360 s. SEKIYA 



seconds of time from the commencement of the shock up to the 

 seventy-second second.* 



In the model the motion -path is represented by means of u 

 copper wire, the course of which was determined by successively 

 compounding the three rectangular components recorded on the 

 earthquake diagram ; numbers marked on small metal plates attached 

 to the wire at different intervals correspond to the number on the 

 radial lines on the diagram. In the actual model the motion is 

 magnified fifty times. To avoid confusion the model was made in 

 three parts each showing the motion for twenty seconds or so; thus,. 

 Fio-, 1 Plate XXYII indicates the motion from the beginnino- of the 

 shock to the end of the ■ twentieth second, Fig. 2 from the latter 

 instant to the end of the fortieth second, and Fig. 3 thence to the 

 end of the seventy-second second. They are not traced beyond that 

 point as the vertical motion practically ceases to exist and the move- 

 ments may be simply represented on a horizontal plane. Each model 

 is firmly mounted on a stand. The figures shcnv the northern 

 aspect of the model, but looking slightly from above. 



During these seventy-two seconds, quantitative relations of hori- 

 zontal and vertical displacements and constantly varying changes in 

 their directions and oscillating periods — in fxct everything concerning 

 the movement of the ground — can be studied with ease. 



Looking at the model one will observe the complexities and 

 irregularities of the earthquake motion ; at certain moments, the 

 ground moves nearly in straight lines, while in others, it describes 

 somewhat circular or elliptical paths. Similarly the vertical component 

 varies in its range and period and consequentl}- the angles which the 

 motion-path makes with the horizontal plane are constantly changing. 



* For iiiorj Jtt liled descriptiou of tliese diagi'iiius, see Comparison of Eartliqiiake Diigraius,. 

 etc., by S. Skkiya. Vol. T., Part I, of this Jounnl. 



