The floating of the tubes on pontoons, from the places where they had been constructed, to the recesses in the masonry of the towers, up which they were to be hoisted to the positions they were permanently to occupy, was an anxious and exciting operation. The first part of this process was performed at Conway, where Mr. Stephenson directed it in person, assisted by Captain Claxton, Mr. Brunel, and other engineering friends. On the 6th March, 1848, the pontoons bearing the first great tube of the up-line were floated round quietly and majestically into their place between the towers in about twenty minutes. Unfortunately, one of the sets of pontoons had become slightly slued by the stream, by which the Conway end of the tube was prevented from being brought home; and five anxious days to all concerned intervened before it could be set in its place. In the mean time, the presses and raising machinery had been fitted in the towers above, and the lifting process was begun on the 8th April, when the immense mass was raised 8 feet, at the rate of about 2 inches a minute. On the 16th, the tube had been raised and finally lowered into its permanent bed; the rails were laid along it; and, on the 18th, Mr. Stephenson passed through with the first locomotive. The second tube was proceeded with on the removal of the first from the platform, and was completed and floated in seven months. The rapidity with which this second tube was constructed was in no small degree owing to the Jacquard punching-machine, contrived for the purpose by Mr. Roberts of Manchester. This tube was finally fixed in its permanent bed on the 2nd of January, 1849. [Picture: Conway Tubular Bridge]