The use of a geophysical method in mineral prospecting dates back to the beginning of the seventeenth century. The primitive but adequate magnetic method then used in search of the highly magnetic iron ores was perhaps as important to the general economy of the seventeenth and eighteenth centuries as are the modern methods to the economy of the present day. Despite considerable experimentation with the magnetic and other principles the present extensive development of physical methods in geological exploration was delayed until it came almost explosively in the 5 years, 1925-1929.

Neither the history of geophysics nor even of its methods is covered by this paper. The term “Geophysics” generally includes the application of physical principles to problems of the earth; hydrology, meteorology, geodesy, seismology, terrestrial magnetism, and vulcanology all have a common bond in their interest in some special phase of the physics of the earth. The history traced herein is concerned only with those methods which are used in mineral prospecting.