In Fig. 12 is shown a chain 8' long, one end of which B is attached
to a wire-strainer, while the other end is fastened to a small piece
of pine A, which is 0"·5 square in section, and 5" long between the
two upright irons by which it is supported. By means of the nut of
the wire-strainer I straighten the chain as I did the string of Fig.
11, and for the same reason. I then put a piece of twine round the
chain and pull it gently. The strain brought to bear on the wood is so
great that it breaks across. Here, the small force of a few pounds,
transmitted to the chain by pulling the siring, is magnified to upwards
of a hundredweight, for less than this would not break the wood. The
explanation is precisely the same as when the string was broken by the
thread.
[Illustration: FIG. 12.]