156 TKE WORLD. 



culiar climate where it thrives best, and beyond certain limits il 

 ceases to exist. The successive zones of vegetation, as we recede 

 from the equatorial regions, have sometimes been supposed to be 

 represented by the different altitudes upon the mountains under 

 the equator, as it is evident we have in ascending fro in the valleys 

 to their snow-capped summits, every variety of temperature. 

 The analogy fails however in one essential point, for as we ascend 

 the mountains the pressure of the atmosphere is continually di- 

 minished and it is evident that less nutriment is thus afforded for 

 the growth of the plant. The influence which the variations of 

 climate alluded to, must have upon vegetation is very evident, 

 thus in many parts of Siberia, wheat and rye are raised upon a 

 soil which is constantly frozen at a depth of three feet, while in 

 Iceland, where the mean temperature of the year is much warm- 

 er, and the winter's cold but inconsiderable, it is not possible to 

 raise any of the ceralia or common grains, as the low summer 

 temperature does not suffer them to ripen. It is for the same 

 reason that the vine does not flourish in England, for although 

 it can endure a tolerably great degree of cold, yet it requires a 

 hot summer to make the fruit ripen, and yield a drinkable wine. 

 There is no subject connected with meteorology which requires a 

 more careful, and studied investigation than that of climates. 

 So many causes influence the temperature of the air, and some 

 of them are so variable, that no labor short of a well conducted 

 series of observations, extending through a long course of years 

 can give a satisfactory result. In the brief account we have given, 

 we have been able to present little else than the leading facts, 

 and must refer the reader to the writings of Leslie, De Candolle, 

 Mirbel, and Humbolt, for further information. 



