CHAPTEE VII. 



AIR TEMPERATURE. 



The most recent definition of heat is that 

 it is a mode of motion; not movement of a 

 mass of substance, but movement of its ulti- 

 mate particles. It has been determined by 

 experiment that the ability of any substance 

 to absorb heat depends upon the number of 

 atoms it contains, rather than its bulk or its 

 weight. 



It has also been stated that the atmosphere 

 at sea-level weighs about fifteen pounds to the 

 square inch, which means that a column of 

 air one inch square extending from sea-level 

 upward to the extreme limit of the atmosphere 

 weighs fifteen pounds. The density of the air 

 decreases as we ascend. Each successive 

 layer, as we ascend, is more and more ex- 

 panded, and consequently has a less and less 

 number of air molecules in a given space. 

 Therefore the capacity of the air for holding 

 heat decreases as we go higher. 



We deduce from these facts that the higher 

 we go the colder it becomes; and this we find 

 to be the case. Whoever has ascended a high 



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