294 Prof. Bischof on the Temperature of 



below, under a pressure sufficient to force it to the surface, the 

 temperature of the well cannot be the same as that of the rock 

 at the bottom. And even if the lowest point of the course of 

 such a spring were exactly on the same level as the bottom of 

 the well, yet it could only assume the temperature of the sur- 

 rounding rock, in case it should have remained long in contact 

 ■with it. This may, with probability, be supposed to be the 

 case, when the temperature of the spring is constant. How- 

 ever, it may also take place, even though its temperature be 

 variable, if its variations follow late after those of the air. So 

 that the later in the year a spring reaches its maximum tempe- 

 rature, the more likely it is to shew the true temperature of the 

 lowest point of its course. 



On the contrary, springs whose variations of temperature 

 take place nearly or exactly at the same time as those of the 

 atmosphere, will not give the real temperature of the lowest 

 point of their course. Thus, the salt-springs of Werl can 

 hardly be expected to shew the real temperature of the low- 

 est point of their course, as'their variations of temperature 

 correspond almost exactly with those of the air. * 



Spasky and Kupflf'er calculated, from the observations on the 

 temperature of the artesian wells at Vienna, f an increase of 

 temperature of 1° R. or 2°.25 jin 88—5.5 and 83— 1.5 feet. 

 KupfFer foimd the same at 80 — 11.9 and 74.7.2 feet from those 

 of Rochelle and Epinay. \ From Mr Griffith''s § observations 

 on the temperature of two springs encountered at difiFerent 

 depths, it was calculated at 490.3 feet. 



So rapid an increase of temperature gives room for the con- 

 jecture, that the depths of all these wells are not equal to the 

 lowest point of the course of the springs, but that the springs 

 rise from a still greater depth. 



* These thermal springs indicate the immediate influence of the external 

 temperature, which is certainly not communicated through the earth. Their 

 yearly mean temperature, however, coincides nearly with the temperature of 

 the earth at the lowest point of their course. In so far it might otiter a nu- 

 merical element for the calculation of the increase of temperature with the 

 depth, provided the well were as deep as the lowest point of the spring's 

 course. 



+ Baumgartner Journ. fur Phys. und Mathem., vol. viiL No. 3. 



X Journ. de Geologic. 1830. Vol. i. p. 8D. § Ibidem, p. 87. 



