SEISMIC METHODS 



643 



Fig. 398. 



-Critically damped vertical seismograph employing electrical recording. (Reproduced 

 from Galitzin's Seismometrie.) 



Fig. 399. — L. Grumach's seismometer. (Inductive type.) M = mass to which two coils are 

 attached. (The coils vibrate freely in the field of the electromagnets £i and En, their axes being 

 parallel to the direction of vibration.) ^i and S2 are silver strips, 0.02 mm. thick, which connect 

 the binding posts K^, and K2 with the lead to the coils. K^ and K^ are the binding posts for the 

 lead to the fixed electromagnet £1. (Reproduced from Gutenberg's Grundlagen der Erdbebenkunde, 

 Vol. 12, 1927. Published by Gebriider Borntraeger, Berlin.) 



