£90 Examination of recent Experiments 



scarcely suffice to raise one-half a degree Fahr. the temperature 

 of a mass of water equal to that which has flowed off in the same 

 period. In short, whatever may have been the tempieratufe of 

 the air which may have been for an hour in contact with the 

 waters drained off, it is not possible that it could have communi- 

 cated to them a quantity of heat so superior to that of which 

 they would have been deprived, in consequence of their filtration 

 through the rocks covering the mines, were there no central 

 heat. 



These data being laid down, I come now to the examination 

 of the different experiments considered under the point of view 

 of the assistance which may be derived from them in determin- 

 ing the law which the increase of the subterranean temperature 

 follows. 



There is an infinity of chances against the water of filtrations 

 and springs manifesting a temperature perfectly equal to that of 

 the rock from which they issue. In fact, the original heat of 

 the rain-water which penetrates into the soil continually varies, 

 being sometimes superior and sometimes inferior to the mean 

 temperature of the country. These differences are often very 

 great during a whole season. Moreover, the original heat is 

 subjected to many modifications, which depend upon the depth 

 to which the waters descend, the number and length of the ca- 

 nals, the slowness of the circulation, the length of time that it 

 has been established, and the number and extent of the masses of 

 water traversed, if there be any such in the lines of passage. 

 These elements are very complicated, and it would be necessary 

 to possess their expression, in order to appreciate the merit of their 

 result which each experiment furnishes. This, however, we can- 

 not have. All that we are permitted to conclude is, that most of 

 the experiments are probably very approximative, and that they 

 give in general temperatures lower than those of the zones of 

 rock at whose level they have been made, especially when the 

 depths are considerable. I say in general, for, in strictness, it 

 might be possible that the water of a spring, or filtration in a 

 mine, had passed along canals descending much more deeply 

 than the orifice from which it issues, and had time to acquire the 

 temperature of these canals ; it might also be the case that it had 

 passed through old works, in which the rubbish had undergone 



