Chap. 7] 



GRAVITATIONAL METHODS 



249 



for simplicity at the corners of a triangle are shown in Fig. 7-95c. They 

 happen to show a large error of closure which has been adjusted graphically 

 as shown in Fig. 7-95d. The adjustment follows the rule that the tangents 

 at the points B and C must be kept constant, and that the curve must 

 close at A. When gravity differences have been so calculated, ''isogams" 

 may be plotted as shown in Fig. 7-95e. 



/ffJ 



f2)\ 



H^.Vh 



(a) 







Fig. 7-95. Calculation of relative gravity from gradients in station triangle (after 



Jung). 



A third procedure is based on a graphical integration of the gradient 

 curve. Stations are arranged on straight lines, and projections of gra- 

 dients are plotted as ordinates in a continuous gradient curve. The 

 station lines should be so laid out that they close back to the original 

 station. The gradient curve is then integrated numerically or by the use 

 of an integraph (such as those designed by Abdank-Abakanovicz, Harbou, 



