182 F. OMORI AND K. HIKATA : 



superposed on well-defined slow undulations of an average 

 period of 0.65 second in the (EW), and 0.G4 second in the 

 (NS). One of the largest vibrations of the latter kind was 

 2a = 1.0mm., T=0.74 second, direction N 30° E. In the (EW), 

 there were also present vibrations whose average period was 

 1.3 seconds. 



27. Eqke. No. 19. The 4th December, 1897; 9.19.21 a. m. 

 Intensity, weak. The maximum H.M. was about 1.6 mm., the 

 V.M. being also present. As the rotation of the record receiving- 

 drum was unfortunately not good, further measurement could 

 not be made. 



28. Eqke. No. 20. The 8th December, 1897; 5.20.48 

 p. m. Intensity, weak. Two shocks, {a) and {b), of nearly the 

 same range of motion happened one after the other, the time 

 interval between their occurrences being 43 seconds. The origin 

 of disturbance was, like that of Eqke. No. 4 and its after-shocks, 

 situatedinland at about 100 km. W of Miyako. (See fig. 4). 

 The total duration of the two shocks was 100 seconds. 



{a) First shock. The jireliminary tremor, whose duration 

 was 11 seconds, and whose amplitude was greater in the (EW) 

 than in the (NS), consisted of ripples of an average period of 

 0.089 second in the (EW), 0.088 second in the (NS), and 0.08 

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

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

 and 1.0 second in the (NS). 



The prhicipal portion, whose duration was about 12 seconds, 

 consisted of ripples of the following elements : 



(EW) (NS) (V) 



Maximum 2a 0.74 mm, 0.9 mm. 0.1 mm. 



Average period 0.10 second 0.10 second 0.10 second. 



