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EXPLORATION GEOPHYSICS 



Fig. 501. — Fifteen element galvanometer, with cover open for inspection; 

 two elements are connected, a, non-magnetic screw driver; b, single element; 

 c, terminal supports for galvanometer units; d, dust-tight lid; e, plane glass 

 window; /, air gap in permanent magnet for each galvanometer unit. 

 (Courtesy of Wm. Miller.) 



Fig. 502. — 25-eIement galvanometer, using sealed 

 tubular construction. A, galvanometers (25 units, each 

 y%" in diameter); B, focusing mirrors; C, magnetic 

 block; D, multi-conductor cable. (Courtesy of Century 

 Geophysical Corporation.) 



