Hot and Thermal Springs. 369 



Bat, if we compare the mean temperature of the springs at 

 Stuttgart with that of the spring at Tubingen, we shall be in- 

 clined to suspect that the latter is thermal, for this place lies 

 higher, and in a less mild climate, than Stuttgart, and yet the 

 mean temperature of the spring at Tiibingen was somewhat 

 higher than that of the springs at Stuttgart. 



The uniform nature of the soil in Basel, out of which rise 

 eight fresh- water springs, in the space of about half an English 

 mile, offers a particularly favourable opportunity of observing 

 the temperature of the earth in that locality. The soil of Basel 

 is covered with considerable deposits of rolled stones, under 

 which there is a bed of marl and clay, falling gently to the north- 

 east towards the Rhine. The meteoric waters, after having fil- 

 tered through the layers of loose stones, meet with this imper- 

 vious bed, the gentle slope of which directs them towards the 

 Rhine. 



Among these springs the Lochbrunnen, on the Herbrigberg, 

 is remarkable for its low temperature. To my question whe- 

 ther this low temperature might not perhaps be derived from 

 the neighbouring heights of the Jura, Professor Merian answer- 

 ed that such a conjecture could not be borne out by the circum- 

 stances of the locality. He is much rather inclined to ascribe tlie 

 low temperature of that spring to the phenomenon observed by 

 Forchhammer on the Faroe Islands, viz. that those springs 

 which rise out of loose stones are invariably colder than those 

 which rise out of the solid rock at the same elevation. (See 

 a subsequent chapter.) On the other hand, the St Alban Thal- 

 brunnen may be considered as a thermal spring. If these two 

 be excluded, and die mean deduced for the rest, we obtain 49°.26 

 for the mean temperature of the earth at Basel. According to 

 the comparison made by Merian, with the mean temperature of 

 the air at Strasburg, and at Geneva, this value can differ but 

 little from the mean temperature of the air at Basel. 



As it was assumed that in high latitudes the temperature of 



