188 THE CHEMISTRY OF CREATION. 



below freezing point, so as to insure its not 

 melting, we should find in a little while that all 

 the ice had disappeared; the reason would be, 

 that it had evaporated away. From this we may 

 learn, that if the atmospheric pressure were 

 removed, not only would liquids evaporate, but, 

 in all probability, many solids also. From all 

 these considerations, we may learn the wisdom 

 and beautiful adaptation to existing circumstances, 

 exhibited even in the apparently less important 

 particular of atmospheric pressure. 



There is yet another circumstance to be 

 noticed in reference to the physical constitution 

 of the atmosphere, and that is, the temperature 

 of its higher regions. It has been mentioned 

 that in proportion as we rise from the earth, the 

 density of the air becomes continually less and 

 less. The balloon of the aeronaut, after rising 

 to a certain height, can rise no longer. It then 

 remains stationary, for above it the air is so 

 thin as to be unable to support it, with its car 

 and weights, even in spite of its buoyant con- 

 tents of hydrogen gas. This effect is due to 

 the elasticity of the air. In proportion as 

 the pressure on its particles diminishes, their 

 tendency is to separate farther and farther from 

 each other ; or, in other words, the air expands. 

 By calculation it has been found that this ex- 

 pansion of the air, as we ascend takes place in 



