Mr. Stephenson’s time was so much engrossed with his extensive engineering business that he was in a great measure precluded from devoting himself to the consideration of the practical details. The results of the experiments were communicated to him from time to time, and were regarded by him as exceedingly satisfactory. It would appear, however, that while Mr. Fairbairn urged the rigidity and strength of the tubes without the aid of chains, Mr. Stephenson had not quite made up his mind upon the point. Mr. Hodgkinson, also, was strongly inclined to retain them. Mr. Fairbairn held that it was quite practicable to make the tubes “sufficiently strong to sustain not only their own weight, but, in addition to that load, 2000 tons equally distributed over the surface of the platform,—a load ten times greater than they will ever be called upon to support.” It was thoroughly characteristic of Mr. Stephenson, and of the caution with which he proceeded in every step of this great undertaking—probing every inch of the ground before he set down his foot upon it—that he should, early in 1856, (_sic_) have appointed his able assistant, Mr. Edwin Clark, to scrutinise carefully the results of every experiment, and subject them to a separate and independent analysis before finally deciding upon the form or dimensions of the structure, or upon any mode of procedure connected with it. At length Mr. Stephenson became satisfied that the use of auxiliary chains was unnecessary, and that the tubular bridge might be made of such strength as to be entirely self-supporting. While these important discussions were in progress, measures were taken to proceed with the masonry of the bridges simultaneously at Conway and the Menai Straits. The foundation-stone of the Britannia Bridge was laid on the 10th April, 1846; and on the 12th May following that of the Conway Bridge was laid. Suitable platforms and workshops were also erected for proceeding with the punching, fitting, and riveting of the tubes; and when these operations were in full progress, the neighbourhood of the Conway and Britannia Bridges presented scenes of extraordinary bustle and industry. About 1500 men were employed on the Britannia Bridge alone, and they mostly lived upon the ground in wooden cottages erected for the occasion. The iron plates were brought in ship-loads from Liverpool, Anglesey marble from Penmon, and red sandstone from Runcorn, in Cheshire, as wind and tide, and shipping and convenience, might determine. There was an unremitting clank of hammers, grinding of machinery, and blasting of rock, going on from morning till night. In fitting the Britannia tubes together, not less than 2,000,000 of bolts were riveted, weighing some 900 tons.