254 Mr W. J. Heuwoud on the Temperature 



\vhilst but little issues from the rocks, whether granitic or 

 slaty. It is an equally recognised fact, that a considerable 

 portion of the water pumped out of our mines has been rain- 

 water, which must have entered the ground at a temperature 

 nearly the same as that of the atmosphere ; consequently, 

 nuich lower than that prevailing at even comparatively small 

 depths in the mines. 



It therefore is obvious, that, as the cross-veins receive the 

 largest quantity of this cold water, they will be most affected 

 by its cooling influence ;* whilst, as the rocks absorb the 

 smallest proportion of it, they avIU therefore suff'er the least 

 depression of temperature. 



That this is one cause of the observed difference can admit 

 of no doubt ; whether it is the only one, is foreign to this 

 inquiry. 



It may be true that the ascent of vapoux", which would tend 

 to raise their temperature,! is facilitated by the more porous 



* At 264 fathoms deep, in Mr Pemberton's Colliery, at Monk-Wear- 

 iiiouth, Professor Phillips found, that, as bubbles of gas rose through tlie 

 water, its temperature fluctuated; in one case, from C9°'l to 69'"7, .ind in 

 another, from 71°-6 to 72°-6. Lend, and Edin. Pliil. Mag., v. (1834), p. 449. 



At 230 fathoms deep, in Dulcoath, Mr R. W. Fox placed a long thermo- 

 meter in the copper lode ; and, unless overflowed by water, it for many 

 months indicated a temperature varying only Irom 75°-0 to 75^'5. Cornwall 

 Geo. Trans., ii. p. 27. 



But in metalliferous districts, the constancy of the temperature of water 

 issuing from the same spot, at distant periods, must depend on the subter- 

 ranean works remaining unaltered ; for, if the deeper levels are untouched, 

 and the shallower ones are extended, the warm water from below will rise 

 as before, whilst the cold from above will be intercepted, and thus the tem- 

 perature of that flowing from intermediate spots will rise. If, ou the other 

 Land, the shafts are deepened and levels dricm beneath, whilst the shallower 

 ones are unwrought, the former will intercept the warm water and prevent 

 its rising, and the cold water from above still flowing as before, the tenr- 

 pcrature of intermediate stations will decline. 



Such, in fact, is the case at East Wheal C'ro/iy, where the temperatures at 

 two difierent spots, within two years, diminished — the one 3°0 to 7°2o, and 

 the other 7°0, — both parts of the mine having in the interval been deepened 

 30 fathoms. 



Whatever cause may increase the water from above, must lower the tem- 

 perature ; whilst any addition to that from below must elevate it. 



t Mr R. W. Fox, Cora. Geo. Trans., ii. p. 16. 



