FEBRUARY 157 



tliey travel rapidly along ? What do they form when 

 they go slowly ? 



Show the childi'en such pictures as those of the Canons 

 of the Colorado, and tell them the story of the Missis- 

 sippi or of the ISTile. 



For the proper study of snow and frost, the children 

 should have some knowledge of the results of crystalliza- 

 tion and the conditions under which it takes place. This 

 is most easily done by allowing a saturated solution of 

 salt in hot water slowly to cool and then to evaporate. 

 Compare the resulting cubes with those found in ordinary 

 cooking salt and in rock salt. The children will at once 

 see that the difference is one of size only. They should 

 be told that the crystals of rock salt are formed when the 

 cooling and evaporation are very slow, so that the parti- 

 cles of salt are not hurried, and are thus free to build up 

 large crystals. 



This lesson will be more attractive, perhaps, if, instead 

 of salt, sugar and rock candy are used. 



For other suggestions, read the chapters on crystals in 

 Euskin's " Ethics of the Dust." 



The work of frost was illustrated, doubtless, in January, 

 if one of the seed tumblers was placed on the window 

 ledge. The water probably froze, and by its expansion 

 in turning into ice broke the tumbler. ^Nlake use of this 

 incident, taking up the work of frost in general. 



Dew has already been illustrated by bringing a pitcher 

 of ice water into the warm room. Where is dew formed ? 

 What must then be true of the temperature of the blades 

 of grass ? Why are they colder ? AMiy does everything 

 get colder at night ? What will prevent the formation 



