72 



WELLS'S NATURAL PHILOSOPHY. 



In TThat cnn- The skill of the plaj'cr of billiards and bagatelle depends 



of the Gamu of upon his dexterous application of the principles of incident 

 Billiards ? and reflected motion, which he has learned by long-continued 



experience, viz., that the angle of incidence is always equal to the angle 

 of reflection, and that action and reaction are equal and contrary. An illus- 

 tration of the skillful reflection of billiard balls is given in Fig. 42, which rep- 

 resents the top of a billiard-table. The ball, P, when struck by tho stick, Q, 



Fig. 42. 



is first directed in the line P 0, upon the ball P', in such a manner, that being 

 reflected from it, it strikes the four sides of tho table successively, at the points 

 marked 0, and is finally reflected so as to strike the third ball, P". At each 

 of the reflections from the ball P', and the four points on tho side of the table, 

 the angle of incidence is exactly equal to the angle of reflection. 



152. Imperfectly elastic bodies oppose the 

 momentum of bodies in motion more perfectly 

 than any others, in consequence of their yield- 

 ing to the force of collision without reacting ; 

 opposing a gradual resistance instead of a sud- 

 den one. 



Hence a feather-bed, or a sack of wool, will stop a bullet much more ef- 

 fectually than a plate of iron, from its deadening, as it is popularly called, the 

 force of the blow. 



Why are Im- 

 pprfictly elas- 

 tic bi)(1ies yi.cii- 

 liarly fiUerl to 

 oppose and de- 

 stroy momeu- 

 tuiu? 



SECTION III. 

 COMPOUND MOTION. 



What is Sim- 

 ple Motion ? 



153. A body acted upon by a single force, 

 moves in a straight line, and in the direction 

 of that force. Such motion is designated as Simple Mo- 

 tion. 



