526 



EXPLORATION GEOPHYSICS 



Continuous Contact Electrodes 



To minimize the time and labor necessary for closely spaced intermit- 

 tent readings, a mobile continuous contact electrode has been developed, t 

 The mobile electrode obviates the necessity of driving electrodes into the 

 ground at each predetermined electrode position and of surveying-in the 

 various stations. Also, because the electrode is always in contact with the 

 ground, oscillographs may be employed for continuous recording of the 

 potential and current. 



The electrode is a small tractor which moves forward at a constant 

 speed which is determined by a governor on the engine. (Figure 318.) 



Fig. 318. — Continuous mobile electrode, a, reel of flexible insulated wire; b, measur- 

 ing sheave wheel; c, steel tractor wheel; d, steel contact stakes; e, guide for reeling-in 

 cable; f, weighted flanged wheels; g, contact ring which actuates measuring signal system. 

 (Courtesy of International Geophysics, Inc.) 



The uniform movement of the tractor allows accurate control of the time 

 of current flow. The rear wheels of the tractor have a steel rim to which 

 short steel stakes are bolted. The stakes are approximately ten inches 

 long in order to make good contact with the subsoil. Usually four stakes 

 on each wheel are in continuous contact with the ground. The tractor 

 is equipped with special low-gear ratios. A large reel holding about 

 20,000 feet of heavy insulated wire is mounted on the tractor as shown 

 in Figure 318. A carriage, mounted on top of the reel, supports a measur- 

 ing sheave wheel and wire spooling device. The measuring sheave is 

 connected to a relay signalling system mounted on the tractor. The relay 

 system automatically transmits to the recording truck the exact footage 



t J. J- Jakosky, "Method and Apparatus for Electrical Exploration of the Subsurface," U. S. 

 Patent 2,105,247, issued Jan. 11, 1938; Canadian Patent 374,475, issued June 14, 1938; other U. S. 

 and foreign patents pending. 



