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,
and the new bridge was pushed into its place, the whole operation
occupying less than three minutes. The new replaced the old between the
passing of trains that run at four or five-minute intervals. The Eads
Bridge, which crosses the Mississippi at St. Louis, was built on a novel
plan. Its deep foundations have already been mentioned. The great
"Father of Waters" is notoriously fickle; its channel is continually
changing, the current is swift, and the frequent floods fill up and
scour out new channels constantly. It was necessary, therefore, in order
to span the great stream, to place as few towers as possible and build
entirely from above or from the towers themselves. It was a bold idea,
and many predicted its failure, but Captain Eads, the great engineer,
had the courage of his convictions and carried o