Hot and Thermal Springs. 333 



3. The capacity of heat of the strata. 



If the earth be very much cleft, as is the case with the chalk, 

 rocks, and if the fissures be of considerable width, the tempera- 

 ture of the percolating waters will be little altered ; if, on the 

 other hand, the clefts be few and inconsiderable, or the soil be 

 composed of an earth, such as sand, which easily allows the pas- 

 sage of water through it, that temperature will be considerably 

 modified.* 



In order to have an idea of the probable effect in one of these 

 cases, I made the following experiments : — 



I allowed water to filter through a bell glass 14 inches high 

 and 4.75 inches in diameter, filled with fine sand of the lignite 

 formation. The temperature of the water which was poured 

 upon the sand, and which filtered through it, as well as the tem- 

 perature of the sand itself, was observed from time to time, be- 

 fore and during the experiment, with very sensitive and per- 

 fectly harmonizing thermometers ; and the following results were 

 obtained : — 



First Series of Experiments vsith Sand moderately Damp. 



Time — 4 12 18 20 27 32 34 47 62 m 



Water 70°.'25 76°.55 — 76M0 75°.65 _ 75''.20 — 73°.85 72°.27 

 Sand 40 .35 — 60 .57 63 .95 67 .77 69°.8 _ 71°.37 71 .60 71 .37 



filtered [• _ _ — _ 63.27 61.92 — 62.1562.8263.27 

 through J 



The temperature of the air during the experiment remained 

 at 61°.25, and 6.75 lb. (of 16 oz.) of water were filtered through. 



Second Series of Experiments with Sand thoroughly wetted with Water. 

 Time — 3 11 15 19 25 28 33 36 '41 45 m 

 Water 74°.75 76°.32 75».87 75°.65 75°.20 74°.97 74°. 75 74°.52 74° -30 73°.85 73°.62 

 Sand 63 .72 _ 64 .17 64 .85 67 .10 69 .35 70 .70 71 .60 72 .50 72 .50 72 .50 



Water"* 



filtered {-63 .27 63 .50 63 .95 63 .72 63 .50 63 .61 63 .95 63 .95 64 .85 63 .97 65 .10 



through J 



The temperature of the air during the experiment fluctuated 



* Thus it has been found, that, in the chalk rocks, even thermal springs 

 may bear signs of the influence of the external temperature ; as, for example, 

 the salt springs at Werl, mentioned in the preceding chapter. On the other 

 hand, in a sandj soil, where the meteoric waters are very much divided, and 

 come in close contact with the particles of sand, the influence of the external 

 temperature is no longer perceptible, at a very moderate depth. For this 

 reason, springs rising through sand shew such small variations of temperature ; 

 as is the case with the springs in the neighbourhood of Berlin and Potsdam. 



