TEMPERATURE OF SPRING-WATER. 51 



fertility to some parts of their land, surrounded as 

 it is by sandy deserts ; and this they accomplish 

 by watering it from springs which they have 

 opened and conducted underground from distant 

 heights. 



Since the ground is a very bad conductor of 

 heat, the water can take but very slowly the tem- 

 perature of the strata with which it is in contact. 

 The amount of heat, which it has when en- 

 tering the earth, or which it acquires by its 

 intimate mixture with loose soils, the length and 

 depth of the natural channels through which it 

 finds its way, and lastly the time it has remained 

 in the lower strata, have for this reason consider- 

 able influence on the temperature of the springs. 

 From this you will understand at once, that you 

 can draw no sure inference, from the temperature 

 of a spring, as to that of the stratum from which it 

 rises. Thus on the slopes of high mountains, espe- 

 cially of such as are covered with perpetual snow, we 

 very often meet with cold springs which are doubt- 

 less in connection with reservoirs at higher levels, 

 to which they owe their low temperature. 



On the other hand we must suppose that well- 

 water, rising from water-veins or basins at a 

 great depth underground, will bring up with it 

 a temperature higher than the mean of the soil at 

 the welTs mouth ; and that its excess above this will 

 be the greater, the greater the depth from which it 



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