The side towers stand
at a clear distance of 460 feet from the great central tower; and,
again, the abutments stand at a distance from the side towers of 230
feet, giving the entire bridge a total length of 1849 feet,
corresponding with the date of the year of its construction. The side
or land towers are each 62 feet by 52 feet at the base, and 190 feet
high; they contain 210 tons of cast iron.
[Illustration: CONWAY CASTLE AND TUBULAR BRIDGE.]
The length of the great tube is exactly 470 feet, being 12 feet longer
than the clear space between the towers, and the greatest span ever yet
attempted. The greatest height of the tube is in the centre--30 feet,
and diminishing towards the end to 22 feet. Each tube consists of sides,
top and bottom, all formed of long, narrow wrought-iron plates, varying
in length from 12 feet downward. These plates are of the same
manufacture as those for making boilers, varying in thickness from
three-eighths to three-fourths of an inch. Some of them weigh nearly 7
cwt., and are amongst the largest it is possible to roll with any
existing machinery. The connexion between top, bottom, and sides is made
much more substantial by triangular pieces of thick plate, riveted in
across the corners, to enable the tube to resist the cross or twisting
strain to which it will be exposed from the heavy and long-continued
gales of wind that, sweeping up the Channel, will assail it in its lofty
and unprotected position.
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