WOODEN BRIDGING. Of the forces at work in bridges 122 Extension 123 Compression 123 Cross strain 124 Detrusion 126 Strength of materials 126 Rules for practice 131 Of the truss 139 Of the arch 169 Of the road-way 174 Lateral bracing 175 Pile bridging 178 Trestling 180 Draw bridges 181 Centres 182