e adjoining spans. The shore piers
carry cantilevers projecting one way over the river openings and the other
way over a shore span where it is secured to an anchorage. The girder spans
are 525 ft., the cantilever spans 547 ft., and the shore spans 201 ft.

[Illustration: FIG. 25.--Quebec Bridge (original design)]

(6) The Quebec bridge (fig. 25) over the St Lawrence, which collapsed while
in course of construction in 1907. This bridge, connecting very important
railway systems, was designed to carry two lines of rails, a highway and
electric railway on each side, all between the main trusses. Length between
abutments 3240 ft.; [v.04 p.0542] channel span 1800 ft.; suspended span 675
ft.; shore spans 5621/2 ft. Total weight of metal about 32,000 tons.

[Illustration: FIG. 26.--Jubilee Bridge over the Hugli.]

(7) The Jubilee bridge over the Hugli, designed by Sir Bradford Leslie, is
a cantilever bridge of another type (fig. 26). The girders are of the
Whipple Murphy type, but with curved top booms. The bridge carries a double
line of railway, between the main girders. The central double cantilever is
360 ft. long. The two side span girders are 420 ft long. The cantilever
rests on two river piers 120 ft. apart, centre to centre. The side girders
rest on the cantilevers on 15 in. pins, in pendulum links suspended from
similar pins in saddles 9 ft. high.

[Illustration: FIG. 27.--Coalbrookdale Bridge.]

11. (f) _Metal Arch Bridges._--The first iron bridge erected was
constructed by John Wilkinson (1728-1808) and Abraham Darby (1750-1791) in
1773-1779 at Coalbrookdale over the Severn (fig. 27). It had five cast iron
arched ribs with a centre span of 100 ft. This curious bridge is still in
use. Sir B. Baker stated that it had required patching for ninety years,
because the arch and the high side arches would not work together.
Expansion and contraction broke the high arch and the connexions between
the arches. When it broke they fished it. Then the bolts sheared or the
ironwork broke in a new place. He advised that there was nothing unsafe; it
was perfectly strong and the stress in vital parts moderate. All that
needed to be done was to fish the fractured ribs of the high arches, put
oval holes in the fishes, and not screw up the bolts too tight.

Cast iron arches of considerable span were constructed late in the 18th and
early in the 19th century. The difficulty of casting heavy arch ribs led to
the construction of cast