786 



ELECTRICAL METHODS 



[Chap. 10 



The coils are connected in series opposition to a detector. One coil is 

 laid flat on the ground at one location; the second is placed at another 

 location. With the second coil, the plane of the ellipse of polarization is 

 determined first on the second location. The axis of rotation of the coil 

 is then so oriented as to be in the plane of the ellipse. After this, the 

 coils are connected and the coil on the second location is rotated about a 



/, E. Hawkins 



Fig. 10-1076. Colorado School of Mines dual-coil field ratiometer. 



horizontal axis until a null is obtained. If the phase difference between 

 successive locations is small, this method will give the ratio of the in-phase 

 components at the two locations with sufficient accuracy. For a complete 

 determination of intensity ratios and phase differences between two points, 

 a three-frame arrangement must be used.^^ 



{d) Elliptical -polarization. In the discussion of potential methods 



" Sundberg, A.LM.E. Geophys. Pros., 134 (1929). 



