THE COMPOSITION OF THE ATMOSPHERE 75 



a shadow is the direction of the light? How do you 

 define these two directions? 



4. How can you tell the time of sunrise if you 

 know the time of sunset? 



5. What is the proper temperature for the school- 

 room and the home? 



6. Why does the ground become warm faster than 

 a pond? 



7. Which will burn us the more, a piece of wood 

 or a piece of copper, if both are at the same temper- 

 ature? Explain. 



8. Where do we live in our ocean of air, at the bot- 

 tom or the top? Could we live anywhere else than where 

 we do? 



9. Would it do any harm to water plants so much 

 that the ground would be covered with water? 



10. What collects on the inside of a glass of cold 

 water if left in a warm room? 



29. The Composition of the Atmosphere. 



Some mornings when you come to school it is fogg> 

 and you think how damp the air is. Even if it is not 

 foggy you have often noticed that the air is damp and 

 you have heard persons say, "Clothes will not dry today." 

 On other days, however, it has been brisk and bracing 

 and the air has been called dry. Though the air has 

 seemed dry it still contained water in an invisible form. 

 It is from the invisible form of water that dew, fog, and 

 clouds are formed. 



The amount of water in the air varies from day to 

 day and even from hour to hour. The air near large 

 bodies of water usually contains more moisture than 



