ON THE KARTIIQUAKE PHENOMENA OF JAPAN. 



247 



lents o£ 



ulll. 



2S j 



illiracti'vs 



ti.mlU. 



•041 

 •OS 

 •08 

 •OS 



clocitics in 

 I amplitwdos 



iiul 



lilt 



ionlll. 



;nlatfd from 



■r >ei'oiHl 



^iMtlllll 



KV7 



18 



101 



:if.-i 



From this last tablo wo see that, although the period of motion at 

 Station II. is slow ia consequence of the very large amplitude usually- 

 experienced at that staiion, the niaxiraum velocity, and more markedly 

 the maximum acceleration, which may bo taken as a measure of the 

 intensity or destructive power of a disturbance, have been much greater 

 than at Stations I. and III. 



One of the most remarkable earthquakes in the series was that of March 

 26. Although the amplitude of this was sufficiently great to constitute 

 a destructive shock, the period was so long that the disturbance almost 

 escaped attention. Several persons observed lamps and pendulums 

 swinging, and thought there might be an earthquake occurring, but 1 only 

 founti one or two persons who detected any motion of the ground or 

 building. 



Speaking generally about these observations, it may be said that had 

 three independent obsovvei-s been placd at the three stations which are 

 only 8U0 feet apart, and each had been provided with similar instruments, 

 they could not have failed in giving very different accounts of the same 

 earthquake, both as to its period, its duration, and, I may add, its direc- 

 tion. A result of practical interest that is dependent in the records whicli 

 I have obtained, is the benefit to be derived by engineers and architects 

 by making a systematic seismic survey of tlie ground, on which they 

 intend to erect important structures in earthquake-shaken districts. 



Observations ivitli the Graij-'Mlliie Seisinorjrapli. 



As this instrument has been described and illustrated in the ' Quarterly 

 Journal of the Geological Society of London '(vol. xxxix. p. 218), and in other 

 publications, I will not describe the details of its construction. It consists of 

 a pair of conical pendulum seismographs, v.-hich record upon the smoked 

 surface of a drum, two mutually rectangular components of the horizontal 

 motion of the earth. The I'.rum is kept continuously in motion by clock- 

 work. The vertical motion is described by a spring lever seismograph. 

 At a certain part of the earthquake, a mark is made on the drum, simul- 

 taneously with which time is recorded from a specially arranged time- 

 piece. 13y this means the time can be calculated at which any particular 

 vibration of an earthquake occurred. 



As the instrument is designed more for the systematic observatior. of 

 earthquakes, rather than for experimental purposes, I entered into corre- 

 siiondencc with the Meteorological Dejiartment of this country to admit it 

 into their department as an instrument for regular observation. This 

 Mr. Arai Ikunosuke, the director of the Meteorological Department, has 

 kindly done. Aftc-r repairing slight damage, which it suffered in its 

 transit, it was exhibited to His Imperial Majesty the Emperor of thi,s 

 country. Since then a heavy brick column on a massive poncrcto foun- 

 dation has been built for its instalment, and '.t has been put in charge of a 

 regular observer. During the early part of this year, although several 

 earthquakes were experienced, no results were obtained. This was due to 

 the pointers of the conical or horizontal pendulums, which are extremely 

 sensitive to slight changes in level, slowly wandering to the right and left 

 of their normal position on the revolving drum. The conscquouco of 

 this was, that instead of simply tracing in the smoked surface a single 

 line, they made a path sometimes an inch in breadth, and when the earth- 



