246 



GRAVITATIONAL METHODS 



[Chap. 7 



values from magnetic to astronomic directions, or, in certain interpreta- 

 tion problems, for referring different sets of vectors to a uniform system. 



Fig. 7-92. Diagram for the calculation of curvature values. 



Mai 

 observtd 





pfrueture 

 effect 



(a) ' (b) 



Fig. 7-93. Vectorial addition and subtraction of gradients and curvatures. 



The transformations may be made analytically or graphically. If two 

 systems, (a:, y) and (x', y'), make the angle a with each other (positive 



