1873-] Limits of oar Coal Supply. 355 



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 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 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 spontaneously, as 

 the cold air of the downcast shaft will travel by a descend- 

 ing 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 differ- 

 ence 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 work- 

 ings that were once opened. Let us suppose the depth to 

 be 5000 feet, the rock temperature at starting 133 , and 

 that of the outer air 6o°, we should have a torrent of air 73 

 cooler than the rocks rushing furiously downwards, then 

 past the face 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 work- 

 ings of the future places at our disposal another and vastly 

 more efficient cooling 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-bearing strata would be encountered, 

 and the ordinary means of " tubbing" or " coffering" would 

 probably be adopted for temporary convenience during 

 sinking. Doorways, however, would be left in the tubbing 

 at suitable places for tapping at pleasure the wettest and 



