(Jeoloyy, as Illustrated by Chemistry and Physics. 30 



creation it had the same low temperature as cosmical space, 

 then it would have been gradually heated from the exterior 

 inwards, by the influence of the sun, and would now present 

 either an equal temperature throughout, or a decrease from 

 the surface towards the centre. But precisely the contrary 

 is observed ; for at every part of the earth where, either in 

 mining operations or by boring, any considerable depth has 

 been reached, an increase of temperature presents itself. 

 This is a fact which, since the time when Trebra, Saussure, 

 and d'Aubuisson first directed attention to it, has been fully 

 established by numerous observations. The earth, then, 

 had, at the time of its formation, a higher temperature than 

 cosmical space, and gradually lost a part of its heat to a 

 certain depth below the surface. But in its interior it still 

 preserves its original temperature, either not at all or in a 

 very slight degree lessened ; for in a body of such a magni- 

 tude as the earth, and consisting as it does of bad conductors 

 of heat, the process of cooling is one of extreme slowness. 



Some years since I took great pains to shew,* that warm 

 springs occur in very great numbers in all rock formations, 

 in all latitudes, at all heights above the level of the sea, as 

 well as beneath it, if we consider as warm springs all such 

 whose water is but one degree, or even less than that, above 

 the mean local temperature. It is necessary that the signi- 

 ficance of the term " warm springs" should be thus extended, 

 for the mean temperature of cold springs is a function of 

 the mean temperature of the air at the place of their occur- 

 rence. Every excess of heat, however minute, cannot there- 

 fore originate from this temperature, but must be owing to 

 some other cause. A phenomenon so general as the occur- 

 rence of thermal springs can only be the consequence of a 

 general cause. Since, now, the springs are warmer in pro- 

 portion as they rise from a greater depth, since the water 

 which fills and generally overflows the borings is warmer, 

 the deeper the boring is extended, it is clear that the cause 

 of this temperature exceeding the local temperature can 



* See Physical, Chemical, and Geological Researches on the Internal Heat 

 of the Glohe. London, 1841. 



