600 



EXPLORATION GEOPHYSICS 



Fig. 376. — Apparatus for measuring angle of electromagnetic wave front, a and a', two 

 identical coils; b, shielded tuning condensers; c, shielded amplifier and phase compensator. 



Experimental verification of the distortion of the wave front has been 

 carried out by means of the apparatus illustrated in Figure Z76. This 



apparatus comprised a shielded, an- 

 tenna-compensated receiver and a 

 double coil antenna rotatably mount- 

 ed on a 6-foot arm. A graduated arc 

 and vernier were attached to the arm 

 for reading the position of the coils 

 for zero signal input. The two coils 

 had substantially identical electrical 

 characteristics and were connected to 

 a winding of a shielded differential 

 transformer. The secondary of the 

 transformer was connected to the 

 input circuit of an amplifier and 

 detector. In carrying out the meas- 

 urements, the apparatus was so placed 

 that the axis of rotation of the coil 

 support was parallel to the axis of 

 the conductor. The arm was then 

 rotated until a minimum signal was 

 heard, at which angle the two coils 



Fig. 377. — Distortion of electromagnetic WCrC Symmetrically dispOScd with 

 waves in traveling from earth to air. {Eng. „„^„„^j. +^ ^.Ur. ,,,^,r« -f^^*,*- 

 and Min. Journal, Feb. 11-18, 1928.) rCSpCCt tO the Wave frOUt. 



