Galvanometer
2 of the 7 encyclopedias on this shelf carry an entry for Galvanometer. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
an instrument used to indicate the presence, the direction, or the strength of an electric current. If a wire or other conductor through which a current of electricity is passing be brought near a freely suspended magnetic needle , the latter betrays a tendency to swing around and place itself in a position at right angles to the path of the passing current. The amount of the deflection of the needle from a north and south direction is proportioned to the strength of the current. If the wire through which the current is passing be coiled back and forth, the deflection is proportionate to the number of the turns of the wire. By giving the wire many turns it is possible to discover the presence, as well as the direction, of a very small current. Such an instrument is called a galvanoscope. If the needle be provided with a dial, and the dial be marked with figures to indicate the number of degrees of deflection, the instrument is called a galvanometer. There are several models, known as the tangent, the astatic, and the d'Arsonval. The facts on which the galvanometer rests were discovered by a physicist named Oersted.
Collier's New Encyclopedia (1921)
an instrument for detecting the presence and measuring the intensity of feeble galvanic currents. A differential galvanometer is an instrument designed to ascertain a difference in the intensity of two galvanic currents. A marine galvanometer is a galvanometer designed to test the insulation of submarine cables, and at the same time unaffected by the pitching and rolling of the ship. GALVESTON SEA WALL