336 Piof. BischofF on the Temperature of 



ations of temperature, when meteoric waters only filter to the 

 depth of fourteen inches, and then immediately rise again as 

 springs. It is evident that the influence of the temperature of 

 the meteoric waters on that of springs must decrease in pro- 

 portion to the depth to which they filter into the earth. If the 

 quantity of water absorbed by a certain surface, during a cer- 

 tain period of time, and farther, the depth to which it sinks, the 

 capacity of heat of the soil, and the mean difference between the 

 temperature of the meteoric waters and the strata which receive 

 them, be known, the variations of temperature caused in the 

 earth's crust by the meteoric waters, during a certain period, 

 may be calculated from those data. For these variations of 

 temperature, which take place after a certain length of time, are 

 the same which would ensue, if the whole quantity of water 

 were to sink to the given depth into the earth in a moment. 

 Since the scale of the yearly variations in the temperature of 

 springs evidently depends on the depth from which they rise, 

 this depth may be learned from a knowledge of that scale. 

 Supposing that springs issue with the temperature of the lowest 

 point to which the meteoric waters have sunk, the depth at which 

 the same scale of variations of temperature prevails, as that of 

 a certain spring, may be found by observing the temperature of 

 the earth, at different depths, in the vicinity of that spring. 

 Thus, for example, a thermometer in the Gopel shaft of the 

 Trappe coal-mine, near Welter, in the Grafschqft Mark, gave 

 only 0°.83 as the greatest difference of temperature, at a depth 

 of 26.5 feet,* from which the origin of a neighbouring spring, 

 having the same scale of variation of temperature, may be easily 

 deduced. And such a deduction will, in most cases, be very 

 near the truth ; for meteoric waters^ filtering in fine drops 

 through the earth, and through the narrow fissures and clefts 

 in the rocks, assume the surrounding temperature the more 

 nearly the deeper they sink. But if, on reaching the lowest 

 point of their course, they unite themselves with another more 

 or less abundant spring, and are brought to the surface by an 

 impervious stratum, or by hydrostatic pressure, the change 

 thereby operated on their temperature will be the less consider- 



• Poggendorff's Annal. xxii. p. 620, table. 



