The Britannia Bridge was commenced in May, 1846, and the first of the main tubes was completed in June, 1849. The work was carried on close to the bridge, on the Anglesea shore; and when the tube was ready to be transported to its place on the piers, which had been prepared to receive it, eight flat-bottomed pontoons were provided to carry it, which, being brought underneath, floated the ponderous mass on the water as they rose with the tide. The floating and fixing in its place of the tube took place on the 27th of the same month, in view of an immense concourse of spectators. After the preliminary arrangements for letting go had been completed, Mr. Stephenson, and other engineers, got on the tube, with Captain Claxton, R. N., to whom the management of the floating was entrusted. A correspondent of the _Illustrated London News_ thus describes the proceeding, and its successful result:--"Captain Claxton was easily distinguished 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 be worked; and flags, red, blue, and white, signified what particular movement should be made. About 7.30 p.m. the first perceptible motion, which indicated that the tide was lifting the mass, was observed, 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 as gently and easily forward as if she had been but a small boat. The spectators seemed spellbound, for no shouts or exclamations were heard, as all watched anxiously the silent course of the heavily freighted pontoons. The only sounds heard were the shouts of Captain Claxton, as he gave directions to 'let go ropes,' to 'haul in faster,' &c.; and 'broadside on,' the tube floated majestically in 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 through the stream--the distant hills covered with trees, two or three small vessels and a steamer, its smoke blending well with the scene, forming a capital background; whilst on one side, in long stretching perspective, stood the three unfinished tubes, destined ere long to form, with the one then speeding on its journey, one grand and unique roadway. It was impossible to see this grand and imposing sight, and not to feel its singleness, if we may so 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 until then unique.