THE LIMITS OF OUR COAL SUPPLY. SOS 



"on the deep" of the whole range. The pits are not sunk 

 at that part of the same range where, at first sight, the coal 

 appears the most accessible, but, on the contrary, at the 

 deepest part. It is then carried on to some depth below 

 the coal seam which is to be worked, in order to form a 

 " sumpf " or receptacle from which the water may be wound 

 or pumped. The necessity for this in water-bearing strata 

 is obvious enough. If the collier began at the shallowest 

 portion of his range, and attempted to proceed downwards, 

 he would be "drowned out" unless he worked as a coal- 

 diver rather than a coal-miner. By sinking in the deep he 

 works upwards, away from the water, which all drains down 

 to the sumpf, from which it is pumped. 



The modern practice is to sink " a pair of pits," both on 

 the deep,, and within a short distance of each other. The 

 object of the second is ventilation. By contrivances, which 

 I need not here detail, the air is made to descend one of the 

 pits, "the downcast shaft," then to traverse the roads and 

 workings wherein ventilation is required, and return by a 

 reverse route to the "upcast shaft," by which, it ascends to 

 the surface. 



Thus it will be seen that, whenever the temperature of 

 the roads and workings exceeds that of the outer atmos- 

 phere; the air currents have to be forced to travel through 

 the mine in a direction contrary to their natural course. 

 The cooler air of the downcast shaft has to climb" the in- 

 clined roads, and then after attaining its maximum temper- 

 ature in the fresh workings must descend the roads till it 

 reaches the upcast shaft. The cool air must rise and the 

 warmer air descend. 



What, then, would be the course of the mining engineer 

 when all the existing difficulties presented by water-bearing 

 strata should be removed, and their place taken by a new 

 and totally different obstacle, viz., high temperature? 

 Obviously to reverse the present mode of working to sink 

 on the upper part of the range and drive downwards. In 

 such a system of working the ventilation of the pit will be 

 most powerfully aided or altogether effected by natural 

 atmospheric currents. An upcast once determined by 

 artificial means, it will thereafter proceed spon taueousl} r , 



