a Hanging Iron Bridge across the Menai Strait. 13 



2. The Iron Work. — Mr. Telford proposes to have four lines 

 of suspension in the breadth of the bridge, by which means his 

 cables will be disposed in such a manner, as to divide it into two 

 carriage-ways of twelve feet each, and one footway in the centre 

 of four feet. Along each line he will have four cables, making 

 in the whole sixteen ; these cables will pass over rollers fixed on 

 the summits of the jiyramids, and be fastened at their extremities 

 to an iron frame, lying horizontally over the tops of the small 

 arches, and under a mass of masomy, as described by the dotted 

 lines on the plan. (Plate.) 



From these cables the roadway will be suspended by vertical 

 iron rods, connected at their lower extremities with wrought iron 

 bars, both transversely and longitudinally, thus forming a frame 

 on which timber will be laid for the roadway. 



Mr. Telford intends to make a temporary wire bridge from 

 one abutment to the other, in order to carry over the cables, and 

 arrange the several .parts of the bridge. 



3. The Strength of the Bridge. — Mr. Telford informed your 

 Committee, that for many years past he has bestowed great pains 

 and consideral)le expense on making experiments for the pur- 

 pose of ascertaining the strength of malleable iron : he says, in 

 his evidence, that he has not made less than 300 experiments 

 upon iron, from one-twentieth of an inch to two inches in dia- 

 meter, and from 30 feet in length to 900 feet ; that he has made 

 them verticallv, horizontally, and with a variety of different de- 

 grees of curvature ; that he has combined iron into the shape in 

 which be has proposed to make the bridge, in a model of 50 feet 

 in length, and tried experiments upon it. That the greatest part 

 of his experiments were made from absolute weight, by tearing 

 iron to pieces bv mere weight, and that all his calculations were 

 founded upon the true and actual strength of iron, as proved by 

 the weight it would sustain before it would stretch or bre^k 

 asunder. In respect of the larger pieces of iron, which could 

 not conveniently be torn asunder by weight only, Mr. Telford 

 made several experiments upon the strength of it, by means of 

 an hydraulic press of Mr. Brunton's, made on Mr. Bramah's 

 princi|)Ie; and by this it appeared, that it re(|uired a weight of 

 from 2() to 30 tons to tear a square inch bar asunder : similar 

 experiments have been tried with other machines, which gave 

 very nearly the same result. Mr. Rennie and Mr. Uonkin, in 

 their evidence, entirely agree with Mr. Telford's statement of the 

 absolute strength of malleable iron, Mr. Ileniiic recommends, 

 that this bridge should be constructed, so as to be four times be- 

 yond tlie strength reciuisite to carry its own weight ; that is, to 

 make it something stronger than it is proposed to be made by 

 Mr. Telford j but Mr. Telford says, there will be no difliculty in 



giving 



