Hot and Thermal Springs. 293 



From the above observations we find that from 106 — 6.9 feet 

 (to which depth the temperature remains constant at 51°.68) 

 to 724 — 8.6 feet deep, the temperature increases in direct pro- 

 portion to the depth, and that the increase of depth correspond- 

 ing to each additional degree of Reaumur is 122 — 2.8 feet. 

 There is no doubt that this regularity in the increase of tem- 

 perature is owing to the place of observation being perfectly free 

 from all causes of disturbance. As former observations in other 

 places have generally shewn great irregularities in the increase 

 of temperature, it is probable that they have been influenced 

 by accidental circumstances. 



The lowest degree observed, 50°.9, still exceeds by 1°.35. the 

 mean temperature of Geneva (49°.5.5). De la Rive and Mar- 

 cet are of opinion that they would have found this last in a 

 depth of 42 — 7.6 to 53 — 3.5 feet, if they had been able to pene- 

 trate into the rock itself. They think that the higher tempe- 

 rature of the water in the upper part of the well must be 

 ascribed to currents of water which brought up heat from be- 

 low, and which seemed probable from the clearness of the above. 

 The influence can, however, only have extended to the first 

 106—6.9 feet. 



Chap. XX. — Can the Progression of the Increase of Temperature to- 

 wards the centre of the Earth he with certainty deduced from the 

 Temperature of Artesian Springs, and the depth from which they 

 rise ? 



Arago long ago declared that artesian wells were peculiarly 

 adapted to the determination of the rate of increase of tempera- 

 ture in the earth. More lately Spasky * and Kupff'er t have 

 endeavoured to calculate that rate from existing observations. 



In order that such a calculation should yield accurate results, 

 it is necessary that the following conditions should take place : 

 — 1st, That the spring should not rise from below the place of 

 its first appearance in the well ; and, 2d, That it should also 

 have exactly the temperature of the lowest point of the well. 



If the well have been sunk to within a short distance of an 

 impervious stratum, the first condition will easily be fulfilled. 

 But if it happen to have encountered a spring, coming from 



* Poggend, Annal. vol. xxxi. p. 3G5. f Ibid. voL xxxii. p. 284 



