228 SCIENCE IX SHORT CHAPTERS. 



coal-pits of the future.* It is true that the Royal Commissioners 

 have collected many facts showing that the actual difference between 

 the face of the rocks of certain pits and the air passing through them 

 is but small ; but these data are not directly applicable to the ques- 

 tion under consideration for the three following reasons : 



First The comparisons are made between the temperature of tho 

 air and the actual temperature of the opened and already-cooled 

 strata, while the question to be solved is the difference between the 

 theoretical temperature of the unopened earth depths and that of 

 the air in roads and workings to be opened through them. 



Second. The cooling effect of ventilation must (as the Commission- 

 ers themselves state) increase in a ratio which " somewhat exceeds 

 the ratio of the difference between the temperature of the air and 

 that of the surrounding surface with which it is in contact." Thus, 

 the lower we proceed the more and more effectively cooling must a 

 given amount of ventilation become. 



The third, and by far the most important, reason is, that in the 

 deep mining of the future, special means will be devised and applied 

 to the purpose of lowering the temperature of the workings ; that, as 

 the descending efforts of the collier increase with the ascending value 

 of the coal, a new problem will be offered for solution, and the 

 method of working coal will be altered accordingly. In the cases 

 quoted by the Commissioners, the few degrees of cooling were 

 effected by a system of ventilation that was devised to meet the 

 requirements of respiration, and not for the purpose of cooling the 

 mine. 



It would be very presumptuous for any one in 1873 to say how this 

 special cooling will actually be effected,' but I will nevertheless vent- 

 ure to indicate one or two principles which may be applied to the 

 solution of the problem. First of all, it must be noted that very 

 deep mines are usually 'dry ; and there is good reason to believe that, 

 before reaching the Commissioners' limit of 4000 feet, dry mining 

 would be the common, and at and below 4000 feet the universal, case. 

 At present we usually obtain coal from water-bearing strata, and all 

 our arrangements are governed by this very serious contingency. 

 With water removed, the whole system of coal-mining maybe revolu- 

 tionized, and thus the aspect of this problem of cooling the workings 

 would become totally changed. 



Those who are acquainted with the present practice of mining are 

 aware that when an estate is taken, and about to be worked for coal, 

 the first question to be decided is the dip of the measures, in order 

 that the sinking may be made " on the deep" of the whole range. 

 The pits are not sunk at that part of the range where, at first sight, 

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

 deepest part. It is then carried on to some depth belo\v the coal 

 seam which is to be worked, in order to form a " surnpf " or recepta* 

 cle from which the water may be wound or pumped. The necessity 

 for this in water-bearing strata is obvious enough. If the collier be* 



* In a paper on the Comstock Mines, read at the Pittsburg meeting of the 

 American Institute of Mining Engineers in 1879, by Mr. John A. Church, the hot 

 mine waters are described as reaching 158 Fahr. (?o hot that men have been scalded 

 to death by falling into them). The highest recorded air temperature there is 128. 

 These are silver mines, and vigorously worked in spite of this temperature and 

 great humidity. A much higher temperature is endurable in dry air. 



