[110] Though it is convenient to explain the nature of the strains in the Saltash bridge as an arch and suspension bridge combined, it is not intended to imply that there is any virtual difference between this truss and the one at Chepstow, for in both the strain on the tube counteracts the strain on the chains, though the one tube is curved and the other straight.
[111] Humber’s Bridge Construction, vol. i. p. 231; vol. ii. pl. 78, 79, 80.
[112] This load amounted to two and three quarter tons per foot run, in addition to the weight of the truss. Under this load the central deflection was about 5 inches.
The strain on the iron of the tube and of the chains with a load of one ton per foot run, in addition to the weight of the truss, flooring, and ballast, is under four tons per square inch.
[113] The difficult operations of floating and lifting the superstructures of the Chepstow and Saltash bridges were carried out entirely by Mr. Brunel and his assistants, there being no contractor engaged in, or responsible for, the work in either case.
[114] A photograph taken shortly after the floating of the second tube forms the frontispiece of the first volume of Humber’s Bridge Construction.
[115] See above pp. 190 and 193.
[116] It has been observed with much truth that full justice has not been done to Mr. Brunel’s exertions in this department of practical science.—See ‘Address of George Parker Bidder, Esq., on his election as President of the Institution of Civil Engineers, January 10, 1860.’
[117] Captain Claxton died on March 27, 1868, in his 79th year. The manuscript of this and the three following chapters was fortunately completed in time to be submitted to him. He spared no trouble either in giving or procuring original documents and other materials for all parts of this book, in the preparation of which he took the liveliest interest.
[118] To enable the ship to resist the action of the heavy Atlantic waves, especial pains were taken to give her great longitudinal strength. The ribs were of oak, of scantling equal to that of line-of-battle ships. They were placed close together, and caulked within and without before the planking was put on. They were dowelled and bolted in pairs; and there were also four rows of 1½-inch iron bolts, 24 feet long, and scarfing about 4 feet, which ran longitudinally through the whole length of the bottom frames of the ship. She was closely trussed with iron and wooden diagonals and shelf pieces, which, with the whole of her upper works, were fastened with bolts and nuts to a much greater extent than had hitherto been the practice.