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EXPLORATION GEOPHYSICS 



tance from the magnetometer. (The distance may be read directly on a 

 graduated scale etched on the magnet holder.) 



Accessories consist of a compass which can be fitted into the tripod 

 head for determination of the magnetic meridian, auxiliary magnets of 

 various strengths, and small tools for adjusting and cleaning the instru- 

 ment. Canvas cases are provided for carrying the magnetometer and the 

 tripod. 



Factors Affecting Magnetometer Readings 



Orientation. — Orientation of the vertical component magnetometer 

 must be such that the axis of rotation of the magnetic system is in the 

 plane of the magnetic meridian and is horizontal. Orientation of the hori- 

 zontal component magnetometer must be such that the axis of rotation of 



A B 



Fig. 51. — Tripod leveling and orientation, a, tripod; b, level screws; c, level bubble; d, 

 turntable; e, extension tube for auxiliary magnet; f, compass; g, compass needle clamp screw; It, 

 graduated arc of 360°; i, compass needle; j, leg clamps; k, jewel support. 



the magnetic system is perpendicular to the plane of the magnetic meridian 

 and is also horizontal. The instrument is oriented indirectly as one of 

 the steps in the initial set-up of the tripod; which consists of a turntable, 

 adjustable auxiliary magnet holder, turntable stop-ring, turntable bearing, 

 and leveling screws. The tripod head is also provided with three lugs 

 to which are fastened three wooden tripod legs. The top of the turn- 



