a.^o 



REroRT — 1884. 



still going on. At the Imperial Obsei'vatory a special colanin has been 

 constructed for these latter observations, and a large series of records are 

 l)eing collected. To work up the observations already nmdo on earth- 

 tremors and earth-pulsations will require consideriiblc time, and I 

 therefore am compelled for the present to reserve any report on them. 



Xutrii ill. raiiiwrtioii vitJi Ohscn'ttlions made iii tin; UuJrrjnjimd 

 Ohserrafori/ at the Talcashima Colliery near yuijasa/.i. 



01 iser rations with fixed Spirit Levels, ^'c 



These levels have been tried both on the surface and below grnnud, but 

 1 find that, owing to the extensive underground workings, the move- 

 ment in the Avliole mnss of the island is so great as to entirely vitiate any 

 record of the more minute earth-movemonts. 



The excess ;ind irregularity of the movement in the sti'ata of the 

 island is owing to the fact that wo are working simultaneously three 

 seams of coal ol; the aggregate thickness of IM) to 3G feet. Tlie lowest 

 seam (which is the only one in which we can hope to get a stable founda- 

 tion) mciisui'os IH feet in thickness, with a soft shale lioor of great depth, 

 on account of which it takes both ' creep ' and ' crush ' ; giving a con- 

 stantly varying set of movements from which it is impossible to obtain 

 any reliable statistics. 



The same reasons render the observations by the microphone and 

 microseismoraeter totally unreliable. 



The lever microphone — with which we have been experimenting — 

 when delicately balanced, registers an almost continuous i-attle of sounds 

 caused by the passage of coal-trucks, the ' falling ' of coal, and the 

 ' working' or crushing of the strata. 



Even when the delicacy of the balance is reduced, so that it docs not 

 render a single vestige of sound away from the colliery, it still continues 

 to register intermittent sounds, which can only be attributed to those 

 above-named causes when brought into the mine or on the island. 



The microseismometcr alst) shows constant tremors going on, accom- 

 panied by very considerable deflections, but without any periodicity or 

 constancy of direction. 



In Older to be sure that this irregularity was caused by the under- 

 ground workings, I made a short series ol" experiments on tho mainland 

 at Nagasaki, nine miles distant, with such results as perfectly convinced 

 me of the unreliableuess of the observations at Takasima. 



T am, however, strongly of opinion that observations of considerable 

 value in their application to the prediction of the out-flow of carburetted 

 hydrogen in coal mines can be obtained from the microseismometcr under 

 the following conditions. 



l.st. That it would need to be erected at a sufTicient distance from tbe 

 mines to insure its being unaflccted by tremors caused by the under- 

 ground Avorkings. 



'Jnd. That it must be close enough to the mines to iiisurc its being 

 affected by the same earth-tremors as are likely to affect the coal strata. 



I am led to form the above opinion from the fact that in the brief 

 experiments which I was able to make on tho mainland, any increase in 

 the intensity of vibration and amplitude of deflection seemed as a rule to 

 precede a diniinution of the barometrical preasurc. and it also seems 



fatei. 



