ELECTRICAL METHODS 531 



8 gauge sheet aluminum or No. 12 gauge sheet steel. The flanges are sepa- 

 rated by a core and are mounted 5 inches apart on a steel axle, one end of 

 which is extended and bent to form a crank. An "A" frame built of 1-inch 

 seamless, welded, steel tubing is used for supporting the reel. The upper 

 portion of the frame serves as a handle for carrying the reel. The core 

 consists of a 5-inch piece of 3-inch diameter Shelby steel tubing. The in- 

 side end of the wire passes through an insulating bushing in the flange 



Fig. 322. — Mobile reel for handling field lines. (Courtesy of International Geo- 

 physics, Inc.) 



and connects to a well-insulated terminal block. This terminal is con- 

 nected to the electrode by means of a short flexible lead provided with a 

 spring contact. 



For deep subsurface investigations requiring long lines, the reel illus- 

 trated in Figure 322 is very satisfactory. This reel has flanges 20 inches 

 in diameter which are separated by a piece of 6-inch diameter tubing 

 20 inches long. The pneumatic tires are the conventional type employed 

 for concrete wheelbarrows and other industrial uses : namely, 4-ply, 4 

 inch X 8 inch I. D. These reels hold from 5500 to 6000 feet of the 3/16- 

 inch diameter wire. The frames are made of 1^-inch welded steel tubing. 

 Roller bearings are employed for mounting the reel and the wheels. These 

 reels weigh approximately 350 pounds when loaded, but can be handled 

 by one man in areas of fairly even terrain. 



