208 



EXPLORATION GEOPHYSICS 



mounted on a platform so that the vertical distance between the needle of 

 the instrument and the top of the steel plate was 88 cm. Measurements 

 were made of the vertical anomalies at various points along a line parallel 

 to the magnetic meridian through the center of the plate. A second set of 

 measurements was then made along the same "traverse" with the needle 

 111 cm. above the top of the steel plate. 



The results of the laboratory investigations are shown in Figure 98. 

 In plotting these curves, the experimental readings were all multiplied by 

 an arbitrary factor to facilitate the comparison of the theoretical and ex- 

 perimental results. 



Readings are taken over the center of the dike at two levels separated by 

 a vertical distance H, assuming two horizontal, linear distributions of mag- 

 netic charge (different polarity) of finite length separated by a distance 

 h (cf . p. 191 and Figure 98a) . 



ground 



2nip 



tan-1 i/p 

 \ cos (j> d(}> — 



2tn (p + h) 



{p + hy 



tan-i l/p + h 

 \ cos ^ d<l> 



tan-i l/p 



2m . 



:— — sm <f) 



p 



tan-1 l/p + h 



2m 



- — —r— sin <h 

 (P + h) ^ 



Fsin (tan-i — =-—j^^7^^^; see Figure 98(a) j 



i nUS, P ground 



(/'2 + /j2)y. 

 2m I 



2m 



I 



p {p~ + i-y' ip + h) [ip + hy + p]"^ 



= 2ml < 



1 



1 



2m (p + H) 

 (p + H) 



iPiP' + l'V'^ (P + h) [ip + hy + P] 

 tan-i l/p + h 



V2J 



1' height H — / >, 4- U\2 \ ^^^ *^ ^^ 

 



2m {p + h + H) 



(p + h + H) 



tan-i i^p + k + H 

 :r^l cos ^ d4> 



= 2m/|^ 



1 



+ H)[{p + Hy + /2] % {p + h+H)[{p-\-h + Hy + 



r~]A 



