[84 TI1E 



'Train up a child in the way he should go ; and when he is old, he will not 

 depart from it." PROVERBS xxn. 



that they deface each other, and impart an, impression of coloured 

 rings, instead of definite objects. 



814. Why does a top stand erect when it spins, but fail 

 when it stops ? 



Because the top is under the influence of, and is balanced 

 between opposing forces. The rapffi rotation of the top gives 

 to all its particles a tendency to fly from the centre. If the atoms 

 of the wood were not held together by the attraction of cohesion, 

 they would fly away in a circle outward from the top, just ax drop* 

 of water fly off from a mop, while it is being twirled. If you 

 take a spoonful of sand, salt, or dust, and drop it upon the top, it 

 will be scattered in a circle, just as the atoms of the top would be, 

 if they were free to separate, but not with the same force, because 

 the atoms of the salt, &c., not being in an active state of rotation, 

 would only be influenced by momentary contact with the rotating 

 body. This tendency of the particles of a rotating- body to fly 

 outward from the centre, is called the centrifugal force. 



Centrifugal. From two Latin words meaning receding from the centre. 



The other force influencing the top is the attraction of gravita- 

 tion: the attraction which, were the top not spinning, would draw it 

 towards the earth. The " spill " projecting from the bottom of the 

 top stands in the line in which the top is drawn towards the earth 

 and keeps it from obeying the law of gravitation. Therefore the 

 rotatory motion given to the top, by the rapid unwinding of the 

 string, and the tendency of its 'atoms to fly outward, balance the top 

 upon the line in which it is drawn to the earth, and which is occupied 

 by the spill, which prevents it fulling to the ground. 



815. Why does a top Jirst reel around upon the spill, then 



become upright, and "sleep" and then reel 

 again, and fall ? 



Because, in being thrown from the hand, the 

 top is delivered a little out of the perpendicular, 

 but the spill is rounded off' at the point, and 

 when the top is rotating rapidly, the graviH- 

 tive force which attracts the top to the ground 

 continually acting upon it, draws the weight 

 Fi*. 86. pE<*-rop " KEELING." 



