SEISMIC METHODS 



795 



ductor coil with respect to the fixed Hnes of magnetic flux of the magnet 

 system. This motion causes the conductor to cut the flux lines of force, 

 thus inducing a current to flow in the coil. Figures 480, 481, 482, 483 and 

 484 illustrate modern types of electromagnetic inductance seismometers. 



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Fig. 482. — Sealed, moving-coil type seismometer with view of cut-away 

 model. A and A', connection clips; B, waterproof bushing; C, carrying chain; 

 D, permanent magnet; E, armature; F, suspension spring. (Courtesy of Seis- 

 mograph Service Corporation.) 



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Fig. 483. — Electromagnetically damped moving-coil type geophone. A and 

 A', connection clips; B, waterproof bushing; C, carrying chain; D, permanent 

 magnet; E, armature; F, suspension spring; G, shunt damping resistor. 

 (Courtesy of Engineering Laboratories, Incorporated.) 



