18 THE ATMOSPHERE. 



air contained in a receiver, is removed by an air pump, 

 the remaining one hundredth is immediately expanded so 

 as to occupy the space which was before occupied by the 

 whole. If a common Florence flask, while containing 

 nothing but air, be heated to a high degree, and then the 

 mouth immersed in water while it is suffered to cool, the 

 water will rise to occupy almost the whole contents of the 

 flask. 



Familiar examples might be adduced, almost without 

 number, to show the great capability airs possess, of being 

 expanded and compressed to an unlimited degree. 



And every kind of air possesses this property at all 

 temperatures. In this respect, gas differs from vapor, 

 which in other respects resemble each other. All vapors, 

 whether produced from liquids or solids, are, like air, 

 highly elastic, and capable of great expansion and com- 

 pression. But by lowering the temperature to which 

 they are exposed, the vapor again becomes a liquid, or 

 solid, when it loses its elasticity, and its compressibility. 

 While air retains both at all temperatures, and in all sit- 

 uations. 



This peculiar and highly interesting property of all 

 gases, gives to the atmosphere some of its most important 

 powers and uses. It is evidently essential to the exist- 

 ence of winds, and to every motion of the air, unless it 

 may be in a slight degree. It is from this property, that 

 the atmosphere so readily gives place to all other sub- 

 stances passing through it. Were it not for this, we 

 should be met with a powerful resistance, whenever we 

 attempted to move from place to place. This is the ori- 

 gin of the trade winds, occupying about sixty degrees of 

 the equatorial regions of the earth, blowing constantly 

 from east to west, of the monsoons blowing six months 

 of the year in one direction, and the other six months 

 directly opposite, of the deadly simoom, of land and sea 

 breezes, of the most variable and shortest currents of 

 air, of the gentle breeze, the brisk gale, the raging tem- 

 pest, the sweeping hurricane, the water spout, and the 

 tornado. It is by the great expansion and compression 

 of air, that ships are constantly moving from continent 



