THE LIMITS OF OUR COAL SUPPLY. 229 



gan at the shallowest portion of his range, and attempted to proceed 

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

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

 upward, 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 v/ithin 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 atmosphere, 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 inclined roads, and then after attaining its maximum tem- 

 perature 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 obsta- 

 cle, viz. high temperature ? Obviously to reverse the present mode 

 of working to sink on the upper part of the range and drive down- 

 ward. 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 spontaneously, as the cold air of the downcast 

 shaft will travel by a descending road to the workings, and then 

 after becoming heated will simply obey the superior pressure of the 

 heavy column behind, and proceed by an upward road to the upcast 

 shaft. As the impelling force of the air current will be the difference 

 between the weight of the cool column of air in the downcast shaft 

 and roads and the warm column in the upcast, the available force of 

 natural ventilation and cooling will increase just as demanded, i.e. it 

 will increase with the depth of the workings and the heat of the 

 rocks. A mining engineer who knows what is actually done with 

 present arrangements, will see at once that with the above-stated 

 advantages a gale of wind or even a hurricane might be directed 

 through any particular roads or long-wall workings that were once 

 opened. Let us suppose the depth to be 5000 feet, the rock temper- 

 ature at starting 133, and that of the outer air 60, we should have a 

 torrent of air 73 cooler than the rocks rushing furiously downward, 

 then past the faco of the heated strata, and absorbing its heat to such 

 an extent that the upcast shaft would pour forth a perpetual blast of 

 hot air like a gigantic furnace chimney. 



But this is not all ; the heat and dryness of these deep workings of 

 the future place at our disposal another and still more efficient cool- 

 ing agency than even that of a hurricane of dry-air ventilation. In 

 the first part of the sinking of the deep shafts the usual water-bear- 

 ing strata would be encountered, and the ordinary means of " tub- 

 bing" or " coffering" would probably be adopted for temporary con- 

 venience during sinking. Doorways, however, would be left in the 

 tubbing at suitable places for tapping at pleasure the wettest and 



