Popular Science Monthly/Volume 4/March 1874/Electric Signaling on English Railroads

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I TAKE it for granted that most Americans who have traveled in England know of, if they don't actually know, Clapham Junction. It is a marvelous place is that Clapham Junction—a half-dozen or more naked-looking graveled platforms, destitute of almost every convenience in the shape of waiting and refreshment rooms, forming altogether one of the most important, not to say intricate, railway-depots in the United Kingdom. One arrives at a platform by a train belonging to one company going in one direction, and by turning right about, or walking three yards on the same platform, one may secure a seat in another train belonging to an entirely different company going no one knows whither. Once give way, or lose your head at this particular junction, and you may find yourself, should you happen to be wanting to go to the west of England, suddenly whirled away to the south, and vice versa. Even your traveling Londoner has an instinctive dread of "the Junction," as he familiarly terms it. Should you ever take up that indispensable requisite of English traveling, a Bradshaw, and stumble upon Clapham Junction in the list of stations your train is timed to stop at, go no farther. Don't tempt Fate. Rather court resignation. Throw yourself upon the cushions of your carriage, pitch Bradshaw out of the window, and in a moment of leisure work out this sum: If upon the average eight hundred trains (to say nothing of specials, excursions, and stray locomotives) pass through Clapham Junction in the course of twenty-four hours, allowing just about two minutes' interval of time between train A going out and train B coming in, what should be the chances of train B dashing into the tail of train A?

So remote as scarcely to be thought of, the reason being that the "block" system is in full force. What is this "block" system? To endeavor to answer that inquiry is the very object of this article.

To understand thoroughly what railway traveling in England really means, one should bear in mind a few facts now given for the purposes of this article, in the order of their importance.

At the beginning of last year there were in the United Kingdom about 15,500 miles of railway, distributed as follows: England and Wales, 11,000 miles; Scotland, 2,500 miles; Ireland, 2,000 miles; and 290 companies shared these miles of railroad between them. The total number of depots, or stations, as they are termed in England, including junctions and sidings, is about 10,000 for the whole kingdom; of these 6,000 are passenger-stations, giving approximately one station to about every two miles of railway, but not in reality, because there are no less than 150 stations in London and the suburbs alone. As a matter of course the great centre of the railway system of the United Kingdom is London. Every company which can by any possible means find a way to the capital does so, and strives to provide the route which will be most attractive to the public. To do this the majority of the companies must, of necessity, make use of the lines of the great companies having their termini in London. Only imagine the number of branch lines, junctions, and sidings, this must involve; what "shunting" of trains and adjusting of points there must be; what an efficient system of signaling must be required; what care, steadiness, and application to work must be demanded of the men who look after the signals and points at the branch lines, junctions, and sidings. Take the Great Western line of England, for instance, with its 1,387 miles of road. Besides its own system, it falls in with the principal systems of the Bristol and Exeter, South Devon, North Wales, and ever so many more minor systems for the traffic of which it has in a measure, of course, to provide as well as for its own. Over all these lines trains are traveling daily at express speed, their ultimate destination being London. Now, express speed in England means an average rate of 47¾ miles an hour, a pace which is probably greater by ten miles than that attained on any other railroads in the world. Indeed, on the Great Western and Great Northern lines even this rate of traveling is exceeded. On the first-mentioned system a train runs 77¼ miles (from London to Swindon) without stopping, in 87 minutes, giving a uniform pace of 53¼ miles an hour: on the Great Northern a train completes the journey from London to Peterborough (76¼ miles) in 90 minutes. Just one little error on the part of the signal man, one omission to adjust the points on the part of his mate, and down swoops the express on to the wrong line, and the result is an appalling catastrophe such as happened at Wigan the other day.

In the above little sum, which I suggested to be worked out, I mentioned that about 800 trains passed through Clapham Junction regularly every day. You take your stand upon the platform. Whish-h-h—Bang—Rattle a train has passed you. Take out your watch, mark the second-hand going round, and before it gets to 60—Whish-h-h—Bang—Plunge—a second train has rushed out into the open, to catch the first one up. But it can't. The line is blocked by the sharp-sighted man in the signal-box yonder, who has no fear even if a train per minute were to work through. He has nothing to do with time. His duties are to maintain a certain and invariable interval of space between two trains, and he does it. How does he do it? If the reader will be good enough to follow me into the signal-box, he shall see.

Not much of a place certainly. On the whole rather like a second-rate sea-shore shanty, stuck upon four posts, so placed it seems that every train going into the station, and every train coming out from it, shall rush full tilt against the box and smash it and its occupants to atoms. In reality, the signal-box is so situated to command for a certain distance a full view of one line just where it joins to another. Interiorly our box is not unlike an unfurnished private box at a theatre, into which some of the machinist's properties have been put by mistake. Regarding a printed notice on the wall that strangers are particularly requested not to distract the attention of the signal-man from his duties, we take a look round, and the general impression to be got from a cursory glance is that it must be rather jolly to be a signal-man. Every thing looks so clean and neat; there is plenty of excitement to be had in watching the trains from the window; the work does not appear to be very laborious, and what there is of it (which, truth to tell, is a great deal) would seem to be especially interesting and not unconnected with the gaining a full and accurate knowledge of the working of the electric telegraph. On the left-hand wall of the box as you enter, and on a level with the eye, are a number of little ebony handles, technically known as "keys," but variously termed in English railroad parlance "piston-keys" or "plungers." They are on the principle of the little "pea" bell fitted to the bedrooms of most large American hotels, and communicate telegraphically between the stations—"up" and "down." Over each of these "plungers" is an electric bell, which rings to give notice of the approach and departure of a train, its nature—that is, whether it is a passenger or goods, express or special—and to which company it belongs, when two or more companies have running powers over the same line. The custom universally adopted by English railroad companies to distinguish trains, and I believe it is the case with our own, too, in addition to the particular disks and lights carried upon the buffer-plank of the locomotive, is to blow the whistle a certain number of times when approaching a junction or station. The same system is adopted with the electric signals in the signal-box, only, in place of blowing the whistle, a bell is sounded. Every depression of the "plunger" transmits a current of electricity to the other station "up" or "down," as the case may be, which there sounds a bell or gong, and by varying the number of currents sent a code of signals is formed. For instance:

1 Depression of the "key" Acknowledgment.
2 Depressions Passenger-train.
3 " Goods.
4 " Special.
5 " Obstruction-signal,

and so on. This code may, of course, be varied at pleasure; and it is possible to give fifteen distinct and unmistakable signals upon a bell by varying the number of beats and repetitions. By means of these bells, then, a perfect means of communication is kept up between two stations, signal-boxes, or gate-houses, on a railroad.

The fundamental principle of the "block" system which we are now endeavoring to explain is, that no train traveling in the same direction shall ever approach nearer to another than the distances which the signal-men's boxes are apart. These distances vary on English roads according to circumstances, but, so long as the signals are properly made by the signal-man, and attended to by the driver of the locomotive, it becomes simply impossible for one train to run into another. For sake of illustration, let us take three signal-boxes, which we shall call B, and C, and D, on a line of railroad between B and E. We will suppose that the express from a station A has arrived at B, and is about to proceed on its journey to E, and that an ordinary train has preceded it a quarter of an hour, which would allow about time enough for it to "shunt" or go off into the siding at D. When the train has passed the signal-box at C, the signal-man there telegraphs to the one at B that the line is clear, which means that there is no train on the "up" line between stations B and C. Directly the express referred to arrives at B, the signal-man there, if he has received the signal "all clear," allows the train to pass him, and at once telegraphs to C that there is a train on the "up" line. The C signal-man, if he has received a signal from D of line clear, allows the express to pass him also, but, if not, he exhibits his signal accordingly. We will now suppose that the express is yet between B and C, and that another train, approaching in the same direction, whistles to the man at B for leave to go on. This is refused until the C signal-man telegraphs that the line is clear. The same plan is carried out at every signal-box the train has to pass, of whatever nature it may be, whether "express," running at the rate of fifty-five miles an hour, or "goods," steaming along easily at a pace of twenty-five. It will thus be seen that, however great the traffic, it can be conducted with almost absolute safety, the only difference being that, with a very large number of trains per hour, the signal-boxes are placed nearer together, as on the Metropolitan or Underground Railroad of London, which has as near as possible one thousand trains passing over its system in the course of every twenty-four hours. No accident of any importance has ever occurred on this line.

But there are other objects in our signal-box besides plungers and little bells to attract attention. Four very noticeable toys—I use the term advisedly, for they struck me at once as being particularly suggestive of liliputian railroads, and dolls' houses, and toy signal-men—are the miniature electric semaphores used for instructing the signal-man as to setting the semaphore-signals on the line for the guidance of drivers of locomotives. Having stated the principle of the "block" system to be that no two following trains are to be allowed to proceed in the same direction upon the same section of line at the same time, it follows that a danger-signal must be exhibited and maintained at the station or depot from which a train has departed until it has been cleared out of the section of the line over which it is traveling. To do this effectually necessitates that this signal should be under the control of the signal-man toward whom the train is approaching; and no accident, mechanical or electrical, should be allowed to remove this signal until the train has arrived. The signals used on most of the English lines of railroad to guide the driver are, the raising and lowering of a semaphore arm to denote "danger" and "all clear." If it were possible to work these huge out-door signals by electricity, the system would be perfect; but, inasmuch as the power of electricity is circumscribed, the production of force sufficient to actuate, with any degree of certainty, these exposed signals, has not yet been attained. It has become necessary, therefore, to rely upon small electrical instruments, miniatures of the out-door semaphores, which direct the signal-man in the box how to exhibit his out-door signals by displaying the signals which they themselves ought to give. The same principle which produces a blow upon the bell-signal lowers the semaphore arm on the miniature to "all clear." A current of electricity, flowing through the wire of an electro-magnet, converts the iron core into a magnet, and exerts precisely the same action upon a rocking lever that a pull or strain of a signal-wire does upon the large rocking lever of a signal-post. A counter-weight, when the current ceases, restores the arm to "danger," as it does in ordinary railroad-signals. So that the miniature semaphore will remain at "all clear" so long as a current flows, but, the moment the current ceases, the arm by the action of gravity flies up to "danger." It is impossible to lower the signal at one station except by the action of an electric current, and to maintain that signal at "all clear" except by the persistent effect of the battery at the other station. The signal, therefore, is under the sole control of the signal-man toward whom the train is approaching. The instrument employed to raise and lower this miniature signal is called a "switch," from the similarity of its appearance and construction to the switch-handles or levers employed to raise and lower the larger signals on the line. Its electrical construction is precisely similar to that of the "plunger." By removing the handle over from one side to the other, it places the battery in connection with the line wire, and thereby causes a current of electricity to flow which lowers the signal.

There were four of these miniature "switches" in our signal-box, and this was the way they appeared to us to work: When the switch-handle was placed so as to be nearest us, or On, no current was transmitted, and the little signal stood at "danger;" when, however, it was pushed over farthest from us to Off, a current flowed, and the little arm was lowered to "all clear." As the arm could only be lowered when a current was flowing, it was only when the switch-handle was pushed over to Off that the "all-clear" signal could be given. Similarly, when the switch-handle was at On, the flow of electricity at once ceased, and the signal flew to "danger." The signal "all clear" could therefore only be given when the little switch was intentionally placed over to Off, and there was no other means of accomplishing this object by willfulness or accident. No accident, mechanical or electrical, could alter the miniature danger-signal. The man at our signal-box had the sole and complete control over the signal at the next box, and it was simply impossible for him to interfere with or alter the signal in his own box. This in effect is the "block" system, which answers so admirably on the principal lines of English railroad. The instructions given to signal-men who work the signals we have been describing are as follows, and we give them that the reader, when next traveling upon an English line of railroad and passing a signal-box, may give a passing thought of thanks to the inventor of the "block" system, and the gentleman who framed these rules, Mr. William Henry Preece, of the Institute of Civil Engineers, and to the individual, let us hope, who follows them closely—the signal-man:


1. No train or engine is to be allowed to pass your box unless the electric signal for the section into which it is about to proceed stands at all clear.

2. When a train has entered the section of line which you have protected (under Rule 4), you will signal to the next station, two beats on the bell twice, to signify "Train coming; be ready."

3. On the approach or arrival of the train or engine at your box, you will, provided the electric signal stands at all clear, at once signal it on the bell to the next station in advance, thus:

If a passenger-train... by 2 beats
" goods-train..... " 3 "
" special or engine... " 4 "

4. This signal will be acknowledged by the corresponding station, by throwing his switch-handle over to "on," thereby placing the electric signal at your station at danger, and protecting the line from any train following that already in the section.

5. You will acknowledge this signal by returning one beat of the bell.

6. On the arrival of the Down
train at , the signal-man at that station will pull his switch-handle over to off, thereby removing your danger-signal, intimating the arrival of the train and clearing the line.

7. This you will acknowledge by one beat on the bell.

8. In case any obstruction exists upon the line to necessitate its being blocked, give five sharp beats on the bell (which must be repeated), and raise the electric signal to Danger, which must be maintained as long as the obstruction lasts.

9. No signal is to be considered complete until it has been acknowledged.

I beg leave to state that this article is written without being at all acquainted with the system of signaling on American lines of railroad, so that I am unable to say how far our own bears comparison with the English system.