GEOPHYSICAL METHODS OF INVESTIGATING 



227 



where at right angles to the current Hnes, so that if the 

 spacial distribution of the current Hnes is determined in any 

 manner the equipotential planes are also located. These 

 current lines have the construction of an ellipsoid of many 

 shells, Fig. 153 being a hemispherical section for the current 



Fig. 154. — Horizontal section through the equipotential lines. 



lines between two electrodes in a homogeneous under- 

 ground. In many cases the ore body itself also generates 

 a polarization current in its surroundings. The distribu- 

 tion of the current in a body depends upon the form and 



Fig. 155.- — Right section through the equipotential lines. {After Schhimberger.) 



spacial arrangement of the conductivity in the body and 

 on the position of the field electrodes. Simple regular 

 bodies are amenable to direct mathematical estimation, 

 as in the well-known school example, while approximate 

 rules are applied to the complicated cases of nature; 

 deformation of the equipotential curves is sought (Figs. 

 154, 155) after observing the potential at a sufficient num- 

 ber of plotted places on or under the earth's surface. 



