ON THE VOLCANIC PHENOMENA OF JAPAN, 



415 



The successful working of the seismograph giving the above records 

 has led the Meteorological Department of this country to have a number 

 of somewhat similar, but less expensive, instruments constructed. These 

 are gradually being distributed throughout the empire. One feature 

 peculiar to the new instruments is that the drum on which the records are 

 written instead of being in continuous motion is only set in motion at the 

 time of an earthquake. When a drum or record-receiving surface is in 

 continuous motion beneath the pointers of a seismograph, these latter, 

 even with the best of instruments, will in time often describe a line the 

 breadth of which may be greater than the range of the preliminary 

 tremors of a disturbance. These tremors are therefore not visible on the 

 record. We find by experience that a record-receiving surface which is 

 only started at the time of a disturbance may be set in motion to receive 

 the preliminary movements, and is therefore, in the opinion of observers 

 in this country, better than an instrument where the record-receiving 

 surface is in continuous motion. 



In conclusion to this portion of the subject, I may remark that observa- 

 tions made with instruments at a distance of about half a mile from where 

 the Gray-Milne seismograph is situated give for the same earthquakes 

 amplitudes which are about twenty-five per cent, greater than those given 

 in the preceding table. These instruments are on low flat ground, while 

 the Gray- Milne seismograph is on ground which is relatively high and 

 hard. Another point worthy of record is that very small earthquakes are 

 sometimes felt upon the low ground which are altogether unnoticed by 

 the instruments upon the high ground. 



II. Freqxiency and General Character of recent Earthquakes. 



From the precediBg list of earthquakes it will be seen that between 

 the end of May 1885 and May 1886 fifty-six earthquakes were recorded 

 at the Meteorological Observatory in Tokio. Many of these were very 

 slight. During the previous year (May 1884-May 1885) seventy-three 

 shocks were recorded. 



As I did not return from the Australian colonies until last November, 

 I was unable to make observations on earthquakes which occurred during 

 the previous autumn and summer. In consequence of this, I regret to 

 state that the most important shocks of the season (Nos. 624 and 625) 

 were not recorded by the instruments which are employed for special 

 investigations. The special investigations now going on are observations 

 in a pit and on a piece of ground which I have the intention of endeavour- 

 ing to partially isolate from earthquake movement by trenching. If these 

 experiments are ever completed they will remain to be described in a 



