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, there- 

 fore, 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 effica- 

 cious 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 ma- 

 chines, 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 ap- 

 plied to draw the current of air through the workings. 



All those different methods have their advantages and disadvantages, ac- 

 cording 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 passage 



VOL. II. 3 T 



