Mr Stevenson's Description of Bridges of Suspension. 249 
strong shackles, as shewn in the connecting diagram, Fig. 4. ; and 
a bolt is passed through them, which is of an oval form, mea- 
suring 2 \ by 2 1 inches. At each joint of the three tiers of 
the catenarian chains respectively, one of the saddle pieces of 
cast-iron, formerly alluded to, are introduced. The first saddle 
piece, with its suspending rod, for example, on either side of 
the bridge, may be conceived as resting on the upper pair of 
chains, as will be observed in the elevation of Fig. 4. ; the next 
saddle-piece in the longitudinal direction of the roadway, rests 
upon the middle pair of chains, and the third upon the lower 
pair, and so on alternately, throughout the whole extent of the 
bridge. By this means all the chains bear an equal strain, and 
the joints are arranged in so precise and orderly a manner, that 
a saddle-piece and perpendicular suspending-rod occurs at every 
5 feet, so that the distance between each pair of suspending-rods 
forms a space of 5 feet. By this beautiful and simple arrange- 
ment, the suspending-rods are made to rest upon the joints of 
the catenarian chains, so that the links or rods of which they are 
composed, are kept free of distortion, when loaded with the 
weight of the suspended roadway. 
The spaces of 5 feet between the suspending rods above al- 
luded to, are formed into meshes of 6 inches square, to the 
height of 5 feet on each side of the bridge, and answer the pur- 
poses of a parapet wall for the safety of passengers. 
Though the timber roadway is only about 861 feet in length, 
yet the chord-line of the main-chains measures no less than 432 
feet between the points of suspension, with which they make an 
angle of about 12°, and in forming the catenarian curve-drop, 
at the rate of 1 perpendicular to about 7 feet in the length of 
chain, the versed sine of the middle pair of chains being 
about 26 feet. The twelve main chains, with their apparatus, 
weigh about 5 tons each, and the weight of the whole bridge, 
between the points of suspension, has been estimated at 100 tons. 
On the Scotch side of the river, the catenarian chains pass over 
a pillar of aisler masonry, which measures 60 feet in height, is 
about 36 feet in its medium width, and 17 \ feet in thickness. The 
sides of the lower 10 feet of the walls of this pillar are square, but 
at this height the walls begin to slope at the rate of 1 perpendicu- 
lar to 12 horizontal. The archway in the masonry of this pillar. 
