bridge, the first of its kind, was demolished and taken away.

Over the Niagara gorge also was built one of the first cantilever
bridges ever constructed. To uphold it, two towers were built close to
the water's edge on either side, and then from the towers to the shores,
on a level with the upper plateau, the steel fabric, composed of slender
rods and beams braced to stand the great weight it would have to carry,
was built on false work and secured to solid anchorages on shore. Then
on this, over tracks laid for the purpose, a crane was run (the same
process being carried out on both sides of the river simultaneously),
and so the span was built over the water 239 feet above the seething
stream, the shore ends balancing the outer sections until the two arms
met and were joined exactly in the middle. This bridge required but
eight months to build, and was finished in 1883. From the car windows
hardly any part of the slender structure can be seen, and the train
seems to be held over the foaming torrent by some invisible support, yet
hundreds of trains have passed over it, the winds of many storms have
torn at its members, heat and cold have tried by expansion and
contraction to rend it apart, yet the bridge is as strong as ever.

Sometimes bridges are built a span or section at a time and placed on
great barges, raised to just their proper height, and floated down to
the piers and there secured.

A railroad bridge across the Schuylkill at Philadelphia was judged
inadequate for the work it had to do, and it was deemed necessary to
replace it with a new one. The towers it rested upon, therefore, were
widened, and another, stronger bridge was built alongside, the new one
put upon rollers as was the old, and then between trains the old
structure was pushed to one side, still resting on the widened piers,