HKB
a part of the structure, was of more than questionable utility; and if Mr. Pritchard's plan had been adopted, the problem of the iron bridge would still have remained unsolved.
The plan, however, after having been duly considered, was eventually set aside, and another, with the entire arch of cast-iron, was prepared under the superintendence of Abraham Darby, by Mr. Thomas Gregory, his foreman of pattern-makers. This plan was adopted, and arrangements were forthwith made for carrying it into effect. The abutments of the bridge were built in 1777-8, during which the castings were made at the foundry, and the ironwork was successfully erected in the course of three months. The bridge was opened for traffic in 1779, and proved a most serviceable structure. In 1788 the Society of Arts recognised Mr. Darby's merit as its designer and erector by presenting him with their gold medal; and the model of the bridge is still to be seen in the collection of the Society. Mr. Robert Stephenson has said of the structure: "If we consider that the manipulation of cast-iron was then completely in its infancy, a bridge of such dimensions was doubtless a bold as well as an original undertaking, and the efficiency of the details is worthy of the boldness of the conception." [10] Mr. Stephenson adds that from a defect in the construction the abutments were thrust inwards at the approaches and the ribs partially fractured. We are, however, informed that this is a mistake, though it does appear that the apprehension at one time existed that such an accident might possibly occur.
To remedy the supposed defect, two small land arches were, in the year 1800, substituted for the stone approach on the Broseley side of the bridge. While the work was in progress, Mr. Telford, the well-known engineer, carefully examined the bridge, and thus spoke of its condition at the time:--"The great improvement of erecting upon a navigable river a bridge of cast-iron of one arch only was first put in practice near Coalbrookdale. The bridge was executed in 1777 by Mr. Abraham Darby, and the ironwork is now quite as perfect as when it was first put up. Drawings of this bridge have long been before the public, and have been much and justly admired." [11] A Coalbrookdale correspondent, writing in May, 1862, informs us that "at the present time the bridge is undergoing repair; and, special examination having been made, there is no appearance either that the abutments have moved, or that the ribs have been broken in the centre or are out of their proper right line. There has, it is true, been a strain on the land arches, and on the roadway plates, which, however, the main arch has been able effectually to resist."
The bridge has now been in profitable daily use for upwards of eighty years, and has during that time proved of the greatest convenience to the population of the district. So judicious was the selection of its site, and so great its utility, that a thriving town of the name of Ironbridge has grown up around it upon what, at the time of its erection, was a nameless part of "the waste of the manor of Madeley." And it is probable that the bridge will last for centuries to come. Thus, also, was the use of iron as an important material in bridge-building fairly initiated at Coalbrookdale by Abraham Darby, as the use of iron rails was by Richard Reynolds. We need scarcely add that since the invention and extensive adoption of railway locomotion, the employment of iron in various forms in railway and bridge structures has rapidly increased, until iron has come to be regarded as the very sheet-anchor of the railway engineer.