil with very thin wires wound around a very light rectangular frame, a permanent horseshoe magnet and a soft iron cylinder placed inside the coil and, with this, in the space between the two arms of the magnet; two brass plates attached to the platform bear the words: "J. Carpentier, Paris" and "galvanomètre Deprez d'Arsonval".
At the top of the coil there is a round mirror for the optical reading of the angles of rotation. The entire system lies on a circular wooden platform (diameter 19 cm) with one fixed foot and two adjustable ones. It is protected by a glass bell (diameter at the base 16.5 cm, height 26 cm). The edge of the bell fits into a groove on the platform. The magnet is attached to the platform with the poles facing upward; the mobile element is suspended at the end of a curved brass column from a conducting elastic suspension wire and a device with screws for adjusting its height ...continues