at Wallsend Colliery, June, 1835. 349
nearly equal at the two points, the weight of the additional column a b on the mouth of the Pit A, naturally causes the column of air in the Pit B to ascend, and to cause a continuous current of fresh air to pass through the workings c d, between the two pits. Nothing but the temperature of the air at the top of the Pit A, being raised to such a degree as to more than compensate for the lesser weight of the atmospheric column at the top of the Pit B, could alter this natural law of the current of air between the pits.
It does not, however, often happen in practice that we find this sort of natural ventilation applicable, or sufficient for our purpose. We are, therefore, obliged to resort to other more powerful and efficient means.
We find the water-fall amongst the most ancient contrivances resorted to by miners, for urging a current of air through underground workings Bellows, and circular blowing machines, were also used, at an early period for the same purpose, but rarifaction by fire, which is by far the most efficacious and certain mode, seems to have been the latest in being discovered.
The water-fall is effected by pouring a stream of water down one of the pits, A or B, which, carrying a column of air with it, forces the current through the workings, and up the opposite pit. Bellows, and blowing machines, have been used in the same manner, for forcing a current of air down one pit and up another; but the blowing of a current of air has long been discontinued, and the circular machine has been more advantageously applied to draw the current of air through the workings.
All those different methods have their advantages and disadvantages, according to the circumstances in which they are used. In deep collieries, the water-fall is objectionable, on account of the expense of pumping the water out again, and also from the inconvenience of having the stream of water falling down a working pit. The circular machine is objectionable on account of its being dependent, on mechanical means for its operation,
and because it cannot be employed in the same pit, up which coals are to be drawn.
None of those objections attach to the furnace. It can be applied in a working pit, and is certain and steady in its operation. The only defect of the furnace is, its liability to explosion when the current of air by which it is supplied, becomes so charged with inflammable air, in its passageVOL. II. 3 T
