Mr Vincent, Experiments on Impact. 



337 



The points in Fig. 5 indicated by circles were obtained as in 

 the above described experiments, but those shown by crosses are 

 the results of a series of experiments performed on another day 



\ 



Vel. of Approach in cms. a sec. 

 Fig. 5. Steel Ball impinging on rubber bung. 



by the pendulum method. The pendulum was 245 cm. long so 

 that the velocity on impact in cm. a sec. was numerically equal 

 to twice the length of the chord in cms. The pendulum experi- 

 ments were not easy to perform, as the thread supporting the 

 steel ball stretched considerably even under a small tension. 

 Thus it was found necessary to release the ball (this was done 

 by the wooden lever apparatus described above), to let it strike 

 the rubber surface once, to read the length of the chord for the 

 first rebound and for the second ; these last two readings were 

 the ones used and gave fairly concordant results. 



Parallax was avoided by using a scale fastened to a plane 

 mirror parallel to the plane of motion. 



The resistance of the air had so small an effect that no 

 allowance was made for it, and the results for e are probably 

 not appreciably different from what would have been obtained 

 from experiments in a vacuum. 



The coefficient of restitution is again a linear function of the 

 velocity of approach. 



e = -81, 

 ra = -00011, 



and e is zero when u = 7400 cms. a sec. The maximum velocity of 

 rebound is 1840 cms. a sec. and the velocity of approach corre- 

 sponding to this is 3700, while e = '40. 



