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Tin: WORLD. 



perature produced. The heated portions of air distribute their 

 warmth throughout the great body of the atmosphere, and some- 

 times in the form of winds sweeping over colder regions of the 

 earth, moderate the rigor of the climate. 



Ascending from the earth we find the temperature of the air 

 constantly diminishes until we arrive at a region of frost, the 

 limit of which, is called the term of perpetual congelation. The 

 height of the term of congelation varies for every change of 

 latitude. In the following diagram taking A B, for the height of 



\ 



B 10 20 30 40 50 60 70 80 C 



perpetual congelation at the equator, and B C, for the line of lati- 

 tudes, then the decrease in the height of the term of congelation 

 from the equator to the poles, may be represented by the several 

 parallels bounded by the curved line A C. The region of per- 

 petual frost at the equator is at a height of 3 miles, at a distance 

 of 35 from the equator, about 2 miles, at 54 about 1 mile, at 

 80 very near the surface of the earth, and at 90 the surface of 

 the earth. It will be well to fix in the mind, the limits here as- 

 signed, as we shall often refer to this varying elevation in explain- 

 ing the phenomena of rain, hail and snow. The clouds almost 

 always float below the term of congelation. 



Although the temperature of the surrounding atmosphere is 



