Chap. 9] 



SEISMIC METHODS 



611 



Heiiand Research Corp. 



Fig. 9-114. Portable seismic four-channel apparatus. A, Four-channel amplifier; 

 B, blaster; C, camera with timer, dry-cell operated; D, daylight developing tank; 

 E, detectors. 



_^ 



(a) 



Fig. 9-115. Reluctance detectors. 



records showed that a capacitive detector of proper frequency and damping 

 adjustment records sustained ground motion and transients accurately and 

 in proportion to the ground displacement. In the course of the experi- 



