" Iron bridges quickly followed
upon these early experiments, for we hear of several being built on
the arched system, and large cotton-mills being erected upon fireproof
principles at the commencement of the present century, the iron girders
and columns of one mill being designed by Boulton and Watt. A little
later, Eaton Hodgkinson proved by experiments the uncertainty of cast
iron with regard to tensile strength, which he showed to be much less
than had been stated by Tredgold. Cast iron was afterwards largely
adopted by engineers. The experiments of Hodgkinson supplied a safe
foundation of facts to work upon, and cast iron has ever since retained
its hold. Thomas Paine's celebrated bridge at Sunderland had a span of
236 feet and a rise of 34 feet, and was constructed of six ribs, and is
remarkable from the fact that the arched girder principle used in the
Coalbrookdale and Buildwas bridges was rejected, that the ribs were
composed of segments or voussoirs, each made up of 125 parts, thus
treating the material in the manner of stone. Each voussoir was a
cast-iron framed piece two feet long and five feet in depth, and these
were bolted together.
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