PRELIMINARY TREMOR OF EARTHQUAKE MOTION". 159 



pendulum is 24 seconds. The length of the smoked paper 

 wrapped round a drum, on which the record was taken, is 

 745 mm., the drum making one complete revolution once in 

 70 seconds. The proper motion of the horizontal pendulum is 

 not shown in the diagram, and therefore all the waves are to 

 be regarded as indicating real earthquake movements. The 

 motion was here recorded only as far as the 210th second from 

 the commencement, but the real duration was much longer. 

 According to the diagram, there were the following four kinds 

 of waves superposed one upon the others : — 



1. Waves, whoge average period was 0.36 second, and whose 

 maximum range was 0.6 mm. 



2. Waves, whose average period was 0.88 second, and whose 

 maximum range of motion was 0.6 mm. 



3. Waves, whose average period was 1..5 seconds, and whose 

 maximum range of motion was 0.9 mm. 



4. Waves, whose average period was 3.4 seconds, and whose 

 maximum range of motion was 1.7 mm. 



This earthquake, whose origin was about 100 kilometres 

 west of Tokyo, was in the N8 component recorded by the Hori- 

 zontal Pendulum. According to the diagram, the total duration 

 was about 20 minutes, the average period of the principal 

 undulations, whose maximum motion was 2.2 mm., being about 

 6.3 seconds. The duration of the preliminary tremor was 15 

 seconds. (In fig. 4 is given the earlier portion of the diagram). 



November, 1898. Seism ological Institute, Tokyo. 



