93 
vertical was .36. Another beam of the same material was then taken whose cross- 
section was a square, the side being equal to the greater side of the rectangle in 
the preceding. The mean value obtained by large number of impacts was .355. 
It will be understood that the mass in this case was three times as great as that in 
the preceding cases, and that all three values agreed very closely. Hence it is 
assumed that the thickness in these cases was sufficient and that practically the 
base acted like a very great mass. 
In the preceding, the drops were from the same height. The next point 
tested was whether or not the height was so great that the limit of elasticity of 
the wood was passed. A series of determinations was made with all other cir- 
cumstances similar, but with different heights of drop each time, varying from 1 
to 6 feet, and the values of e while varying from .34 to .38 showed no regular de- 
pendence on the height of drop. It may be stated that such differences as here 
obtained occurred frequently, although usually smaller in amount. They are 
mostly attributable to the lack of homogenity in parts which seem superficially | 
quite similar in structure. The mean value of e¢ in this series was .363. 
It may be stated that the same impinging block was used over and over again. 
Had there been any effect produced by the crushing of the impinging surface of 
the block, it seems evident that it would have shown itself in a change of the value 
of e. As no such appeared, it seems evident that no such effect existed. To settle 
the question, however, a series of determinations was made with a newly turned 
impinging surface each time. The radius of curvature was much larger in this 
ease. The result was that the values for e obtained in these tests were practically 
constant and unchanged by the successive impacts of the impinging surface, but 
were notably large with this larger radius of impinging surface, the mean 
value being .42, while with the smaller radius of curvature it was .36. The effect 
of curvature will be spoken of later. 
In all the preceding tests the impacts were on new and undinted surfaces of 
the base plate. This was necessary because an effect due to the dinting of the plate 
had been observed though not accurately examined. We now more carefully tested 
this point and found that under successive impacts on the same spot of the base 
plate the value of e rose steadily from the earlier value of .36 to .49, showing a 
permanent effect due to a crushing of the material of the base plate. The radius 
of curvature as formerly was 7 cm. 
Again, to find the effect of curvature of the impinging block, a series of tests 
were made, first with a curvature of 3 cm., then of 7 cm., and then of 10 cm., 
and it was found that the eorresponding values of e were-—for 3 cm., .32; for 7 
cm., .37; for 10 cm., .42, thus showing that the value of e increased with increas- 
ing values of the radius of curvature. 
