There are so many descriptions of roof-principals used in railway stations that it would be impossible here to introduce more than a few examples. Figs. 387 to 405 illustrate by diagram sketches a series of types taken from actual practice. Fig. 406 gives more in detail the particulars of the roof-principal of 60 feet span, Fig. 392. As will be noted from Fig. 406, the width of 120 feet between the walls is divided into two spans of 60 feet each, the ends of the principals in the centre of the 120 feet being carried on arched wrought-iron girders of 48 feet span, supported on strong ornamental cast-iron columns placed at 48-foot centres. The rain-water from the large centre gutter is taken down inside the columns and conveyed away to drainage pipes laid down for the purpose. The 60-foot principal above described forms a very strong roof, and is light in cost and 271 maintenance. The weight of ironwork, both wrought and cast, in the principals, arched wrought-iron girders, cast-iron columns, centre gutters, etc., is only 0·51 of a ton per square (of 100 square feet) of area covered. For comparison, the weight of ironwork in the roof, Fig. 402, of 198 feet span is 1·42 ton per square of area covered; and of the roof, Fig. 404, of 210 feet span, is 2·07 tons per square. This increase in weight per square as the spans go on increasing results, not only in a much larger outlay for original construction, but entails also a proportionally heavier expenditure for maintenance and painting. The item of painting alone is an expensive one in all iron-roof work, and must be attended to regularly for the proper protection and appearance of the ironwork. With the smaller spans, the roof-trusses form very convenient supports for painters’ scaffolding or planking, but with the very large spans the greater height and the form of the roof-principals render specially designed scaffolding and appliances necessary for the painting and repairs.