130 



EXPLORATION GEOPHYSICS 



The opposing gravitational torque is 



Tg = m'ga cos 6 + m'gh sin 6 (52a) 



At equilibrium, these two torques are equal and opposite, so by equating 



EARTHS FIELD 



MAGNETIC 



CENTER 

 OF GRAVITY 



Fig. 55. — Diagram showing relationships of different 

 parts of compensated magnetic system for horizontal 

 magnetometer. 



the two equations we determine that, 



MH 



tan 6' = 



mga 



(53) 



MZ + m'gh 

 m' = mass of the magnetic system in grams ; 



g = acceleration due to gravity in cm. per sec. per sec. 

 21 = distance in centimeters between magnetic poles of the system ; 



o = the horizontal distance and 



h = the vertical distance of the center of gravity of the system from the axis of 

 rotation, in cm., when = 0°. 



P = pole strength of the system, c.g.s. units ; 

 M =z 2pl = magnetic moment of the system. 



Z = vertical component of earth's magnetic field, gammas ; 



H = horizontal component of the earth's magnetic field, gammas ; 



