76 Dr Daubeny on Thermal Springs. 



the surface, the actual temperature being at present as nearly as 

 possible that which would be imparted to it by solar radiation 

 alone *. 



As we descend, however, into the interior of the globe, an 

 augmentation of temperature becomes sensible to a degree, which 

 leaves us in no doubt as to the existence of some other cause 

 of heat, whatever uncertainty may remain as to its nature. That 

 it cannot be entirely referred to artificial sources, such as the 

 presence of workmen, lights, &c. seems to follow from its being 

 manifest in neglected as well as in frequented mines, and that it 

 is not attributable to the condensation of air, is implied by the 

 fact, that water pumped up from deep artesian wells indicates a 

 temperature equally elevated with that from mines. 



Nevertheless, the general tenor of the observations seems 

 rather to suggest a local and variable, than a general and uni- 

 form cause. The heat of mines is neither equal for equal depths 

 in the same district, nor, when examined in different ones, does 

 it appear to depend upon the relative depth of the place below 

 the level of the sea, as ought to be the case, if it arose from an 

 intensely heated body occupying the interior of the globe. 



Thus, M. Cordier has shewn, that in Brittany two different 

 mines indicate an increase of 1° of Fahrenheit, the first for every 

 57 feet, and the second for every 206 feet ; and that the mines 

 of Freyberg in Saxony, and those of Schemnitz in Hungary, 

 shew an elevation of temperature sometimes more considerable 

 in proportion to their depth than those of Brittany, although 

 the former are at so much higher a level above the sea than the 

 latter. The case is rendered still stronger, if we compare the 

 mines of Cornwall, or of Newcastle, with those of South America, 

 the former of which are often below the sea, whilst the latter are 

 many thousand feet above its level, and yet, although the lowest 

 point to which they are worked must be above the mouth of any 

 of those noticed in England, the increase of temperature seems 

 to be as great in both, — that in Guanaxuato beuijg 1° of Fahren- 

 heit to every 46 feet, whilst that in Dolcoath mine is the same 

 to only 45. 



In short, nothing can be more capricious, or seemingly irre- 



• See Fourier's Memoir on the Temperature of the Terrestrial Globe. 



