524 



EXPLORATION GEOPHYSICS 



Long metal electrodes of this type can be driven most advantageously 

 by a gasoline or air power hammer, of the general type shown in Figure 

 316. After the measurements have been completed, the electrode is with- 

 drawn by means of a hollow-stem hydraulic jack, of the general type illus- 

 trated in Figure 317. 



Fig. 316. — Driving long electrodes with power-driven hammer. 

 A, gasoline hammer; B, 6-foot, tapered steel electrode; C, spare 

 electrodes; D, hydraulic jack for withdrawing electrode; E, folding 

 "A" frame for supporting hammer; F, reel carrying insulated 

 wire; G, loud speaker for short wave radio communication. (Court- 

 esy of Union Oil Company of California.) 



The electrodes are preferably of mild tempered alloy steel, and approx- 

 imately six feet long. The upper end should be about 1 inch in diameter, 

 tapering uniformly to about y% inch above the point at the lower end. The 

 tapered electrode gives much better contact with the ground, and can be 

 removed more easily. 



Mobile Stake Electrodes 



Various procedures have been tried for obtaining readings at closer 

 electrode spacings without increasing unduly the time required for a series 

 of measurements. In areas of fairly even topography and moderately 

 hard surface materials, success has been obtained with an intermittent 

 type of electrode mounted upon a light truck. By means of a gear drive 



