CHARGE OF MOISTURE. 215 



of its moisture. Many substances — for instance, 

 burnt lime — have this property in so high a degree 

 that they can be made use of to dry the air com- 

 pletely. With the greatest number of bodies, and 

 among these, with plants, the power of sucking up 

 this water adjusts itself to the relative condition 

 as to moisture, or to the degree of water-charge 

 of the air. In very moist air, and this whatever 

 the temperature may be, such substances take up 

 the greatest amount of water that their peculiar 

 property will allow at the given temperature, — they 

 become fully charged with moisture. If the 

 moistness of the air is removed from the point of 

 full charge, the bodies that are in it lose some of 

 the water which they contain ; they begin to be- 

 come dry, and this goes on until the power with 

 which they absorb moisture — a power which, in all 

 bodies, is the more active the more the store of 

 water which they have condensed from the air is 

 lessened — is balanced by the tendency, of the 

 water which they still retain, to evaporate. 



If, for instance^ the air contains three-quarters 

 of its possible water-charge, any bodies around 

 which it plays will keep more water condensed 

 than when the air is only half charged- Only in 

 very dry air, and that whether its temperature be 

 high or low, all the water which a body has taken 

 up will be drawn off from it. 



Atmospheric air, which in a warm day seems 



