Differential galvanometer invented by Leopoldo Nobili, mounted on a wooden base carrying a slender pillar from which the needle system is suspended. The glass protection dome is missing. The brass scale is divided into four quadrants. There are four independent coils of silk-covered wire, each connected to two brass terminals. Different currents could be circulated in the coils. If the currents circulated in opposite directions, the needle indicated the effect produced by their differential—hence the name of the instrument. A differential galvanometer was already developed by Antoine-César Becquerel in 1826. Provenance: Lorraine collections.