202 801ENOE IN SHORT CHAPTERS. 



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 

 Commissioners 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 temper- 

 ature 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 

 Avorking coal will be altered accordingly. In the cases 

 quoted by the Commissioners, the few degrees of cooling 

 were effected by a sytem of ventilation that was devised to 

 meet the requirements of respiration, and not for the pur- 

 pose of cooling the mine. 



It would be very presumptuous for anyone in 1873 to 

 say how this special cooling will actually be effected, but I 

 will nevertheless venture 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 reach- 

 ing 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 sys- 

 tem of coal-mining may be revolutionized, and thus the 

 aspect of this problem of cooling the workings would be- 

 come 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 



