Chap. 7] 



GRAVITATIONAL METHODS 



229 



where n is the number of "compartments" (or dots) covered and 8 the 

 density. Fig. 7-786 is a diagram for the curvature values, likewise for 

 50 to 500 linear scale units. The unit effect of five inner rings is 10~^"; 

 that of the outer rings, 10~" C.G.S. The calculation of a "strip" of mean 

 elevation h covering n dots proceeds in accordance with: effect = nS-h. 

 In the application of the Numerov diagrams, it must be remembered 

 that the}^ do not hold for very rugged terrain or for very short distances 

 from the instrument, since f is disregarded compared with p^. A rigorous 



Fig. 7-78a. Numerov diagram for terrain gradients. 



method has been proposed by Jung. Its only inconvenient feature is that 

 lines of equal terram angle (from the instrument) must be drawn about the 

 station. This method was described before in connection with terrain 

 corrections for gravity measurements (formulas [38c to 38e]). 



The rigorous mathematical representation of the terrain variation is 

 made possible by figuring all elevations in respect to the center of gravity 

 of the instrument, which eliminates f from eqs. (7-68a). With the angle 

 ^ = tan" (h/p), the gradients and curvatures due to one segment are 



