Chap. 9] 



SEISMIC METHODS 



495 



circuit before firing. At the instant of firing, the circuit is broken and the 

 armature released. Instead of feeding directly into the transmission line, 

 the firing line may be coupled to it preferably by a transformer, or by a 



£ 



> 



indictttor 



had around 

 char^ or sen'es 

 cap 



' phoni 



)phone 



} 



'P^ 



r 



Fig. 9-33. Arrangements for shot-instant transmission by circuits separate from 



firing line. 



(o) 



An^ifiar output, 

 iransformer steomhrif 



\C3 



^f}y 



,H5^ 



C^) 



(1 



sMpomf Q>) Truck 



amplifitr and Sjptaktr am/J/f/tr and tptaitr 





(c) 



injuJc microphtnt 



Fig. 9-34. Arrangements for shot-instant transmission over single and double 

 communication lines from firing circuit. 



resistor. This method is the most prevalent. Fig. 9-34 shows three 

 varieties. A transformer is connected in parallel to the firing circuit in 

 such a manner that a portion of the firing circuit passes through its primary. 



