LARY BRIDGE. 163 



wide, and 3 inches thick, are firmly bedded in the 

 masonry of the piers and abutments, and receive 

 the ends of the ribs in shoulderings or sockets, formed 

 thus 



The intermediate ends of the ribs are cast with 

 flanges, and are connected together transversely, by 

 strong plates of iron, fixed at right angles to their line 

 of direction, and to which they are connected by screw- 

 bolts, two inches square. 



The arch thus formed by lateral and transverse 

 pieces, has 25 divisions or spaces ; in each are fixed 

 two braces, having the form of the letter X : their encjs 

 being screw-bolted to the ribs, operate as a system of 

 diagonal bracing to the whole arch, and fix the ribs 

 immovably in a vertical plane. 



The spaces between the extrados of the arch, and the 

 roadway, are filled up with a system of triangles, the 

 diagonal formed by their apexes being the true line of 

 bearing, or perpendicular to the line of forces ; thereby 

 equalizing the weight of the superstructure over the 

 whole arch. These triangles are preserved in a verti- 

 cal plane by cast-iron tubes, abutting against their inter- 

 sections, being tightened by a wrought-iron screw-bar, 

 embracing the whole transversely. 



Above the springing of the arches, the piers are 

 composed of cast iron framing, fixed perpendicularly 

 by diagonal braces and cross ties; their upper ends 

 terminating in a plate 4 feet long and 8 inches wide. 

 On these plates, the ends of the bars which carry the 

 covering or road-way plates, rest in grooves, and admit 

 of a reciprocating motion, in the direction of their 

 length ; in order that any expansion or contraction in 



