Mr Vincent, Experiments on Impact. 347 



The time of impact is 



7r<P_7rI) <P_ 



Now Y£- is a constant, thus the time of impact is directly 



proportional to the diameter of the impinging ball. The above 

 expression for the time may be written 



D 



t = 



8^' 13' 



and thus the time of impact for a ball of 1 cm. diameter is 

 •745 x 10 -4 . The time of impact of the three balls is thus : — 



After performing the experiments described above, it was 

 necessary to test the accuracy with which d and D are pro- 

 portional. For this purpose another piece of lead was taken and 

 three sets of experiments performed without replaning the surface. 

 The results are set out below : — 



Number of experiments of V27d 



D a which d is the mean. h ~~~])~ P 



127 -3033 12 100 -3033] 



2-54 -6117 6 100 "30581 12 x 10 8 



3-81 -8975 4 100 -2991 ) 



The numbers in the last column are nearly the same, and thus 

 d and D are proportional to a considerable degree of accuracy. 

 To test this point further a number of steel spheres were obtained 

 from the Automachinery Company of Coventry. They were 

 made of " hard " steel, and had a highly polished surface ; no 

 difference in the density of the material could be detected by the 

 balance. 



Fig. 11 shows the results of a series of experiments with this 

 set of spheres. The height of fall was 100 cm. in all cases. The 

 block of lead on which the spheres fell weighed about 100 kilos. 

 and was approximately cubical. It was a chilled casting, the 

 lead being allowed to cool until solidification began, before it was 

 poured into the mould. The mould consisted of four blocks of 

 iron set up on a slab of iron. The surface which was used in the 

 experiments was that in contact with the slab of iron forming 



