^6 M. Kupffer on Iso-gcothermal Lines. 



may be presumed, that the minima of the temperature of the 

 ground meet in the neighbourhood of the pole, but this is what 

 the formula cannot indicate, since it gives the greatest value of 

 t when Z = o, and the smallest when I ::= 90°. 



The iso-geothermal line of 0°, approaching greatly to the 

 north pole under the first meridian, and even reaching it, — if 

 we admit the result of the formula in this case, it follows, that 

 the space terminated by this line is marked in this place with 

 a great break, and appears to separate into two portions, of 

 which the central points may he considered as two poles of cold 

 for the gro7ind. One of these poles will probably be in North 

 Arnerictty and the other in the North of Siberia. Unfortu- 

 nately observations are wanting for these regions. The tem- 

 perature of these poles cannot be much below 0°. 



With regard to the temperature of the ground under the 

 equator, it is obviously lower at points situated on the coast, 

 or in the islands, than at those which are in the interior of a 

 great continent. The warmest part is in the interior of Africa. 

 To the north of this point, at least in latitudes which do not 

 exceed 50°, the iso-geothermal lines take a great bend to the 

 north. The point of the equator situated at 60° of longitude, 

 has a lower temperature by 1°|. We find nearly the same 

 depression for the nearest points of Teneriffe and Cumana. It 

 may hence be presumed, that the coldest point of the equator 

 is between 60 and 80° of west longitude in the Atlantic Ocean. 

 Setting out from this point, the temperature of the ground in- 

 creases rapidly from east to west. It may be said of the 

 equator, as of the poles, that the formula is not applicable to it. 



With regard to the more elevated temperatures of the 

 ground which are observed in the latitudes of the second me- 

 ridian, we have only conjectures to propose. The phenome- 

 non may be explained in the vicinity of the equator, by the 

 heat of the sandy deserts ; but this cause could have no influ- 

 ence under higher latitudes. We may perhaps seek for it in the 

 volcanic condition of the earth under this meridian. We there 

 find, indeed, two active volcanoes, Vesuvius and Mtna. Ger- 

 many is covered with basaltic and other volcanic formations. A 

 multitude of springs, more or less warm, attest the high tern- 



