370 Prof. Bischof on the Temperature of 



the earth was higher than that of the air, so it was conversely 

 supposed, that in lower latitudes, the mean temperature of the 

 springs was somewhat lower than that of the air. This suppo- 

 sition was founded particularly upon Humboldt's observations 

 between the tropics. But that philosopher himself remarks*, 

 that in steep and high mountains, where either the snow-water 

 quickly mixes itself with lower springs, or where they rise near 

 their origin in lofty regions, the mountain springs show a lower 

 temperature than the mean of the place where they burst forth. 

 He refers for examples of this to the above mentioned observa- 

 tions in Jamaica, and to his own in the mountains of Cumana 

 and Caraccas. Von Buch-j* adds to these, similar observations 

 on springs near the Havannah, and in the interior of Congo, 

 and remarks, that the inferior temperature of springs begins to 

 shew itself already in the south of Europe ; and that there are 

 probably many springs in Portugal, Spain, and Italy, which dif- 

 fer in their constant temperature from that of the air, much 

 more widely than the springs in tropical countries. Thus, for 

 example, he refers to a spring at St Cesareo, not far from Pa- 

 lestrina, near Rome, the temperature of which he found, on the 

 29th of August, to be 53°.37, whilst the mean temperature of 

 the air at the same place, is 60°.35. But may not this low tem- 

 perature have been brought down with it from the neighbour- 

 ing Apennines, which, in the immediate vicinity, attain a height 

 of 2000 to 3000 feetj ? 



It is easy to prove that it is contradictory to the hypothesis 

 of an increase of temperature towards the centre of the earth, to 

 suppose that the temperature of the soil in low latitudes is lower 

 than the mean temperature of the air ; for if the temperature 

 of the earth's crust in those regions were lower than that of the 

 air, there must be a stratum at a certain depth, whose tempera- 

 ture would be equal to the mean temperature of the air. Thus 

 the external crust of the earth would be inclosed between two 



• Gilbert's Annalen, vol. xxiv. p. 45 and 46. 



-f- Poggendorff''s Annal. vol. xii. p. 407. 



* From a personal communication of Professor Hoffmann, I have learned 

 that a great number of springs, in the deep valley of Teverone, between Ti- 

 voli and Subiaco, are remarkable for their low temperature, which amounts, 

 on an average, to from 47^' to 52k°. 



