A medium-sized travelling-crane is a most useful appliance about a 297 railway station; it has a much greater range of utility than a fixed crane, but it is not always appreciated as it should be. It merely requires a line of rails laid down parallel to the rails of siding, and may be placed either on the same level as the siding, or on the level of the loading-bank. Being laid flush with the roadway, the rails do not present any obstacle to the passage of carts or movement of merchandise. As one waggon on the siding is loaded or unloaded, the crane can be moved along its own line of rails, and be put to work at another without the necessity of moving or drawing out any of the railway waggons on the siding. Five, ten, or twenty, or more railway waggons can be dealt with in this way, according to the length of crane-line laid down. The crane can also be readily removed to another part of the station-yard, or to another station along the line. For stations with an intermittent or spasmodic traffic in heavy timber, large blocks of stone, or other unwieldy articles, a travelling-crane is particularly suitable, as it will meet all the wants so far as the lifting is concerned, and when the rush of traffic is over, it can be easily transferred to some other sphere of usefulness. The crane-siding itself is never very costly, as the rails are generally old rails taken out of the main line, and laid on good second-hand sleepers. They have little to do, and merely form a track for the moving crane. Fig. 451 is a sketch of an ordinary Goliath crane constructed of timber. The general arrangement and capabilities of this crane are somewhat similar to those of the gantry shown in Fig. 447. Both of them are designed to lift heavy weights, and move them sideways into, or out of, ordinary road waggons, but the methods of application are different. In the gantry the verticals are permanently fixed, whereas in the Goliath the verticals and overhead girders are all attached and braced together, forming a complete framework which is carried by double flanged rollers running on the lines of rails R, R. The winches or gearing for lifting the weights, or slinging them sideways, or for propelling the crane forward on the rails, are attached to the verticals as shown, and are worked from the ground-level instead of the overhead platform, as indicated in the gantry. As each Goliath crane is complete in itself, there is nothing to prevent two or three of them working at the same time on a long length of crane-line. [Illustration: Fig. 451, 452] Fig. 452 shows an ordinary derrick crane, which, on account of the 299 large and varying sweep of the jib, is found very convenient for certain classes of work. It occupies a considerable amount of room, and its adoption is therefore limited to situations where space is of secondary importance.