The free width secured to navigation is 28 feet. The bridge is usually
kept raised to a height of 16 feet above the level of the water in order
to allow boats to pass (Fig. 2). In this position it is balanced by four
counterpoises suspended from the extremities of chains that pass over
pulleys. These counterpoises are of cast iron, and weigh, altogether,
44,000 pounds--the weight of the bridge to be balanced, say 11,000
pounds per counterpoise. Moreover, each of the four chains is prolonged
beneath the corresponding counterpoise by a chain of the same weight,
called a compensating chain.
The pulleys, B and C, that support the suspension chains have
projections in their channels which engage with the links and thus
prevent the chains from slipping. They are mounted at the extremity of
four latticed girders that likewise carry girder pulleys, D. The pulleys
that are situated at the side of the bridge are provided laterally
with a conical toothing which gears with a pinion connected with the
maneuvering apparatus.
The two pinions of the same side of the bridge are keyed to a
longitudinal shaft which is set in motion at one point of its length by
a system of gearings.
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