158 F. OMORi : 



For the cases of the Mino-Owari Earthquake (No. 1, § 6) 

 and the Hokkaido Earthquake (No. 2, § 6), we obtain : — 



Mino-Owari Eqke. V,=2.1 km. ¥3 = 1.6 km. 



Hokkaido Eqke. Vi=2.3 km. V,= 1.8 km. 



It is, however, to be observed that equation (1) has been 

 deduced from the observation of earthquakes, the distances of 

 whose origins from the observing stations do not exceed 900 

 kilometres, and it would evidently be absurd to apply the same 

 equation to cases of very distant earthquakes, for instance, those 

 originating in Japan and observed in Europe. Such earthquakes 

 give the high values for the transit velocity of 12 to 14 kilo- 

 metres per second. 



16. What was said in the preceding paragraphs seems to 

 show the coexistence in earthquakes of two principal kinds of 

 waves whose velocities of propagation are different. It must 

 not, however, be supposed that the motion of an earthquake 

 consists of only two kinds of waves. On the contrary, an 

 earthquake motion consists, when the origin is not very far 

 distant from the observing station, of several kinds of waves 

 with different periods of vibration, ranging generally between a 

 fraction of a second and several seconds. Short-period vibra- 

 tions, which always occur most markedly at the beginning of 

 the motion, gradually die away, leaving behind only the vibra- 

 tions of long periods. Perhaps it may be that waves with 

 different periods are propagated with different velocities. 



Fig. 5 is a reproduction of the EW component diagram 

 of the moderately stroug earthquake of the 3rd April, 1898, 

 recorded in Tokyo by my long-period Horizontal Pendulum 

 Seismograph, tlic period of proper oscillation of whose horizontal 



