EARTHQUAKE MEASUREMENT AT MIYAKO. 183 



The average period of slow undulations was 1.6 seconds in 

 the (EW), 1.8 seconds in the (NS), and 0.8 second in the (V), 

 one of the maximum movements of this kind, whose period was 

 1.4 seconds, being : 



0.8 mm. towards E, 0.6 mm. towards N, 0.7 mm. upwards. 

 Kesultant 2a = 1.2 mm., direction . E 40° N, the angle of 

 emergence =36". 



In the end portion, the average period of the ripples was 

 0.085 second in the (EW), 0.08 second in the (NS), and 0.09 

 second in the (V) ; these being superposed on slow undulations 

 of an average period of 1.7 seconds in the (EW), 0.9 second in 

 the (NS), and 0.4 second in the (V). 



{b) Second shock. The principal portion, whose dura- 

 tion was 7 seconds, consisted of ripples of the following 

 elements : — 



The ripples were superposed on slow undulations, whose 

 average period was 1.6 seconds in the (EW), and whose maxi- 

 mum H.M. = lmm., V.M. =0.2 mm. 



In the end portion, the average periods were as follows : — 



(EW) (NS) (V) 



Kipples: 0.074 second 0.077 second 0.079 second. 



Slow undulations : 1.5 „ 0.9 „ 0.9 „ 



29. Eqke. No. 21. The 23rd December, 1897 ; 0.29.16 

 p. m. Intensity, iveok. The origin was situated at about 70 km. 

 NE of Miyako. The duration was about 35 seconds. 



