228 ANSWERS TO PRACTICAL QUESTIONS 



76. Why are the tops of high mountains in the tropics 

 covered with perpetual snow I 



(See Question 62.) 



MISCELLANEOUS QUESTIONS AND -PROB- 

 LEMS FOR REVIEW. 



1. Does a plumb-line point to the earth's centre of figure 

 "* Centre of gravity ? 



2. In a dark room, let the light of a candle pass through 

 a small hole in a card, and the image of the candle on the 

 opposite wall will be inverted. Explain. 



3. Why does drift on the Mississippi accumulate for the 

 most part on the west bank ? 



4. How many times heavier is the earth than an equally 

 large globe of water ? 



5. Why does the arc of a rainbow seem a part of an 

 ellipse instead of a circle ? 



6. Why does a rocket ascend into the air ? 



7. Is the water at the foot of Niagara Falls warmer 

 than that in the river above ? 



8. What causes wheel fire-works to rotate ? 



9. A brass-rod covered tightly with thin paper may be 

 held some time in a fiame without the paper being scorched ; 

 while, if the rod be of wood, the paper will scorch at once. 

 Why is this difference ? 



10. How would it affect the action of a siphon if it were 

 carried up a mountain ? 



