Obrázky na stránke
PDF
ePub

or glass as there are wires to be

sup

In France, on the other hand, and ported. Each wire passes through a in the United States, the wires, even tube, or is supported on a roller ; and in the cities and towns, are conducted the material of the tubes or rollers on rollers at an elevation, as on other being among the most perfect of the parts of the lines. In Paris, for ex. class of non-conducting substances, ample, the telegraphic wires proceedthe escape of the electricity at the ing from the several railway stations points of contact is impeded.

are carried round the external boule. Notwithstanding these precautions, vards and along the quays, the rollers a considerable escape of electricity being attached either to posts, or to still takes place in wet weather. The the walls of houses or buildings, and coat of moisture which collects on are thus carried to the central station the wire, the tube or roller, and at the Ministry of the Interior. the post being a conductor, carries In Europe, the telegraphic wires in. away more or less of the fluid. Con- variably follow the course of railways, sequently, more powerful batteries are and this circumstance has led some to necessary to give effect to the tele- conclude that, but for the railways the graph in wet than in dry weather. electric telegraph would be an unpro

In England, and on the Continent, fitable project. the material used for the supports of This, however, is a mistake. In the the wires is porcelain. In the United United States, where a much greater States it is glass, which is a more per- extent of electric telegraph has been fect insulator. In England the sup: erected and brought into operation ports are tubes-on the Continent and than in Europe, the wires do not fullow in America they are rollers.

the course of the railways. They are In some cases, as for example in the conducted, generally, along the sides streets of London, it is found incon. of the common coach-roads, and somevenient to carry the wires elevated on times even through tracts of country posts, as here described. In such cases where no roads have been made. other methods are adopted.

It is contended in Europe that the The wires proceeding from the cen- wires would not be safe, unless placed tral telegraph station in London are within the railway fences. The reply wrapped with cotton thread, and coat- to this is, that they are found to be ed with a mixture of tar, resin, and safe in the United States, where there grease. This coating forms a perfect is a much less efficient police, even in insulator. Nine of these wires are the neighbourhood of towns, and in then packed in an half-inch leaden most places no police at ail. It may in-pipe, and four or five such pipes be observed, that the same apprehenare packed in an iron pipe about sions of the destructive propensities of three inches in diameter. These the people have been advanced upon iron pipes are then laid under the foot first proposing most of the great impavements, along the sides of the

provements which have signalised the streets, and are thus conducted to the present age. Thus, when railways terminal stations of the various rail- were projected, it was objected that ways, where they are united to the mischievous individuals would be conlines of wire supported on posts along tinually tearing up the rails, and the sides of the railways, already de. throwing obstructions on the road, scribed.

which would render travelling so danProvisions, called testing-posts, are gerous, that the system would become made at intervals of a quarter of a impracticable. inile along the streets, by which any When gaslighting was proposed, it failure or accidental irregularity in the was objected that evil-disposed persons buried wires can be ascertained, and would be constantly cutting or breakthe place of such defect always known ing the pipes, and thus throwing whole within a quarter of a mile.

towns into darkness. In Prussia, and one or two other Experience, nevertheless, has proved continental states, the system of sub- these apprehensions groundless; and terranean conducting-wires is exclu- certainly the result of the operations sively adopted, not only in cities, but on the electric telegraph in the United generally along the entire telegraphic States goes to establish the total inulines.

tility of confining the course of the

[ocr errors]

wires to railways. Those who have gards the strong galvanised iron wires been practically conversant with the which in the open air run parallel system, both in Europe and in America, to our arterial railways, if in wet weago further, and even maintain that the ther, in spite of the many ingenious telegraph is subject to less inconve- precautions taken, the rain should nience, and that accidental defects are form a continuous stream between the more easily made good, and that an ef- several wires and the ground, the ficient superintendence is more easily electric fluid, escaping from the wires, insured on common roads, according is conducted by the water till it finds to the American system, than on rail- earth, the best of all conductors ; and, ways according to the European sys- therefore, instead of the intelligence tem. Our limits, however, preclude going on, say to Edinburgh, it follows us from entering into all the details of the axiom of electricity by selecting this question.

the shortest road, and thus completing Nothing in the history of the in- its circuit through the earth, it refluence of the arts on social progress turns to London. Sometimes, instead presents a more curious subject of re. of going to earth, it flies back to the Hection than do these systems of me. office in London, along another wire, tallic wire passing under our feet as we to which, by means of a continuous walk the streets, and beside us as we line of water, or of entanglement of the traverse the railways.

two wires, it has managed to escape;

in which case, the messages on the two “In our metropolis," observes a lively wires wrangling with each other, the contemporary, “there is scarcely a street communication is stopped. which does not appear to take pride in exposing, as often as possible, to the public " It is commonly asserted and believed, view, a series of pipes of all sizes, in which

that many birds are killed by merely perchfire of various companies, pure water of va

ing upon the iron wires of the clectric telerious companies, and unmentionable mixtures,

graph; but at any time they can do so with common to all, pass cheek by jowl with in

perfect impunity. If, indeed, a bird could finitely less trouble than the motley hu

put one of his feet on the wire, and with the man currents flow above them. But among other manage to reach the earth, he would all the subterranean pipes laid bare be

then, no doubt, be severely galvanised. That fore us, there is certainly no one which

the railway company's men often pick up has more curious contents than the three

under the wires of the electric telegraph, inch iron pipe of the electric telegraph

partridges, and other birds, which have evicompany; and yet of all the multitudes who

dently been just killed—indeed some are walk the streets, how few of them ever care found with their heads cut off—is quite true; to reflect what a singular contrast exists be

but these deaths and decapitations have tween the slow pace at which they themselves

proceeded, not from the electricity, but from are proceeding, and the rate at which, be

the birds, probably during twilight or a fog, neath their feet, forty-five electric wires are having at full speed flown against the wires, transmitting in all directions, and to a va

which, of course, cut their heads off, just riety of distances, intelligence of every pos- as an iron bar would cut off the head of sible description !

any man, or alderman on horseback, who at “ How singular is it to reflect, that within

a full gallop was to run foul of it. the narrow space of the three-inch iron pipe

" In windy weather, the electric wires form which encases them, notice of a murder is

an Æolian harp, which occasionally emits flying to the London papers, passing news most unearthly music. "I say, Jack !' said from India going into the country; along an engine-driver to his stoker, who like another wire an officer is applying for his

himself was listening for the first time to regimentals, while others are conducting this querulous sort of noise, proceeding from to and fro the price of stocks,'' news of the

the newly-erected wires along his line, I Pope,' a speech from Paris of the collapsed

say, Jack ! ain't they a-giving it to them poet,'' &c. &c. &c.

at Threapstone.'

“When the posts and wires of the electric In case, from the abrasion of the telegraph between Northampton and Petercotton that surrounds the numerous

borough were being erected, an honest far

mer, who for many minutes had been very copper wires within the pipe, any of

attentively watching the operation, inquired them come into contact with each

of the chief superintendent to what use it other, the intelligence which each is

was to be applied ? On being told that by its conveying is suddenly confounded; in means he would in a few minutes receive at which case other wires must instantly Willingborough a list of the Mark-lane be substituted. Indeed, even as re- prices in London, he evidently incredulously

asked how that was to be done?-and on its signals sufficiently varied for telegrabeing explained to him that the intelligence pliic purposes. would be sent down to him letter by letter,

1. To explain the deflection of a he exclained, But you don't mean to say that besides letters it will bring down pur

magnetic needle, let us suppose a copcels too ?'"*

per wire extended over the magnetic needle of a common compass, so that

the direction of the wire shall be paBut to return to the admirable

rallel to the needle, without touching means whereby those extraordinary it. In this state of things, the needle effects are produced, and to answer will remain undisturbed; but if we the worthy farmer's inquiry somewhat

send an electric current along the more intelligibly, let us now see how wire, which may be done by connect. the electric current which flows alonging the ends of the wire with those of the conducting-wires is made to speak,

a galvanic battery, the needle will in. to make dumb signs, or to write the

stantly throw itself at right angles to despatch when it arrives at its desti.

the wire, and will remain in that po. nation.

sition so long as the galvanic current There are a great variety of pro- is maintained; but if that current be perties of the electric current which

discontinued, by withdrawing either supply means of accomplishing this.

end of the wire from the trough, the If the electric current can be made needle will instantly resume its posito affect any object in such a manner tion of rest. as to cause such object to produce any It is found, also, that the north pole effect sensible to the eye, the ear, or of the needle will turn, in this case, in the touch, such effect may be used as one direction or in the other, according a sign; and if this effect be capable of

to the direction given to the galvanic being curied, each distinct variety of current. If this current flow in one which it is susceptible may be adopted direction, the north pole will throw as a distinct sign. Such signs may itself to the east, and the south to the then be taken as signifying the letters west ; if it flow in the contrary direcof the alphabet, the digits composing tion, the north pole will be thrown to numbers, or such single words as are

the west, and the south pole to the of most frequent occurrence.

east. The rapidity and precision of the 2. To explain the sudden convercommunication will depend on the rate sion of iron into a magnet, and the at which such signs can be produced sudden destruction of the magnetic in succession, and on the certainty and virtue thus imparted, let us suppose a accuracy with which their appearance copper wire to be coiled round a piece at the place of destination will follow of soft iron spirally, so that the sucthe action of the producing cause at cessive coils shall not touch each other the station from which the despatch is nor touch the iron, which may be done transmitted,

by coating the wire with silk, or any These preliminaries being under- resinous or non-conducting substance. stood, it remains to show what effects

This being done, let us suppose that of the electric current are available

an electric current is transmitted for this purpose.

through the wire, so that it shall flow These effects are:

spirally round the rod of soft iron, · I. The power of the electric current which may be effected by placing, as to deflect a magnetic needle from its before, the ends of the wire in a galposition of rest.

vanic trough. If steel filings, a needle, II. The power of the current to or any light piece of iron, be brought impart temporary magnetism to soft near the rod or iron thus circumiron.

stanced, they will instantly be attracted III.- The power of the current to by it, showing that it has acquired the decompose certain chemical solutions, magnetic virtue ; and this effect will

We shall now briefly show the man. continue to be produced so long as the ner in which these properties supply galvanic current shall be maintained

• “Stokers and Pukers." By the Author of “ Bubbles from the Pruunens of Nassau," any

pp. 123-7.

along the spiral wire; but the instant independently of that which is prothat the end of the wire is withdrawn duced by a single movement to the from the galvanic trough, the mag- left. In like manner, two successive netic virtue deserts the iron, and it niovements to the right will supply will no longer attract.

another signal; and thus we have four 3. If a sheet of paper, moistened independent signals. with a chemical solution which is ca- But from these four signals we may pable of decomposition by the galvanic immediately produce four more, as we current, be laid upon a metallic plate, may combine one movement to the which is in connexion with one end of right with two to the left, and vice the battery, and the point of a wire in versa; and one to the left with two to connexion with the other end of the the right, and vice versa: and thus battery, be brought into contact with we would bave eight independent the paper, a decomposition will take signals. place, and a change of colour will be We may carry this method further, produced upon the paper under the and so arrange the system that three point of the wire, just as if a dot were successive movements to the right and made upon it by a pen charged with three successive movements to the left coloured ink. If the wire be moved shall have independent significations ; upon the paper, a coloured line will be

and these again may be combined with traced ; and if the point of the wire each of the eight signals already exbe moved as a pen or pencil might be, plained ; and, in short, we may carry characters

may

be thus written on this system to an extent which shall be the paper as they would be with a pen limited only by the inconvenience of charged with coloured ink, similarly the delay which would take place in moved. If in this case the current be making the repetitions necessary for discontinued during any intervals, the such signals. wire, though still in contact with the Subject to this delay, however, it is paper, will leave no trace or dot. clear that with a single machine we

To render intelligible the means may easily obtain expressions for all whereby these three poperties have the letters of the alphabet and the ten been made instrumental to the trans- numerals. mission of intelligence to a distance- But to obviate the inconvenience

We have explained how a magnetic which would attend multiplied repetineedle over which an electric current tions in the movements of a single passes will be deflected to the right needle, we may provide two indepenor to the left, according to the direc- dent wires, which shall act upon two tion given to the current. Now, it is independent needles. always easy to give the current the Each of these needles primarily will one direction or the other, or to sus- afford two independent signals by their pend it altogether, by merely changing movements right and left. These four the ends of the galvanic trough with signals may be combined in pairs, so which the wires are connected, or by as to afford four other signals produbreaking the contact altogether. cible by a single movement. Thus,

A person, therefore, in London, simultaneously with the right-hand having command over the end of a movement of one needle we may prowire which extends to Edinburgh, and duce the right-hand movement of the is there connected with a magnetic other. In the same way we may simul. needle, in the manner already de- taneously produce the left-hand movescribed, can deflect that needle to the ment of both, or the right-hand of right or to the left at will.

either combined with the left-hand Thus a single wire and a magnetic movement of the other, which would needle are capable of making at least give eight independent signals, the protwo signals.

duction of each of which would occupy But signals, whatever be the form no more time than that of a single of the telegraph used, may be multi- movement. We may then adapt the plied by repetition and combination. signals by double movement of each Thus the operator at London may needle, which, combined with each make the needle at Edinburgh move other, and with the single movements, twice successively to the left, and this will afford another set of combinations; may be conventionally settled as a sign, and by combining these systems, we

may obviously obtain all the signals about to be sent, and which should, as requisite to express the letters and it were, awaken the attention of the numerals.

person on duty ?

Such an expedient has, in fact, been Such is, in general, the nature of contrived. The person in London who the signals adopted in the electric tele. desires to communicate a message to graphs in ordinary use in England, and the telegraphic agent at Edinburgh can in some other parts of Europe. actually make the clock strike at his

It may aid the conception of the will, and thus command attention. mode of operation and cominunication The manner in which this is accom. if we assimilate the apparatus to the plished is as admirable by its simplicity dial of a clock with its two hands. and efficiency as that which we have Let us suppose that a dial, instead of just described. carrying hands, carried two needles, The quality resorted to in this case and that their north poles, when qui.

is the last of those we have mentioned escent, both pointed to 12 o'clock. above, namely, the power to impart

When the galvanic current is con- the magnetic virtue at will to soft ducted under either of them, the north iron. pole will turn either to 3 o'clock or to One of the wires conducted from 9 o'clock, according to the direction London passes into the chamber of the given to the current.

telegraphic apparatus at Edinburgh, Now, it is easy to imagine a person

where it is connected with a coil of in London governing the hands of such wire which envelopes a rod of soft iron. a clock erected in Edinburgh, where The ends of this rod, which has the their indications might be interpreted form of a horse-shoe, are placed in according to a way previously agreed contiguity, but not in contact, with the upon. Thus, we may suppose that detent of a striking apparatus like an when the needle No. 1. turns to 9, the alarm-bell. When a message is about letter A is expressed ; if it turns to 3, to be sent from London, this bell-wire the letter B is expressed. If the is put in communication with the gal. needle No. 2. turn to 9 o'clock, the vanic trough in London. Immediately letter C is expressed ; if it turn to 3, the subtle fluid flows along the wire the letter D. If both needles are and converts the horse-shoe rod at turned to 9, the letter E is expressed ; Edinburgh into a powerful magnet. if both to 3, the letter F. If No. 1. The attractive power which it thus be turned to 9, and No. 2. to 3, the suddenly receives irresistibly draws letter G is expressed ; if No. 2 be towards it the detent of the alarum, turned to 9, and No. 1. to 3, the letter and lets go the bell, which continues H, and soforth.

to ring until the agent of the telegraph It may be presumed that there can at Edinburgh answers the demand of be but little difficulty in conceiving the messenger from London, and tells how, by practice, two persons may

him he is attentive. Then the London communicate with each other by such communicator withdraws the galvanic means, almost, if not altogether, as current from the bell-wire, the horserapidly as they could write and read. shoe at Edinburgh is instantly deprived

But a difficulty will doubtless suggest of its magnetic virtue, the detent Aies itself to the intelligent and inquisitive back to its place by the action of a reader. It will be asked, whether a sen- spring, and silences the bell.* tinel must be kept ever on the watch to In the practical arrangement of elecobserve when a message is coming for tric telegraphs, constructed on this as the hands of our clock do not speak, principle, the magnetic needles are notice could only be received of a com- placed vertically and not horizontally, ing message by the incessant vigilance as in the mariner's compass, and they of an observer.

are kept, when not affected by the Would it not, however, be admir. current, in the vertical position, by able if we could attach to this clock a laying two needles having their poles striking apparatus, which should ad- at opposite ends, one upon the other, dress the ear the moinent a message is by which means the polarity of the

* Railway Econonny, by Dr. Lardner, pp. 352-5. VOL. XXXVI.-NO, CCXI.

с

« PredošláPokračovať »