Magnetic methods

Abstract

It was in the year 1600 when William Gilbert, Physician to Queen Elizabeth I, published his book De Magnete (abbreviated title), that the concept arose of a general geomagnetic field with a definite orientation at each point on the surface of the earth. In its wake, observations of the local anomalies in the orientation of the geomagnetic field were used in Sweden for iron-ore prospecting, for the first time probably as early as 1640 and regularly by the end of that century. They constitute the first systematic utilization of a physical property for locating specific, small-scale features within the earth’s crust. Two centuries later, in 1870, Thalén constructed his magnetometer for comparatively rapid and accurate determinations of the horizontal force, the vertical force and the declination, by the familiar sine and tangent methods used in elementary physics courses. This and its somewhat simplified modification due to Tiberg were in widespread use, especially in Sweden, as a tool for prospecting surveys for more than the following half century.