Читать книгу Scenes in North Wales - G. N. Wright - Страница 5

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The union of Ireland with Great Britain rendered it an object of paramount importance to facilitate and expedite communication between the capitals of both kingdoms. The shortness and security of the voyage between Holyhead and Howth at once suggested the advantage of improving the line of road through North Wales to Shrewsbury, and so on to the metropolis of the united kingdom. In the year 1810 a select committee was appointed by the House of Commons, to inquire into the best mode of accomplishing this desirable end, and, amongst the valuable improvements recommended by them, none have given so remarkable and so dignified a character to their proceedings, as the suggestion of throwing a suspension bridge across the Mænai, a deep and rapid strait, where delay always attended transmission, and danger not unfrequently. Amongst the many melancholy tales of disasters that befel passengers in crossing Porthaethwy, [3] two possess a lamentable notoriety, from the number of souls then hurried in an instant to a watery grave. On the 5th of August, 1820, the ferry boat was overturned, containing twenty-six passengers, of which number but one escaped with life; and thirty-seven years before an event of increased horror happened here in a similar way, when sixty-nine poor beings perished, one only, as before, escaping. It is a singular fact that the name of the survivor in both instances was Hugh Williams. The Mænai, or “Narrow Water,” is about fifteen miles in length, its breadth varying from two miles to two hundred yards. Six ferry stations have been established on its banks since the reign of Henry the Eighth, who granted five of them to William Gifford. These stations passed subsequently into the possession of the Bulkeley family, and were afterwards dispersed amongst various owners. Porthaethwy, or Bangor Ferry, when the idea of constructing a bridge over the strait was first suggested, was found to be the property of Lady Erskine, from whom it was purchased at the expense of twenty-six thousand three hundred and ninety-four pounds, being thirty years purchase, according to an average of the annual receipts for a number of years preceding.

Various designs were presented, by Mr. Telford, for the adoption of the committee, from amongst which a suspension bridge was selected. This species of structure is now very generally preferred chiefly where centering is attended with difficulty and expense; but it is by no means a modern invention. It has long been known to the eastern countries: a Jihoola, or suspension bridge, was found amongst the inhabitants of the Himalä vales, on the river Touse, in the East Indies, by Mr. Frazer; and an ingenious and well executed work of this description made of bide-ropes, was discovered by Captain Hall, on the river Maypo in South America. The magnitude of the Mænai Bridge, and the boldness of the design render it still the most interesting and wonderful work of the kind in existence; and, although the bridge of Avignon possesses a span of fire hundred feet, and is also a truly admirable work, yet it is still inferior in the breadth of the principal span, the height above the water-level, and is constructed in a situation where there existed little difficulty in placing each bar, pin, and bolt, in their allotted berths.

The Mænai Bridge consists of one principal opening, the breadth of which, between the centres the supporting pyramids, is five hundred and sixty feet, in addition to which spacious waterway there are four arches of stone on the Anglesea site, and three on the Caernarvon, to complete the communication, each having a span of fifty feet, with a springing line sixty-five feet above the level of high water, spring tides. The whole breadth, of the channel, or rather length of the bridge, amounts to eight hundred and eighty feet, and the roadway is elevated one hundred feet above the surface of high water. The sea-end of each series of arches is terminated by a pyramid, rising fifty feet above the level of the roadway; over the summits of these pass sixteen supporting chains, from which a horizontal roadway is suspended by vertical iron rods, linked at their lower extremities with the sleepers of the roadway. The whole breadth of the roadway is divided into two carriage tracks, each twelve feet broad, and a footpath of four feet in breadth, in the intermediate space, each protected by guards ten inches in height and six in thickness. The carriage ways pass through arches constructed in the supporting pyramids, and, to prevent the possibility of a collision of vehicles, are continued separate to the land extremities of each series of arches.

In order to obtain a safe tenure for the main chains, the extreme links are enlarged and pierced with eyes, through which strong iron bolts are passed, constituting a species of framework, and the whole mass imbedded securely in the solid rock. The sixteen chains are formed into four lines of suspension, extending one thousand seven hundred and fourteen feet in length; five hundred and seventy-nine and a half of which form a catenary curve, between the pyramids, from which the roadway is suspended. A weight of six hundred and thirty-nine tons, nineteen hundred and nine pounds, is suspended between the pyramids, and the estimated weight of the iron work, from one extremity of the suspension chains to the other, amounts to two thousand one hundred and thirty tons, eighteen hundred being of wrought iron and only three hundred and thirty of cast. To give the iron work a fair bearing in their respective chambers, the following precaution was adopted: each bar and pin were wrapped in flannel, saturated with white lead and oil, and, to establish close and impenetrable joints, Borradaile’s patent felt was introduced between them, eight thousand superficial feet of which were consumed in this manner. The floor is composed of three strata of planks, the first three inches in thickness, the middle and the lowest two inches each, layers of patent felt being introduced between the planking strata. Twenty-four thousand seven hundred and ninety feet of felt were consumed in the roadway alone. Screens, or trellis-work of light bars protect each side, and permit the breezes to pass freely through; and a hand-rail of African oak directs and confines the hesitating steps of the foot passenger. The floor of the suspended part frequently assumes an arched appearance, which is not its original form, but arises from a contraction in the chains on the land side of the pyramids, the effect of which, being diffused equally over the chain of the suspended part, causes a temporary elevation of the roadway. It must be remarked that the sixteen main chains recline on saddles on the summits of the pyramids, without being attached to them, whereby every contraction or expansion which may occur on one side is communicated to the other, and over the whole, without any danger of rocking or disturbing the masonry.

In the construction of the stone arches the same care and scientific knowledge are displayed which characterize every part of this noble work. The arches on each side, adjacent to the main piers, are semicircular, the others are less segments gradually diminishing as they approach the land: the crowns continuing parallel to the roadway admit a handsome entablature and cornice. A beautiful marble, raised at Penmon in Anglesea, is employed in the mason work, and Aberdaw lime was used in bedding the blocks that were laid under water.

The first stone of this great work was laid, without ceremony, by W. A. Provis, Esq. on the 10th of August, 1820; it is a block of marble about three tons in weight, placed in the centre of the sea front of the main pier erected on Ynys-y-Moch. Messrs. Straphan and Hall contracted for the execution of the masonry.

On the 20th day of April, 1825, the first main chain was thrown across the strait, in presence of an immense concourse of spectators. At half flood, and about half past two o’clock, p.m. a raft, stationed near the Caernarvonshire coast, bearing a part of the chain intended to be raised, was freed from its moorings, and towed by four boats, down the current of the tide, to the centre of the strait between the pyramids or main piers: when the raft was placed in its proper position it was secured to buoys anchored in the channel for that purpose. This first operation occupied a space of twenty-five minutes. The end of the chain, hanging from the top of the pyramid on the Caernarvonshire side, was then bolted to one end of the chain laid upon the raft, while two powerful blocks were attached to the other end, for the purpose of raising it over the saddle of the Anglesea pier. This being completed, two capstans with twenty-four men at each, and two preventive capstans, employing an equal number of hands, were set to work. To ensure equability in the rotatory motion of the principal capstan, a fifer was at hand who continued to play a lively tune, to which the men stepped with regularity, having been previously trained to do so. At fifty minutes after four o’clock the bolt which completed the whole line of chain was fixed, so that from the first unmooring of the raft to the uniting of those portions of the chain, which have their extremities made fast in the shores of the two opposite counties, only two hours and twenty minutes were consumed. Upon the completion of this important step, upon the success of which all further advances entirely depended, the assembled crowd gave way to much enthusiastic expression of admiration: three of the workmen, in the ardour of the moment, had the great good fortune to succeed in walking across upon the upper surface of the chain, and a shoemaker from Bangor seated himself near the centre of the curve, and there drove the last sparable into one of those useful productions of his art, called clogs.

It is a tribute justly due to the scientific projector of this stupendous work, while we admire its beauty, also to acknowledge its utility and entire success; and posterity will yet learn, with gratification, that Mr. Telford has lived to see the offspring of his great genius attain an age of maturity, without diminution of strength or incipient decay. If, when he has placed his laurel crown upon its cushion he perceives some leaves are wanting, let him not regret to hear that a few were gathered by his “fidus Achates,” W. A. Provis: the winds have strewn a few more on the grave of Wilson, and Hazledine grasps the others that are missing with an iron hand.