The fidlo•ing graphic description, by an eye-witness, of the floating of the first tubes, is too interesting to he omitted. The operations were conducted by Captain Claxton, who, with Mr. Stephenson, and other gentlemen, was on the tube directing the proceedings. "Captain Claxton was easily dis tinguished by his speaking trumpet, and there were also men to hold the letters which indicated the different capstans, so that no mistake could occur as to which capstan should he worked ; and flags red, blue, or white, signalled what par ticular movement should he made with each. .About half= pastseven o'clock in the evening, the first perceptible motion, which indicated that the tide was lifting the mass, was ob served, and, at Mr. Stephenson's desire, the depth of water was ascertained, and the exact time noted. In a few minutes the motion was plainly visible, the tube being fairly moved forward some inches. This moment was one of intense interest; the huge bulk gliding gently and easily forwards as it' she had been but. a small boat. The spectators seemed spell-bound ; fins no shouts or exclamations were heard, as all watched silently the silent course of the heavily-freighted pontoons. The only sounds heard were the shouts from Captain Claxton ; as he gave directions to let go ropes,' to haul in tinter,' &e., and broadside on,' the tube floated majestically into the centre of the stream. I then left my station, and ran to the entrance of the works, where I got into a boat, and bade the men pull out as far as they could into the middle of the straits. This was no easy task, the tide running strong; but it afforded me several splendid views of the floating mass, and one was especially fine. The tube coming direct, on down the stream.—the distant hills covered with trees,—two or three small vessels and a steamer, its stnoke blending well with the scene, forming a capital back-ground ; whilst on one side, in long stretching per spective, stood the three unfinished tubes, destined ere lung to form, with the one then speeding on its journey, one grand and unique roadway. It was impossible to see this imposing sight. and not feel its singleness. so to speak. Anything so mighty of its kind had never been before; again it would assuredly be 'but it was like the first voyage made by the first steam-vessel, something till then unique. At twenty live minutes to nine o'clock, the tube was nearing the Angle sea pier, and at this moment the expectation of the spectators was greatly increased, as the tube was so near its destination ; and soon all fears were dispelled, as the Anglesea end of the tube passed beyond the pier, and then the Britannia pier end neared its appointed spot, and was instantly drawn back close to the pier, so as to rest on the bearing intended for it. There was then a pause of a few minutes while waiting for the tide to turn, and when that took place the huge bulk floated gently into its place on the Anglesea pier, rested on the bearing there, and was instantly made thst, so that it could not move again. The cheering, till 110W was loud and hearty, and some pieces Of cannon on the shore gave token, by their loud bootning, that the great task of the day was done." The preparations for pertlirming, so important and perilous an undertaking as that of hoisting the enormous fitbric, to place it in its permanent position over the straits, were on a scale of immense magnitude. This will he the more readily understood, when it is stated that the total dead weight lifted 100 feet high from high-water mark. was upwards of 2,000 tons, or equivalent to the elevation to that height of upwards of 30,000 men. During the progress of this great work, a general impression appeared to prevail with the public, that when the tubular bridge was floated, the whole operation would be completed ; but that, if it may be so termed, was a vulgar error. The floating was notlfng more than the launch of the great iron ferry to the precise site, where it was to he raised by mechanical power, specially constructed for the purpose, to a height nearly equal to that of the dome of St. Paul's. The stroke of the hydraulic presses employed for the purpose, was 6 feet, that is to say, they were only capable of raising 6 feet at one lift. The tube of 2,000 tons weight was consequently to be sustained while the presses were lowered, and a fresh hold obtained. This sustentation, owing to the immense magnitude of the labour, was effected by building up successive layers of masonry at every 6 foot lift, under the tube, to support it securely in its upright ascent, during which arrangements were made for another 0-foot hoist, until the whole 100 feet were finished. Ilad it not been for this process of building up, the operation would have only occupied about a day, but as it was, it took a fortnight. The precaution was adopted by Mr. Stephenson and Mr. Clark, to guard against the probability of casualty, seeing that, should any accident occur, the labour of years, and the outlay of half a million of money, would have been inevitably sunk. To insure security, however, some con trivances were adopted, by which the supporting chains, as they rose, were continually followed up by wedges of wood, so that in the event of any accident having arisen to the lifting machinery, no injury, it was expected, would happen to the tube. The mechanical contrivances for the purpose were the largest in the world, and the most powerful ever constructed.
We are enabled, from a close inspection, to give a descrip tion of the vast apparatus for hoisting the huge burden. The machine used to effect this, was an enormous hydraulic press, a contrivance invented by Bramah, and used in operations where intense pressure is required. Its construction was of the most simple character, and consisted only of an exceed ingly thick and very heavy iron cylinder, like a mortar.
A strong piston, or plunger, also of iron, called the ram, and fitted with a leather collar at the shoulder, so as to render it water-tight, worked up and down inside this cylinder. Water was forced into the cylinder by a force-pump, through a small orifice which might be compared to the touch-hole of a gun. The whole secret of the immense power of this machine, consisted simply in the prodigious force with which the water was driven into it, and which in the present instance was so great, that it threw the water to the height of nearly 20,000 feet, which is more than five times as high as the neighbouring noble pinnacle of Snowdon, and 5,000 feet higher than the monarch of mountains, Alum Blanc. It in tact resembled the piston of a steam-engine, but instead of using steam at 30 or 401b, pressure to the inch, water was used at a pressure of 800 or 9001b. The cylinder of course was of almost adamantine strength, to enable it to sustain and withstand that pressure. The sides of the largest of these presses used in raising the bridge, were 11 inches thick. The weight of the cylinder, which was of east-iron, in one piece, was 16 tons alone ; but the whole machine complete was •10 tons. The ram or piston within it, was 20 inches in diameter, and when worked to its utmost power, would alone he quite capable of raising one of the tubes. The marvellous thing above all was this, that in spite of its immense propor tions, its stupendous action was guided and controlled with the most perfect ease and precision by one man. This hydraulic giant was constructed by Messrs. Easton and Amos, engineers of Southwark. It stood on two beams on a sort of eyrie, at the top of one of the towers, whence a grand and open view is obtained of the straits seaward, while its elevation above the ravine was upwards of 200 feet. The press was composed of wrought-iron plates, riveted together at the top of the side towers, where, with its assistant machinery, it occupied a large chamber to itself, about 21) feet above the level to which the bridge had to be raised.
The sensations experienced on looking down from this lofty elevation over the rushing stream of the straits, and the great tubes and machineries strewn round about below, were of a peculiarly impressive character. In addition to this large press, there were two smaller presses, with yarns 18 inches in diameter, placed side by side at a similar level on the Britannia tower, and w hich :toted in conjunction with the large press. The chains by which the power exerted by these presses in their lofty position was communicated to *Iv>, tubes lying at the base of the tower, resembled the chains or an ordinary suspension-bridge, and were similar to those of the bridge at I lung,erford. They were mannthctured by the patent process of Messrs. Howard and Ilavenhill, of London, and consisted of flat links seven inches lone, one inch thick, and six feet in length, with an eye at each end, and were bolted together in sets of eight and nine links alternately. The weight of the chains employed in lifting the 2,000 tons, was about 100 tons, fin• exceeding that of the well-known equestrian statue of the Duke of Wellington at Ilyde Park, which has hitherto been regarded as one of the greatest "lifts" of the age. These chains were attached to the tube at two feet from the end, and in order to get sufficient pur chase at the part, three strong flames of cast iron were built into each end of the tube. The innermost frame only stiffens and supports the sides, while the tube was resting on its ends. The two outer frames were the lifting frames. The chains were attached to them by three sets of massive cast-iron beams, placed across the inside of the tube, one above another. their ends fitting under deep shoulders or notches in the lifting frames, where they were secured by screw-bolts. As an additional precaution, two very strong wrought-iron straps passed over the upper pair of beams, and descended into the bottom cells beneath the frames, where they were strongly keyed. The weight of these lifting frames and east-iron beams was 200 tons, and it was even a matter of wonder among the engineers themselves. how machinery could be made strong enough to raise the ponderous load. The way in which the chains were connected with the press, was by an exceedingly thick and heavy beam of east-iron, strengthened by •rought-iron ties across the top. It rested like a yoke on the shoulder of the rani, and was called the cross head of the press. The two chains passed through square holes at either end of the cross head, and were securely gripped at the top of it by an apparatus called the clams, consisting of two strong cheeks of wrought-iron, drawn together by screws like a black smith's vice. The beams on which the presses stood, the cross heads, and all the parts that were subjected to a very heavy strain, were either constructed of; or strengthened by •rought-inn, whieh was found to be less brittle and more trustworthy than east-iron. As the tube was 12 feet longer, allowing 0 feet at each end, than the distance between the towers in which the presses worked ; recesses or grooves were left in the fret: of each, of 6 feet deep, in order to receive the additional length, and of sufficient width to allow the end of the tube to slide up easily within them. The recesses extended from the bottom of the towers to nearly ' the height of the hydraulic machines. It was in the low end of these recesses, on a soft bed of timber placed to receive it, that each great tube rested, lifter being tloated there, until the vast mechanical equipments f r ballooning it to its per manent level, 102 feet above high water mark, were cum ' pleted.