1 4C Prof. Bischoff on the Temperature of' 



From this it follows, tliat a chthonisothermal line of any tem- 

 perature, which was under a small district parallel to the sur- 

 face, cannot continue its course under a neighbouring mountain, 

 either parallel to the external configuration of the mountain, 

 or in the continuation of its former direction, but must curve 

 upwards as in the figure. 



It might be for a moment supposed that the decrease of 

 temperature from the base of a mountain to its summit, would 

 follow the same law as that which takes place in the same ele- 

 vation in the atmosphere. But in that case we could never 

 findca higher temperature in the interior of a mountain than 

 at its basis ; which, however, is contradicted by the observa- 

 tions made in some mines situated in very high mountains in 

 America. 



The wori<men in the mines of Guanaxuato in Mexico (21°15 

 north latitude) find tliemselves at a depth of 1607 feet in a tem- 

 perature of 98°.15. This is about 15°.75 higher than the 

 temperature of the equator at the level of the sea, and yet this 

 point lies at a height of 4617 feet above the sea*. Boussin- 

 gault -f- found the temperature of the soil near the Hacienda del 

 Rodeo, at an elevation of 4128 feet, to be 68° ; and Von Hum- 

 boldt, at an elevation of about 11,200 feet above the sea, in the 

 Mina del Purgatorio., in Peru, and in about the same latitude, 

 found a temperature of 67°.28. The chthonisothermal line of 

 68°, therefore, rises 7072 feet between these localities. 



The rising of the chthonisothermal lines in mountains of less 

 considerable elevation is also proved in our quarter of the globe. 

 In the bore at Pregny, near Geneva, (Chap. XIX.), a tem- 

 perature of 63°.05 was found at a depth of 680 feet below 

 the surface, and 51 1 feet above the level of the sea. De Saus- 

 sure j found the same temperature in the mine at Bex, 677 feet 

 below the surface, and about 2300 feet above the sea. Thus 

 the chthonisothermal line of 63°.05 rises about 1789 feet between 



give a very different result from those made between D and B. This point 

 was first mentioned in Von Dechen's thermonietrical observations in various 

 Prussian mines. 



* Von Humboldt in Gilliert's Annal. Ixxvi. p. 450. 



t Annal. de Chim. and de Phys., vol. liii. p. 245. 



X Voyages dans les Alpes, § 1088. 



