AIR AND WATER 



25 



amount that the air can contain at that temperature. For 

 example, a cubic meter of air at 16 centigrade (60.8 F.) 

 might contain 13.50 grams of water. If we tiiul that it actu- 

 ally does contain 6.75 grams (absolute humidity), it has 

 one half, or 50 per cent (relative humidity), of the amount 

 of water it might contain when fully saturated. 



The relative humidity of the air over the surface of the 

 earth varies widely. As an average the relative humidity 

 over the land is about 60 per cent, and over the ocean it is 

 about 85 per cent. But variations from these averages are 

 so great that the averages do not tell us much about any 

 given day or given locality. If the relative humidity is low, 

 we say the air is dry; if the relative humidity is high, we 

 say the air is moist, or " muggy." 



