Atmosphere and the Earth. 



249 



We see from these examples, 



1. That the temperature of the earth, as well as the mean 

 temperature of the air, is not the same on the same parallel. If 

 we draw hnes through all the points which have the same ter- 

 restrial temperature, these isogeothermal lines resemble the iso- 

 thermal, that they are parallel to the equator, but diverge from 

 it in several points. 



2. That the terrestrial temperature, as well as the mean tem- 

 perature of the air, decreases with the increase of the latitude, 

 but irregularly. The diminution of temperature from the equa- 

 tor to the poles, happens so much the quicker the nearer we ap- 

 proach the parallel of 4-5°. Beyond this, again, it decreases with 

 less rapidity. By this we may explain, why, in low latitudes, 

 it is less than the mean atmospheric temperature ; for the latter 

 decreases very little to Lat. 20^ The terrestrial temperature, 

 therefore, which is continually decreasing, must, in these lati- 

 tudes, be less, though, at the equator, it be as high as the mean 

 of the air. In middle latitudes, again, the terrestrial tempera- 

 ture again equals the mean of the air, as it does not decrease so 

 rapidly as the latter. In higher latitudes, for the same reason, 

 the terrestrial temperature finally exceeds the atmospheric. 



3. We may express the distribution of the terrestrial tempe- 

 rature, inidcr the same meridian, pretty well by the following 

 formula : 



n — h bin' l—t. 



