A NEW WONDER OF THE WORLD, THE BRITANNIA BRIDGE.

New Zealand Spectator and Cook's Strait Guardian, Volume IV, Issue 254, 5 January 1848, Page 4

A NEW WONDER OF THE WORLD, THE BRITANNIA BRIDGE.

- The following description of this stupendous work is given by a correspondent of the Manchester Examintr : — The Menai Strait is an arm of the sea, separating the island county of Anglesea from Carnarvonshire, on the mainland of Wales. It is fourteen miles long, varying from 200 yards to two miles in width. An impetuous -tide sweeps through it, which, at one time, • with the mid-water and under water rocks, •rendered its navigation exceedingly dangerous. The worst of the rocky dangers have been removed> and vessels of the largest size may now pass from Carnarvon Bay, on the south of Anglesea, to Bangor Bay, on the north, without sailing round Anglesea, should the stormy weather or winds at Holyhead render the passage of the Menai Strait preferable. The necessity of a passage across the Strait was, originally, to conuect the island and the mainland ; and while that was all, the passage -was by ferry boats upon the water. Ultimately the harbour of Holyhead, on the extreme west of Anglesea, the nearest point to Ireland, was decided upon as the English landing place. Roads were made from England through Wales, and a bridge, unequalled in beauty and magnificence, suspended by ponderous chains, on lofty piers, was thrown across the Strait, at a narrow point about two miles from Bangor. In process of time it was deemed expedient to supersede the turnpike roads leading to Holybead by a railway. At first it was proposed to use the suspension bridge for the railway trains, by having stations at each end, at which the locomotive engines would be detached, and between which a stationary engine would draw the trains. The bridge was declared capable of sustaining a weight of 2600 tons, of which 1094 tons were its own weight; thus giving a surplus strength of 1500 tons. If the bridge was covered with loaded railway carriages over all its length, and on each of its roadways (it is divided into two, with a spacious pathway between), the weight of the carriages would have been 865 tons, leaving still a surplus strength of 621 tons. But other objections to its use for railtray trains arose, the chief of which was its undulatory motion. One would suppose the wind would cause it to swing to and fro, rather than to heave up and down in undulations. But it has hardly any sideway or swinging motion. Nor has it now as much of the undulatory motion as it once had. Mr. Fisher, the resident engineer, told me that he had known it heave six feet above and deflect six feet below the level in gales of wind. It has been improved by adding weight to the roadway, and tension rods between the chains, so as to prevent that extreme motion which in gales of wind ran along it like a heaving wave from end to end, tearing up the flooring which formed the paths and waggon tracks. Still, it is undulatory. I stood on it in a gale, and felt it heaving beneath me as a ship heaves when a billow passes underneath. This being a characteristic inseparable from its construction, it was resolved that a new bridge should be erected for the use of the railway on a new principle. The inventive genius of Robert Stephenson declared that this new bridge should be two iron tubes or i ail way tunnels made of iron plates, laid parallel to each other, on piers built on the rocks beneath. If we suppose ourselves stationed in a boat in the middle of the Menai Strait, a few hundred yards distant from the new bridge on the louth side, and suppose it finished, we shall see a wonder of the world of this kind ; first, there is the middle pier rising out of the water founded on the Britannia rock, after which the bridge is named. This rock can be seen at low water. The breadth of this pier is 62 feet by 53 feet and a quarter of an inch. The blocks of stone are seven and eight feet long by three and four feet in breadth and deepness, and they rise, stone upon stone, until the pier is 230 feet high. At the distance of four hundred and sixty feet on each side of the centre pier there rise, near the water's edge, two other piers of the fame gigantic breadth and height ; while on each side of these two piers, at the distance of tw ; o hundred and fifty feet, there rise two W|lls. Continuing outwards, the wall on our right hand, on the Carnarvon shore, does not extend it* ponderous bulk far back, for the land is high and bold, and the railway comes along its elevated brow, and at once lays bold of the bridge. But on our left hand, which is the Anglesea shore, the wall is the forehead and end of a mighty embankment on which the railway is raised to the level of the bridge. There, then, are the four spaces before us, across which, in the iron tubes, the railway is laid, two spaces on each side of the centre pier of 460 feet each — (let the reader measure 460 feet on a street or on a road, and he will wonder at th 3 vastness of this structure,);( and -two moire spaces of 250 ieet re-

spectively, at each end. The tubes are eight in number, each of them 30 feet on the exterior side, and 27 feet high in the interior. Each is 14 feet wide, and they are laid in couples parallel to each other. Taking ourselves in our boat underneath the bridge, and looking up, glancing from the Carnarvon side of the Strait, we see two tubes, rather, we should say, masses of iron, for they do not seem to be tubes, lying side by side from the wall already named across the space of 250 feet. They have each a hold upon the stone work, several feet at each end, and they rest upon moveable rollers and balls made of gun metal, the hardest known : those rollers and | balls resting on beds of metal, and moving [ outwards or inwards as the massive tubes of iron expand with heat or contract with cold. Next we see two others of the same height and width, viz., thirty feet high and fourteen feet wide, lying side by side across the next space of 460 leet, and resting on the masonry as the others. Thirdly we see two more lying side by side across a space of 460 feet ; and lastly, two crossing the space of 250 feet. In the whole, with the breadth of the piers and the landward buildings, the length of the bridge is one third of a mile. In height the three piers are, as already said, 230 feet. But they are seventy feet higher than the tubes, These are so massive that their actual elevation above the water seems less than it really is ; and so dead and inelegant to the eye, that it was necessary to raise the piers seventy feet above them, to give a show of elegance to the structure. Measuring from low water mark to the bottom of the tubes, the height is 130 feet, the tubes being thirty feet on the side, and the piers seventy feet above their upper surface. As ornaments to the two walls which rise upon each shore, are four lions, two at each end of the bridge. The lions contain about 8000 cubic feet of stone. They lie couched, and yet the height of each is twelve feet; the greatest breadth across the body is nine feet ; the length twenty-five feet ; the breadth of each pair two feet four inches. As we are now so high as to see the lions in detail, we may look into the interior of the iron tubes. They are made of plates of iron of various thicknesses, rivetted together. The iron increases in thickness as we proceed towards the centre. We now see that the roofs of the tubes are formed ol cells, and also the floors. Those cells are formed of iron plates set on edge, the cells of the roof being within a fraction of one foot nine inches square, and those of the floor being one foot nine inches wide, and two feet three inches deep. The rails on which the trains run are laid on those cells of the floor. The flat bottom, the two upright sides, and the flat roof of each tube are formed of plates, the thinnest of which is a quarter of an inch, and the thickest twelvesixteenths of an inch, but the number of them laid together, and the internal joining, cannot yet be explained. The weight of each of the four long tubes will be about 1300 tons ; the weight of each of the four short ones about 600 tons. In the whole there will be at least 7600 tons of iron used. No contracting estimate of the expense of the irou part of the work has been made, as the work may cost more or less according to circumstances. The masonry was contracted for by B. J. Nowell and Co., at £130,000 ; but, from alterations iv the plans, it will cost (no further alterations being made) £200,000. They expect to finish the masonry by August, 1848. It will contain one million and a half of cubic feet of stone. When I was there, in May, fifty vessels, of sixty or seventy tons each, were employed in conveying the stones to the works ; the red sandstone, of which the inside courses are built, from Runcorn — the blue limestone, of which the outside courses are built, from the sea shores of Anglesea. The quarries on the Anglesea shores opened for this work extended over twenty miles. In the whole there I were 1300 men employed, 600 of them at the J bridge, the fortnightly wages of the latter | amounted to £1300. 3000 cubic feet of timi ber had been used at that time for stages and ■ scaffolding. Two steam engines were at work on each shore, and a third was being erected on the Britannia Rock, in the centre of the Strait, to hoist the stones, grind mortar, taw timber, and perform other heavy work. On each shore there was a lime kiln, the chips of the limestone falling from the irons of the hewers, being burned into lime : and the chips of the red sandstone being ground to powder to make mortar with the lime. There were seventeen gauntries with travelling crabs an each for moving the blocks of stone. Railways diverged and converged, on which trucks run along ; and every heavy weight in the building of this wonderful structure was moved as if men were gods, who only willed that huge blocks should take motion, and they took it. | The building of the iron tubes had not then, began ; but the stages upon which they are to be built are 1 erected, extended alobg the Car-

narvon shore about a quarter of a mile. The plates of iron are in preparation at different places in England and Scotland, and they will be conveyed separately to Wales, and put together on these stages. The tubes will then be conveyed from the shore and elevated to their places in this way. We shall imagine ourselves present while the mighty thing is in process of being done ; each of them requiring only about six or eight hours to be removed from the stage upon the shore, and raised to its lofty elevation. Imagine, then, the day. Is it not a scene worth living for ? We are on the shore of Carnarvon, looking across the rapid tide now flowing, to the high shores of Anglesea. A mile below, on the wooded slope, is the beautiful residence of the Marquis of A.nglesea ; and on the hill nearly opposite to us, overlooking the great work of this day, is the column erected to commemorate the Marquis and Waterloo, the column having the familiar name of " Lord Anglesea's Leg," he having got this column on the Anglesea hills because he lost a leg on the plains of Belgium. May Stephenson achieve a triumph in art this day, as undoubted as was the triumph of war of Wellington- and Anglesea on that day ! How glorious for him and for England if he does ! But, why if? He will triumph. He risks nothing here ; he has reduced everything to certainty. The tide is now favourable. A line of barges lying side by side have been placed beneath the stage on which one of the great masses of iron have been built. The stage is removed, and the tube of 1300 tons rests upon the barges. They are towed out upon the water with their monster freight, are brought round, and drawn forward until they and it occupy the space between two of the piers. They are moored and made fast there. The outside width of the tube being fourteen feet, there is a groove in each of the piers wider than that; and at the bottom of the piers stones have been left out to admit the ends of the tubes into grooves. Those grooves extend upwards as high as the iron is to be elevated, namely, one hundred and thirty feet. At a height considerably above that, within an archway which is in each pier, an hydraulic press of great power is stationed. A chain of remarkable construction, which we cannot now stop to examine and talk about, extends downward from the hydraulic press, and is fastened to the end of (he tube. The press is put to work, and it has the power of lifting the mass of iron six feet. This we see, looking only at one pier and at one end of the tube. But a second press and chain are employed simultaneously with this at the other end. When they have raised the large thing six feet, iron girders of great strength are placed underneath it, across the groove, the ends of the girders resting oo the stone work of the pier which abuts on each side of the grooves. These being placed, the press stops and allows its iron burthen to rest on them, and the chains are slackened. While slackened, a link, or section of each chain, measuring six feet, is removed. Each is agaiu fastened to its load ; the presses are again at work, and the tube is raised six feet higher. Again girders (or bearers) are laid across the grooves : again the gigantic wonder of the world rests in its upward progress; and again the chains are shortened by six feet each ; and again and again the press goes to work. And now this aerial tunnel is high enough — its bottom being 130 feet above the water. The iron bearer, which is never to be removed and which has upon its upper surface the rollers and balls of metal already named, is placed * underneath each end ; the press allows the obedient monster to sink into its place ; and there it is more solidly at rest than any one will be in his bed to night who has been witness to this day's mighty enterprise. To-morrow, and the next to-morrow, and the next again, and so forth, the others will be raised, and laid in their places, never to be shaken by gales of wind or deflected bj railway burthen. Their own preponderous weight will keep them immovable ; the augmentation of burthen will only strengthen them — at least we are told so.