e., its power to resume its former shape
and position when stress is removed. Now, in the case particularly of
steel wire as commonly furnished in spiral coils, the curve put into the
wire in the process of manufacture seriously diminishes this available
sustaining power.

For it is evident that it would be unsafe to subject these cables at any
time to a stress beyond their elastic limit. If, e.g., a snowstorm or a
great crowd of people should load a bridge beyond this limit, when the
extra weight was removed the cables could not bring the bridge back to
its normal place, and the result would be a permanent flattening and
weakening of the arch.

By a process invented and patented by Col. Paine, the wire in the New
York and Brooklyn bridge was furnished _straight_ instead of curved. Now,
if a short piece of common steel wire is taken from the coil, and pulled
toward a straight position, and then released, it springs back into its
former curve; but if a short piece of the straight-furnished wire that
was put into this bridge is bent, and then released, it springs back
toward its straight position.

It is easy to see that if a curved wire is pulled straight, there must
occur a distention of the particles on the inside of the curve and a
compression of those on the outside. The inside is in fact strained past
its elastic limit before _any_ stress comes upon the outside. Hence,
after the wire has been pulled straight, the elastic limit of only a
portion of it can be taken into the account in calculating the load that
can safely be put upon it. In the case of curved steel wire pulled
straight, its ultimate strength was found to be only about 90 per cent.
that of similar wire furnished straight by this process. The superior
ductility of iron wire in some measure compensates for the distention of
the particles on the inside of the curve, and that is a reason why it has
heretofore been used for suspension bridges. But with straight steel wire
there is no such distention, and its _entire elastic limit_ is available.
This elastic limit is 66 per cent. of the ultimate strength, and,
besides, that ultimate strength is 10 per cent. greater than that of
similar curved wire. Thus if we have a curved steel wire large enough to
sustain 1,000 lb. without breaking, a similar straight wire, such as
those in this bridge, will hold up 1,100 lb., and 66 per cent. of this
1,100 lb = 720 lb.

The elastic limit of curved wire has never been d