CHAPTER X. 



WIND WHY IT BLOWS. 



We have said that globules of moisture, re- 

 leased by the action of the sun's rays in the 

 process of evaporation, tend to rise because 

 they are lighter than the air. Right here let it 

 be said that all material substances have 

 weight; even hydrogen, the lightest known 

 gas, has weight, and is attracted by gravita- 

 tion. If there were no air or other gaseous 

 substances on the face of the earth except hy- 

 drogen, it would be attracted to and envelop 

 the earth the same as the air now does. Car- 

 bon dioxide is a gas that is heavier than the 

 air. If we take a vessel filled with this gas 

 and pour it into another vessel it will sink to 

 the bottom and displace the air contained in 

 it until the air is all driven out. If we fill a 

 jar with water up to a certain height and then 

 pour a pint of shot into it the water will be 

 caused to rise in the vessel because it has been 

 displaced at the bottom by the heavier ma- 

 terial. RTow if we remove the shot the water 



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