onsequently the amount of traffic
which could be passed over such a bridge. Thus, taking the length of the
Victoria Bridge into account, it was found that not more than 20 trains
could pass within the 24 hours, a number insufficient for the
accommodation of the anticipated traffic. To introduce such an amount of
material into the suspension bridge as would supply increased rigidity,
would only be approximating to the original beam, and neutralizing any
advantages in point of cheapness which might be derivable from this form
of structure, without securing the essential stiffness and strength.
Iron arches were also considered inapplicable, because of the large
headway required for the passage of the ice in winter, and the necessity
which existed for keeping the springing of the arches clear of the
water-line. This would have involved the raising of the entire road, and
a largely increased expenditure on the upper works. The question was
therefore reduced to the consideration of the kind of _horizontal beam_
or _girder_ to be employed.

Horizontal girders are of three kinds. The _Tubular_ is constructed of
riveted rectangular boiler plates. Where the span is large, the road
passes within the tube; where the span is comparatively small, the
roadway is supported by two or more rectangular beams. Next there is the
_Lattice_ girder, borrowed from the loose rough timber bridges of the
American engineers, consisting of a top and bottom flange connected by a
number of flat iron bars, riveted across each other at a certain angle,
the roadway resting on the top, or being suspended at the bottom between
the lattice on either side. Bridges on the same construction are now
extensively used for crossing the broad rivers of India, and are
especially designed with a view to their easy transport and erection.
The _Trellis_ or Warren girder is a modification of the same plan,
consisting of a top and bottom flange, with a connecting web of diagonal
flat bars, forming a complete system of triangulation--hence the name of
"Triangular girder," by which it is generally known. The merit of this
form consists in its comparative rigidity, strength, lightness, and
economy of material These bridges are also extensively employed in
spanning the rivers of India. One of the best specimens is the Crumlin
viaduct, 200 feet high at one point, which spans the river and valley of
the Ebbw near the village of Crumlin in South Wales. This viaduct is