182 NATURE-STUDY LESSONS. 



8. (a) Do you observe any moisture on it ? Can this 



be dew ? 

 (b) Give your reasons for not regarding it as dew. 



9. Supposing the temperature were very low, below 



the freezing point of water, what would become of the 



dew as it formed ? 



When the water-vapor at the surface of the earth freezes as it condenses, 

 it is called hoar-frost. 



10. (a) Where have you seen hoar-frost ? 

 {b) Of what color is it ? 



(c) When did you see it ? 



(d) Under what conditions is it formed ? 



LVI.-THE SUN. 



Procure a strip of board two inches wide and two feet long, and to one 

 end nail a strip of the same width and six inches long at right-angles to the 

 board. At noon each clear day have the length of the shadow cast by the 

 upright piece marked on the long strip by placing this horizontally on a 

 north and south line. Write the date on the 21st of each month along the 

 line marking the length of the shadow at that time. 



1. What causes a change in the length of the shadow? 



2. During which months does the shadow grow longer? 



3. During which months does the shadow grow shorter? 



4. When is the shadow longest ? 



5. When is the shadow shortest ? 



6. When does the shadow reach about half-way 

 between its longest and shortest positions ? 



7. How often in the year is the shadow an average 

 length between its longest and shortest lengths? 



8. At the time when the shadow is an average length, 

 compare the length of the day with that of the night. 



The time of the year when the days and nights are of equal length all 

 over the world is an equinox. The one in the spring is the vernal equi- 

 tiox and that in the fall is the autumnal equinox.- 



