Editing Galvanometer (section)

====Geomagnetic field measurement====
A tangent galvanometer can also be used to measure the magnitude of the horizontal component of the [[geomagnetic field]]. When used in this way, a low-voltage power source, such as a battery, is connected in series with a [[rheostat]], the galvanometer, and an [[ammeter]]. The galvanometer is first aligned so that the coil is parallel to the geomagnetic field, whose direction is indicated by the compass when there is no current through the coils. The battery is then connected and the rheostat is adjusted until the compass needle deflects 45 degrees from the geomagnetic field, indicating that the magnitude of the magnetic field at the center of the coil is the same as that of the horizontal component of the geomagnetic field. This field strength can be calculated from the current as measured by the ammeter, the number of turns of the coil, and the radius of the coils.