EARTHQUAKE MEASUEEMENT AT MIYAKO. 181 



25. Eqke. jSTo. IT''. The elate is not given, but the record 

 was taken on the same smoked paper as Eqke. No. 17. In- 

 tensity, very slighi. The duration was 26 seconds, there being 

 no V.M. The average period of vibrations, whose maximum 

 2a was 0.1 mm. in each horizontal component, was 0.09 second 

 in the (EW) and also 0.09 second in the (NS). 



26. Eqke. No. 18. The 2nd October, 1897 ; 9.42.3 p. m. 

 Intensity, strong. This was an extensive earthquake, whose 

 origin was probably situated at about 150 km. ESE of Miyako. 

 The duration of H.M. was 110 seconds. 



The preliminary tremor, whose duration was 12.Ö seconds, 

 consisted of small ripples of an average period of 0.07 second 

 in each horizontal component. These movements, whose maxi- 

 mum 2a was 0.2 mm. in each horizontal component, were 

 superposed on slow undulations of an average period of 0.9 

 second in each horizontal component. 



The jyrmcipal i^ortion lasted for 13.6 seconds, and consisted 

 of ripples, whose average period was 0.09 second in the (EW), 

 and 0.08 second in the (NS). The V.M. was confused by the 

 proper pendulum oscillations. The maximum horizontal ripple 

 was 2a = 1..5mm., T=0.12 second, direction S 7o° W. The 

 ripples were superposed on slow undulations of an average 

 period of 1.3 second in the (EW). 1.0 second in the (NS), 

 and 1.0 second in the (V); the maximum motion of this kind 

 being 



(H.M.) 2a=2.3mm., T = 1.0 second, direction S ;5.5° W. 

 (V.M.) 2a = 1.4 mm. 



The end j^ortion consisted of ripples of an average period 

 of 0.06 second in each horizontal component ; these being 



