532 



EXPLORATION GEOPHYSICS 



Figure 323 shows the method of moving the reel between readings. 

 In this view, the stakes for the next reading position have been driven 

 and are ready for the reelman. An assistant is removing the previously 

 used set of stakes and will have them in position at the next set-up. 



Fig. 32-3. — Mobile reel in operation, a. small portable telephone; b, steel elec- 

 trodes; c, flexible connectors; d, previously used set of electrodes. (Courtesy of 

 International Geophysics, Inc.) 



Handling Field Lines 



The lines are laid out by connecting the end of the wires to the proper 

 terminals of the measuring instruments. The wire should be anchored 

 on a convenient wood stake to prevent disturbing the instruments when 

 the wire is pulled. Usually one potential wire and one energizing wire will 

 extend outward in each direction from the instruments. The potential 

 and power lines should be separated 15 feet or more, in order to minimize 

 mutual inductive effects and leakage between circuits. 



After testing for line leakage and continuity of circuits, the initial 

 reading may be made. The reels must then be moved consecutively to the 

 various points of measurement. On reaching each of these points, the 

 reelman drives in the required electrodes, carefully connecting each elec- 

 trode with the reel, and then signals the instrument operator. Upon com- 

 pletion of the reading, the instrument operator signals the reelman and 

 telephones the number, usually the distance in feet, of the next station. The 

 reelman then removes the electrodes from the ground and proceeds to 

 the next station, and the process is repeated. 



Proper precautions must be taken to prevent the reelman from setting 

 up at the wrong point. It is usually a good plan for the instrument 



