In order to enable railway trains to pass from one line of rails to another as becomes necessary on various occasions, at certain parts of the line small portions of the rail are formed of bars, termed switches, which are moveable upon a pivot at one end of the bar. Various arrangements of switches have been proposed, or are in operation, depending partly on the nature of the service for which they are required, some of which are self-acting, and others require to be mored by an attendant.
The annexed figure represents a mode of passing carriages from one line of road to another, adopted by Mr. Stephenson, on the Liverpool & Manchester Railway, and described in Wood's Treatise on Railways.
Let ef be the road into which the carriages are to be made to pass, ab c d being the main line of road, two rails are made moveable upon the joints a and c: these two rails are joined together at the other end by an iron rod, which is extended to one side of the road. This end of the rod is terminated by an oblong box, as shown in the figure, and within this box an eccentric cam or wheel is placed with an upright axle, on which is fixed the handle h. The difference between the radii of this wheel from the centre of motion, is precisely equal to the distance between the ends of the two rails; when, therefore, the eccentric wheel is in the position shown in the figure, the carriages will pass along the main line: but on turning the handle round to k, and with it the eccentric wheel, the latter pushes the rod and rails into the position shown by the dotted lines. This mode of turning the carriages into another road is quite safe, and can admit of no mistake if the handle be turned sufficiently round, as the eccentric wheel is made to move it the proper distance and no further.