. Deep borehole surveys and problems. Boring. 226 DEEP BOREHOLE SURVEYS AND PROBLEMS 3. Combinations of 1 and 2. 4. Electrical waves. Broadly speaking for our purpose electrical methods can be grouped into two main groups, , potential and electromagnetic. A brief sketch is essential to a compre- hension of the method of electrical borehole investigation due to the brothers Schlumberger, the only electrical method which has been employed for this Fig. 153.—Normal course of electric current lines between two electrodes in a homogeneous underground. Potential Method.—If an electric
. Deep borehole surveys and problems. Boring. 226 DEEP BOREHOLE SURVEYS AND PROBLEMS 3. Combinations of 1 and 2. 4. Electrical waves. Broadly speaking for our purpose electrical methods can be grouped into two main groups, , potential and electromagnetic. A brief sketch is essential to a compre- hension of the method of electrical borehole investigation due to the brothers Schlumberger, the only electrical method which has been employed for this Fig. 153.—Normal course of electric current lines between two electrodes in a homogeneous underground. Potential Method.—If an electric potential of +e volts be applied to a point a, while at another point b the voltage is zero, then between the two field electrodes, a and b, a pressure (potential) difference or electromotive force e prevails, which produces a current i, that flows from a to 6 in imaginary current lines, the pressure decreasing all the time from +e at a to nil at b. The planes or sections which show equal potential difference toward the electrode a or 6 can be connected by planes of equal pressure called equi- potential planes or level planes. From the potential theory we learn that such equipotential planes stand every-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Haddock, M. H. (Marshall Henry). New York, McGraw-Hill
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