CHAIN-BRIDGES.
(SeeFrontispiece.)
It appears, from a description of bridges of suspension, communicated by R. Stephenson, civil engineer, some time ago, to the “Philosophical Journal,” that the first chain-bridge constructed in this country is believed to be one over the Tees, forming a communication between the counties of Durham and York. It is supposed, on good authority, to have been erected about 1741, and is described in the “Antiquities of Durham” as “a bridge suspended on iron chains, stretched from rock to rock, over a chasm nearly sixty feet deep, for the passage of travellers, particularly miners. This bridge is seventy feet in length, and little more than two feet broad, with a hand-rail on one side, and planked in such a manner that the traveller experiences all the tremulous motion of the chain, and sees himself suspended over a roaring gulf, on an agitated and restless gangway, to which few strangers dare trust themselves.” In 1816–17, two or three bridges of iron were constructed; the first, by Mr. Lees, an extensive woollen manufacturer, at Galashiels, in Scotland. This experiment, although made with slender wire, and necessarily imperfect in its construction, deserves to be noticed, as affording a practical example of the tenacity of iron so applied.—These wire bridges were suspended not upon the catemarian principle so successfully adopted in the larger works subsequently undertaken, but by means of diagonal braces, radiating from their points of suspension on either side towards the centre of the roadway. The unfortunate fabric next mentioned was constructed on this defective principle. Among the earliest practical exhibitions of this novel architecture in the United Kingdom, may be mentioned the uncommonly elegant and light chain-bridge whichwas thrown over the Tweed at Dryburgh, in 1817, by the Earl of Buchan, for the accommodation of foot passengers. Its length, between the points of suspension, was two hundred and sixty-one feet, being considered the greatest span of any bridge in the kingdom. This useful structure, the theme of such just applause, and which harmonised so finely with the far-famed scenery of Dryburgh Abbey, was entirely destroyed by a tremendous gale of wind, at the beginning of the year following its erection.—This bridge was subsequently restored upon a more secure system.