INTRODUCTION 



and later Dr. Carl Barns in 1882 were convinced that the phenomenon of 

 spontaneous polarization in rocks and minerals had possible application in 

 locating ore bodies. Subsequent to the discovery by Fox, this phenomenon 

 was studied by several investigators. The self-potential method used by 

 Barus on the Comstock Lode in Nevada was essentially the same self- 

 potential technique employed today. The first commercial use of the effects 

 produced at the surface of the earth by spontaneous polarization as the 



Fig. 2. Geographical distribution of gravity operations in the United States, 

 1947. (E. A. Eckhardt, Geophysics, XIII, 4, Oct. 1948.) 



basis of a prospecting method was made by C. Schlumberger. Applied in 

 1913 at Bor, this technique resulted in what was probably the world's first 

 geophysical discovery of a non-magnetic ore deposit. A published account 

 of the results of these studies (deferred on account of World War I) 

 appeared in 1920. 



A second factor in the development of electrical methods was the 

 general concept that subsurface bodies of relatively high conductivity 

 should in some way afifect conductivity measured between two points at 

 the surface. Williams and Daft in 1897 attempted to determine differences 

 in conductivity by an alternating current method which consisted in passing 

 the current through the ground and observing the variations in the intens- 

 ity of sound in a telephone receiver connected to two grounded electrodes. 

 Professor James Fisher first experimented with electrical conductivity 



