Fig. 137 gives the particulars of one 60-foot span of a viaduct 137 carrying a double line of railway over tidal water. The main girders are placed one under each line of rails, and all the four are strongly tied together by lattice-work bracing the full depth of the girders. The outside footpaths for the platelayers are carried on strong brackets, riveted to the main girders. Longitudinal timbers, coped with angle iron, are placed as outside guards, alongside each rail, for the full length of the viaduct. Wrought-iron ballast-plates are placed between the running-rails. The remainder of the footways consist of timber planking, laid with half-inch spaces, and covered with a layer of small pebbles as a protection against fire. Fig. 138 shows a very similar arrangement in a viaduct carrying a single line of railway across a river. The two main lattice girders--66 feet span--are placed at 9-foot centres, to obtain greater stability. The cross-girders are extended to carry the outside footpaths and handrailing. Outside guards are placed alongside each rail as in the preceding example. Wrought-iron ballast-plates are fixed all along between the running-rails, and timber planking used for the rest of the floorway. Fig. 139 gives cross-section of a lattice-girder bridge, 82 feet span, carrying a single line of railway over a river, with the load carried on the lower flange. The cross-girders are placed at 4 feet 3 inch centres. Wrought-iron ballast-plates compose the floorway between the rails, and timber planking covers the rest of the bridge. Plate diaphragms, or stiffeners, of the form shown at A, A, A, A, are riveted to the main girders at five places in their length. Fig. 140 shows cross-section of a lattice-girder bridge of 200 feet span, carrying a single line of railway over a river, the load being placed on the lower flange. The floorway consists of plate-iron cross-girders, spaced at 4-foot centres, on which are placed the longitudinal rail-bearers and planking, the latter being covered with a layer of clean pebbles for the width between the running-rails. As the depth of the main girders was sufficient to admit of overhead bracing, strong plate-iron diaphragms, of the form shown on the sketch, were riveted to the main girders at every 50 feet. These diaphragms thoroughly brace the two girders together, and effectually prevent any tendency to side-canting, at the same time imparting an effective appearance to the bridge. [Illustration: Fig. 138, 139, 143]