Popular Science Monthly/Volume 5/July 1874/Field Telegraph
|THE FIELD TELEGRAPH.|
IN the year 1802, when Napoleon was first consul, there arrived in Paris two artisans of Poitiers. One of these men, Jean Alexandre, had invented a rudimentary form of the electric telegraph, and, with his friend Beauvais, he had left the little country town full of high hopes to submit his discovery to the great soldier who was then guiding the destinies of France. He requested a personal interview with the first consul, refusing to communicate his secret to anyone else. He was referred to the astronomer Delambre, whom he succeeded in convincing of the value of his invention; still, however, declining to reveal the way in which the electric signals were transmitted, unless to Napoleon himself. But the latter refused to grant the required interview, saying he had no time to trouble himself with such matters; and Alexandre and Beauvais went back to Poitiers in bitter disappointment. Had Napoleon listened to the proposals of Alexandre, the course of history might have been changed; for, had he been able to secure the exclusive possession of the electric telegraph, it is easy to imagine the effect it would have had upon his campaigns, and how difficult it would have been for even the allied armies of all Europe to contend against a great commander, who, by some secret means unknown to them, could obtain accurate and instantaneous information from every point of the theatre of war, and flash his orders to corps-d'armée divided from him and each other by miles of country, while his opponents had only to trust to horses and couriers to carry their orders and dispatches.
A very little study of the wars of the French Revolution, in comparison with those of our own time, will be sufficient to show what an advantage the telegraph is to the modern commander. A striking instance of the extreme difficulty of combining the operations of separate corps or armies in the same theatre of war, without the aid of the telegraph, is afforded by the history of the campaign of 1796, in Germany, when Moreau and Jourdan were "acting in concert" against the Austrians. The Archduke Charles left a weak retarding force in front of Moreau, while he directed all his available strength against Jourdan; and the former general was actually advancing in triumph through Southern Germany, under the full conviction that his colleague had obtained a like success to the northward, while the latter had actually been defeated at Amberg, Wurtzburg, and Aschaffenburg, and driven back upon the Rhine, and Moreau only heard of his disaster in time to save his army from destruction by a hurried retreat through the defiles of the Black Forest. As a contrast to this, let us take the campaign of 1866, when the two Prussian armies advanced from separate bases into Bohemia, laying down the lines of the field telegraph as they moved forward, which, being connected by the permanent telegraphic system of Saxony, kept each army in constant communication with the other, and thus enabled them to combine their operations, and at length to unite with decisive effect on the battle-field of Sadowa.
It is just twenty years since, for the first time, the electric telegraph was used in the field, and to the British army belongs the honor of having led the way in its adoption. The trenches and batteries before Sevastopol were traversed and connected by lines of telegraph, and the French soon followed our example and constructed a similar system in their own lines; while later on a cable laid across the Black Sea put the armies in the field in direct communication with Paris and London.
Since that time a regular telegraph corps has been organized in every European army. And the field telegraph was used by the French in Italy in 1859, and in their campaigns against the Kabyles in Algeria; and, in America, both the Federals and Confederates made free use of permanent and temporary lines during the war of secession, the Southern cavalry in particular displaying great daring and enterprise in riding round the flanks of the Federal armies, seizing their telegraph-lines, sending false messages to the Northern generals, and then cutting the line and retiring as rapidly and secretly as they came. It was, however, in the Prussian army, and in the great campaigns of 1864, 1866, and 1870-'71, that military telegraphy attained its greatest development; and, after the experience of these three wars, the Prussian telegraph corps is probably the most efficient in Europe. We have already seen how well it did its work in the campaign of 1866, and in 1870 it established the net-work of wires over the northeast of France, that enabled Moltke, sitting in his bureau at Versailles, to move his armies as accurately and certainly as pieces on a chessboard; while round Paris itself a circle of telegraph-wires that in a moment flashed information of a sortie, and orders for a reënforcement of the threatened point, to every part of the long line of sixty miles, on which the besiegers lay—contributed almost as much toward the reduction of the vast fortress as the circle of steel and iron, of batteries, earthworks, and redoubts, which, without the connecting link of the telegraph-wire, could not have been maintained for a single month. On their side the French displayed no less energy. The regular telegraph corps was shut up in Metz or lost at Sedan; but a fresh corps was organized for the armies of the republic, and at Paris the telegraph-lines linked together the enceinte, the forts and outworks, and the headquarters of General Trochu. But it was in the second siege of the capital that the French telegraph corps obtained its greatest success. During the fighting in the streets of Paris, in May, 1871, the moment a barricade was taken, a telegraph-station was established in a neighboring house, and when another post was carried the telegraph corps would again move forward with the troops, and thus MacMahon was able to watch every turn of the fight, and provide for every contingency, in a way that otherwise would have been utterly impossible. For ourselves, we have had no European war since 1854; but our armies have carried the telegraph with them into India and China, and through the ravines and passes of Abyssinia; and now the "talking wire" stretches from Cape Coast Castle through the bush, across the Prah into the heart of Western Africa, hanging on the trees, with here and there a few poles, the whole having been erected by Fantee laborers, under the direction of a handful of Royal Engineers.
The object of the field telegraph is to keep the headquarters of an army in communication with its several corps, and, at the same time, with the general telegraph system of the country. In the Prussian army, when the telegraph corps was reorganized after the war of 1866, it was formed into two divisions—the Field Telegraph Division and the Etappen Division—with view to the more efficient performance of these two services. Both divisions consist of several companies or sections, each of which contains about 150 men, including officers, telegraph operators, pioneers, workmen for the erection of the line, and drivers for the station-, store-, and baggage-wagons. In all armies the telegraph matériel is, of course, very similar, and we shall therefore describe that of the Prussian army, adding a few notes on that of other countries.
The two essential portions of the field telegraph are the station and the line. In order that there may always be a sheltered place for erecting the instruments and transmitting messages, each detachment of the telegraph corps carries with it one or more wagons fitted up as stations; but, wherever a halt of more than a few minutes is made, and there is a suitable building available for that purpose, a telegraph-station is established in it by removing the batteries and instruments from the wagon. Fig. 1 is an outline sketch of a Prussian station-wagon, Fig. 2 being a section of the same. The wagon is about 9 ft. long, with an interior height of 4 ft. 6 in., and a width of 4 ft. It is built as lightly as possible, and weighs when loaded only 14 cwt., and is easily drawn by two horses. On the outside are two insulated brass conductors i (Fig. 2), to which wires can be attached. Inside the windows is a shelf with a drawer d, on which the instrument t can be placed when in use, and opposite to this is a seat or bench s for the
|Fig 1.||Fig 2.|
|Prussian Station-wagon.||Section of Prussian Station-Wagon.|
operators, on which a man can sleep at night. Under the seat is a recess in which a spare instrument t is kept, while the batteries are arranged in a box b under the shelf. When a message is to be sent from this movable station the wagon is stopped, and the line-wire is attached to the insulated conductor i. This is connected with the instrument and battery, and in order to complete the circuit the battery is placed in electrical communication with the second insulated conductor, to which another wire is attached which joins it to the earth-conductor or earth-stake (piquet d terre) (Fig, 5). Thus the course of the current, when transmitting a message, is from the battery to the instrument, and by the first insulated conductor e (Fig. 2) to the line of wire, the earth-plate of the receiving-station returning it to the earth-conductor, driven into the ground near the wagon, and thus back by the second insulated conductor to the battery.
The instruments are of the Morse pattern, constructed so as to fit in a very small space, and recording the signals with ink. The battery (of which there are two in each station-wagon) is a simple form of M. Marié Davy's sulphate-of-mercury battery. It consists of ten elements, one of which is shown in section in Fig. 8; c is a charcoal vessel, containing sulphate of mercury moistened with water to the consistency of paste, and in this the zinc plate z is suspended by means of the India-rubber cover I. The whole is placed in the India-rubber vessel i, and a copper collar y is added, to which a connecting wire can be attached. This battery has the advantage of being very portable, while the India-rubber cover prevents the charge of sulphate of mercury from being spilt by the motíon of the wagon.
The line may be either an aërial or a ground wire, or a combination of both, the former being stretched on poles, while the latter is insulated by being inclosed in a light cable, about half an inch thick, and laid along by the road-sides or across the fields. The uninsulated wire and the cable are both issued to the telegraph corps coiled on small drums, several of which are carried by each store-wagon. In those companies which are to erect a wire stretched on poles, the wagon carries five English miles of uninsulated galvanized iron wire, one mile insulated in gutta-percha, 1,000 yards of the cable, and 200 poles with insulators attached, all the wire being coiled on twelve
|Fig 3.||Fig. 4.|
|Hand-barrow for uncoiling Wire.||Wheelbarrow.|
drums. If it is intended to lay a ground-line, the wagon carries eleven drums of the cable, one of wire covered with a light coat of gutta-percha and tarred hemp, and a few poles and insulators, for carrying the line across small hollows, or raising it overhead in crossing roads. Beside these stores the wagon contains all the tools necessary for the work, and a light step-ladder is hung underneath it.
The wire is uncoiled from the drums by placing them successively on a hand-barrow, from which it is paid out as the barrow is carried along. The hand-barrow (Fig. 3) consists of a light iron frame, with wooden legs and handles, which are made to fold up when not in use. On this frame the drum a is placed; one man carries it in front and two behind, the wire uncoiling and running out between them. A wheelbarrow (Fig. 4) is sometimes employed, and is improvised for this purpose by attaching iron handles d to the step-ladder b b, and placing it on a pair of light iron wheels c, the drum a being hung in a socket near the top of the ladder.
The poles are made of well-seasoned and selected red pine, about 12 ft. long and a little more than an inch thick. At the bottom is an iron point for fixing them in the ground, and at the top a socket s (Fig. 6), of the same metal, with a hollow screw to receive the spindle or stem of the insulator. This consists of an iron spindle b, with a male screw cut in it, which supports either a cap of gutta-percha g or an earthen-ware cup surmounted by a metal bell. In both cases there is on the top of the insulator a metal hook a, in which the line-wire is hung. There are also insulators, the spindles of which terminate in spikes or sharp screws for driving into walls and trees, thus saving the trouble of erecting a post (Fig. 9).
When all the wire of the first drum is laid down, the end of it is roughly spliced on to the wire of the next drum, and the joint secured by means of the conductor (Fig. 7). This consists of two semi-cylindrical pieces of hard wood a, their flat side being grooved to receive the wire, and covered with a layer of India-rubber b to act as packing, and insulate the joint, in the case of a ground-line, and the whole is held tightly together by the brass collar and screw c c s (Fig. 8).
The line is very rapidly and easily constructed. In the case of a ground-line it is simply paid out from the drums on the hand or wheelbarrow, being buried in a shallow trench or elevated on poles, when it is necessary to cross a road, where the insulation of the cable might otherwise be injured by the wheels of passing vehicles. During the invasion of France the Prussians frequently avoided the roads in order to protect the line from the franc-tireurs, and made considerable détours, concealing it in woods, ravines, and water-courses. Where the uninsulated wire is used, poles are erected about fifty paces apart, the hole to receive each pole being made by driving a sharp pointed iron bar into the ground with a heavy mallet. As soon as a pole is fixed the wire
is run through the hook on the top of the insulator, and stretched tight by a man holding it over his shoulder, who keeps it in this position until the next pole is ready to receive it. Wherever there are trees or walls near the line, the work is still further lightened by dispensing with the poles, and merely attaching the wire to the insulators specially constructed for this purpose. In this way the line was erected for the Ashantee expedition, the negro laborers carrying only a light ladder to ascend the trees, a small axe to clear away the boughs, and a gimlet to make a hole for the spindle of the insulator. It never took, we are informed, more than five minutes to fix an insulator to a tree; but, in those few places where trees were not available, fully half an hour was occupied in erecting each pole, and even then it was often unsteady, and had to be propped and guyed.
In Europe, where there is an extensive telegraph system in operation in every country, there is no need of the field telegraph-lines extending from the front of the army to the base of operations. Far less than this is required. All that is necessary is to connect the headquarters of the army with the nearest point on a permanent telegraph-line, and in most European countries an army in the field would seldom, if ever, be more than ten miles from such a line. Ten miles of the field telegraph can easily be erected in half a day; indeed, the Austrian engineers assert that on favorable ground they could do the work in two hours. In most cases, of course, the advancing army would have to repair the permanent lines which would be partially destroyed by the retreating forces, and in this way twenty-five miles of wire were often erected by the Prussians in a single day. As soon as an army moves forward, the field-telegraph line previously erected is taken down and recoiled on the drums, while a fresh line is laid from the new headquarters to the nearest permanent telegraph. This is done with a view to economizing the material, an enormous amount of which would have to be carried with the army, if the lines it left behind it in its advance were not removed, and the poles, wire, and insulators, employed in their construction again utilized. The hand-barrows of the Austrian telegraph corps are designed to be used in recoiling as well as uncoiling the wire; and for this purpose are fitted with a crank-handle and ratchet-wheels, so as to enable a man to turn the drum and wind the cable upon it.
Besides the ordinary field-telegraph companies, the French army includes a mountain-telegraph corps, organized with a view to operations
|Fig. 6.||Fig. 7.||Fig. 8.|
|Telegraph-Pole, Socket, and Insulator.||Wire-connector.||Marié Davy Battery.|
on the mountainous frontiers of the south, or to be ready to carry a line over a range of hills in an ordinary campaign, thus avoiding a long détour in the valleys, or securing lateral communication with troops divided from the main army by the hills. As the mountain line would have to be laid along narrow, rocky paths, and through lofty passes, all carriages and wagons are dispensed with, and their place is taken by a train of mules. In a mountain-telegraph company several of the mules are each laden with two drums of the insulated cable, the instruments and batteries are carried on pack-saddles on the backs of others, and others again transport the baggage, provisions, and forage of the company, and also a light tent to form a station whenever messages are to be sent along the line.
While the field telegraph affords a commander a rapid and certain medium of communication with his base of operations and the various corps of his army, it must be remembered that it is one which is continually liable to interruption by an enterprising enemy. Wherever a general has to contend with ah army well provided with good cavalry, he will find it extremely difficult to protect his telegraph-lines from being destroyed by daring raids of his opponents. There are several easy ways of making a telegraph-line temporarily useless. The simplest and most obvious method is to pull down the poles and cut the wires into pieces; but when this is done the damage is easily detected,
and the repairs at once commenced. The interruption will, therefore, be far more serious if it can be effected in a way which will not permit of its exact locality being so readily discovered. This can be done by cutting the wire, introducing a piece of gutta-percha, or any other non-conducting substance, into the course of the circuit, and connecting the ends of the wires with it, so as to give it the appearance of one of the ordinary joints or splices of the line. At the same time a few poles can be pulled down in another place, and the wires cut, and the probability is that the engineers who repair the line will not discover the hidden interruption of the circuit until after they have restored the gap, and found that the wire is still cut somewhere else, and even then the place where the non-conducting substance is introduced will not be discovered until some time has been employed in carefully testing the line with the galvanometer.
But there are other dangers to telegraphic communication in the field besides the mere damage to the line. If the enemy's cavalry get possession of a station, they can easily send messages containing false information or delusive orders to well-known officers of the opposing force, while the place from which they are sent, and the assumed name in which they are dispatched, will give the messages an appearance of authenticity which, if it does not completely deceive the recipient, will at least be the cause of considerable doubt and perplexity to him, and perhaps make him hesitate to accept the accurate information or authentic orders received from other sources. Again, even without occupying a station, it is possible to read the messages which are passing along a telegraph-line, and thus perhaps discover important secrets. All that is required for this purpose is a small portable receiving instrument, and a few yards of copper wire to connect it with the line. A single individual, thus equipped, can "tap" a telegraph-line, in the daytime, by receiving the message in the ordinary way; and at night (when, of course, it would be easier to approach the line) by listening to the clicking of the armature against the electro-magnet of the instrument. But all these dangers are only of a partial or temporary character. By carefully patrolling and testing the line, it cannot be interrupted for any length of time without the damage being observed and repaired. By adopting a secret arrangement that there shall be a certain number of letters in the two or three words at the beginning or end of every message, a dispatch sent by an enemy can, in most cases, be detected; and again, by employing a cipher alphabet, it will be difficult for any one who taps the line to obtain information from the messages which fall into his hands.
From this brief sketch of the structure and uses of the field telegraph, the reader will understand what an important part it plays in modem warfare. On the march it directs the movements of advancing columns, on the battle-field it flashes orders and information with the speed of thought to right, centre, and left, of the immense lines extended over mile after mile of country; in beleaguered cities it places the whole defense from moment to moment under the eyes of those intrusted with its direction, and it is of no less value in the attack. It is not too much to say that, without this wondrous power, it would be almost impossible to direct the movements of the thousands on thousands of men, and guns, and horses, which form the vast armies of Continental Europe. It has effected a revolution in military science, none the less important because it is hidden from the general view, arid seldom attracts the attention of even the ubiquitous special correspondent. Armed with all the weapons which inventive genius and mechanical skill can devise, the modern commander has the lightning also to do his work, and the electric current gliding on its secret path through the wide network of cable and wire tells him what is passing each hour in the remotest parts of the theatre of war, and transmits the mandates which decide the fate of nations.—Popular Science Review.
- Villefranche, "La Télégraphie Française, Étude Historique."
- During the armistice which preceded the Treaty of Prague in 1866, the Prussians displayed great carelessness about their telegraphic communications, and the troops often tore down a line to light their fires with the telegraph-poles, and tie up their horses with the wire. (See Stoffel, "Rapports Militaires.")