M. Kupffer on Iso-geothermal Lines. 

 1829. 



251 



Art. XII. — On Iso-geothermal Lines, or the distribution of 

 the Mean Temperature of the Ground, By M. Kupffer 

 of Casan. 



In the year 1819, when Dr Brewster was occupied with the 

 inquiries respecting the mean temperature of the earth, of 

 which he has published an account in the Edinburgh Trans- 

 actions, vol. ix. p. 201, he was led to a very extensive compa- 

 rison of the temperature of springs with that of the tempera- 

 ture of the air, and he concluded, from this comparison, " that 

 there is a particular isothermal line, which in Europe is near- 

 ly that which passes through Berlin, at which the tempera- 

 ture of springs and that of the atmosphere coincide ; that, as 

 we approach the arctic circle, the temperature of springs is 

 always higher than that of the air, while in approaching the 

 equator it is always lower."*' Notwithstanding this curious dif- 

 ference, he found that the lines which represent the one are 

 always parallel to the lines which represent the other, that is, 

 to use the technical terms of Humboldt and Kupffer, the I so- 



