92 



EEFORT — 1895. 



that had a seismograph been placed in Ivamakura all these shocks and 

 possibly a few others would have been recorded. The horizontal pendulums, 

 however, have only recorded three of the Tokio series, and to the remaining 

 18 they have been insensible. On the other hand, they have recorded 23 

 ■disturbances which the Tokio seismographs have failed to record. Although 

 I have not yet had time to fully analyse the records of earthquakes given by 

 the Tokio pendulums, from what I have seen of them I know that the 

 results will be similar. On many occasions I have watched a horizontal 

 pendulum while a sharp disturbance lasting from 15 to 30 seconds has been 

 taking place. All that happens is that there is a slight elastic switching 

 in a vertical direction of the pointer at the end of the boom. The boom 

 does not swing, and I have not observed a blurr in the photograpliic trace. 

 (Plate II. fig. '!.) On the other hand, whenev^er an earthquake instead of 

 simply produciiig elastic vibrations throws the surface of the ground into 

 undulations, the pendulums behave most erratically. They do not swing, 

 but they are forced first to one position and then to another. Now and then 

 they may pause for two or three seconds, but only to start, perhaps, more 

 vigorously than before. It is interesting to watch a seismograph writing 

 an earthquake, but a horizontal pendulum actuated by earth waves is one 

 of the most attractive sights that a seismologist can witness. When a seismo- 

 graph is disturbed you feel the motion that causes it to move, and in two or 

 three minutes all is ended ; but when a horizontal pendulum is disturbed 

 nothing is felt, and its spasmodic movements may continue for one or two 

 hours. Fig. 3, p. 109, shows what is almost continuous motion for 5 hours 24 

 minutes. Already I have had the good fortune to see this phenomenon five 

 times. On the last occasion, March 22, at 7.27 P.M., I sent a messenger to 

 call my colleague, Mr. C. D. West, who arrived some 15 minutes later, when 

 we watched the big boom stopping and starting from various positions for 1 



