360 Prof. Bischof on the Natural History of 



Their wide distribution, the invariableness of their pheno- 

 mena, the evolutions of gases from many of these, present to 

 every attentive observer matter of investigation and considera- 

 tion on their origin, duration, and connexion with other phe- 

 nomena. If, then, we can succeed in proving that chemical 

 processes can with much less probability be assigned as the 

 cause of their being heated, that, on the other hand, the most 

 convincing reasons shew that their heat is acquired at the expense 

 of the interior of the earth : then will the hypothesis, which en- 

 deavours to explain volcanic phenomena from the same causes, 

 gain no little increased weight. And in fact if hot springs be 

 heated to such a degree as to attain the boiling point at a cer- 

 tain depth in the earth, we have but one step to make, by sup- 

 posing this heat increased up to the fusing-point of volcanic 

 stony masses, in order to attribute with equal probability, 

 volcanic phenomena and hot springs to the central part of our 

 earth. 



I must observe, in the first place, as was formerly re- 

 marked, that, by thermal springs, I understand nothing more 

 than springs whose average temperature exceeds that of the 

 soil at the level at which they rise. It is therefore indifferent 

 whether this excess consists in 1° or less, or in 50° or more. I 

 can form no other idea of the meaning of the word thermal 

 springs ; at least, I do not know what degree of temperature 

 can be laid down as the boundary between cold and thermal 

 springs, unless the distinction were to be perfectly arbitrary. 

 Thermal springs (taken in this sense), are very widely distri- 

 buted over the globe, as I think I have formerly shewn. Nay, 

 I am convinced that, if we take any district of nearly equal 

 height above the level of the sea, several of the springs will be 

 found to exceed in average temperature that of the soil. An 

 exception of this rule will certainly only be found in those si- 

 tuations where springs arise at the foot of hills more or less 

 high, and which have acquired a cooler temperature from the 

 higher regions. 



If, like Professor Daubeny,* we regard chemical processes 



* Report on the present state of our knowledge with respect to mineral 

 and thermal waters. London^ 1837. 



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