26 



Prof. J. Prestwich. 



Mines. The effects are modified in the two cases by differences in the 

 structure of the shafts and galleries, and while in the one the presence 

 of the coal-gases necessitates excessive ventilation, in the other, hot 

 springs and chemical decomposition, though they raise the tempera- 

 ture, do not render so active a ventilation imperative. 



In some of the Cornish mines the current of air is hardly felt, and 

 it is stated generally by Mr. Robert Were Fox,* that in deep mines 

 the temperature of the rock and that of the air do not materially 

 differ, except when the currents are strong. At the same time it is 

 evident that strong currents of air do sometimes prevail. An instance 

 is mentioned by Mr. Robert Hunt,f where at the bottom of a mine 

 1 950 feet deep, the current of air was so strong that it was difficult to 

 keep a candle alight. In another, in all the levels (which were of 

 great extent) of one hot lode at the depth of 1410 feet, the ventilation 

 was so effective that the temperature of the air was never higher than 

 70° F. 



These mines must suffer, as in coal mines, a great and permanent 

 reduction of temperature in the proximity of the down shafts. This 

 is especially noticeable in severe winters, and when the ventilation is 

 active the effects of this will extend to a considerable distance from 

 the shaft. Daubuisson mentions that during a severe winter, and with 

 the outer air at a temperature of —15° R. (—2° F.), the shaft of the 

 Beschertgluck mine, in the Freiberg district, was lined with ice to a 

 depth of 80 toises (480 feet), and that the temperature of the air at the 

 bottom of the shaft was J° R. (33° F.). Dr. Clark (" Travels in Scan- 

 dinavia,") says that in descending the great iron mines of Persberg, 

 in Sweden, which are 450 feet deep, he found large masses of ice 

 covering the sides of the walls, and that it had accumulated in large 

 quantities in the lower chambers. But the formation of ice is not 

 confined to these more rigorous winter climates, for Mr. Moyle speaks 

 of finding, on one occasion, ice in abundance in the Tin Croft Mine, 

 Cornwall, at a depth of 318 feet below the surface, and says that the 

 ladders became impassable, crevices were filled, and icicles formed all 

 around ! That this must produce a permanent effect is clear from the 

 circumstance mentioned in connexion with coal mines, where the walls 

 of deep mines near the shaft are so cooled in winter, that in summer 

 the air circulating by them is of a higher temperature than the rock. 

 On the other hand, the temperature of the air in a metallic mine is 

 more apt than in a coal mine to become heated by the combustion 

 of candles, the explosion of gunpowder, and the presence of the 

 workmen. 



Some of the observations of Mr. Fox show the effects of ventilation 

 in the Cornish mines. Thus at Huel Damsel Mine (No. 21), the tem- 



* Coal Commission Eeport, vol. ii, p. 211. 

 f Ibid., vol. ii, p. 87. 



