MECHANISM OF NATUEE 



run of billiard balls, while fully illustrating this 

 proposition, is influenced by many imperfections 

 of material and inaccuracy of observation. Yet 

 enough can be readily seen to prove conclusively 

 that the balls act as if their acquired force were 

 situated at their centre. 



Let Figure A represent the diameter of two 

 billiard balls, B and C. And let the ball C be 



fig A 



projected so as to strike the ball B at the point 

 D. Then, those particles that make up the point 

 of contact in each respective ball are the only 

 parts of the balls which come in actual contact; 

 and, therefore, these particles, under the force of 

 impact, must tend to separate in a straight line, 

 viz., the line B. F. But they do not fly off in 

 that direction. 



Again, let each ball be considered as one whole 

 particle, regardless of any consideration of its 

 common centre or the point of contact. 



48 



