by tackle from the top of the pier, on the Caernarvon side, so that the men could raise or lower it themselves as they required. The links were brought to the face of the pier next the sea, through the archway; from thence, each link was raised to the proper height where it was wanted; it was then put on to the last by the men in the cradle: proceeding in this way, the chain was carried on dowr wards to the level of the water.

The remaining portion of the chain that was to unite the two ends, was laid on a raft 400 feet long, and six feet wide; one end of this piece being joined on to that which hung down from the pier, the raft was floated across, and the other end of the chain lying on it, was made fast by the second link to a powerful tackle, which was raised by two capstans on shore, till the chain was elevated to the height necessary to admit of the two ends being united; the last link was left disengaged, to admit of the workmen managing the junction.

The first chain was thus raised into its place in an hour and a half, on the 26th of May 1825; the remaining fifteen being got up in the same manner at different times. The road-way consists of two thicknesses of planks,-the lower three, and the upper, two inches thick; the under one is bolted to the wood that fills in the intervals between the road-way bars: this planking was covered with felt, saturated with boiled tar, and the upper thickness was laid over this felt, and spiked down to that beneath. In the middle of each carriage-way, there is a third thickness of plank, laid on felt, as before: the road-way is also stiffened by means of an oak-plank bolted to the underside, between each cross-bearer.

The bridge being completed, was opened on the 30th of January, 1826, six years and a half after its commencement. A few additions and corrections only were found requisite, which were immediately made, and since that time it has remained unimpaired †.

THE SUSPENSION-PIER AT BRIGHTON.

THE successful erection of the Newhaven Pier, proved that the suspension principle was equally adapted to such structures, as to bridges in ordinary situations. The great number of visiters annually attracted to the town of Brighton, by its favourable position, and its proximity to London, rendered the construction of a pier there a promising speculation, which was eagerly seized on; as the total absence of any natural harbour, or port made all

One hundred and fifty men were required to work the two. + The weight of the sixteen main-chains between the piers, including all their pins, plates, ties, &c., amounts to 398 tons; and that of the vertical suspending rods, road-way, planking, &c., is about 246 tons, making the total suspended weight 644 tons, which is equivalent to a strain or tension at each point of suspension, of 1100 tons. The sectional area of the sixteen chains will be found to be (80x3.25) 260 square inches, which, at twenty-seven tons per square inch, will bear 7020 tons without breaking: but to ensure permanence to a bridge, it should never be loaded at a greater rate than would produce a tension of nine tons to the square inch, that being found to be the ultimatum of weight that average wroughtiron will bear without any stretching. At this rate, the bridge would bear 2340 tons constantly, without injury, leaving a surplus of power of enduring over its own tension, of nearly 1240 tons, equivalent to 733 of direct weight. Now the area of the platform or road-way between the piers, is 15,240 square feet: allowing two square feet to each person, the bridge would hold 7620 persons, crowded as close as men can stand; taking 150 lbs. as their average weight, this number would weigh 466 tons, or nearly 300 tons less than the bridge could constantly bear without the slightest injury.

approach by sea inconvenient, and, in rough weather, impracticable; and, in a great measure, precluded the possibility of enjoying one of the chief sources of pleasure at a watering-place.

Accordingly, as early as 1822, Captain Brown was engaged to build a suspension-pier, which he commenced in October, and completed in the month of November of the following year. This beautiful structure runs out into the sea 1014 feet from the front of the esplanade wall; the entire length being 1136 feet, which is divided into four spans, or openings, of 255 feet each; the platform being thirteen feet broad.

The main-chains are eight in number, arranged in two pairs on each side the platform: the links are composed of round rods, not quite two inches in diameter, and ten feet long, with eyes at each end; and are put together with open coupling links, as those of the Union Bridge and Newhaven Pier. The chains are carried over pyramidal cast-iron frames, or towers, twenty-five feet high, resting on clusters of piles; of which the end one, at the head of the pier is spread out laterally, forming a T, and consists of 150 piles, strengthened by others driven in diagonally, and by horizontal bracings; and is covered with a granite paving, eighty feet long, by forty wide, and a foot thick, weighing upwards of 200 tons. The object of this strength and weight is to afford a firm base for the back stay-chains, which are bolted to the diagonal piles.

The main-chains are carried at the land end over a pier of masonry, and through two tunnels cut in the cliff thirty or forty feet deep; at the end of each tunnel is a brick chamber, at the bottom of which the chains are attached to massive stones, and finally to a cast-iron plate, weighing one ton and a quarter.

The adjoining figure shows a portion of the pair of chains on one side, with the coupling links and pins, and the cap resting on them from which the vertical rods are

obtain a sufficiently strong hold of the rocky or artificial abutment.

In France, the engineers, to avoid this source of expense, enhanced as it is by the greater length of the tunnels to be cut in the rock, carry the back-stays down perpendicularly into the earth, after they reach its surface, and guard against the unequal tension on the links by forging them in a curved form, to fit the bed on which they lie at the turn, or else, when wire cables are employed, by spreading out the coils of wire composing them in several smaller bundles at the parts where they change their direction.

With these precautions, however, this mode of construction is objectionable, since the pull of the chains is not perpendicularly in the direction of this last portion, but obliquely, in that of the slanting back-stays; and, consequently, the vertical pit, or tunnel of masonry, is liable to be pulled over on one side, or at least deranged, though it might resist double the force, if it were only exerted in the same direction as its own axis.

The first suspension-bridge erected over the Seine, at Paris, by M. Navier, in 1823-1826, failed from this cause, and was obliged to be removed. It was replaced in 1829, by the present Pont des Invalides, constructed, in most respects, like ours at Hammersmith, which, apparently, was taken as a model for it.

The Pont D'Arcole is another suspension-bridge in that capital, which is made in two spans, by a central tower: but our space will not allow of our entering into any further account, either of these, or of many others on the Continent, preferring to devote all that we have, to a description of the longest suspension-bridge ever yet erected, and which is as yet little known in this country.

THE SUSPENSION-BRIDGE AT FRIBOURG, IN SWITZERLAND. THE city of Fribourg is situated on the brow of the rocky side of a deep valley, through which runs the river Sarine: in the narrowest part, the valley is only three hundred yards wide. The communication between Fribourg and Berne, and the rest of German-Switzerland was by a long, steep, and winding road down the valley, totally impassable in Winter, and dangerous at all times.

In 1830, the inhabitants having collected the necessary funds, and decided on the erection of a suspension-bridge across the valley, they confided the execution of their plan to M. Chaley, a French engineer, who has amply justified their choice, by the able and scientific manner in which he has accomplished his task.

The spot chosen was at the narrowest part of the valley, close to the town; the opposite side of the valley being about eighty yards higher than that on which the city stands, it was necessary to cut a road down through the brow of the hill, with a moderate declivity, to meet the level of that of the bridge.

The view of the structure at the head of this paper, will give the reader a general idea of the locality, the picturesque beauties of which are in no way impaired by the graceful form of this magnificent bridge. The suspension-piers are Roman-Doric archways, surmounted by a plain attic, the distance between the inner faces of which, or the distance between the points of suspension, is no less than 870 feet, or 301 more than that of the Menai. The road-way is 41 feet wide, and elevated 167 feet clear above the surface of the river: a semicircular terrace in front of the piers at each end, reduces the length of the suspended road-way to 807, which is 246 more than that of the Menai.

M. Chaley, contrary to our practice in Britain, decided on wire cables of suspension, of the form and construction of which we shall give a brief account, that the reader may judge of the comparative merits of this system, and that of iron chains.

The wire is 12125 of an inch in diameter, and, by repeated experiments, was found capable of supporting at the rate of 52 tons 15 cwt. per square inch*.

This result is so much greater than that at which English engineers arrive (see ante, p. 211) that we suspect some error in M. Chaley's work, from which our account is taken. Our readers may verify the calculations we made, the following being the data. The diameter of the wire 0.00308 metres. "And that, by repeated experiments, it was found to bear 82 kilogrammes per square millimetre." The French wire must be much better manufactured, and of better iron than ours, if there is no error. The whole of that used in the Fribourg Bridge, was made at Bienne, from iron of Undervilliers. It is worth recording, that M. Chaley thought it advisable to get the bolts and bars for his work from England, and states that, notwithstanding the great distance they had to be brought, they cost 20 per cent less than if he had obtained them from the iron works at Franche-Compté, within 30 leagues of Fribourg.

There are four cables; two on each side of the roadway, each consisting of 1056 wires, united into a cylindrical bundle, 5 314 inches in diameter, and bound round with thinner wire at intervals. Near to the piers, the two cables are separated into flat bundles, which rest on friction rollers on the summits, each roller being 31 inches long; and the bundles of wire extend over the whole of this space; after passing over these, the wires are again united into two cables, as before, down to the mouths of the slanting. tunnels in the rocks. When they each divide into two, and continuing in the same direction to about the level of the ground, they are united to other cables, which pass down vertical wells, cut in the rock in the manner now to be described.

There are two of the slanting tunnels at each end of the bridge; one on each side to receive the four portions of the suspension-cables above-mentioned. At the end of each of these tunnels, there is a vertical well, or chimney, cut down in the rock to a depth of about sixteen yards.

The sides of the chimneys are cut out into chambers at three different depths; the backs of these recesses are hewed into the form adapted to serve as abutments to three masses of solid masonry, the courses of which form inverted arches, while the rest of the chimney between these arches is also filled up with masonry; the whole mass reaching to within about three yards of the tunnel, four vertical holes are left for the cables through the whole depth of this masonry.

These cables, which are four in number in each chimney, are each composed of 528 wires; the cables are 39 inches in diameter, and 27 yards long; at the bottom they are formed with loops or stirrups, through which strong bolts and wedges, or anchors, being passed, which lie across the bottom of the masonry, the cables are kept down immoveably, the inverted arched courses rendering it impossible for the strain to pull the masonry out of the chimneys.

On passing to the top of the vertical chimneys, the cables are carried over friction-rollers at the turn, and then along the slanting tunnels till they meet the ends of the suspension cables; both sets being terminated by stirrups or loops, they are united by half-round bolts, kept tight in the crossed loops by solid wedges. The cables are spread out into flat portions where they pass over the friction rollers, at the junction of the chimney and tunnel; this is done both here, and at the top of the piers, to avoid the unequal strain which a bend would produce in a thick cylinder, if the cables had preserved that form at these places. Like the cables, the suspending cords to carry the road-way are made of wire, thirty in each rod; there are 163 of these on each side of the bridge, the longest being 54 feet, and the shortest only long enough to form a stirrup to receive the beams supporting the road; each cord terminates in a stirrup, made by carrying each coil of wire round cast-iron saddles, of the shape shown in the figure A. The upper saddle rides on a cross-plate; the two branches of this plate lie on the two parallel cables in the manner shown in the figure.

B

A

The lower saddle of the suspending-rods receives the hook of a square stirrup, into which the ends of the transverse beams carrying the roadway are put. (See the figure B.) Four ranges of beams are bolted down on these transverse ones, a space of twelve feet six inches being left in the middle between these longitudinal beams, for the carriage-way; the two beams being placed near each other on the outside of this carriage-read, to support planked foot-paths. The carriage-road was made by

It is obviously of essential importance to the strength of the cables, that every coil of wire composing them should be stretched equally tight, our readers will not be unwilling to be told how this object was accomplished.

Each cable was made in twenty separate skeins (if we may so term them,) of wire; 12 of 56 coils and 8 of 48 coils. Each skein of the whole length was made separately. The saddles round which the wire was to be turned, to form the loops, or stirrups, at each end of the skeins, were put round strong, upright pins, fixed into posts of oak, secured in the strongest manner from any lateral motion; the wire required to make each skein was put on a kind of reel or drum, which was carried on wheels; one end of the wire being temporarily attached to the beam near the saddle, the drum was rolled to the other end, suffering the wire to unwind off from it. When the workman came to the other saddle, or end of the cable, the wire was put into a vice, attached to a cord passing over a pulley, and sustaining a weight of 200 lbs. and upwards; this precaution being taken at each end in succession, every length of the wire was stretched as nearly equally as possible. When the skein was completed and the ends joined, a ligature of of wire was put round each stirrup in the notch left for this purpose, and temporary coils were also wound round the skein at equal distances.

The skeins were all mounted into their places, and united to the end cables in the tunnels, before they were formed into the four cables they were to constitute. This union was done as the suspending rods were put up in succession; the temporary wire ligatures being gradually removed, and the twenty skeins pressed together into a eylinder by a wooden mould worked by a screw; when adjusted to the right form, the skeins composing each cable were bound round by coils of wire at equal distances.

The wire, of course, was joined repeatedly for each skein; this union was effected before it was wound on to the drum. The ends of the two pieces, or hanks, were placed ride by side for about four inches, and then wrapped round from end to end of the double wire with finer, each turn being close to the last, and drawn very tight. This mode of junction was found so effectual, that whenever a piece was proved, and broke in the trial, the rupture always occurred at the single wire, the joined ends never being pulled asunder in any instance.

Every part being completed, the bridge was publicly opened to foot-passengers on the 23rd of August, and on 8th of October for carriages of all descriptions. On the 15th, it was tried by causing a train of fifteen pieces of heavy artillery, drawn by fifty horses, and attended hy 300 persons, to pass over the bridge at one time. Every part of the cables, &c. was subsequently examined, and not the slightest indication of yielding or weakness could be detected either in the iron, wood, or stone-work.

On the 19th, the bridge was publicly opened by the municipal authorities; on which occasion 2000 persons were at once on the road-way, and crossed it in measured march with military bands t.

M. Chaley concludes his account with an honest and generous exultation, that he had accomplished the whole of this construction not only without the loss of a single life, but without one of the workmen having met with any serious accident, a fact reflecting the highest credit on all parties; on the engineer, as proving his attention to this point, and on the workmen, as proving their steadiness and sobriety. The principal data for this paper are taken from the able work of Mr. C. S. Drewry, A Memoir on SuspensionBridges, who allowed us to make this use of it. The account of the Fribourg Bridge, is abridged from the Notice sur le Pont Suspendu le Fribourg, by M. Chaley. The other works that have been referred to, are Provis's account of the Menai Bridge, Sir Howard Douglas on Military Bridges, and the various books of travels cited in our account. + The total suspended weight of the bridge is nearly 296 tons, considerably less than half that of the Menai Bridge. The greatest load to which it can ever be subjected is about 158 tons, making together 454 tons; this, by calculation, gives a tension on the chains equivalent to 835 tons. M. Chaley, by estimating the ultimate strength of his wire at 1348 lbs., states his bridge to be capable of bearing three times the greatest load it can ever be exposed to; but, even taking the strength of the wire at 1000 lbs., which is nearer our English standard, the 4224 wires of the cables would bear 1885 tons. It must, however, be remembered, that the strength of a cable of wires cannot be estimated at that of the wires of which it is composed. However, by making every allowance, the Fribourg Bridge is perfectly safe, as far as mere dead weight is concerned. We should be sorry to forebode evil to such a work, but we cannot help apprehending a weak point in the apparently unnecessary angle in the main chains, caused by making the chimneys vertical, instead of continuing them in the direction of the tunnels and back-stays. We presume the necessity for cutting the drain so much longer was the objection to our plan.