Chap. 9] 



SEISMIC METHODS 



605 



{fg) = l/ulVl + nj and (fd) = l/woVl + no- If the galvanometer 

 frequency is ten times higher than the seismometer frequency, the product 

 of the frequency factors (fg)-(fd) = l/w5V(10* + Wo)(l + nt), which 



Fig. 9-109. Dynamic response of seismograph and galvanometer of equal natural 

 frequency and equal damping. 



is seen to indicate an approximately linear increase of dynamic response 

 with frequency (see Fig. 9-110). In such a case it is comparatively easy 

 to superimpose amplifier-filter characteristics upon the seismometer-galva- 

 nometer response and to peak at any desired frequency. The over-all 



