COLLIERY EXPLOSIONS. 
217 
taken as the ** up-cast shaft ” of a colliery, and the other 
partition the “ down-cast shaft.” In the early days of coal 
mining, the ventilation of coal mines was effected in a way very 
similar to that illustrated by the glass cylinder. A shaft wa& 
sunk and a small portion walled off (the wall doing the work of 
the cardboard in the glass cylinder) and formed the “down-cast,” 
the main portion serving as the “ up-cast.” But the old miners 
did not always trouble themselves to improve their ventilation 
by rarefying the air of the up-cast shaft by means of heat, but 
trusted to the internal heat of the earth to accomplish the work 
for them. When, however, the ventilation became very defective, 
then a bucket containing burning coal was suspended for a time 
in the “ up-cast.” But, as mining operations began to develop, 
this primitive method of ventilation was found to be insufiS.- 
cient, and so the underground workings were connected with 
a second shaft, at the bottom of which there was a furnace. 
The air, on entering this shaft, which was the “up-cast,” 
becomes rarefied, and rushes up towards the surface of the 
ground with increased velocity, and, on the other hand, the 
cold air rushes down the other shaft with increased velocity 
to fill up the vacuum that would otherwise be caused. Thus a 
current of air is established throughout the mine, and it is upon 
this the miner depends to dilute and remove gases, which, if 
allowed to accumulate, would result in disastrous consequences. 
The importance of good ventilation will at once become apparent. 
Furnace ventilation is still extensively practised, but other 
methods have also been introduced. These effect their work by 
artificial draught. The machine consists of a fan or ventilator, 
which exhausts the air in the up-cast shaft, thereby producing 
a partial vacuum, which the air in the down-cast rushes to fill 
up, in the same way as with the furnace. Very effective results 
have been produced by these appliances, and it is a question 
which of the two methods of ventilation is the better. 
