Magnetometers are measurement instruments used for two general purposes: to measure the magnetization of a magnetic material like a ferromagnet, or to measure the strength and, in some cases, the direction of the magnetic field at a point in space.The first magnetometer was invented by Carl Friedrich Gauss in 1833 and notable developments in the 19th century included the Hall Effect which is still widely used.Magnetometers are widely used for measuring the Earth's magnetic field and in geophysical surveys to detect magnetic anomalies of various types.