WINTER EARTH STUDY. 477 



formation of water dust from invisible vapor. Place boil 

 ing water in the open window or other cool place. Th 

 area and amount of water dust will be much increased be- 

 cause more vapor is condensed to water dust. A tin pail 

 filled with ice- water, or better, with finely pounded ice and 

 salt (three or four parts of ice to one part of salt), held 

 over boiling water, will cause a great increase in the 

 amount of water dust produced from the condensation of 

 vapor. The condensation of vapor to water dust and to 

 water can be illustrated by brushing together chalk dust 

 scattered on white paper, first into little piles and then 

 into larger masses. 



Step III. What condensation is. What causes it. 

 Gather up definitely the results of the experiments and 

 illustrations in Steps I and II. 



Step IV. Applications. The water dust coming from 

 mouths of children and horses on cold days. Why not 

 seen in schoolroom ? The water collected on surface of 

 pitcher of ice-water, or on water pipes, or on window panes, 

 due to condensation of vapor in air. The steam (distin- 

 guish from smoke) from boilers of factories, seen so much 

 more clearly on cold days. " Wash-day " at home in win- 

 ter time usually illustrates condensation well. Try to lead 

 children to observe and explain the escape of water dust 

 from the boiler and wash-tub, the water on the windows 

 and walls and ceiling of the kitchen, the cloud of water 

 dust, like fog, with which the kitchen is often filled when 

 the cold air rushes in from open door or window. Leave 

 the wider applications of condensation, illustrated in for- 

 mation of fog, mist, cloud, dew, rain, frost, snow, and ice, 

 until these topics can be studied carefully. 



Step V. Review and summary. Continue the black- 

 board story about " Mother's Helpers on Wash-day," with 

 a chapter on " The Journey of the Water Helpers," telling 



