266 



SCIENCE OF AGRICULTURE. 



Part II. 



upon the whole, to vegetation than the colder, and that nearly in proportion to their 

 distance from the equator. The same plants, however, will grow in the same degree of 

 latitude, throughout all degrees of longitude, and also in correspondent latitudes on dif- 

 ferent sides of the equator ; the same species of plants, as some of the palms and others, 

 being found in Japan, India, Arabia, the West Indies, and part of South America, 

 which are all in nearly the same latitudes ; and the same species being also found in 

 Kamschatka, Germany, Great Britain, and the coast of Labrador, which are all also in 

 nearly the same latitudes. (fVilldenow, p. 374.) 



1730. Rules for determining the temperature of a country. *' The fact that a degree of 

 latitude is equal to a degree of Fahrenheit, and that 400 feet of elevation is equal also to 

 a degree of Fahrenheit, is original and curious, and will go far to assist us in determining 

 the clime of any country." {Amer. Quart. Rev. March, 1829. p. 174.) 



1 731 . The most remarkable circumstances respecting the temperature in the three zones are 

 exhibited in the following Table by Humboldt. The temperature is taken according to 

 the centigrade thermometer. The fathom is 6 French feet, or 6 '39453 English feet. 



1732. Elevation, or the height of the soil above the level of the sea, determines, in a 

 very marked manner, the habitation of plants. The temperature lessens in regular gra- 

 dation, in the same manner as it does in receding from the equator, and 600 feet of 

 elevation, Humboldt states, are deemed equal to one degree of latitude, and occasion a 

 diminution of temperature equal to 23 of Fahrenheit ; 300 feet being nearly equal to 

 half a degree. Mountains 1000 fathoms in height, at 46 of latitude, have the mean 

 temperature of Lapland ; mountains of the same height between the tropics enjoy the 

 temperature of Sicily ; and the summits of the lofty mountains of the Andes, even where 

 situated almost directly under the equator, are covered with snow as eternal as that of the 

 north pole. The highest land in Scotland where corn has been found to attain maturity 

 in favourable seasons is said to be at the mining ground on Lead Hills. (See General 

 Reports of Scotland, chap. Climate.) 



1733. Hence it is that plants of high latitudes live on the mountains of such as are much 

 lower, and thus the plants of Greenland and Lapland are found on tlie Alps and Pyrenees. 

 At the foot of Mount Ararat, Tournefort met with plants peculiar to Armenia ; above 

 these he met with plants which are found also in France ; at a still greater height he 

 foundhimself surrounded with, such as grow in Sweden; and at the summit with such 

 as vegetate in the polar regions. This accounts for the great variety of plants which are 



