have to be sufficiently elastic to enable trains to be run out of course, if necessary, as safely and well as at the specified times.
Goods trains, starting from terminal stations where the shunting and marshalling of the waggons take place, cannot always leave with absolute punctuality; nor can those having waggons to attach and detach at roadside stations, where a margin is allowed for the purpose, always accomplish their task within the specified time. The weight of the load, the capacity of the engine, the state of the rails and the weather, the varying gradients, and the more or less frequent running of special trains, are all disturbing elements which have to be reckoned with, and which tend materially to upset the calculations made in compiling the time bill, so that the arrangements for shunting goods trains off the running lines into sidings to allow passenger trains to pass them, have to be left very largely to the discretion of the station-masters and foremen. The most that can be done on the part of the management is to lay down certain rules and principles for the guidance of the men, and this is done. For instance, as a general rule, passenger trains take precedence of goods, cattle, and coal trains, and such trains are not allowed to be started from any station within a given space of time before a passenger train is due. This regulation is, however, subject to modification according to circumstances, and a light through goods or cattle train, on a clear day or night, may be started before a passenger train, if the latter has to call at all the stations. Again, if the station-master or foreman has been informed by means of the telegraph or otherwise, that a passenger train which is due, may not be expected for some time, he may
