Smithsonian Report. 1931. — Heck 



Plate 1 



ik^^ 



1 . Galitzin Vertical Component Seismometer 



This consists essentially of a heavy mass, known as the steady mass, mounted on an arm which is 

 pivoted to a rigiil column in such a manner that the boom will move freely in a vertical plane. The 

 free end of the hoom carries a series of coils which move in a strong magnetic field as the boom oscil- 

 lates. The terminals of this series of coils are connected to a sensitive galvanometer. As the coil 

 moves in the magnetic field, a current of electricity is generated in the circuit which deflects the gal- 

 vanometer by an amount depending upon the amplitude <if the motion and the frequency. The 

 ground movements, highly magnified, are recorded photographically by reflecting a beam of litrht 

 to a photographic recorder described under Plate 2, P'igure 2. 



2. Tilt-compensation Seismograph. McComb- Rom berg Type 



In order to eliminate the troublesome effects of slow (daily) tilting of the ground due to temi)eratiire 

 changes, the steady mass of this instrument is coupled to the Tmiltii)lying lever through oil. Except 

 for relatively rapid oscillations the mirror of the niultiiilying lever temls lo reni;uii in a horizontal 

 position and the elTects of slow tilting are ade'juately eliminated. 'I'he operating principle of the 

 pendulum depends upon the inertia of the steady mass. This instrument is designed to register orUy 

 horizontal motion. 



