The wire suspension bridge erected across the Cumberland River at Nash villd has the following measurements. The length of the bridge is 656 feet, and the whole length of the bridge and em bankment 1,956 feet. Width of super structure, 28 feet ; carriage way, 20; two footways, each 4 feet. The bridge will span the Cumberland opposite the south east corner of the public square of the city, at an elevation of 110 feet above low water, over the main steamboat channel. Base of pier, 60 by 20 feet, solid mason work ; anchorage, 60 by 56 on the north side ; solid limestone cliff On the south side. There .are to be 16 cables, each cable composed of 200 strands of No. 10 wire, each wire tested to bear 1500 lbs. The whole work is calculated to bear a weight of 4,800,000 lbs., or 2400 tons. The cost of this mag nificent structure is estimated at but $100,000, though the Wheeling Bridge, 1010 feet long, cost $225,000.
The wire suspension bridge over the Niagara River is the largest of its kind in the world. It is built over the river It miles below the Falls, and directly over the rapids, which commence at this point. It is nearly 800 feet long, and 260 feet above the river. Towers 80 feet high are erected on the bank each side, and at a point 100 feet in their rear the immense wire cables which sustain the. bridge are firmly secured. These strands pass from their fastenings immediately over the top of the tower upon either cliff; they pass thence across the chasm, and then over the top of the tower on the opposite cliff, in the rear of which the ends are fastened in the rock. It is 10 feet wide, and a temporary path of wire and slats of wood has been constructed on each side. The flooring is composed of light planks resting upon their scant lings to which the wires are fastened. Mr. Ellett is the architect.
' Mr. Dredge, of Bath, England, builds his suspension bridge on a very improved plan, in which bars connected the road way to the catenary chain, are not verti cal, as in other suspension bridges, but are made by him to pass obliquely from the tower toward the centre, as shown in the cut, where C represents the cen tre, B the tower, and E the platform ; g shows the point to which dependence on the tower extends : this tends to strength en the bridge considerably. The chains in his bridge are made of great thick ness at the points of suspension, and taper off to the middle of the bridge, where the strain is least. Mr. Dredge has erected in England, Ireland, and Scotland, many bridges on this plan, which are models of cheapness, beauty, and durability.
This represents a portion of the bridge at Ballock Ferry, Loch Lomond, Scotland, erected on that principle.
Mr. Remington has planned a bridge which appears to be the simplest as yet designed, and is remarkably cheap in construction, according to the length of span. Models of his bridge have been exhibited in New-York and the other cities of the Union, as well as in London.
That exhibited in New-York was 160 feet in the clear, composed of four stringers of a little over two inches square at the abutments, and tapering to about an inch square at the centre. It is of the form of an inverted arch. The stringers are made of several pieces of white pine joined to gether by a scarfe joint ; their ends, when they are joined, being bevelled at a very slight angle, and the bevelled parts lapped over each other, and attached with glue, so that when united, each stringer ap pears to be a continuous and single piece. These jointings are so arranged as that only one of them ever occurs in the same cross section of the bridge, and they are neither bolted nor clamped, but depend entirely upon the glue for their adhesion. Each of these stringers have about nine feet bearing on the abutments or suspen sion piers, to which they are firmly at tached by iron bolts.
At New Orleans, Mr. R. exhibited a model, extending " across a space of nine ty-six feet, and elevated some ten feet from the floor. Its appearance is so fragile, that few men, judging from this alone, would willingly trust themselves upon it, yet plenty walk over it and stand on it. It has four longitudinal supporters, each less than one inch square at the centre, but increasing gradually in size, until at the ends or points fastening, they are 21 inches square. The bridge has one caten ary and two parabolic curves, by which strength and beauty are both secured. The flooring is attached diagonally, and is made to sustain a portion of the strain. The deflexion of the supporters is 221 inches. It is capable of bearing the pres sure of 7 tons ; while each of the support ers, occupying their place in the bridge, will sustain a weight greater than the ab solute strength of the timber and the di rect cohesion of its fibres." Upon this . Mr. Remington has erected one in Montgomery, Alabama, that was opened for travel last year. The span is 436 feet, and the track is 10 feet wide. It is without hand-rails, and is described as appearing at a dis tance like a slight ribbon, or shaving of wood, flung across a ravine—apparently too frail to bear the pressure of a bird, but proved to be capable of bearing al most any amount of weight that can be placed upon it. Hundreds of people crossed it on the day it was opened, who were completely convinced of its strength. Its strength is due to the fact that the fibres of the stringers are not subject to any transverse strain, the only action upon them being exerted in the direction of the length of. the fibre. Each end of one of its 'stringers is firmly bolted down to an abutment, and any weight being laid upon them between the abutments, causes just the same tension of the fibres as in the case of an attempt to break a walking-stick by drawing it apart, while holding the ends.