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Impact upon Beams . By Eaton Hodgkinson. 
The object of the present paper is an inquiry into some of the 
effects of impact upon beams when struck by bodies of different 
weight, hardness, and elastic force; and to compare theory with, 
and endeavour to adapt it better to, the results of experiment. 
The paper is a continuation of some experimental researches on 
the collision of imperfectly elastic bodies, which were published 
in the Fourth Report of the Association ; and it is intended to 
contain proofs of the principal statements made in a short com¬ 
munication read at the Cambridge Meeting. 
The preliminary conclusions, and some calculations with their 
results, will tirst be given; and afterwards the experiments, to 
which constant reference will be made for proofs and illustra¬ 
tions. 
With the castings and every assistance in making the experi¬ 
ments I have been supplied, as on former occasions, through 
the liberality of Mr. Fairbairn, engineer, of Manchester. 
Conclusions from Experiments, &c. 
Conclusion 1.—If different bodies of equal weight, but differ¬ 
ing considerably in hardness and elastic force, be made to strike 
horizontally with the same velocity against the middle of a 
heavy beam supported at its ends, all the bodies will recoil 
with velocities equal to one another. 
This is shown by the experiments on the 3rd beam, in which 
two balls 8^ lbs. each, one of lead and the other of cast iron, 
suspended as pendulums, were made to fall through equal arcs 
against the middle of the beam, 13f lbs. weight between the 
supports; and the recoil of the leaden ball was nearly the same 
as that of the iron ball, though the hardness and elasticity of 
the two balls were widely different. This equality of recoil in 
the two balls was likewise shown to exist whether both fell 
through a small or large arc. 
To vary the weight and quality of the balls, two were used, 
half the weight of the former, 4^ lbs. each, one of lead and the 
other of bell-metal. In these, as before, when both were let 
fall through equal arcs, whether great or small, the recoil of one 
ball was nearly equal to that of the other. 
To vary further the experiment on this beam, three balls were 
