872 Prof. Bischof on the Temperature of 



should both be made in the same year. For this reason, no 

 importance can be attached to the above differences. 



Taking all circumstances into consideration, we find that 

 there are grounds for assuming, that in high latitudes the earth 

 has a higher, and in low latitudes a lower, temperature than 

 the mean temperature of the air. The springs in high latitudes 

 which led to this assumption were, therefore, without doubt, 

 thermal, that is to say, springs which receive their heat from 

 the interior of the earth. On the other hand, those springs 

 which led to the conclusion that in low latitudes the tempera- 

 ture of the soil is lower than the mean temperature of the air, 

 seem to have been mountain-springs, which brought down their 

 lower temperature from higher regions. Boussingault remarks 

 in general, that in the Cordilleras there are often no springs to 

 be met with for a distance of several hundred miles. Wherever 

 he did find any, for example at Santa Marta and at Cartage- 

 na, their temperature exactly corresponded with the mean tem- 

 perature of the air. It- is, therefore, the more plausible to sup- 

 pose, that the few springs of which the temperatures have been 

 determined in those countries, have only been found in moun- 

 tainous districts. 



Kupffer's isogeotkermal* lines, drawn through all points of 

 the earth^s surface which have an equal temperature of soil, an 

 imitation of Humboldt'*s isothermal lines, lose their importance 

 in consequence of the above considerations, as, in general, iso- 

 geothermal and isothermal lines coincide. 



There is, however, no doubt that differences will here and 

 there be found between the mean temperature of the air and 

 that of the soil. Thus, in valleys which are surrounded by 

 high and steep mountains, the temperature of the soil may be 

 rendered lower by springs which bring down cold from above. 

 In this case, the mean temperature of the air will be higher 

 than that of the earth. The severe climate of certain mountain- 

 valleys may perhaps proceed from this. In like manner, as the 

 highest mountains on our globe are situated for the most part 

 in low latitudes, it is to be expected that the temperature of the 

 earth would there be lower than the mean temperature of the 

 air, rather than in high latitudes. Thus the hypothesis of a 



• Poggendjrff's Annalen. vol. xv. pp. 190 and 183. 



