iti 



SCIENCE. 



[Vol. Xxli. Mo. 55^ 



EAILEOAD SIGNALINa. 



BY REGINALD GORDON, COLUMBIA COLLEGE, NEW YOBK. 



The chief object of signaling on railroads is to inform 

 enginemen positively, at given points, whether they must 

 stop or proceed, and the universal method of conveying 

 this information is by a visible signal. Audible signals 

 have been tried, but their use is rather limited. At the 

 hio-h sr)eeds now usual on our railroads, an engineer 

 ou'ght to be able to interpret the meaning of a signal at 

 some distance before he reaches it, so that if obliged to 

 stop, he can bring his train under control and stop 

 it, before reaching the point where actual danger 

 exists, whether it be a train, an open switch, or some ob- 

 struction. The necessity of an easily distinguishable sig- 

 nal is thus obvious. In the early days of railroading, 

 when trains were comparatively few and speeds were low, 

 it was sufficient to have flagmen or watchmen, waving a 

 flag by day, and a lantern at night. These men were of 

 course governed by orders of the local superintendent or 

 roadmaster. If a train stopped unexpectedly, or longer 

 than usual, a brakeman was sent back with a flag or lan- 

 tern to protect his train against a following one. Two 

 "•reat improvements were made in railroad operation when 

 fixed signals, on poles or posts alongside the track, were 



tion and recent rapid extension of block-signal systems of 

 various kinds has led to the almost universal employment 

 of semaphores, and even where an absolute block system 

 is not maintained, train movements, either on the open 

 road, or within yard limits, are controlled mainly by this 

 form of sio'nal. The necessity of keeping two trains apart 

 by a space interval, rather than by a time-interval, has 

 been demonstrated in a most forcible manner by the long 

 list of rear-collisions on railroads relying solely on the 

 rear brakemen to keep trains apart. In the former 

 method the road is divided up into spaces or blocks, and 

 no train is allowed to enter any block unless the last pre- 

 ceding train shall have passed beyond its limits. The 

 limits of each space or block are marked by signals, usual- 

 ly semaphores, operated directly by a signalman, or else 

 controlled by him through the intervention of compressed 

 air and electricity. The safety of trains, then, rests main- 

 ly upon the faithfulness of the signalmen, as well as the 

 vigilance of the locomotive engineers. 



Under the time-interval system, trains are not allowed 

 to follow one another closer than after an interval of five, 

 seven or ten minutes, according to the class of trains and 

 their relative speed. With this system everything de- 

 pends upon the faithful and active performance of duty 

 by the rear brakeman of a train. Some railroads, unable 



adopted, and when the method of keeping trains apart, and 

 protecting them, one against another, known as the "block 

 signal" system was introduced. These fixed signals were 

 moved by a combination of rods, wires and levers, worked 

 by an operator situated at some distance and controlling, 

 at the same time, several other signals in a similar man- 

 ner. 



Of all the different forms for signals that have been 

 tried, the disc and the semaphore are the only ones in use 

 now. The disc signal may give its indications for safety, 

 either by turning through 90°, so as to show only its edge, 

 or by moving bodily out of that part of the signal case 

 which, when occuj)ied, means "danger." Fig. 1 shows an 

 electrically oijerated disc signal at "danger;" and the 

 dotted lines show the "safety" position. The semaphore 

 signal, fig. 2, is more positive in its indication, because 

 it is more easilj' discernible than a disc. The safety posi- 

 tion of the semaphore is shown by the dotted lines in fig. 

 2. The blade or arm carries a frame, F, in which a red 

 glass is fixed, so that at night, when the blade is raised to 

 indicate danger, the lamp, I, fastened on the bracket, 6, 

 will show a red light. When lowered for safety, the lamp 

 is uncovered, and, of course, shows white. The introduc- 



FIG. 2. 



to incur the expense of installing and maintaining a first- 

 class block-signal system, have jDrovided signals at every 

 regular station, where the station agents, being in tele- 

 graphic communication with one another, can, if neces- 

 sary, carry out a very fair "absolute" block system. Each 

 station, then, marks the end of one section and the begin- 

 ning of another. In times of heavy traffic, however, these 

 blocks between stations are too long; that is, trains are 

 kept too far apart, and compelled to wait so long at sta- 

 tions that the road could not be kept clear, and the ser- 

 vice would become demoralized if this method were strict- 

 ly adhered to. For these reasons, and under the circum- 

 stances cited, it is quite usual to allow trains to follow 

 one another after an interval of time, determined in each 

 case to suit the circumstances, and the j^i'actice thereby 

 becomes "permissive," as opposed to "absolute" blocking. 

 This method of opierating is in use at present on many 

 roads, and, though it no doubt prevents many collisions, 

 is vastly inferior to an absolute, interlocking system of 

 block signals. 



Railroads with very heavy traffic, and traversing thick- 

 ly settled regions, have lately found it necessary and ex- 

 pedient to equij) their lines with this latter system, and it 



