98 Mr. R. W. Fox on the Increase of Heat in Mines. 



incessant agitation of the ocean produced by currents and 

 tides, &c. For these reasons, it appears to me that a low 

 temperature at the bottom of the sea is not at all inconsistent 

 with a high degree of terrestrial heat. 



The temperature about the poles of the earth must also be 

 governed by the relative impressions of the heat and cold to 

 which they may be exposed ; and if frost and snow are found 

 on Hecla and other volcanic mountains and districts, owing 

 to the very slowly and imperfectly conducting medium of the 

 rocks and the ground, surely the effects produced by the cold 

 in the polar regions cannot be deemed incompatible with an 

 elevated temperature under the surface. The zones of equal 

 temperatures at accessible depths in the earth having been 

 found to conform, in some degree, to the irregularities of its 

 surface, this fact affords another instance that whilst the in- 

 ternal parts of mountains and hills may be sustained at a high 

 temperature, their sides and even the valleys which separate 

 them may be quite cold. This arrangement of the zones of 

 heat must, I conceive, cause the water or moisture in the in- 

 terior of mountains and hills to give out vapour more or less 

 copiously, according to circumstances; and this ascending 

 towards their summits and sides, gradually condenses into 

 drops in proportion as the temperature of the ground di- 

 minishes. The drops accumulating into small streams, ulti- 

 mately appear, in part at least, at the surface, and form a more 

 or less considerable proportion of springs or fountains. 



If the terrestrial temperature could be determined with cer- 

 tainty at any given depths within our reach, I much question 

 whether it ought to be considered as furnishing us with pro- 

 per data for calculating the ratio of increase to a far greater 

 depth, because it appears to me to be highly probable that in 

 the former case the heat may be due to the ascending portions 

 of warm water, more than to the conducting power of the 

 rocks ; and this idea derives confirmation from the fact, that 

 those rocks which most readily transmit heat (compact granite 

 for example) are usually found at a lower temperature in mines 

 than clay-slate and other rocks which are the most pervious 

 to moisture and the worst conductors of heat. 



It must however be acknowledged that whether the ter- 

 restrial heat increases more or less rapidly towards the centre, 

 the frequent occurrence of volcanos and hot springs, in di- 

 stricts far separated from each other, tends strongly to confirm 

 the opinion that a very high temperature exists in the interior 

 of the globe. ... ^ 



TT i L t to too, ROBERT W. Fox. 



Falmouth, Jan. 13, 1831. 



XVIII. On 



