Well-made instrument consisting of a copper ball rotated by a weight-driven mechanism and housed in a wooden cabinet. The axle of the ball is connected to the mechanism by means of a double universal joint so that it can be rotated at different angles, indicated on a circular horizontal scale and a vertical quadrant.

This is probably a sophisticated version of Jean-François-Dominique Arago's disk. In 1824, Arago demonstrated that a magnetic needle placed on a rotating copper disk produces induced electric currents that influence the needle itself, causing it to rotate as well. Arago's disk experiments—taken up by Peter Barlow, Leopoldo Nobili, and others—were one of the principles used in the development of the electric motor and dynamo. Provenance: Lorraine collections.