476 NATURE STUDT. 



away from the dirt and mud and all other impurities in it. 

 Evaporation makes the water pure, leaves the dirt behind, 

 and sends the pure water into the air and the sky. What 

 becomes of this water ? What does it do in the sky ? To- 

 morrow we will begin to find out. 



CONDENSATION. 



Important points. What condensation is the chan- 

 ging of water dust or vapor into water. Cold or the 

 absence or lessening of heat as the cause of condensa- 

 tion. Common phenomena due to condensation. 



Step I. How water dust can be turned into water. 

 Boil water in tin cup over alcohol stove. Hold over it a 

 slate or plate or tumbler, which has been slightly warmed, 

 and then a similar vessel which has been placed out on the 

 window-sill to cool. Water forms or collects more quickly 

 on the cold vessel. Eepeat the same experiment with a 

 funnel inverted over the cup. Place on radiator, or near 

 stove, a pan partly filled with water, covered with glass, 

 Note how the drops of water collect on lower surface of 

 glass. Cool the glass, and note the result. Cold, or cold 

 things, make water dust turn into water. Compare with 

 the way in which children like to get close together when 

 it is cold, and thus help to keep one another warm, 



Step II. How vapor can be turned into water dust and 

 into water. When water is boiling vigorously in a tea- 

 kettle, no water dust can be seen very near the end of 

 the spout. The water in the spout is changed into vapor 

 by the heat, and turns to water dust after it has escaped 

 from the kettle, and has been cooled. Cold objects will con- 

 dense this vapor into water dust or wa,ter. Heat a little 

 water in a tightly closed vessel with small opening such 

 as the little oil-can used with sewing-machines to show 



