Engine turn-tables are rarely made with more than one road on the top. The most modern types generally consist of two strong wrought-iron or steel-plate girders well braced together and securely attached to a middle framework which rests on and revolves round a centre-piece fixed on a solid foundation To the ends of the girders are attached 290 large roller wheels which travel round a solid iron or steel roller-path laid down along the circumference. These modern turn-tables are generally worked on the balancing principle, by bringing the engine and tender to a stand in such a position on the rails that the greater portion of the weight is thrown on to the cup-shaped steel centre, so that a small force applied to the long outrigged hand-levers at the ends is sufficient to turn one of the heaviest locomotives. Figs. 441 and 442 give sketch plan and section of one of these steel-plate girder turn-tables, which has few parts, and very little to get out of order. The end rollers guide the table when making any portion of a revolution, and carry such part of the weight as may not be taken up by the centre. A recess is shown in side wall to facilitate the inspection of end rollers. In the earlier forms of engine turn-tables, the revolving movement was effected by attaching to the upper portion of the girders a strong winch, which acted upon gearing fixed either to the end rollers, or direct on to a toothed ring forming part of the roller-path. In cases where the engine turn-table was in constant use, as in connection with a large running-shed, the winch was sometimes driven by a small steam-engine to expedite the movement. The great increase in the lengths and weights of modern locomotives has necessitated the removal of many of the old small turn-tables, and replacing them with others of 45 or 50 feet, or more, in diameter. [Illustration: Fig. 441, 442, 443, 444, 445]