Galvanometer

In 1820, Hans Christian Oersted of Denmark discovered that a compass needle changes direction when an electric current flows through a nearby conductor. Based on this effect, the first tangent galvanometer was developed by Frenchman Claude Pouillet in 1837.
The meter consists of an upright ring around which an electrical wire is wrapped, the coil, and a compass. When a current to be measured flows through the coil a magnetic field is created. This causes the compass needle, which normally points north, to change direction. The strength of the current can then be calculated based on this change.
Initially this device was only used for scientific research, since there were no practical uses of electricity at that time.