Hot and Thermal Springs. 373 



lower temperature of the springs than of the air, may hold good 

 for several points in the mountainous parts of the torrid zone. 



On the contrary, the temperature of the soil will be raised if 

 the rocks be so fissured and cleft as to admit of the rising of 

 thermal springs. If such waters rise in considerable quantities, 

 and with a great heat, they may cause the temperature of the 

 earth to rise perceptibly above the mean temperature of the air. 

 Thus, the temperature of the soil at Aachen and 13urtscheid, 

 where waters of 90° to 112°.5 higher than the mean temperature 

 of the air spring up in large quantities, is probably higher than 

 that mean. The same may be expected at Paderborn, where, 

 according to my measurements, more than a million pounds of 

 water are ejected in a minute by all the Padersprings together, 

 which are 6°.75 warmer than the mean temperature of the air. 

 The earth's crust being cleft to a great depth, and thus allow- 

 ing warm springs to rise, may therefore cause an elevation of 

 the temperature of the soil. 



But the temperatures of the soil and of the air must by no 

 means be invariably considered as identical. Copious springs, 

 heated to any degree above or below the mean temperature of 

 the air, and rising in great numbers, communicate ;their tem- 

 perature to the strata through which they flow. Single and 

 scantily supplied springs can, however, cause but trifling alter- 

 ations. The above mentioned springs in the Teverone valley, 

 between Tivoli and Subiaco, whose temperature is only 47°.75 

 to ^^..''^.B^ and whose number is very great, although they yield 

 but little water, must certainly tend but slightly to cool the earth, 

 for in this valley all the products of middle Italy, as the vine 

 and the olive, flourish most luxuriantly. 



There is another phenomenon, which, although it is only 

 local, must not escape notice. It is well known that in certain 

 places there are cavities beneath the surface, in which there 

 is ice both in summer and winter. The mean temperature 

 of the ground in such caverns cannot be above 32°, whilst that of 

 the atmosphere may be much higher. This is not the place to 

 examine how such natural ice cellars are caused ; it is only neces- 

 sary for us to point out their frequent occurrence. 



VOL. XX. NO. XL. APRIL 1836. B b 



