498 
LIMITS OF THE &BOWTH OF COBH, 
bary and in Egypt, from 27° to 29°; within the tropics, 
between fourteen and three hundred toises of height, from 
14° to 25 5° of the centigrade thermometer. 
The fine harvests of Egypt and of Algiers, as well as 
those of the valleys of Aragua and the interior of the island 
of Cuba, sufficiently prove that the augmentation of heat is 
not prejudicial to the harvest of wheat and other alimentary 
grain, unless it be attended with an excess of drought or 
moisture. To this circumstance no doubt we must attri- 
bute the apparent anomalies sometimes observed within the 
tropics, in the lower limit of corn. We are astonished to 
see, eastward of the Havannah, in the famous district of 
Quatro Villas, that this limit descends almost to the level 
of the ocean ; whilst west of the Havannah, on the slope of 
the mountains of Mexico and Xalapa, at six hundred and 
seventy-sevon toises of height, the luxuriance of vegetation 
is such, that wheat does not form ears. At the beginning 
of the Spanish conquest, the corn of Europe was cultivated 
with success in several regions now supposed to be too hot, 
or too damp, for this branch of agriculture. The Spaniards 
on their first removal to America were little accustomed to 
live on maize. They still adhered to their European habits. 
They did not calculate whether corn would be less profitable 
than coffee or cotton. They tried seeds of every kind, 
making experiments the more boldly because their reason- 
ings were less founded on false theories. The province of 
Carthagena, crossed by the chain of the mountains Maria 
and G uamoco, produced wheat till the sixteenth century. 
In the province of Caracas, this culture is of very ancient 
date in the mountainous lands of Tocuyo, Quibor, and Bar- 
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° N. latitude. On 
the other hand, we find the mean temperature of the valleys of Aragua, 
lat. 10® 13', and of all the plains which are not very elevated in the torrid 
aone, in the summer temperature of Naples and Sicily, lat. 39° to 40° 
These figures indicate the situation of the isotheric lines (lines of the 
same summer heat), and not that of the isothermal lines ythose of equal 
annual temperature). Considering 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, at 300 and 1400 
toises of elevation, correspond to the mean temperatures of the coasts at 
23° and 45* of latitude. 
