On Underground Temperatures. 



11 



depth had been reached of 810 feet. In February, 1857, at a depth 

 of 1450 feet, the temperature was 67J°, which rose with abnormal 

 rapidity to 72J ° in August, at a depth of 1689 feet. It then slightly 

 decreased, partly recovering and ending in October at 72 when the 

 depth was 1840 feet. In March, 1858, it had fallen to at 1881 



feet, and then rose by July, at 2055 feet, to 75^°. After the winter, in 

 March, 1859, at ^151 feet the thermometer stood at 75°, or half a degree 

 less than it did in July at a depth of nearly 100 feet less. I can 

 only attribute these fluctuations to the influence of the seasons and 

 convection currents, or to some unmentioned form of ventilation. A 

 new shaft sunk in 1858, not far from the other, gave, in the same way, 

 analogous results, viz., an increase of 1° F. for every 90 feet. 



When, however, at a subsequent period, and when the works of 

 this colliery had been carried to the great depth of 2700 feet, observa- 

 tions were made in galleries at a distance from the shaft, with instru- 

 ments furnished by the British Association Committee, and in holes 

 4 feet deep, an amended reading of 1° for every 72 feet was obtained. 

 Still that rate of increase is slow, and Professor Everett has drawn 

 attention to the fact that there are other collieries such as those of 

 Ashton Moss, Denton, and Bredbury, within a few miles of Dukin- 

 field, in which the results are in close agreement with those obtained 

 in the latter. It has been suggested in explanation of this, that the 

 rapid dip of the strata at Dukinfield facilitates the transmission and 

 escape of heat. It is quite possible that this cause may have an 

 influence, as the experiments of Herschel and Lebour have shown 

 experimentally that the conduction of heat is more rapid along the 

 planes . of cleavage, or bedding, than across them. Nevertheless no 

 such difference exists in other mines where the strati graphical condi- 

 tions are alike ; the strata in the Liege, Mons, and Valenciennes coal- 

 fields (Nos. 140, 214-16, 145) are more disturbed, and dip at more 

 rapid angles than at Dukinfield, and yet the deep temperatures there 

 give no such slow rate of increase. 



Again, Mr. Garside draws attention to the circumstance that the 

 Red Sandstone, overlying the Coal-measures in the area, is highly 

 charged with water, which is largely drawn npon for water supply. 

 This may reduce the temperature of that mass of rock, but the effects 

 would hardly reach to the great depths and extent observed. 



Some of the anomalous results may also be attributable partly to 

 the excellent ventilation of these deep pits. At the Dukinfield 

 Colliery, about 58,000 cubic feet of air circulate through the pit per 

 minute. The mean annual temperature of the air at the surface is 

 48° F., while the return air from the pit has a temperature of 73°. 

 But then again the ventilation at Rosebridge and other large pits — 

 where the rate of the increase of temperature is more rapid and 

 nearer the probable normal — is not less carefully attended to. Still, 



