Introduction to Magnetic Exploration - Historical Overview
Unlike the gravitational observations described in the previous section, man has been systematically
observing the earth's magnetic field for almost 500 years. Sir William Gilbert (right) published the
first scientific treatise on the earth's magnetic field entitled De magnete.
In this work, Gilbert showed that the reason compass needles point toward the earth's north pole is because the
earth itself appears to behave as a large magnet.
Gilbert also showed that the earth's magnetic field is roughly equivalent to that which would be generated by a
bar magnet located at the center of the earth and oriented along the earth's rotational axis.
During the mid-nineteenth century, Karl Frederick Gauss confirmed Gilbert's observations and also showed that
the magnetic field observed on the surface of the earth could not be caused by magnetic sources
external to the earth, but rather had to be caused by
sources within the earth.
Geophysical exploration using measurements of the earth's magnetic field was employed earlier than any other geophysical technique. Von Werde located deposits of ore by mapping variations in the magnetic field in 1843. In 1879, Thalen published the first geophysical manuscript entitled The Examination of Iron Ore Deposits by Magnetic Measurements.
Even to this day, the magnetic methods are one of the most commonly used geophysical tools. This stems from the fact that magnetic observations are obtained relatively easily and cheaply and few corrections must be applied to the observations. Despite these obvious advantages, like the gravitational methods, interpretations of magnetic observations suffer from a lack of uniqueness.