246 Mr Stevenson’s Description of Bridges of Suspension. 
the curve of each pair of chains coming under the top of their 
corresponding side-rails, as shewn in Fig. 3. The links of the ca- 
tenarian chains are formed of rods of bar-iron, measuring Ifth 
inches in diameter, constructed in lengths of about 10 feet each. 
The eyes at each end of these long rods are connected by short 
links of an oval form, measuring about 9 inches in length. The 
platform or roadway is suspended from the catenarian chains, 
by perpendicular rods of iron, of the strength of | inch in dia- 
meter, which are attached at their upper ends to the short 
links above described, by a kind of cross head, while the under 
ends of these perpendicular rods, forming a screw-bolt, pass 
through the side-beams of the platform, and are attached to 
them with screw-nuts, resting upon corresponding washers , or 
plates of iron. 
The points of suspension of this bridge rest upon upright 
posts, and are elevated 28 feet above the level of the roadway, 
on each side of the river. The catenarian chains pass over these 
upright posts or piers, which are formed of logs of Memel tim- 
ber, 14 inches square, erected in pairs, as shewn in the left 
hand diagram of Fig. 3., marked “ Approach of Fig. 3.” 
These pieces of framed work leave a space of 9 feet in width, 
as an approach to the roadway of the bridge. The tops are 
connected by the transom-beam , on which the catenarian chains 
rest, and from thence they descend in curved lines, as shewn 
in the figure. Each pair of chains are 12 feet apart at tbe 
approaches of the bridge, but they are made to converge to- 
wards its centre, where they are attached to the side-rails, and 
measure only 4| feet apart, being the breadth of the roadway 
between the side-rails. By this converging form, the chains an- 
swer in some measure the purpose of guys to the roadway. It 
is, however, questionable, how far it is proper to give an ob- 
lique direction to the main chains ; indeed wc are rather in- 
clined to think, that the main chains of bridges of suspension 
should be kept parallel to the direction of the strain. 
The platform or roadway of Dryburgh Bridge is elevated 
about 18 feet above the surface of the river, when in its state of 
summer water. It consists of two beams of fir-timber, which 
run along the extent of the bridge, and are connected to each 
