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EXPLORATION GEOPHYSICS 



dh in general also equals r • e so that : 

 r« ds r 



Fig. 167. — Showing a torsion balance with equi- 

 potential surfaces U2 and Ui which pass through 

 the upper and lower weights respectively. 



Moment Due to Gradient Forces. — The application of the above 

 considerations to a torsion balance is brought out in Figures 167 and 168. 

 They show equipotential surface Uz passing through the upper weight on 





Fig. 168. — Showing the difference in 

 direction of the gravity forces at the 

 upper and lower weights of a torsion 

 balance for the condition shown in Fig- 

 ure 167. e is the angle of convergence 

 of the equipotential surfaces U2 and Ui. 



Fig. 169. — Illustrating the horizontal 

 component of gravity force H tending to 

 twist a torsion balance. 



the end of the balance beam, and the equipotential surface Ui through the 

 lower, or hanging weight. 



The direction of the gravity forces is not the same at the two weights. 

 Because of this, as is shown in Figure 169, a horizontal component of force 



