178 F. OMOm AND K. HIRATA : 



and indicative of a rather distant origin. In the principal portion, 

 the amplitude was much greater in the (EW) than in the (NS). 



The preliminary tremor, whose duration was 16 seconds, 

 consisted of ripples of an average period of 0.0(85 second in the 

 (EW), and 0.08 second in the (NS). These movements, whose 

 maximum 2a was 0.12 mm. in each horizontal component, were 

 superposed on slow undulations of an average period of 1.0 

 second in the (NS). The transition from the preliminary tremor 

 to the principal portion was marked in the (NS) by the slow 

 undulations becoming more prominent. The (EW) was unfor- 

 tunately confused by the proper ossillations of the pendulum. 



The principal portion. The maximum motion of the ripples, 



which, including the preliminary tremor, lasted for 70 seconds, 



was 



(H.M.) 2a =0.64 mm., T = 0.12 second, 



(V.M.j very small ; 



their average period, which remained nearly constant through- 

 out the earthquake, being 0.081 second in the (EW), and 0.083 

 second in the (NS). The maximum slow undulations were the 



following : 



(H.M.) 2«=2.8mm., T= 1.6 seconds. 



(V.M.) 2a=0.4mm., T =0.7 second. 



20. Eqke. No. 15^. The date is not given, but the record 

 was taken on the same smoked paper as Eqke. No. lo. Inten- 

 sity, very slight. The earthquake was evidently a small local 

 one, and the motion, whose duration was 23 seconds consisted 

 entirely of minute ripples, the V.M. being practically zero. 



The preliminary tremor, whose Induration was 7.8 seconds, 

 was composed of vibrations of an average period of 0.078 

 second in the (EW), and 0.074 second in the (NS). 



