ELECTRICAL PROSPECTING 
17 
about one twentieth of the effect at 100 cycles. This curve illustrates the im- 
ng Current. 
portance of using a low frequency alternati 

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2000 
Fig. 9. Electromagnetic survey across a salt dome. 
In order to illustrate the results that may be obtained in the field by a 
good electrical survey under favcrable conditions, two surveys made by the 
Swedish American Prospecting Corporatio 
n for the Gulf Oil Corporation will 
161 
