40 SCIENTIFIC RECREATIONS. 



forcibly, you will be enabled to draw away the paper without causing the coin 

 (say a five-shilling-piece) to fall down (fig. 34). 



It is not impossible to draw away a napkin laid as a tablecloth for one 

 person's dinner, without disturbing the various articles laid upon it. A quick 

 motion is all that is necessary, keeping the napkin tightly extended by the 

 hands at the same time. This latter experiment, however, is not recom- 

 mended to boys home for the holidays, as they may unwillingly practise a 

 feat analogous to that executed by Humpty-Dumpty, and find equal difficulty 

 to match the pieces. 



We will now examine the term Motion. A body is said to be in 



** 34- Drawing a slip of paper from beneath a coin. 



motion when it changes its position in relation to surrounding objects. To 

 perceive motion the surrounding objects must be relatively at rest, for if they 

 all hurried along at the same rate no motion would be perceptible. This is 

 evident, for when we stand still trees and houses appear stationary, as do we 

 ourselves, but we know we all are rushing round with the earth, though our 

 relative positions are unchanged. Hence there is no absolute rest. 



What are the causes of motion ? Gravity is one. The influence of 

 heat, which is itself caused by the motion of atoms, the effects of electricity, 

 etc., and finally, the power of force in men or animals any of these causes 

 will produce motion. But a body at rest cannot put itself in motion, nor 

 can a body in motion stop itself, or change its condition of motion. 



