Page:Royal Naval Biography Marshall v4p1.djvu/36

 “On the Scotch side of the river, the catenarian chains pass over a pillar of aisler masonry, which measures sixty feet in height, is about thirty-six feet in its medium width, and seventeen and a half feet in thickness. The sides of the lower ten feet of the walls of this pillar are square, but at this height the walls begin to slope at the rate of one perpendicular to twelve horizontal. The archway in the masonry of this pillar, which forms the immediate approach to the roadway, measures twelve feet in width, and seventeen feet in height. Each pair of main chains, being suspended horizontally, pass through corresponding apertures in the masonry, at the distance of about two feet above one another, and go over rollers connected with the building. The links of the main chains at these points are made as short as the strength or thickness of the iron will permit of their being welded, in order that they may pass over the rollers, without distorting or unduly straining the iron. After going through the masonry of the pillar, the chains are continued in a sloping direction to the ground. Here they are sunk to the depth of twenty-four feet, where they pass through great ballast-plates of cast-iron, into which they are stopped by a strong iron spear or bolt, of an oval form, measuring three inches by three and a half inches in thickness. The cast-iron ballast plates measure six feet in length, five feet in breadth, and five inches in thickness in the central parts; but towards the edge, they diminish in thickness to two and a half inches. The ends of the chain thus fixed, are loaded with mound-stones and earthy matters, to the level of the roadway of the bridge.

“On the south side of the Tweed, the pillar or tower of masonry forming the abutment or point of suspension, is built upon a bench or foundation, excavated in the face of a precipitous sandstone rock, and is only about twenty feet in height; but its other dimensions correspond with the upper part of the masonry on the Scotch side. The chains on the English side are made to rest upon plates of cast-iron, included in the masonry, instead of rollers, as on the opposite side. Here the ballast-plates are of the same dimensions as those already described; but, instead of being sunk into the ground, as on the Scotch side, their position is rather above the foundation of the pillar, where they are set nearly perpendicular, but are placed so as to correspond with the direction of the strain or weight of the bridge. For the greater security of the position of these ballast-plates on the English side, they are connected with a horizontal arch of masonry, which is dovetailed into the rock.

“The whole works of the Union-bridge, for masonry, carpentry, and smithery, were undertaken by Captain Brown for the sum of about £5000, whilst the execution of a bridge of stone must have cost at least four times that sum. The object of its projector, says Mr. Stevenson, (from whose paper we abridge this article,) was not the realization even of the cost of this bridge, but chiefly with a view to shew the application of chain-cables to his favourite object of bridge-building. The trustees for this bridge