Hot and Thermal Springs. ' 365 



If we apply these general conclusions to Wahlenl)crg''s obser- 

 vations, it is easy to perceive that he has determined the mean 

 temperature of the soil at Upsala, at the Ynger See, at Umeo, 

 Soderkciping, and Carlscrona, in all cases too high, because he 

 deduced them from observations made either on constant warm 

 (thermal) springs, or on variable springs in months in whidi 

 they could not [wssibly have their mean temperature. We must 

 therefore call in question his conclusion, that the mean tempe- 

 rature of the earth in the north is every where higher than the 

 mean temperature of tlie air, and that the difference between 

 them is greater the higher the latitude, or the colder the win- 

 ters. 



It was shewn in chap. i. how universally thermal springs are 

 dispersed over the earth. In rocks which are very much dislo- 

 cated, and in which the atmospheric waters descend to a consi- 

 derable depth, the number of thermal springs may probably sur- 

 pass that of the cold ones ; indeed, perhaps, scarcely one will be 

 found from which the mean temperature of the soil can be de- 

 termined. I found this assertion upon numerous observations 

 which I made in April 1833, and May 1834, upon the springs 

 at the foot of the chalk rocks of the Teutoburger Wald, in strata 

 which are very much fissured. In April 1833, I found among 

 sixty-six running fresh-water springs, only three whose tempera- 

 ture was below 47|° ; all the rest varied from 47|° to C0°.6. In 

 May 1834, the temperature of those three springs had risen 3°.6. 

 As, according to the table, no spring, as yet observed, reaches 

 its mean temperature earlier than April, and most springs not 

 until June, and sometimes even July, the mean of those three 

 springs cannot fall below 471°. If it falls above 47|° they may 

 be considered as thermal, lor the mean temperature of the air at 

 that place cannot be much above 47 1°. Another circumstance 

 in favour of this is, that, in May 1834, I found a fourth spring 

 near those three, the temperature of which was 47J° or 8°.6 

 colder than the coldest of the others. If this fourth spring ob 

 serves the same law in the variations of its temperature as the 

 other three do, there is no longer any doubt that they are ther- 

 mal. There can be no question whatever tliat the other sixty- 

 three springs are thermal. 



Besides those sixty-six fresh-water springs, I observed in May 



