496

HISTORY OF ENGINEERING.

Book I.

After the abutments were built, ami a timber scaffolding constructed across the Wear,six of the frames were placed on the abutments, in the manner of voussoirs, and wrought-iron bars were fitted into the grooves, so as to hold several of them together. Hollow pipesof cast-iron, 4 inches in diameter, fitted to reach between each two frames, were introducedentirely across the softite; upon the ends of these pipes were dandies, having holes drilledinto them to answer to those in the 4-inch pieces of the frames, as well as to those of tlje

SUNDERLAND BRIDGE.

wrought-iron bars ; through these holes wrought-iron bolts were passed, which brought allthe parts together by means of forelocks. The frames do not meet at the upright pieces,but only on the three points of the 4-inch pieces; at the ends of the hollow pipes are smallprojecting pieces, embracing both the upper and lower edge of the frames, which opposeeach other. When the whole of the frames were placed upon the centre, and the archkeyed, in the manner of a stone bridge, the upright pillars were fixed ; between them were

SUNDERLAND BRIDGE.

cast-iron circles, resting upon the extrados of the voussoirs. The road is carried upon atimber platform, and the railing is of cast-iron.

This magnificent bridge, from its elevation and lightness of construction, is perhaps theboldest attempt that had hitherto been made to cross a river, and at once proved what couldbe accomplished by the aid of cast-iron ; some objections have been made to the numberof joints in the main ribs, which might possibly have been lessened, and considerable