Hot and Thermal Springs. 335 



through, as a cylinder having a base equal to this area, wc shall 

 find the height of the column for the first series of experiments 

 = 10,3 inches ; second = 8,58 inches ; third 10,68 inches. 



But the quantities of water used in the above experiments, 

 were, in each series, greater than the yearly fall of rain at Cvr- 

 mana, which, according to Humboldt, only amounted to from 

 seven to eight inches ; and, as on sloping ground, however po- 

 rous * it may be, only a small proportion of the rain-water soaks 

 in, perhaps hardly two of those seven or eight inches actually 

 penetrate into the earth. Admitting the probability of this 

 supposition, scarcely one quarter of the quantity of water made 

 to sink through the sand in one hour, in each of the above ex- 

 periments, is absorbed in a whole year by the soil of Cumana. 

 These considerations are already sufficient to shew, that at Cur 

 mana, where it very seldom rains, the temperature of the me- 

 teoric waters can have no sensible influence on the temperature 

 of the springs.f 



The quantity of meteoric water which sinks into the earth, 

 and serves to feed the springs, may be calculated from the 

 quantity of water they yield. I have undertaken this calcula- 

 tion for a district where copious springs are abundant. It com- 

 prises a part of the volcanic group in the vicinity of the Laa.- 

 cker See. I found the district drained by a brook, which re- 

 ceives the waters of all these springs, to measure 668,539,072 

 square feet : and, according to a measurement, made at a time 

 when it had not rained for some days, the rivulet supplies 16,25 

 cubic Rhenish feet of water per second, or 512,460,000 cubic 

 feet+ per annum From this we learn that only 0,9 feet of 

 the yearly fall of meteoric waters on the district drained by this 

 brook filters nito the earth, and serves for the production of 



springs. 



The results of the above series of experiments, shew the vari- 



* Voyages iii. 371, xi. 19. 



t In the Corderillas, one may sometimes wander for hundreds of miles 

 without meeting with a spring; and it is impossible that such rare springs 

 should have a temperature lower than that of the air. 



+ This value should have been taken somewhat higher, because the re- 

 evlporation of the water during its course was not taken into account in our 

 calculation. 



