IN NATURAL PHILOSOPHY. I J 



14. Why does a rope-walker carry a heavy balancing-pole ? 

 Because in this way he can easily shift his centre of gravity. 



15. What would become of a ball if dropped i*ito a hole 

 bored through the centre of the earth ? 



In falling, it would gain a momentum which would carry it 

 past the centre of the earth. But as it is constantly coming 

 to a part having a slower axial revolution than itself, it would 

 scrape on the east side of the hole until it reached the centre ; 

 beyond that point it would scrape on the west side. This 

 friction would prevent its reaching the opposite side of the 

 earth. It would therefore vibrate to and fro, each time through 

 a shorter distance, until, at last, it would come to rest at the 

 centre of the earth. 



1 6. Would a clock lose or gain time if carried to the top of 

 J a mountain ? 



It would lose time, because the force of gravity would be 

 lessened. At the North Pole it would gain time, because there 

 the force of gravity would be increased. 



1 7. In the winter, would you raise or lower the pendulum- 

 bob of your clock ? 



I would lower it, since the cold of winter shortens the pen- 

 dulum, and this movement of the bob would counteract that 

 change. 



1 8. Why is the pendulum-bob always made flat? 

 To decrease the friction of the air. 



19. What beats off the time in a watch f 

 The vibration of the balance-wheel. 



20. Is solved in the book. 



21. What should be the length of a pendulum at New YorA 

 to vibrate half-seconds ? 



(1 sec.) : (V a sec.) 2 : : 39.1 in. : x = 9.7 + inches. 

 To vibrate quarter-seconds ? 



(1 sec.)' : (V 4 sec.)' : : 39.1 in. : x = 2.4 + inches. 

 To vibrate hours f 



(1 sec.) 3 : (3600 sec.) 3 : : 39.1 in. : x - 7997.7 miles.* 



* Nearly the diametor of the earth. 



