Now you begin to see the use of the train-despatcher. If the unforeseen never came to pass upon the railroad, instead of coming to pass nearly every hour, there might be no need of that officer. Each engineer, each conductor, each station agent would have his complete time-tables, and the road would run every day in full accordance with them. That was the very earliest and the most primitive way of operating railroads. Almost as early the need arose of having a special direction over the operation of the trains. Emergencies arose daily. Trains were often late; storms beat down upon the line; the snow covered its rails; what might have been, according to the time-card, an orderly operation of line, became chaos. If a train was ordered by schedule to meet a train bound in the opposite direction at P----, it might wait there for long hours, not knowing that the other engine was broken down at A----. The invention of the telegraph and its almost instant application to the railroad service made such special direction possible. So now we find the explicit directions of the schedule supplemented by even more explicit directions from the train-despatcher at the head of the train movements upon each division. Briefly stated, it may be said that the engineer and the conductor in charge of a train are first guided by the schedule, which, after many revisions, has been compiled with great care, and in reference to connecting lines, branches, and adjoining divisions. This schedule acts in conjunction with certain simple fundamental rules of operation, the A, B, C of every railroader. By one of these, trains of the same class bound north or east are given precedence, all other things being equal, over trains bound south or west. This rule is sometimes superseded by one giving right-of-way to trains bound up the line--or the reverse. High-class trains, like the fastest limited expresses, have precedence over trains of graduated lower classes--down to the slow-moving heavy freights. When any sort of train loses a certain length of time--usually half an hour or more--it loses all rights that it might ever have had, and everything else on the line has precedence over it. A train may lose time if it has to, but there are never any circumstances that will justify it in running ahead of time. All this is the part of railroad operation which governs the relation of one train to another. There are even simpler but not less vital rules that control its own operation. In order that the engineer who is guiding the train, and the conductor who shares the responsibility, may keep in touch with one another, the device was adopted many years ago of having a cord run through the cars of passenger trains to a bell signal in the cab of the engine. This bell signal during recent years has given way to an improved form of locomotive signal, sounded by means of compressed air in tubes throughout the train, and operated in connection with the air-brake equipment.