M. KupfFer on Iso-geothermal Lines. '^155 



From these tables M. KupfFer draws the following conclu- 

 sions : — 



1. The temperature of the air, and the mean temperature 

 of the ground, are not the same under the same parallel. If 

 we make the lines pass through those points where the tem- 

 perature of the ground is the same, those lines which may be 

 called Iso-geothermal^ have been hitherto synonymous with the 

 isothermal lines. 



2. The temperature of the ground, as well as that of the 

 air, decreases as the latitude increases. This decrease is more 

 rapid as we approach the parallel of 45% and at greater lati- 

 tudes it decreases more slowly. This circumstance explains 

 why in low latitudes the temperature of the ground is inferior 

 to that of the air. For the same reason in mean latitudes the 

 temperature of the ground reaches that of the air, and rises 

 above it in higher latitudes. 



3. M. Kupffer states, that we may represent the relation be- 

 tween the latitude and the temperature of the ground, by the 

 formula, a — 6, Sin. Z = ^, in which I is the latitude, t the cor- 

 responding temperature, and a and b constant quantities to be 

 determined for each meridian. Having determined these co- 

 efficients, he finds, that the observed and calculated tempera- 

 tures agree pretty well, except for Cumana, Teneriffe, Ko- 

 liigsberg, and Umeo, places upon which local circumstances 

 appear to impress an anomalous character. 



It must not be forgotten that this formula gives only ap- 

 proximations, and that it may give false results for points too 

 remote from those where the observations have been made. 

 Among these points are the poles, for which the four equa- 

 tions ought to give the same value, which is not the case. It 



