32 ELEMENTS OE AGRICULTURE 



observation on the part of the farmer, but now the 

 weather bureaus supply, for the asking, information 

 which has been collected as the result of years of 

 patient labor. Each farmer should, however, keep a 

 record for his own farm or locality, and if the work be 

 done carefully and systematically, it will prove of value 

 not only to him, but to his community and to his chil- 

 dren after him. 



Questions 



1. Why is carbon dioxide important to growing plants? 

 2. Why is there usually more carbon dioxide- in the air of 

 cities than in the air of the country? 3. What is ammonia? 

 4. What is water vapor? 5. Which contains the more water 

 vapor, warm or cold air? 6. When the water vapor in the air 

 condenses on the surface of the earth, what is it called? 7. How 

 is frost formed? 8. How does dense, moist air behave towards 

 the heat waves from the earth? 9. Why are the tops of high 

 mountains colder than the country below? 10. What do the 

 dust particles in the air often carry with them? 11. What is 

 meteorology ? 



