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tube, inasmuch as the electric fluid passes through the metal included by the coating, in exactly the same manner as water or gas passes through the pipes which conduct it; with this difference, however, that the electric fluid moves along the wire more freely, in an almost infinite proportion, than does either water or gas in the tubes which conduct them.

If, then, a wire, coated with a nonconducting substance, capable of resisting the vicissitudes of weather, were extended between any two distant points, one end of it being attached to one of the extremities of a galvanic battery, a stream of electricity would pass along the wireprovided the other end of the wire were connected by a conductor with the other extremity of the battery.

To fulfil this last condition, it was usual, when the electric telegraphs were first erected, to have a second wire extended from the distant point back to the battery in which the electricity was generated. But it was afterwards discovered that the EARTH ITSELF was the best and by far the cheapest and most convenient conductor which could be used for this returning stream of electricity. Instead, therefore, of a second wire, the extremity of the first, at the distant point to which the current is sent, is attached to a large metallic plate, measuring five or six square feet, which is buried in the earth. A similar plate, connected with the other extremity of the battery, at the station from which the current is transmitted, is likewise buried in the earth, and it is found that the returning current finds its way back through the earth from the one buried plate to the other buried plate.

Of all the miracles of science, surely this is the most marvellous. A stream of electric fluid has its source in the cellars of the Central Electric Telegraph Office, Lothbury, London. It flows under the streets of the great metropolis, and, passing along a zigzag series of railways, reaches Edinburgh, where it dips into the earth, and diffuses itself upon the buried plate. From that it takes flight through the crust of the earth, and finds its own way back to the cellars at Lothbury !!

Instead of burying plates of metal,

it would be sufficient to connect the wires at each end with the gas or water pipes which, being conductors, would equally convey the fluid to the earth; and in this case, every telegraphic despatch which flies to Edinburgh along the wires which border the railways, would fly back, rushing to the gas-pipes which illuminate Edinburgh-from them through the crust of the earth to the gas-pipes which illuminate London, and from them home to the batteries in the cellars at Lothbury.

The atmosphere, when dry, is a good non-conductor; but this quality is inpaired when it is moist. In ordinary weather, however, the air being a sufficiently good non-conductor, a metallic wire will, without any other insulating envelope except the air itself, conduct the stream of electricity to the necessary distances. It is true that a coated wire, such as we have already described, would be subject to less waste of the electric fluid en route; but it is more economical to provide batteries sufficiently powerful to bear this waste, than to cover such extensive lengths of wire with cotton, or any other envelope.

The manner in which the conducting wires are carried from station to station is well known. Every railway traveller is familiar with the lines of wire extended along the side of the railways, which, when numerous, have been not unaptly compared to the series of lines on which the notes of music are written, and which are the metallic wires on which invisible messages are flying continually with a speed that surpasses imagination. These wires, in the case of the English telegraphs, are galvanised so as to resist oxydation, and are of sufficient thickness to bear the tension to which they are submitted. They are suspended on posts, erected at intervals of sixty yards, being at the rate of thirty to a mile. These posts, therefore, supply incidentally a convenient means by which a passenger can ascertain the speed of the train in which he travels. If he count the number of telegraph posts which pass his eye in two minutes, that number will express in miles per hour the speed of the train.

To each of these poles are attached as many tubes or rollers of porcelain

or glass as there are wires to be supported. Each wire passes through a tube, or is supported on a roller; and the material of the tubes or rollers being among the most perfect of the class of non-conducting substances, the escape of the electricity at the points of contact is impeded.

Notwithstanding these precautions, a considerable escape of electricity still takes place in wet weather. The coat of moisture which collects on the wire, the tube or roller, and the post being a conductor, carries away more or less of the fluid. Consequently, more powerful batteries are necessary to give effect to the telegraph in wet than in dry weather.

In England, and on the Continent, the material used for the supports of the wires is porcelain. In the United States it is glass, which is a more perfect insulator. In England the supports are tubes-on the Continent and in America they are rollers.

In some cases, as for example in the streets of London, it is found inconvenient to carry the wires elevated on posts, as here described. In such cases other methods are adopted.

The wires proceeding from the central telegraph station in London are wrapped with cotton thread, and coated with a mixture of tar, resin, and grease. This coating forms a perfect insulator. Nine of these wires are then packed in an half-inch leaden in-pipe, and four or five such pipes are packed in an iron pipe about three inches in diameter. These iron pipes are then laid under the foot pavements, along the sides of the streets, and are thus conducted to the terminal stations of the various railways, where they are united to the lines of wire supported on posts along the sides of the railways, already described.

Provisions, called testing-posts, are made at intervals of a quarter of a mile along the streets, by which any failure or accidental irregularity in the buried wires can be ascertained, and the place of such defect always known within a quarter of a mile.

In Prussia, and one or two other continental states, the system of subterranean conducting-wires is exclusively adopted, not only in cities, but generally along the entire telegraphic lines.

In France, on the other hand, and in the United States, the wires, even in the cities and towns, are conducted on rollers at an elevation, as on other parts of the lines. In Paris, for example, the telegraphic wires proceeding from the several railway stations are carried round the external boulevards and along the quays, the rollers being attached either to posts, or to the walls of houses or buildings, and are thus carried to the central station at the Ministry of the Interior.

In Europe, the telegraphic wires invariably follow the course of railways, and this circumstance has led some to conclude that, but for the railways the electric telegraph would be an unprofitable project.

In the

This, however, is a mistake. United States, where a much greater extent of electric telegraph has been erected and brought into operation than in Europe, the wires do not follow the course of the railways. They are conducted, generally, along the sides of the common coach-roads, and sometimes even through tracts of country where no roads have been made.

It is contended in Europe that the wires would not be safe, unless placed within the railway fences. The reply to this is, that they are found to be safe in the United States, where there is a much less efficient police, even in the neighbourhood of towns, and in most places no police at all. It may be observed, that the same apprehensions of the destructive propensities of the people have been advanced upon first proposing most of the great improvements which have signalised the present age. Thus, when railways were projected, it was objected that mischievous individuals would be continually tearing up the rails, and throwing obstructions on the road, which would render travelling so dangerous, that the system would become impracticable.

When gas-lighting was proposed, it was objected that evil-disposed persons would be constantly cutting or breaking the pipes, and thus throwing whole towns into darkness.

Experience, nevertheless, has proved these apprehensions groundless; and certainly the result of the operations on the electric telegraph in the United States goes to establish the total inutility of confining the course of the

wires to railways. Those who have been practically conversant with the system, both in Europe and in America, go further, and even maintain that the telegraph is subject to less inconvenience, and that accidental defects are more easily made good, and that an efficient superintendence is more easily insured on common roads, according to the American system, than on railways according to the European system. Our limits, however, preclude us from entering into all the details of this question.

Nothing in the history of the influence of the arts on social progress presents a more curious subject of reflection than do these systems of metallic wire passing under our feet as we walk the streets, and beside us as we traverse the railways.

"In our metropolis," observes a lively contemporary, "there is scarcely a street which does not appear to take pride in exposing, as often as possible, to the public view, a series of pipes of all sizes, in which fire of various companies, pure water of various companies, and unmentionable mixtures, common to all, pass cheek by jowl with infinitely less trouble than the motley human currents flow above them. But among all the subterranean pipes laid bare before us, there is certainly no one which has more curious contents than the threeinch iron pipe of the electric telegraph company; and yet of all the multitudes who walk the streets, how few of them ever care to reflect what a singular contrast exists between the slow pace at which they themselves are proceeding, and the rate at which, beneath their feet, forty-five electric wires are transmitting in all directions, and to a variety of distances, intelligence of every possible description!

"How singular is it to reflect, that within the narrow space of the three-inch iron pipe which encases them, notice of a murder is flying to the London papers, passing news from India going into the country; along another wire an officer is applying for his regimentals, while others are conducting to and fro the price of stocks,'' news of the Pope,' a speech from Paris of the collapsed poet," &c. &c. &c.

In case, from the abrasion of the cotton that surrounds the numerous copper wires within the pipe, any of them come into contact with each other, the intelligence which each is conveying is suddenly confounded; in which case other wires must instantly be substituted. Indeed, even as re

gards the strong galvanised iron wires which in the open air run parallel to our arterial railways, if in wet weather, in spite of the many ingenious precautions taken, the rain should form a continuous stream between the several wires and the ground, the electric fluid, escaping from the wires, is conducted by the water till it finds earth, the best of all conductors; and, therefore, instead of the intelligence going on, say to Edinburgh, it follows the axiom of electricity by selecting the shortest road, and thus completing its circuit through the earth, it returns to London. Sometimes, instead of going to earth, it flies back to the office in London, along another wire, to which, by means of a continuous line of water, or of entanglement of the two wires, it has managed to escape; in which case, the messages on the two wires wrangling with each other, the communication is stopped.

"It is commonly asserted and believed, that many birds are killed by merely perching upon the iron wires of the electric telegraph; but at any time they can do so with perfect impunity. If, indeed, a bird could put one of his feet on the wire, and with the other manage to reach the earth, he would then, no doubt, be severely galvanised. That the railway company's men often pick up under the wires of the electric telegraph, partridges, and other birds, which have evidently been just killed-indeed some are found with their heads cut off-is quite true; but these deaths and decapitations have proceeded, not from the electricity, but from the birds, probably during twilight or a fog, having at full speed flown against the wires, which, of course, cut their heads off, just as an iron bar would cut off the head of any man, or alderman on horseback, who at a full gallop was to run foul of it.

"In windy weather, the electric wires form an Eolian harp, which occasionally emits most unearthly music. I say, Jack!' said an engine-driver to his stoker, who like himself was listening for the first time to this querulous sort of noise, proceeding from the newly-erected wires along his line, I say, Jack! ain't they a-giving it to them at Threapstone.'

"When the posts and wires of the electric telegraph between Northampton and Peterborough were being erected, an honest farmer, who for many minutes had been very attentively watching the operation, inquired of the chief superintendent to what use it was to be applied? On being told that by its means he would in a few minutes receive at Willingborough a list of the Mark-lane prices in London, he evidently incredulously

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There are a great variety of properties of the electric current which supply means of accomplishing this.

If the electric current can be made to affect any object in such a manner as to cause such object to produce any effect sensible to the eye, the ear, or the touch, such effect may be used as a sign; and if this effect be capable of being varied, each distinct variety of which it is susceptible may be adopted as a distinct sign. Such signs may then be taken as signifying the letters of the alphabet, the digits composing numbers, or such single words as are of most frequent occurrence.

The rapidity and precision of the communication will depend on the rate at which such signs can be produced in succession, and on the certainty and accuracy with which their appearance at the place of destination will follow the action of the producing cause at the station from which the despatch is transmitted.

These preliminaries being understood, it remains to show what effects of the electric current are available for this purpose.

These effects are:

I. The power of the electric current to deflect a magnetic needle from its position of rest.

II. The power of the current to impart temporary magnetism to soft iron.

III. The power of the current to decompose certain chemical solutions.

We shall now briefly show the manner in which these properties supply

signals sufficiently varied for telegraphic purposes.

1. To explain the deflection of a magnetic needle, let us suppose a copper wire extended over the magnetic needle of a common compass, so that the direction of the wire shall be parallel to the needle, without touching it. In this state of things, the needle will remain undisturbed; but if we send an electric current along the wire, which may be done by connecting the ends of the wire with those of a galvanic battery, the needle will instantly throw itself at right angles to the wire, and will remain in that position so long as the galvanic current is maintained; but if that current be discontinued, by withdrawing either end of the wire from the trough, the needle will instantly resume its position of rest.

It is found, also, that the north pole of the needle will turn, in this case, in one direction or in the other, according to the direction given to the galvanic current. If this current flow in one direction, the north pole will throw itself to the east, and the south to the west; if it flow in the contrary direction, the north pole will be thrown to the west, and the south pole to the

east.

2. To explain the sudden conversion of iron into a magnet, and the sudden destruction of the magnetic virtue thus imparted, let us suppose a copper wire to be coiled round a piece of soft iron spirally, so that the successive coils shall not touch each other nor touch the iron, which may be done by coating the wire with silk, or any resinous or non-conducting substance. This being done, let us suppose that an electric current is transmitted through the wire, so that it shall flow spirally round the rod of soft iron, which may be effected by placing, as before, the ends of the wire in a galvanic trough. If steel filings, a needle, or any light piece of iron, be brought near the rod or iron thus circumstanced, they will instantly be attracted by it, showing that it has acquired the magnetic virtue; and this effect will continue to be produced so long as the galvanic current shall be maintained

"Stokers and Pokers." By the Author of "Bubbles from the Brunnens of Nassau," pp. 125-7.

along the spiral wire; but the instant that the end of the wire is withdrawn from the galvanic trough, the magnetic virtue deserts the iron, and it will no longer attract.

3. If a sheet of paper, moistened with a chemical solution which is capable of decomposition by the galvanic current, be laid upon a metallic plate, which is in connexion with one end of the battery, and the point of a wire in connexion with the other end of the battery, be brought into contact with the paper, a decomposition will take place, and a change of colour will be produced upon the paper under the point of the wire, just as if a dot were made upon it by a pen charged with coloured ink. If the wire be moved upon the paper, a coloured line will be traced; and if the point of the wire be moved as a pen or pencil might be, any characters may be thus written on the paper as they would be with a pen charged with coloured ink, similarly moved. If in this case the current be discontinued during any intervals, the wire, though still in contact with the paper, will leave no trace or dot.

To render intelligible the means whereby these three poperties have been made instrumental to the transmission of intelligence to a distance

We have explained how a magnetic needle over which an electric current passes will be deflected to the right or to the left, according to the direction given to the current. Now, it is always easy to give the current the one direction or the other, or to suspend it altogether, by merely changing the ends of the galvanic trough with which the wires are connected, or by breaking the contact altogether.

A person, therefore, in London, having command over the end of a wire which extends to Edinburgh, and is there connected with a magnetic needle, in the manner already described, can deflect that needle to the right or to the left at will.

Thus a single wire and a magnetic needle are capable of making at least two signals.

But signals, whatever be the form of the telegraph used, may be multiplied by repetition and combination. Thus the operator at London may make the needle at Edinburgh move twice successively to the left, and this may be conventionally settled as a sign,

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We may carry this method further, and so arrange the system that three successive movements to the right and three successive movements to the left shall have independent significations; and these again may be combined with each of the eight signals already explained; and, in short, we may carry this system to an extent which shall be limited only by the inconvenience of the delay which would take place in making the repetitions necessary for such signals.

Subject to this delay, however, it is clear that with a single machine we may easily obtain expressions for all the letters of the alphabet and the ten numerals.

But to obviate the inconvenience which would attend multiplied repetitions in the movements of a single needle, we may provide two independent wires, which shall act upon two independent needles.

Each of these needles primarily will afford two independent signals by their movements right and left. These four signals may be combined in pairs, so as to afford four other signals producible by a single movement. Thus, simultaneously with the right-hand movement of one needle we may produce the right-hand movement of the other. In the same way we may simultaneously produce the left-hand movement of both, or the right-hand of either combined with the left-hand movement of the other, which would give eight independent signals, the production of each of which would occupy no more time than that of a single movement. We may then adapt the signals by double movement of each needle, which, combined with each other, and with the single movements, will afford another set of combinations; and by combining these systems, we

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