IN NATURAL PHILOSOPHY. 41 



In summer the non-conducting flannel keeps out the fur- 

 nace-heat, and in the winter keeps in the body-heat. 



5. Why do we blow our hands to make them warm, and 

 our soup to make it cool? 



Our breath is warmer than our hands, but cooler than our 

 soup. 



6. Why does snow protect the grass ? 



The air enclosed between the flakes of snow is a non-con- 

 ductor. No infant in its cradle is tucked in more tenderly 

 than the coverlet of snow about the humble grass that nestles 

 down for its winter's nap on the bosom of mother Earth. 



7. Why does water " boil away" more rapidly on some days 

 than on others f 



Because the atmospheric pressure varies. 



8. What causes the crackling sound in a stove, when a firs- 

 ts lighted? 



The expansion of the iron by the heat. 



9. Why is the tone of a piano higher in a cold room than in 

 a warm one? 



The steel wires lengthen in a warm room, and so lower the 

 tone. 



10. Ought an inkstand to have a large or a small mouth ? 

 A small mouth, to prevent evaporation. 



1 1. Why is there a space left between the ends of the rails on 

 a railroad track ? 



To allow room for the expansion and contraction of the rails 

 with the changes in temperature. 



12. Why is a person liable to take cold when his clothes are 

 damp ? 



The water which evaporates from his clothes, in drying, 

 absorbs heat from his body. 



13. What is the theory of corn-popping? 



The air in the ceiis 01 trie corn expands by the heat and 

 bursts the outer coating of the corn. 



