64 future's 



long as the temperature remains unchanged. 

 If its temperature rises the process of evapo- 

 ration can start up, because the capacity of the 

 air for holding moisture has been increased. 

 But if a temperature is perceptibly lowered 

 another phenomenon will manifest itself. 



In the uncondensed state vaporized moisture 

 is quite transparent, so that we are able to 

 see through it as we do through a pane of 

 glass. If, however, the body of air that is 

 saturated with this invisible moisture becomes 

 suddenly chilled, the moisture condenses into 

 cloud or mist. 



If we watch a passing railroad train we shall 

 notice a mass of fleecy white mist floating 

 away from the smokestack, assuming the bil- 

 lowy forms of some of the clouds in summer. 

 This cloud is produced by the sudden conden- 

 sation of steam, which was transparent before 

 it came in contact with the cold, outside air, 

 the effect being much more pronounced in cold 

 than in warm weather. We may liken these 

 floating globules of mist to the dust of the 

 earth which floats in the air, and it has not 

 been inaptly called water-dust. Anyone who 

 has seen an atomizer used or has stood at the 

 foot of a great waterfall, like Niagara, has 

 seen the fluid so finely divided that it will float 

 in the air, instead of falling to the ground. 

 What takes place is that a number of these 

 transparent atoms of moisture that are re- 



