neer,
daringly resolved to span the strait with a suspension bridge 100 feet
above the water. He began it in 1818, and on the last day of January
1826 the London mail coach passed over the estuary. The bridge remains
to this day a vast and beautiful monument of engineering skill. But
when railways began to play, something more ponderous and powerful
became necessary. A bridge with arches was talked of, but this was
considered likely to be obstructive to the navigation of the strait,
therefore another plan was demanded. At this juncture Robert Stephenson
came forward with a plan. Pounding his opinion on the known fact that
hollow columns are stronger than solid ones; that hollow beams are
better than solid beams, he leaped to the bold conclusion that a hollow
iron beam, or tube, could be made large enough to allow a train to pass
through it! As usual there sprang up a host of cold-waterers, but
thanks to British enterprise, which can dare anything, there were found
enough of men willing to promote the scheme. It was no sooner resolved
on than begun. Massive abutments of stone were raised on each shore to
the height of 100 feet above high-water. The width of the strait
between these abutments is nearly 500 yards. Midway across is the
Britannia Rock, just visible at half tide. The engineer resolved to
found one of his towers on that rock. It was done; but the distance
being too great for a single span of tube, two other towers were added.
The centre towel rises 35 feet higher than the abutments, thus giving to
the tube a very slight arch, which, however, is barely perceptible.

The tubes were rectangular, with double top and bottom made of plates of
wrought-iron, from three-eighths to three-quarters of an inch thick, and
varying in length according to their position--the whole when put
together forming a single tube about 500 yards long. The two centre
ones were the largest and most difficult to manage, each having to be
built on shore, floated off on barges, and lifted by hydraulic power a
height of about 100 feet. Some idea of what this implied may be
gathered from the following fact. Each tube weighed 1800 tons--the
weight of a goodly-sized ocean steamer! A perfect army of men worked at
the building of the tubes; cutting, punching, fitting, riveting,
etcetera, and as the place became the temporary abode of so many
artificers and labourers, with their wives and children, a village
sprang up around them,