ELASTICITY. 



39 



it will shiver the wood or the pane of glass to pieces. When the celerity of 

 the motive force is very great, the particles directly affected are disturbed so 

 quickly that they separate from the adjacent particles before there is time for 

 the movement to be communicated to the latter. 



It is possible, for the same reason, to extract from a pile of money a 

 piece placed in the middle of the pile without overturning the others. It 

 suffices to move them forcibly and quickly with a flat wooden ruler. The 

 experiment succeeds very well also if performed with draughtsmen piled 

 up on the draught-board (fig. 32). 



Fig- 33 represents another experiment which belongs to the laws of 



33- Calling out a sixpenca from the 



resisting force. A sixpence is placed on a table covered with a cloth or 

 napkin. It is covered with a glass, turned over so that its brim rests on two 

 penny pieces. The problem to be solved is how to extract the sixpence from 

 underneath the glass without touching it, or slipping anything beneath it. 

 To do this it is necessary to scratch the cloth with the nail of the forefinger ; 

 the elasticity of the material communicates the movement to the sixpence, 

 which slowly moves in the direction of the finger, until it finally comes 

 out completely from beneath the glass. 



We may give another experiment concerning Inertia. Take a strip of 

 paper, and upon it place a coin, on a marble chimney-piece, as in the illus- 

 tration. If, holding the paper in the left hand, you strike it rapidly and 



