AND ON PREVENTING ITS EXPLOSION. 43 



top. This is a yellowish-coloured diffusion of the light round 

 the flame of the candle, rising higher, and assuming a 

 greenish-blue colour when the quantity is considerable, and 

 when it is still larger, giving rise to a rapid succession of lumi- 

 nous points or flashes. The miner, when judging from this of 

 the presence of fire-damp, advances cautiously in the mine, ob- 

 serving the appearance on his candle, by raising it slowly from 

 a certain height from the floor, — a circumstance I may remark 

 which shews very well the tendency to the accumulation of the 

 inflammable gas in the roof, and the comparative purity of the 

 air below. He thus advances, as far as he can with safety, and 

 it is singular to what length the miners sometimes proceed with 

 this trial. This peculiar appearance seems to arise partly from 

 the extinguishing effect of the reduced air on the flame of the 

 candle ; for a similar effect is produced in immersing a lighted 

 candle slowly in any gas unfit to sustain combustion ; and as it 

 extends so high, it must also partly arise from the imperfect 

 ascension of the inflammable gas. If any inflammable air 

 were to enter the lamp I have described, this aj)pearance, or 

 something similar to it, would take place, even sooner, from 

 the rarefaction of the air, and probably the flame would be en- 

 tirely extinguished before any explosion occurred. It would 

 therefore give an equally sure indication with much more safe- 

 ty ; though it is also probable, that no air, so far impregnated 

 with carburetted hydrogen, could ever enter from the floor of 

 the mine while the atmosphere above was such that it could be 

 breathed. 



When the danger is suspected to exist, the state of the air in 

 any part of the mine may be accurately examined with great 

 facility, and entire safety. With a moveable lamp and tube, 

 such as has been described, or, if it were thought to give more 

 safety in extreme cases, with light obtained by the collision 01 



F 2 steel 



