540 Tron Suspension Bridge over the [Ocr. 
the whole weight would be 120 tons, whence it is calculated that the 
tension to be sustained at each point of suspension would be 85.632 
tons. 
The suspending chains are 12 in number, arranged in pairs, three 
pair on either side, two feet above one another. They pass over rollers 
one foot in diameter, and are securely moored in masonry 16 feet be- 
low the surface of the road. The back chains are 101 feet long, rising 
at an angle of 27 degrees. The angle of the catenarian at the roller 
is 16° with the horizon : the versed sine at the centre of the curve is 
14 feet 3 inches. 
The twelve main chains are of round bar iron, one and half inch 
diameter, bolted together in pairs. They are from 15 to 15.5 feet 
long, and so arranged that the vertical rods may fall from the joints 
of each chain alternately in parallel lines five feet apart. The descend- 
ing chains are.square bars measuring 14 inch on the side: their lower 
ends pass through 24 conically wrought stones, below which they 
are capped and keyed. (Figs. 1 and 2.) 
The connecting links of the chains, and indeed all the bolt holes 
in the bars, and the drops, are bored out of the solid iron, and broach- 
ed to fit the bolts accurately. (Figs. 5, 6.) None were punched at the 
forge. The bolts are 14 inch in diameter, and are secured by rings, or 
washers and keys. Two adjusting links with iron wedges are fitted to 
each chain, close to the masonry landward, to regulate its curve and dip. 
(Figs. 7, 9.) 
The method of constructing the rollers is thus described in the 
memoir : 
“* The iron rollers 12 in number weigh about one cwt. each. They are not solid, 
but are composed each of about 28 separate pieces of wrought iron, viz. a centre 
tube or box for the axle over which thick rings are driven ; and an exterior drum be- 
tween which and the inner ringed tube, flattened bars, as spokes, aredriven. The 
centres were broached out clean and true, and cylindrical axles 3.1 inch in diame- 
ter were turned to fit ; the ends of these axles rest on broad thick iron bearings 
mounted on very strong and solid frames of timber well bolted, clamped and block- 
ed together, covered with pitch cement and secured in the masonry of the pillars.” 
(Figs 7, 8.) 
The platform was made ina different mode from those of our Calcutta 
bridges, as will be understood by the following explanation: 
‘‘ From the short links set between the centre plates of the shackles (of the main 
chains), are suspended alternately from each tier, 74 vertical round rods one 
inch in diameter connected to a short link (Fig. 6) by a one-inch round bolt 
passing through it and the socket at the upper end of the bar ; at their lower 
ends the rods have eyes, through which doubled loops of iron pass (3, 4) for sus- 
taining the flat bars or girders, set on their edges and proceeding from one end to 
the other on both sides of the bridge. 
