52 ON THE FIRE-DAMP OP COAL- MIXES; 



sive, uniformly take place, as all the facts connected with the 

 state of the air in the mines prove ; nor can any accumulation 

 of it take place, which shall reach the floor of the mine, but by 

 its filling the space from the roof downwards, mixed more or 

 less with the atmospheric air. All that is necessary, therefore, 

 is to guard against the chance, extremely small in itself, of the 

 open end of the tube being in the direction of a stream of the- 

 gas, if at any time it should issue from the floor, and this is, 

 easily done by the methods stated in. the descriptions, of the 

 tube being turned up at its extremity, or of its being closed for 

 the height of two or three inches, with apertures above this 

 height, to admit the air. Any small quantity which might be 

 brought by the current of air entering the tube must be unim- 

 portant, and any danger from this source must require such a 

 combination of circumstances as may well be expected never 

 to occur, — that of the tube being in the direction of the cur- 

 rent of gas, — of the mixture of it with atmospheric air being in 

 that limited proportion when it readies the flame of the lamp 

 in which it explodes, and of the whole air at the floor of the 

 mine being also in that state in which it will explode ; and 

 all this independent of the circumstances, that by any such 

 mixed air passing into the lantern, the flame of the lamp will 

 be extinguished instead of explosion happening, and that ex.- 

 plosion, even if it did occur, would not be conveyed along this 

 length of tube. 



The same arrangement, with regard to the tube, obviates 

 another possible inconveniencej — that of the entrance of car- 

 bonic acid gas, which, from its greater specific gravity, may 

 sometimes occupy the floor of the mine. It seems scarcely 

 ever to be accumulated to this extent in mines in which fire- 

 damp is generated ; and if it were, its entrance into the lan- 

 tern, would be productive of no other accident than that of 



extinguishing 



