THE EEASON WHY. 



' Better is a poor and a wise child, than an old and foolish king who will no 

 more be admonished." ECCLESIASTES IV. 



819. Why does a striped marble appear to have a greater 

 number of stripes when rolling, than when at rest ? 



Because the stripes are presented in rapid succession to the 

 eye ; and as the eye receives fresh impressions of stripes before 

 the previous impressions have passed away, the stripes appear 

 multiplied. 



Fig. 26.-MABBLE AT BEST Fig. 27. MAEBLE BOLLING. 



820. Why does a marble rebound when dropped upon the 

 pavement ? 



Because the force of its fall to the earth compresses ihe atoms of 

 which the marble is composed ; and the atoms then exert the force 

 of elasticity to restore themselves to their former condition ; and 

 by the exercise of this force the marble is repelled, or thrown 

 upward from the pavement. Although a marble may be made of 

 very hard stone, yet that stone may be elastic, and possess, though 

 in a much less degree, the same kind of elasticity which causes 

 the India-rubber ball to rebound from the earth. 



821. Why does a marble, assuming it to be impelled with 

 equal force, roll further on ice than on pavement, and further 

 on pavement than on a pebble walk? 



Because the friction is greater upon pavement than upon ice, 

 and greater upon a pebble walk than upon pavement. 



822. JLow many forces contribute to stay t\e progress of 

 rolling marble ? 



