etermined, since any
stress that will cause it to reach a straight line is beyond the elastic
limit of the inside of its sectional area. That of curved iron wire has
been estimated at 40 per cent. of its ultimate strength, which is about
half the ultimate strength of curved steel wire; that is, it would be
unsafe to put more than 40 per cent. of 500 lb.--or 200 lb.--upon a
curved iron wire when a _straight_ steel one can sustain 720 lb. without
injury. In the New York and Brooklyn bridge the cost of a sufficient
amount of such iron wire as is used in all other suspension bridges would
have been some $200,000 greater than that of the straight steel wire
which was used. At five per cent., this effects an annual saving in
interest of $10,000.

There must, too, be a considerable saving in the current expense for
painting and care, to say nothing of the more neat and elegant appearance
of the less bulky steel. And as the whole area of the section of these
wires is subjected to an even strain that is always far within the
elastic limit, there is no danger of a change of structure under that
stress.

It is highly probable--although Col. Paine has been too busy to work up
the matter--that piano wire made in this straight method could be drawn
up to and kept at pitch, without approaching very near the elastic limit.
In that case not only would they seldom if ever require tuning, but
probably all along the tone would be more satisfactory. And there would
not be those exasperating periods when the pitch is not quite perfect,
but yet is not far enough out to make it seem worth while to send for a
tuner.

* * * * *

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