Chap. 9] 



SEISMIC METHODS 



603 



tJO- 



15 



It 



Scale DefMien, 

 millimeters per 10'^^ 

 amptres 



Short permanent maqaet 

 bl filar aullleqrapb 



jfalvanometer 



\^>v flecfromagnetieaify dampett 



ceil (faJvttnometer 



Mutfielement 

 stn'of galyanometer 

 ?aitaailied 10 fm 



0.5 



— 



50 



150 



ciicles 



Fig. 9-108. Response of various commercial reflection galvanometers. 



Hence, the over-all dynamic magnification Wr of a galvanometer for ground 

 motions of the peak amplitude X, when coupled directly to a seismometer, 

 may be written in terms of their respective dynamic magnifications: 



W; = W, . Wd 



coU 

 K 



(9-986) 



Expressions for special cases of over-all magnifications are of interest. 

 When both seismometer and galvanometer are critically damped, the 



