Chairs.--All rails which partake of the double head section, or have a base not wider than the head, require supports or carriers to attach them to the sleepers, and to secure them in their proper upright position. In the days of the original _edge rails_, at the commencement of the railway era, these supports were very appropriately termed _chairs_, and this name has now been adopted in all parts of the world. Cast-iron is the most suitable material for railways chairs, being much cheaper in cost and less liable to loss or deterioration from rust than wrought-iron. Cast-iron chairs can be formed to suit any section of rail, and from the nature of the material they cannot be bent or twisted out of shape so as to interfere with the gauge or cant. They may break during an accident or derailment, but the fracture can be detected at once, and the broken 207 chair quickly replaced. The chair performs the very important duty of distributing the weight of the rolling load on the upper surface of the sleeper. If the under side or base of the chair is small, and the rolling load large, the chair will very rapidly wear or imbed itself into the wood of the sleeper, shortening the life of the latter in a very palpable manner. The short narrow chair naturally gives less stability than the larger and broader chair. The chair shown in Fig. 292, which was much used for 75 lb. rails some twenty years ago, has much less base area and stability than the chair shown in Fig. 293, adopted for rails of a similar weight in the present day. The former had a bearing surface on the sleeper of only 53 square inches, as compared with 89 square inches in the latter. The base area of the chair must be in proportion to the weight it has to carry and distribute, and it would be false economy to stint the surface area of one of the details which influences so materially the stability and durability of the permanent way. As will be seen in Figs. 294, 295, and 296, the chairs at present used for 80, 85, and 90 lb. rails have a much larger bearing surface than the chair shown in Fig. 292. With the wider chair, a much longer and better seat can be given to the under table of rail, and a greater length of jaw for holding the wooden key. The longer the rail-seat the steadier the rail and the smoother the running.