and on the Absorption of Gases hy Water. 259 



an inconsiderable depth, as that is a depth to which the influence 

 of the external air penetrates, will naturally exhibit no constant 

 temperature. The depth, however, at which the temperature of 

 the earth begins to be constant, cannot be the same at all parts 

 of the earth, as it is evidently a function of the extent of the 

 thermometrical variations of the temperature of the air of the 

 place ; the smaller this extent, the smaller the depth, and the 

 teversc. Hence this depth will be greater in low latitudes than 

 in high ones. Thus Boussingault* found, that, in the Tropics, 

 between the 11th degree north and 5th south latitude, this depth 

 amounted to hardly one foot, as the thermometer, when sunk in 

 a covered hole 8 to 12 inches deep, did not vary at all, or o<ily, 

 at ff)Ost, a few tenths of a degree. On the other hand, Arago 

 found, that, at Paris, at a depth of 25 feet, the thermometer 

 was still not constant. D'Aubuisson fixes this depth at between 

 46 and 61 feet, and Kupffer at 77 beneath the surface. In the 

 northern part of Siberia,f this depth seems to extend beyond 90 

 feet, as even at that depth the soil was found to be frozen. Ac- 

 cording to these observations, it would appear that the depth at 

 which the carbonic acid gas joins the water canals at Meinberg, 

 must be about 50 feet beneath the surface.;): 



It is also in favour of the formation of this mineral spring at 

 so inconsiderable a depth, that the carbonic acid gas which is 

 disengaged possesses a much greater power of expansion than 

 any gaseous exhalation does from the many mineral springs which 



• Annal. de Chim. et de Phys. t. lili. p. 225. 



+ Annalen der Physik und Chemie, vol. xxviii. p. 631. Poggendorff's 

 Annal. vol. xxxii. 



X It is nevertheless to be remarked, that even the temperature of wells, 

 which constantly exceeds the mean of the place, can yet shew, during the 

 year, some variations, and can follow the course of the temperature of the 

 external air. Thus the mean temperature of a sail spring at tVerl, in West- 

 phalia, deduced from twelvemonths' observations, is 9°6743 R.,the maximum 

 in July 10°32, the minimum in December 9°. However, we must assume 

 that this salt spring comes from a depth where a temperature exceeding the 

 mean of the air prevails ; for this at Werl is between 7° and 8° R. Water, 

 therefore, can penetrate so far without losing entirely the temperature it 

 brings with it from without. Since, however, the mean temperature of the 

 Meinberg mineral spring is pretty nearly the mean of common springs of the 

 place, or the corresponding mean of Meinberg, the water of this mineral 

 spring cannot reach the place where the increase of the temperature of the 

 interior of the earth commences. 



