432 FLOATING THE CONWAY TUBES. CHAP. XIX. history of the construction of the Britannia and Conway Bridges we would refer the reader for full details as to the methods of construction employed in these extraordinary works. 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. the mean time, the presses and raising machinery had been fitted in the towers above, and the lifting process was begun on the 8th of 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 through 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. In The floating and fixing of the great Britannia tubes was a still more formidable enterprise, though the ex perience gained at Conway rendered it easy compared with what it otherwise would have been. Mr. Stephenson superintended the operation of floating the first in person, giving the arranged signals from the top of the tube on which he was mounted, the active part of the business being performed by a numerous corps of sailors, under the immediate direction of Captain Claxton. Thousands of spectators lined the shores of the Strait on the evening of the 19th of June, 1849. On the land attachments being cut, the pontoons began to float off; but one of the capstans having given way from the too great strain put upon it, the tube was brought home again for the night. By next morning the defective capstan was restored, and all was in readiness for another trial. At half-past seven in the evening the tube was VOL. III. 2 F 434 FLOATING THE BRITANNIA TUBES. CHAP. XIX. afloat, and the pontoons swung out into the current like a monster pendulum, held steady by the shore guidelines, but increasing in speed to almost a fearful extent as they neared their destined place between the piers. "The success of this operation," says Mr. Clark, “depended mainly on properly striking the 'butt' beneath the Anglesey tower, on which, as upon a centre, the tube was to be veered round into its position across the opening. This position was determined by a 12-inch line, which was to be paid out to a fixed mark from the Llanfair capstan. The coils of the rope unfortunately over-rode each other upon this capstan, so that it could not be paid out. In resisting the motion of the tube, the capstan was bodily dragged out of the platform by the action of the palls, and the tube was in imminent danger of being carried away by the stream, or the pontoons crushed upon the rocks. The men at the capstan were all knocked down, and some of them. thrown into the water, though they made every exertion to arrest the motion of the capstan-bars. In this dilemma Mr. Charles Rolfe, who had charge of the capstan, with great presence of mind, called the visitors on shore to his assistance; and handing out the spare coil of the 12-inch line into the field at the back of the capstan, it was carried with great rapidity up the field, and a crowd of people, men, women, and children, holding on to this huge cable, arrested the progress of the tube, which was at length brought safely against the butt and veered round. The Britannia end was then drawn into the recess of the masonry by a chain passing through the tower to a crab on the far side. The violence of the tide abated, though the wind increased, and the Anglesey end was drawn into its place beneath the corbelling in the masonry; and as the tide went down, the pontoons deposited their valuable cargo on the welcome shelf at each end. The successful issue was greeted by cannon from the shore and the hearty cheers of many thousands of spectators, whose sympathy and anxiety were but too clearly indicated by the unbroken silence with which the whole operation had been accompanied."1 By midnight all the pontoons had been got clear of the tube, which now hung suspended over the waters of the Strait by its two ends, which rested upon the edges cut in the rock for the purpose at the base of the Britannia and Anglesey towers respectively, up which the tube had now to be lifted by hydraulic power to its permanent place near the summit. The accuracy with which the gigantic beam had been constructed may be inferred from the fact that, after passing into its place, a clear space remained between the iron plating and the rock outside of it of only about three-quarters of an inch! Mr. Stephenson's anxiety was, of course, very great up to the time of performing this trying operation. When he had got the first tube floated at Conway, and saw all safe, he said to Captain Moorsom, "Now I shall go to bed." But the Britannia Bridge was a still more difficult enterprise, and cost him many a sleepless night. Afterwards describing his feelings to his friend Mr. Gooch, he said: "It was a most anxious and harassing time with me. Often at night I would lie tossing about, seeking sleep in vain. The tubes filled my head. I went to bed with them and got up with them. In the grey of the morning, when I looked across the Square, it seemed an immense distance across to the houses on the opposite side. It was nearly the same length as the span of my tubular bridge!" When the first tube had been floated, a friend observed to him, "This great work has made you ten years older." "I have not slept sound," he replied, " for three weeks." Sir F. Head, however, relates, that when he revisited the spot on the following morning, he observed, sitting on a The Britannia and Conway Tubular Bridges.' By Edwin Clark. Vol. II. p. 683-4. 2 No. 34, Gloucester Square, Hyde Park, where he lived. 436 LIFTING OF THE TUBES. CHAP. XIX. platform overlooking the suspended tube, a gentleman, reclining entirely by himself, smoking a cigar, and gazing, as if indolently, at the aërial gallery beneath him. It was the engineer himself, contemplating his new-born child. He had strolled down from the neighbouring village, after his first sound and refreshing sleep for weeks, to behold in sunshine and solitude, that which during a weary period of gestation had been either mysteriously moving in his brain, or, like a vision -sometimes of good omen, and sometimes of evil—had, by night as well as by day, been flitting across his mind. The next process was the lifting of the tube into its place, which was performed very deliberately and cautiously. It was raised by powerful hydraulic presses, only a few feet at a time, and carefully under-built, before being raised to a farther height. When it had been got up by successive stages of this kind to about 24 feet, an extraordinary accident occurred, during Mr. Stephenson's absence in London, which he afterwards described to the author in as nearly as possible the following words:"In a work of such novelty and magnitude, you may readily imagine how anxious I was that every possible contingency should be provided for. Where one chain or rope was required, I provided two. I was not satisfied with enough I must have absolute security, as far as that was possible. I knew the consequences of failure would be most disastrous to the Company, and that the wisest economy was to provide for all contingencies at whatever cost. When the first tube at the Britannia had been successfully floated between the piers ready for being raised, my young engineers were very much elated; and when the hoisting apparatus had been fixed, they wrote to me, saying, We are now all ready for raising her we could do it in a day, or in two at the most.' But my reply was, 'No: you must only raise the tube inch by inch, and you must build up under it as you rise. Every inch must be made good. Nothing must |