REPORT OF MR. ROBERT B. LINES.
439
3. Signals of warning at grade-crossings of common roads.
4. Signals " covering ” the position of trains in motion from trains following, meeting or crossing.
5. Signals between the various portions of a train.
6. Signals to be used in case of accident.
Through the first four of these classes runs a general, or rather a special subdivision, and one of great importance, if not to the present, at least to future systems of railway signalling. Until recently, signals between stations and trains in motion have been on the one hand purely optical, as the display of flags, lights or semaphores from stations, and on the other optical or aural, as the display of flags and lights and the blowing of wdiistles on trains. Since, however, it has been found practicable to communicate electrically between stations and rapidly moving trains, the possibilities of railway signalling have been greatly extended.
I. Signals of the Movement of Trains.
I have not thought it important to consider at much length the various devices employed to indicate from point to point the forward movement of trains. When there are special functions to be performed (and it is to such points only that I desire to apply the general term " station ”), the stations are usually connected by the ordinary telegraph, and announcements of the arrival and departure of trains may, of course, be made in the ordinary manner by message.
In a purely "signal” service, however, each "station” and intermediate " signal-box ” is on an equality with every other, and a method of communication is necessary wdiich can be employed and interpreted by signal-men as well as by skilled telegraph clerks. This may be easily attained by making each such point the terminus of an electric " circuit,” in which is inserted a " bell-sounder.” This is an ordinary electro-magnet, the armature of which is extended upwards and furnished with a hammer, wdiich strikes upon a bell when the circuit is closed. As this apparatus, though simple, forms an important part of many of the signals in use for other purposes, a brief diagram and description of it may not be out of place here.