Mr Vincent, Experiments on Impact. 



333 



The end of the wooden lever had a small depression in it, and 

 the whole was so arranged that the ball received no initial 

 velocity when the lever was released. The height to which the 



Vet. of Approach in cms. a sec. 

 Fig. 1. Stripped Lawn Tennis Ball rebounding from stone slab. 



ball bounced was determined by noting the highest reading on 

 a millimetre scale which could be observed, the ball obscuring 

 the readings just above this point. Parallactic errors were 

 obviated by placing the eye at the expected height on another 

 vertical scale. If the reading was different from that expected, 

 then a new height was taken for the eye until the eye, bottom 

 of ball, and reading were all at the same height above the plane 

 from which the ball rebounded. 



The points surrounded by circles are obtained by plotting the 

 velocity of rebound against the velocity of impact, both computed 

 without any attempt being made to allow for the effect of the air. 

 Thus it would be more accurate to say that the curve shows the 

 relation between the square roots of the heights of fall and 

 rebound than that of the velocities of concurrence and recession. 



The points indicated by crosses show on the same figure the 

 way in which the value of e thus calculated falls off as the velocity 

 of approach increases. These points lie approximately on a straight 

 line and, without assuming that the value of e thus computed is 

 the ratio of the velocities of recession and approach, we have 



v 7 : 



= C — ky/hrL, 



where h^ and h 2 of the heights of fall and rebound and c and h 

 are constants. 



The results which would follow if such a straight line law 

 connected e with the velocity of approach over an extensive range, 

 are interesting. 



