mechanical function to fulfill apart from the promotion of safety. Signals are one of the most important items of this class, and serve to keep the trains a certain distance apart, as well as to inform the engine runners of the condition of the tracks at switches, crossings, etc. The semaphore is the standard signal in both the United States and England. These are arranged to give three indications, according to the positions and colors of their blades in the daytime and the colors of their lanterns at night. The semaphore consists of a vertical post, to which a blade about two feet in length is pivoted near one of its ends, so as to hang either vertical at right angles to the post or midway between these positions. The short end of this blade behind the pivot carries a disk of colored glass, either red or green, which falls in front of a lantern when the blade is moved. For a clear track the blade hangs at an angle of about 30 degrees from the post and the lantern shows white. For danger a red blade stands horizontal, showing a red light, and for caution a green blade and a green light are shown. The signals and switches are worked from the same station by means of levers, which are provided with interlocking devices, so that only the proper signal corresponding to the position of the switch can be given. The interlocking system is a very ingenious arrangement, by means of which the movements of a number of levers are interdependent, so that it is mechanically impossible for the signalman to move them except in their prearranged order. In approaching a switch there are two signals, the farther one indicating caution, and the home signal danger, if the switch is not locked in position so that the line is clear. The switch lever is the only one which can be moved, and its movement releases the lever of the caution signal. Moving the latter locks the switch lever and releases the danger-signal lever, which, being thrown, locks the caution-signal lever and indicates that the way is clear. The levers can only be moved now in the reverse order, so that in throwing the switch the signals show danger first. In cases where the signals are too far from the signal tower to be seen and a break in the connection occurs, the signal falls by gravity to the danger position. This system of interlocking is capable of broad expansion, as one lever may be made to lock any one or more of the assembled levers in a signal tower.
In a refinement of the above system the manual labor of throwing the levers is replaced by the use of compressed air. The valves which control the various signals and switches are operated by electricity and controlled by small switches, which interlock in the same way as the levers described. A model of the track and signals is placed over the switchboard, and any changes made are reproduced on the model. As with the interlocking system, a signal could not be given which would lead to an accident; such could only occur by the failure to see or obey the signals. In case of fogs, a torpedo is frequently placed on the track, which makes a loud report when the wheels of a locomotive pass over it. In connection with the interlocking system, the detector-bar for switches is important, its function being to prevent the throwing of a switch while a train is passing over it. This is accomplished by means of a bar placed parallel to the rail. The bar is moved by the same mechanism which locks the switch. The movement of this bar raises it above the level of the rail, so the switch cannot be unlocked as long as there are any wheels on the rail which prevent the detector-bar from being raised. Another railway safety appliance is the system of signals which is used to maintain a minimum distance between the trains on the same track. The block system is used for this to some extent in the United States, and is almost general in England. See Block Signal Systems.
Brakes are the most essential safety devices for railway trains, and certain general principles are now recognized as necessary, which are to be found in almost all brake mechanism in use all over the world. They must be quick-acting, must be applied to every pair of wheels in a train, and must be applied simultaneously and controlled from a single point, generally at the locomotive. Air brakes, vacuum brakes, and several electrically controlled brakes fulfill these conditions, the Westinghouse automatic air brake, however, being the standard in this as well as most other countries. See Air Brake.
In addition to the signaling and braking appliances mentioned, a number of minor devices of great value in promoting safety have been introduced. Automatic couplers are important among these, and they are now demanded by law in the United States. A standard form has been adopted by the Master Car-Builders' Association, to which the various manufacturing companies comply, so that any of the different makes will work together. Their use is now general on all cars.
AUTOMATIC CAR COUPLER.
Grade crossings of highways at important points are gradually being abolished, as the percentage of people killed at these points is much greater than that of passenger fatalities. One device used at grade crossings is the well-known arm gate, operated by a flagman, or by compressed air, when several gates near together are used. Another method for crossings where the travel is infrequent is to provide an electric bell at the signal post, which is put in operation by the car wheels, and continues to ring for several minutes before the passing of a train. A considerable number of other appliances are in general use for promoting safety on railways, which would require too much space to describe.
Railway Management. Railway management in the United States is primarily under the control of the directors of the railway companies, who are elected by the stockholders. A president is the chief executive officer of a railway, and the other officers are generally one or more vice-presidents, a treasurer and secretary, and a general manager. The treasurer has charge of all moneys collected and disbursed, and is responsible directly to the president, who is assisted in certain duties by the vice-president. The duties of the general manager extend to every department of the service, all of which are under his control. A superintendent is at the head of each department, who is responsible for every detail
