110 



It is an error that generally prevails under the 

 tropics, to consider grain as plants which dege- 

 nerate in advancing toward the Equator ; and 

 to believe, that the harvests are more abundant 

 in the northern climates. Since calculations 

 have been made on the progress of agriculture 

 in the different zones, and the temperatures 

 under the influence of which corn will flourish, 

 it has been found, that, beyond the latitude of 

 45°, the produce of wheat is no where so consi- 

 derable, as on the northern coasts of Africa, and 

 on the table-lands of New Grenada, Peru, and 

 Mexico. Without comparing the mean tempe- 

 rature of the whole year, but only the mean 

 temperature of the season which embraces the 

 cycle of vegetation of corn, we find for three 

 months of summer* in the north of Europe, from 



* The mean heat of the summers of Scotland in the environs 

 of Edinburgh, lat. 56°, is found again on the table-lands of 

 New Grenada, so rich in wheat, at 1400 toises of elevation, 

 and at 4° of latitude. On the other hand, we find the mean 

 temperature of the valleys of Aragua, lat. 10° 13 7 , and of all 

 the plains that are not very elevated in the torrid zone, in 

 the summer temperature of Naples and Sicily, lat. 89° to 40°, 

 These numbers indicate the situation of the isotheric lines 

 (lines of the same summer heat), and not that of the iso^ 

 thermal lines (those of equal annual temperature). Consider- 

 ing the quantity of heat received on the same spot of the 

 Globe during a whole year, the mean temperatures of the 

 valleys of Aragua^ and the table-lands of New Grenada, of 

 300 and 1400 toises of elevation, correspond to the mean 



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