198 



THE EEASON WHY. 



"Little children, let no man deceive you: he that doeth righteousness 

 righteous, even as he is righteous."! JOHN in. 



Because, as the big boy is then on an inclined plane with the 

 fulcrum, or centre upon which the see -saw moves, the arm of the 

 lever, upon which the big boy sits, is relatively shortened, and be 

 has then less mechanical power. Also, a portion of the weight ot 

 the larger boy is transmitted along the lever to the arm upon 

 which the little boy sits. 



866. Why is the ball 

 propelled upward, in the 

 game of trap and ball, when 

 the trigger is struck ? 



Because, when the trigger is 

 struck at A, it is forced down- 

 wards, turning upon the fulcrum 

 B, the opposite end, forming the 

 spoon, is thereby forced up- 

 Pig. 45. TRAP AND BALL. wards, describing a small arc, or 



curved line ; but directly the ball is set free from the spoon, it rises 

 in a right line with the direction it was taking, at the moment it 

 nas set free. 



*s. A 



Pig. 46. BAT AND BALL. 



867. What principles of natural philosophy are illustrated 

 by the results of bat and ball ? 



Percussion, when the bat strikes the ball ; rotatory motion, when 

 the ball is sent whirling away ; momentum, which it acquires by 

 velocity ; elasticity, when it rebounds from an object against which 



