Image: Galvanomètre de Nobili

Description: Woodcut of an astatic galvanometer from a 1904 physics book. The astatic galvanometer, invented by Leopoldo Nobili in 1825, is a historical instrument that measures electric current. It consists of two magnetized needles, suspended from their centers by a long thin fiber which can turn freely. One needle is inside a coil of wire. When electric current passes through the coil, its magnetic field causes the needle to turn from its equilibrium position perpendicular to the coil to be parallel to the coil's axis. The second needle (visible), located above the coil and magnetized in the opposite direction, serves to cancel out the effect of the Earth's magnetic field (that's what the "astatic" means), and also serve as a pointer to indicate tne magnitude of the current.
Title: Galvanomètre de Nobili
Credit: Leçons de Physique ; Éditions Vuibert et Nony
Author: Gillard
Permission: "avec l'aimable autorisation des Éditions Vuibert"
Usage Terms: Public domain
License: Public domain
Attribution Required?: No