and this weakness is soon made manifest, particularly on curves, where additional crab bolts or other devices are rendered necessary to counteract the tendency of the rail to rock and tilt over sideways. When the head of the rail cannot be kept in its proper position, the gauge becomes widened, and an irregular sinuous motion takes place in the running of the train. This drawback has been found to be a serious matter where light narrow flange rails have been adopted to carry comparatively heavy, short wheel-base engines. In some cases wrought-iron sole-plates, or even cast-iron bracket-chairs, have been introduced to give more bearing surface on the sleeper and increased support to the rail, but neither of the two methods give the same simple complete hold to the rail that is obtained by the cast-iron chair for the bull-head rail. On the other hand, the modern cast-iron chair for the bull-head rail 197 has at least double the bearing surface on the sleeper to that of the flange-rail seat, so that under the same circumstances of rolling load as above described, the weight of 134 lbs. per square inch would be reduced to half, or 67 lbs. The greater length given to the chair effectually prevents any rocking action on the part of the rail, and reduces to a minimum any lifting action on the spike. A good fitting chair--especially when keyed on the inside--provides a most effectual support to the rail both vertically and laterally, and maintains the rail to accurate gauge. By giving proper clearance space at the tops of the chair-jaws, a bull-head rail can be taken out by simply driving out the wooden keys, and a new rail inserted without in any way disturbing the chairs or spikes. To change a flange rail necessitates the slackening and removal of a large number of the spikes and crab bolts. As the sleepers under the chair road suffer less from the crushing of the timber, they have a much longer life in the line, and remain serviceable until they are incapacitated from decay. This is a very important item in places where timber sleepers are expensive. The steadiness of the chair prolongs the efficiency of the spikes. As the actual wearing portion of the rail is the head, or wheel contact surface, a liberal area--consistent with the expected traffic--must be given to that part, whether for a bull-head rail or a flange rail. By comparing the two sections, Figs. 273 and 274, the one for an 85-lb. bull-head rail, and the other for a 100-lb. flange rail, it will be seen from the dotted lines that the heads of each rail are almost identical, the difference of 15 lbs. being disposed of in the flange of the heavier rail. Practically, therefore, we have 15 lbs. per yard extra weight of steel in the rail, on the one hand, as against the cast-iron chairs and steadier permanent way on the other. For lines where the traffic is small, weights light, speeds low, and economy of construction imperative, the flange-rail permanent way will be very suitable.