362 SEVENTH REPORT—1837. 
be equal in the two cases. An experiment of this kind I gave 
in a paper on the strength and best forms of iron beams (Me- 
moirs of the Literary and Philosophical Society of Manchester, 
vol. v.), and it formed indeed the basis of the inquiry in that 
paper. 
I had remarked in some of the experiments upon the Carron 
iron, and more particularly the Buffery following, that the 
elasticity of the bars was injured much earlier than is generally 
conceived; and that instead of it remaining perfect till one- 
third or upwards of the breaking weight was laid on, as is 
generally admitted by writers (Tredgold on Cast Iron, Article 
59, &c.), it was evident that 1th or less produced in some cases 
a considerable set or defect of elasticity, and judging from its 
slow increase afterwards, I was persuaded that it had not come 
on by any sudden change, but had existed, though in a less 
degree, from a very early period. I mentioned the fact and 
my convictions sometime after to Mr. Fairbairn, and expressed 
a desire to have bars cast of greater length than before to ren- 
der the defect more obvious. 
All the future experiments on a transverse strain, whether 
made by myself or Mr. Fairbairn, have tended to prove the 
matter. 
We passed over the experiments placed at the beginning of 
Tables 1 and 2: referring now to them, it will be seen, that in 
3 out of 6 experiments, I16lbs. produced a visible set, whilst 
the breaking weights in these cases were 469, 462, 518: in 
other words, the elasticity was injured with , of the break- 
ing weight, or less. In experiments 4 and 5, Table I., which 
were on longer bars than the others, cast for this purpose, 
and for another mentioned further on, the elasticity in the for- 
mer experiments was sensibly injured with 7lbs., and in the 
latter with 14lbs., the breaking weights being 364lbs. and 
1120ibs. In the former of these cases a set was visible with 
=, and in the other with 4, of the breaking weight, showing 
that there is no weight, however small, that will not injure the 
elasticity. 
In two other bars, from the same model, which were laid 
against vertical supports at the same distance asunder as be- 
fore, the force being applied horizontally by means of a pulley, 
7lbs. showed a defect of elasticity in that which had the rib 
submitted to tension, and 21 in the other. 
The mode used to observe when the elastic force became 
injured was as follows. When a bar was laid upon the sup- 
ports for experiment, a “‘straight edge” was placed over it, 
the ends of which rested upon the bar directly over the points 
. 
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: 
