tter; and no
one can have travelled over the Great Northern line to York without
noting that, as respects rigidity under the passing train, the Tubular
Bridge is decidedly superior. It is ascertained that the deflection
caused by a passing load is considerably greater in the former case; and
Mr. Stephenson was also of opinion that the sides of all trellis or
lattice girders are useless, except for the purpose of connecting the top
and bottom, and keeping them in their position. They depend upon their
connexion with the top and bottom webs for their own support; and since
they could not sustain their shape, but would collapse immediately on
their being disconnected from their top and bottom members, it is evident
that they add to the strain upon them, and consequently to that extent
reduce the ultimate strength of the beams. "I admit," he added, "that
there is no formula for valuing the _solid_ sides for strains, and that
at present we only ascribe to them the value or use of connecting the top
and bottom; yet we are aware that, from their continuity and solidity,
they are of value to resist horizontal and many other strains,
independently of the top and bottom, by which they add very much to the
stiffness of the beam; and the fact of their containing more material
than is necessary to connect the top and bottom webs, has by no means
been fairly established." Another important advantage of the Tubular
bridge over the Trellis or Lattice structure, consists in its greater
safety in event of a train running off the line,--a contingency which has
more than once occurred on a tubular bridge without detriment, whereas in
event of such an accident occurring on a Trellis or Lattice bridge, it
must infallibly be destroyed. Where the proposed bridge is of the
unusual length of a mile and a quarter, it is obvious that this
consideration must have had no small weight with the directors, who
eventually decided on proceeding with the Tubular Bridge according to Mr.
Stephenson's original design.

From the first projection of the Victoria Bridge, the difficulties of
executing such a work across a wide river, down which an avalanche of ice
rushes to the sea every spring, were pronounced almost insurmountable by
those best acquainted with the locality. The ice of two thousand miles
of inland lakes and upper rivers, besides their tributaries, is then
poured down stream, and, in the neighbourhood of Montreal especially, it
is often pi