Chap. 9] 



SEISMIC METHODS 



599 



Cambridge Instrument Co. 



Fig. 9-106a. Multiple string galvanometer in camera. L, Lamp; S, string harp; 

 M, synchronous timer motor; P, prism; F, fork. 



Heiland Research Corp. 



Fig. 9-1066. Multiple-coil galvanometer (four channel) in camera. (4 twelve- 

 element camera is shown in the center of Fig. 9-78.) 



This holds for undamped oscillations. Damping in galvanometers is 

 composed of electromagnetic and viscosity (air or oil) damping. The 

 former results from a counter e.m.f . set up in the coil by its motion when 



i 



