806 



EXPLORATION GEOPHYSICS 



LIGHT — - 



RECORDIhia 

 CAMERA 



the other to the horizontal component. The inertia member of the vertical 

 component unit is supported by a vertical spring. The movement of the 



seismometer case relative to the 

 inertia reactor is first magnified by 

 a light conical lever attached to the 

 inertia member. At the free end of 

 the lever is a "bow and string" 

 mechanism which revolves about a 

 small (3 mm. diameter) spindle 

 supported between two jewelled 

 bearings. The mirror is mounted 

 on the spindle. A modified ar- 

 rangement which has similar me- 

 chanical amplification but eliminates 

 the difficulty due to the bearings is 

 shown in Figure 494. 

 The operation of the instrument may be summarized as follows. The 

 arrival of seismic waves sets the seismometer case, and hence the bow, 

 in motion. The movement of the bow rotates the mirror and hence causes 

 a displacement of a beam of light which is reflected from the mirror to a 

 photographic film in a camera located at a distance of about one meter. 

 A view of the Schweydar type seismograph is shown in Figure 495. 



Fig. 494. — Diagram illustrating one type of 

 mechanical and optical amplification. 



Fig. 495. — Early Askania mechanical scisni(igra])h. a, radio aerial; h. railio receiver for 

 recording instant shot was fired; c, seismograph; d, light-tight tube for optical magnification; 

 e, recording camera. (Courtesy of W. M. Rust, Jr.) 



