250 report— 1884. 



still going on. At the Imperial Observatory a special column 1ms been 

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

 being collected. To work up the observations already made on earth- 

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

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



Notes in connection with Observations made in the Underground 



Observatory at the Talcaskima Colliery near Nagasaki. 



Observations with fixed Spirit Levels, 8fc. 



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

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

 ment in the whole mass of the island is so great as to entirely vitiate any 

 record of the more minute earth-movements. 



The excess and irregulai'ity of the movement in the strata of the 

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

 seams of coal of the aggregate thickness of 30 to 36 feet. The lowest 

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

 tion) measures 18 feet in thickness, with a soft shale floor 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 

 microseismometer totally unreliable. 



The lever microphone — with which we have been experimenting — 

 when delicately balanced, registers an almost continuous rattle 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 does not 

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

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

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



The microseismometer also shows constant tremors going on, accom- 

 panied by very considerable deflections, but without any periodicity or 

 constancy of direction. 



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

 ground workings, I made a short series of experiments on the mainland 

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

 me of the unreliableness of the observations at Takasima. 



I 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 microseismometer under 

 the following conditions. 



1st. That it would need to be erected at a sufficient distance from the 

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

 ground workings. 



2nd. That it must be close enough to the mines to insure 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 the mainland, any increase in 

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

 precede a diminution of the barometrical pressure, and it also seems 



