TEACHER'S LEAFLET NO. 14. 



A SUnnER SHOWER. 



RALPH S. TARR 



RAINSTORM comes, the walks are wet and 

 the roads are muddy. Then the sun 

 breaks through the clouds and soon the 

 walks are no longer damp and the mud of 

 the road is dried. Where did the water 

 come from and where has it gone ? Let us 

 answer these questions. 



A kettle on the stove is forgotten and 

 soon a cracking is heard ; the housewife jumps to her feet for 

 the kettle is dry. The kettle was filled with water, but it has 

 all boiled away ; and where has it gone ? Surely into the air of 

 the room, for it can be seen issuing as "steam" and then disappear- 

 ing from view, as if by magic. The heat of the fire has changed 

 the liquid water to a gas as invisible as the air itself. This gas 

 is water vapor. 



Do you wish to prove that the water vapor is there, although 

 unseen ? Then if the day is cool, watch the 

 windoW' and notice the drops of water collect up- 

 on it. Or if the day is warm, bring an ice cold 

 glass or pitcher into the room and see the drops 

 collect upon it (Fig. i). People sometimes 

 say, when drops of water collect on a glass of 

 cold water, that the glass is " sweating ; " but 

 see if the same thing will not happen with a 

 cold glass that does not contain water. 



These two simple observations teach us two 

 very important facts : (i) That heat will change 

 liquid water to an invisible vapor, or gas, which will float about 

 in the air of a room ; and (2) that cold will cause some of 

 the vapor to change back to liquid water. 



I. — A glass of cold 

 water on which 

 vapor has con- 

 densed in drops. 



