2 ' ' GENERAL SCIENCE 



York only about forty inches; at Denver seventy inches; at Lake 

 Superior twenty inches; and in southern Arizona about one hun- 

 dred inches. 



Water will not evaporate so quickly on some days as on others. 

 Though few can give the reason, we all know, from experience, 

 that there are " good " and " bad " days for drying clothes. We 

 are all aware of the fact. Some days the light wind steals the 

 moisture from the clothes with delightful rapidity; another time 

 they hang for hours without effect, for the air is so full of vapor 

 that it can receive no more, and the " drying " process is at a 

 standstill. 



A sponge or flannel cloth, or even a piece of sugar, will serve 

 as a good example. If any one of these is held over a basin of 

 water so that it just touches, it will soak up water until it can 

 hold no more. The air does the same, but receives the vapor 

 instead of soaking it up. In the examples given, the water is 

 drawn up by capillary attraction. A sponge or cloth or piece of 

 sugar can always take up a certain quantity of water and no more, 

 and always the same amount. Not so with the air. The amount 

 of moisture that the air can take up depends upon its temperature. 

 Warm air holds more moisture than cold air. 



To Show that Warm Air Holds More Moisture than Cold Air. Take a 

 large flask, and put into it just enough water to make a thin film on the 

 inside of the flask when shaken. Now warm the flask gently, never bringing 

 its temperature to the boiling point. When the water disappears from the 

 inside, tightly cork the flask and allow it to cool. 



Notice that when the flask is hot no moisture can be seen. 

 After the flask is corked no moisture can enter; but as soon as 

 the flask cools the moisture is seen collecting on the inside of the 

 flask. As long as the air in the flask is hot it can hold a large 

 amount of moisture, but when the air cools it can not hold as 

 much moisture. 



Effects of Wind on Evaporation. We find also that clothes 

 dry or mud puddles dry up more quickly on a windy day than 

 on a day when there is little wind. When the air around a wet 

 object is full of water, the object is unable to give up any more of 

 its moisture to the atmosphere, but when the air which is saturated 



