THERMAL SPRINGS. 187 



largo inland seas, the Caspian and Aral Sea, in the narrow 

 Ust-Urt, which separates them from each other. In order, 

 however, to clear up such complicated phenomena, the only 

 means to be employed are such as borings of great depth, 

 which lead directly to the knowledge of the internal heat of 

 the earth, and not merely observations of springs, or of the 

 temperature of the air in caves, which give just as uncertain 

 results as the air in the galleries and chambers of mines. 



When a, low plain is compared with a mountain chain or 

 plateau, rising boldly to a height of many thousand feet, the 

 law of the increase and diminution of temperature does not 

 depend simply upon the relative vertical elevation of two 

 points on the earth's surface (in the plain and on the sum- 

 mit of the mountain). If we should calculate from the sup- 

 position of a definite proportion in the change of tempera- 

 ture in a certain number of feet from the plain upward to 

 the summit, or from the summit downward to the stratum 

 in the interior of the mountain mass which lies at the same 

 level as the surface of the plain, we should in the one case 

 find the summit too cold, and in the other the stratum in 

 the interior of the mountain far too hot. The distribution 

 of heat in a gradually sloping mountain (an undulation of 

 the surface of the earth) is dependent, as has already been 

 remarked, upon form, mass, and conductibility ; upon inso- 

 lation, and radiation of heat toward the clear or cloudy 

 strata of the atmosphere ; and upon the contact and play of 

 the ascending and descending currents of air. According 

 to such assumptions, mountain springs must be very abund- 

 ant, even at very moderate elevations of four or five thou- 

 sand feet, where the temperature would exceed the average 

 temperature of the locality by 72 or 90 degrees; and how 

 would it be at the foot of mountains under the tropics, 

 which at an elevation of 14,900 feet are still free from per- 

 petual snow, and often exhibit no volcanic rock, but only 

 gneiss and mica schist!* The great mathematician, Fou- 

 rier, who had been much interested in the fact of the vol- 

 cano of Jorullo having been upheaved, in a plain where for 

 many thousands of square miles around no unusual terres- 

 trial heat was to be detected, occupied himself, at my re- 



* I differ here from tho opinion of one of my best friends, a phys- 

 icist who has done excellent service as regards the distribution of tel- 

 luric heat. See, "upon the cause of the hot springs of Leuck and 

 Warmbrum," Bischof, Lchrbuch der Chemischen und Physikalischen Ge- 

 ologie, bd. i., s. 127-133. 



