1860, however, the link
chains of the Hungerford suspension bridge which was being taken down were
available at small cost, and these were used to complete the bridge. There
are three chains on each side, of one and two links alternately, and these
support wrought iron stiffening girders. There are wrought iron saddles and
steel rollers on the piers. At 196 ft. on either side from the towers the
chains are carried over similar saddles without rollers, and thence at 45 deg.
with the horizontal down to the anchorages. Each chain has an anchor plate
5 ft. by 6 ft. The links are 24 ft. long at the centre of the bridge, and
longer as they are more inclined, so that their horizontal projection is 24
ft. The chains are so arranged that there is a suspending rod at each 8
ft., attached at the joint of one of the three chains. For erection a
suspended platform was constructed on eight wire ropes, on which the chains
were laid out and connected. Another wire rope with a travelling carriage
took out the links. The sectional area of the chains is 481 sq. in. at the
piers and 440 sq. in. at the centre. The two stiffening girders are plate
girders 3 ft. deep with flanges of 11 sq. in. area. In addition, the hand
railing on each side forms a girder 4 ft. 9 in. deep, with flanges 41/2 sq.
in. area.

[Illustration: FIG. 12.--Williamsburg Suspension Bridge.]

Of later bridges of great span, perhaps the bridges over the East river at
New York are the most remarkable. The Brooklyn bridge, begun in 1872, has a
centre span of 15951/2 and side spans of 930 ft. The Brooklyn approach being
971 ft., and the New York approach 15621/2 ft., the total length of the
bridge is 5989 ft. There are four cables which carry a promenade, a roadway
and an electric railway. The stiffening girders of the main span are 40 ft.
deep and 67 ft. apart. The saddles for the chains are 329 ft. above high
water. The cables are 153/4 in. in diameter. Each cable has 19 strands of 278
parallel steel wires, 7 B.W.G. Each wire is taken separately across the
river and its length adjusted. Roebling preferred parallel wires as 10 %
stronger than twisted wires. Each strand when made up and clamped was
lowered to its position. The Williamsburg bridge (fig. 12), begun in 1897
and opened for traffic in 1903, has a span of 1600 ft., a versed sine of
176 ft., and a width of 118 ft. It has two decks, and carries two elevated
railway tracks, four electric tramcar lines, two carriageway