A Model showing': the Motion 

 of an Earth-particle during an Earthquake. 



By 

 S. Sekiya. 



Professor of Seismology, Imperial University. 



With Plates XXVI -XXVII. 



Daring an earthquake, seismographs, such as are now ussd in this 

 country, record the three rectangular components of the successive 

 motions of the ground. These components may then be again com- 

 pounded to form resultants, which, when joined together, denote 

 the real path pursued by an earth-particle daring a prolonged 

 shaking. 



The model represented on Plate XXVII was constructed on 

 the above principle to delineate, on a magnified scale, the earthquake 

 motion. It was copied from the diagram (Plate XXVI) of the 

 earthquake* of January 15th of the present year, obtained by 

 Ewing's Horizontal Pendulum and Vertical-motion Seismographs. 

 The waves of tlie two inner circles in that diagram denote the hori- 

 zontal components of the earthquake magnified five times while those 

 on the outermost of the three circles record vertical motion enlarged 

 eight times. The plate took two minutes and eight seconds to com- 

 plete one revolation and the radial lines on it mark the saccessive 



* Japan Earthqiake of January loth, 1887, by S. Sekiya. Vol. I., Part III, of this Journal. 



