268 M. Kupffer on Iso-geothermal Lines- 



The relation wliich appears to exist between the more north- 

 ern iso-geothermal lines and the limit of the polar ices deserves 

 also to fix our attention. The line of 0° (32° Fahr.) is a lit- 

 tle to the south of the limits of the ice, excepting towards Green- 

 land ; but we know that this country was not formerly sur- 

 rounded with ice as it is at present. Besides, the temperature 

 of the ground can only act upon masses of ice which descend 

 to a certain depth ; but those which are found in the terra 

 Jirma cannot be in this predicament, and it becomes easy to 

 explain in this way the influence of a continent such as Green- 

 land, on the limits of the polar ices. The removal of the ice 

 to the south west, which Mr Scoresby has so well observed 

 on the east coast of Greenland, demonstrates the existence of 

 poles of cold in the North of America, and particularly in 

 Greenland; at least I do not know how we can otherwise ex- 

 plain a phenomenon so contrary to our ordinary ideas of the 

 distribution of temperature on the surface of the globe. It is 

 evident that if the coldest point of the polar sea coincided 

 with the pole, the coldest waters would form in the depths of 

 the sea a current from north to south, while the warmest 

 would transport themselves to the surface from south to north. 

 Modified by the rotation of the earth, the first of these cur- 

 rents would take a south-west direction, and the second a 

 north-east direction, and as it is the superficial waters which 

 transport the icebergs, this transport ought to take place in a 

 north-west direction in place of the very opposite direction 

 which it actually takes. But if the coldest point of this re- 

 gion is at some distance from the pole, the surface current 

 ought to direct itself to the south, or rather to the south-west, 

 on account of the earth's rotation. We shall yet find, I think, 

 a close relation between the phenomenon of currents in the 

 sea, and the distribution of the temperature of the ground. 



But this distribution of temperature appears also to have a 

 great influence on the distribution of the intensiti/ of terrestrial 

 magnetism. This would no doubt be the case, if it is true, 

 as I have tried to show in another memoir, that terrestrial 

 magnetism resides at the surface of the globe. We have here 

 the choice between two hypotheses ; either the earth should be 

 considered as a magnet existing by itself, and then the inten- 



