ON EXPLOSIONS OF FIKE-DAMP IN COAL MINES. 
17 
sudden discharges blow themselves off in a short time : others 
go on for years without showing any signs of abatement, and the 
gas from them has been collected, and used in those parts of the 
mine where present custom looks upon it as safe to employ 
naked lights. 
The reader will now realise the danger which the collier 
stands always face to fece with : gas to some extent is almost 
always present, and should it be mixed with air in the proper 
proportions and come in contact with a naked light, an explo- 
sion more or less severe immediately follows. 
The methods of coping with this difficulty may be grouped 
under two main heads. One will include the processes of ven- 
tilation, by which the gas is diluted with common air to such 
an extent as to render it harmless : the other will take in all 
the contrivances for shielding those lights which must be 
used, so as to prevent their coming in contact with any 
explosive compound that ventilation may have failed to 
remove. 
First of ventilation — absolutely necessary in every case to 
supply breathing air to the miner, and doubly needful where 
the earth is ever pouring out a deadly gas, which lurks in each 
sheltered spot, and can only be driven out by sweeping every 
nook and corner by something like a hurricane of pure air. 
Every well-ordered coal mine is now supplied with at least 
two separate shafts, the size of which depends on its area, 12 to 
15 feet clear diameter within the brickwork being not too 
large if the workings are very extensive. Down one of these, 
known as the “ downcast ” shaft, pure air is constantly passing, 
and is conducted through the workings, driving before it the 
contaminated atmosphere, and in the end forcing it up the 
other shaft, which serves for an outlet, and is called the “ up- 
cast” shaft. The air taken in goes by the name of the “ in- 
take ” current, and the foul compound discharged from the 
upcast is called the “ returns.” It was at one time customary 
to carry all the air in one body through the windings and turn- 
ings of the workings, but by this method the current became 
too much contaminated, and its velocity too much reduced 
before it reached the end of its long journey, to allow of its 
producing any useful result in the parts of the mine most dis- 
tant from the downcast shaft : accordingly the intake air is 
now “ split ” into separate currents, varying in number accord- 
ing to the size of the mine, before it begins to run its course ; 
each of these ventilates a separate district, and in the end all 
unite and are discharged through the upcast. 
The passage of the air through the workings is regulated by 
barriers known as “ stoppings by doors, often double like a 
canal lock, which allow the miner to pass through, but keep 
VOL. XII. — NO. XLVI. 0 
