Page images
PDF
EPUB

The reader can select whichever of the ex- | the universal practice of expositors of these pheplanations now given he prefers, or can devise nomeną, write as if there were but a single curtheories for himself, or dispense with any. But rent of positive electricity flowing at once along the ultimate and only important fact in reference a telegraph wire. The other and opposite negato the telegraph is, that by the marvellously simple live current may conveniently be disregarded, just device of dissolving a few pieces of metal con- as in navigation a compass-needle is referred to as nected with a long wire, we can develop instan- if it had but one pole, pointing to the north. taneously, a thousand miles off, a force which will Having secured the means transmitting at will speak for us, write for us, print for us, and, so far as a current of electricity with great velocity, it the conveyance of our thoughts is concerned, an- remains 10 determine what phenomenon we shall nihilate space and time. This annihilation is not cause it to produce at the distant station. of course complete, but in reference to practice it The phenomena most easily produced by elecmay be called so. Shakspeare's Juliet refers to tricity are magnetic ones; and these, accordingly, “ the lightning which doth cease to be, ere one can are now preferred as the sources of signals. The say it lightens.” The exact velocity of electricity electric telegraph, indeed, remained an unrealized along a copper wire is 288,000 miles in a second. idea in the minds of ingenious men, till the famous It is calculated, accordingly, that we could tel- Danish philosopher, Oersted, discovered that a curegraph to our antipodes in rather less than the five rent of electricity, even though of very small inhundredth part of one second of time !

tensity, if passing near a compass-needle poised The most impatient of correspondents may be on a pivot, will cause the needle to change its satisfied with this velocity; and we may now in- position, and point in a new direction. Let the quire in what way electricity is made to produce telegraph-wire, for example, whilst connected with signals. In discussing this we shall recur to the a battery, be placed so that the needle of a marprovisional theory adopted at the ontset, that elec- iner's compass shall be directly below or above tr.city tiows in currents; and in conformity with and parallel to the wire, and the needle, no longer

true to the pole,” will whirl round and stand development of one force, as of electricity antagonizing electricity, magnetism antagonizing magnétism. Polar- east and west, instead of as before, north and ity, in short

, implies unity quite as much as duplicity, and south. It depends upon the direction in which the may literally be said to exhibit a force or power" divided against itself.” This division, however, never becomes

current of electricity is sent, ch pole of the schism. The one twin is never found detached and alone, compass-needle points east or west.

Let the telbut always side by side with the other, and when permit- legraph-wire stretching from London to Edinburgh ted they combine, neutralize each other.-- and then polarity and back again, be considered as consisting of an double-headed arrow, or to Jove's two-forked ihunderbolt. upper and a lower wire. If the London end of the It might also be compared to the conventional zodiacai şign Pisces with its connected fishes, to the heraldic upper wire he connected with the copper extremdouble eagle, to the Siamese Twins, or perhaps best of ity of the battery, whilst the termination of the all, thougli che comparison is a homely one, to two hunting lower wire is connected with the zinc, the current dogs of the same breed, size, shape, and power, helading of positive electricity (the only one of which we couples, and pulling against each other. agree with each other, and with bodies or forces exhibiting now take cognizance) will flow along the upper polariry, in being double unities. Similes, however, may wire to Edinburgh, and return by the lower one to be pushed too far. The idea of polarity is best based on the spectacle of the compass-needle—with its opposite London. If the upper wire be now attached to powers at its opposite ends, and its one magnetism deter- the zinc, and the lower to the copper, the current inining the tendencies of both.

Another misapplication of the term Polarity is to the will travel north by the lower wire, and come opposite effects which the same force exhibits when its south by the upper. Now, without entering into intensity varies. Thus heat of a certain intensity causes details for which we have not room, and which are quicksilver to combine chemically with oxygen ; and heat of a greater intensity causes the combined oxygen and not essential to the comprehension of the telegraph, quicksilver to separare again from each other. À slight it may suffice to say, that the pole of the compassmechanical impulse increases cohesion ; a more powerful needle, which points east if the electrical current impulse destroys it. But those are not exhibitions of polarity; Heat, for example, either entirely decomposes, or passing near it be sent in one direction, points west entirely combines ; it does not do both at once--as elec. if it be sent in the opposite one ; while, if the tricity does, when it decomposes (electrolyzes) chemical compounds. Variation in intensity, morcover, is not the passage of electricity be discontinued, the needle cause of the opposite powers of the poles of a magnet, or a resumes its original position. We have it thus in voltaic battery. The northern magnetism, on the contra- our power to cause a compass-needle to move to ry, always possesses the same intensity as the southern either side at will; and we can bring it in a momagnetism-positive electricity the same intensity as neg. ative electricity: If the word polarity signified only dual- ment to rest. All those effects are produced still ism, it should he struck out of the language ; for it is more strikingly if the wire, instead of being obscure to ordinary readers, and very far-fetched. But if we discard it as implying one kind, and one kind only of stretched above or below the compass-needle, be dualism, we must introduce some new term to denote the coiled many times around the compass-box, or case duplex unity, which those who employ it wisely, intend it containing the magnetic needle. The wire, in that alone to signify.

Some have inconsiderately sought to render the main case, is covered with thread, which allows its coils truth unter notice more distinct, hy referring to a body to be put close together, without risk of the elechowever, is a useless and vicious tautology. We might tricity passing across from coil to coil where they as well speak of a four-sided square, or a three-angled iri- touch, as it would do, if the thread, which is a angle. A polar body is, by its very definition, bi-polar- non-conductor, did not insulate the electricity. It just as a square is necessarily four-sided, and a triangle ihree-angled.

is more convenient that the magnetic needle should

ceases.

[ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][merged small]

originally stand vertically, so as to move from signal is to be transmitted, a metallic cylinder is
right to left, or vice versâ —like the index of a moved by a handle so as to fill up the gap, and
wheel barometer, than that it should revolve in a establish continuity between the wires and the
horizontal plane like the mariner's compass. It is copper and zinc respectively, of the battery. This
aloo much more easily moved, if ihe effect of the bridge, however, is so contrived, that when the
earth's magnetism on it be neutralized. This is handle which controls it is moved to the left, it
done by placing two magnetic needles on the same stretches in such a manner as to connect the end a
axis, with their poles reversed, so that the north of the telegraph-wire with the copper, and the end
pole of the one is opposite the south pole of the 's with the zinc, and the needle moves to the left.
other. Such an arrangement, is the needles are When the handle is moved to the right, it shifts
of equal power, has no tendency towards one point the cylinder or bridge so as to establish a commu-
of the compass more than another; and by making nication between a and the zinc, and between B
what are to be the lower ends of the needles some- and the copper; and the needle moves to the right.
what heavier than the opposite extremities, the When the handle is placed vertically the current is
needles, when not under the influence of electric cut off from both wires.
currents, will at once resume their vertical po It only remains that an arrangement be made
sition.

between the parties in Edinburgh and London, as
Now, the one needle which is to act as the visi- to the signification of these deflections of the needle.
ble index, appears in front of a dial plate ; the other This having been settled, the message-sender in
surrounded by the coil of covered wire, which is the metropolis, seated before his dial, moves the
continuous with one of the telegraph-wires, is handle which determines the transmission and
placed behind the dial. An arrangement of this direction of the electricity along the wires. Every
kind is provided at Edinburgh, the upper tele- motion of the handle to the right or to the left
graph-wire being drawn out there into a long loop, causes the index-needles at London and Edinburgh
which consists of soft copper wire covered with to move simultaneously to the same sides. We
thread. This is wound round the concealed mag- may suppose, for example, that an answer in the
netic needle, so that a current of electricity moving negative is to be telegraphed from London to an
along the upper wire follows the coiled loop, moves interrogation from Edinburgh. It has been pre-
the needles in passing, and returns to London. At arranged that one movement of the needle to the
London, for a reason to be mentioned immediately, left shall signify n, and one to the right, o. The
there is a similar loop or coil of covered copper respondent accordingly moves his handle to the
wire surrounding a double magnetic needle, and left; thereby transmits the current of electricity in
then rejoining the upper main wire from which it such a direction as to move the index-handle at
proceeded. From the copper end of the battery, a Edinburgh to the left also ; and so represents N.
wire is conducted to one of the strands of this coil, He then places the handle verticaliy so as to cut
and soldered to it. From the zinc end a wire also off the current, and permit the needle to resume its
is conducted, which is soldered to the lower tele- vertical position ; and, after a brief pause, carries
graph-wire. The current setting off from the one his handle to the right, which moves the Edin-
end of the London battery, deflects the needles at burgh needle also to the right—which indicates o,
London and at Edinburgh before it returns to the and thus completes the answer.
former. That the needles may be deflected to The signal-dial at London is not essential, if
either side at will, a contrivance is supplied for London is not to receive messages; but as it must
cutting off and letting on, as well as for reversing, I be provided with a view to their reception, it is so
the electric current from the battery. It is a little arranged that the electricity moves its index-needle
difficult, without a diagram, to explain distinctly before it passes on to Edinburgh.
this important portion of the telegraph. The fol- transmitting a message, has thus figured before
lowing description, however, will perhaps make it him deflections of the index-needles, identical with
sufficiently clear. Let the upper end of the double those which his correspondent is watching and de-
telegraph-wire at London be marked A, and the ciphering, at the same moment, hundreds of miles
lower end B. If a be connected to the copper of away.
the battery, and B to its zinc, the current of elec Only two movements, it will be observed, can
tricity setting off from A, and returning to B, moves really be effected; but it is easy to make them rep-
the index-needle to one side, for example to the resent the whole alphabet, and to telegraph rap-
left. If the arrangement be now reversed, so that idly, although every word be spelled letter by
A is connected to the zinc, and B to the copper, the letter. Man, moreover, is by his natural-history
current flows from B to A, and moves the needle to definition one of the bimana. Two dials can there-
the right.

fore be arranged side by side, with coils and indexIn actual practice, however, the wires are not needles for each, and handles to be managed by shifted from the zinc to the copper, but are cut either hand. Four movements are thus made posacross between the battery on the one hand, and sible; and for most purposes these supply an ample the telegraph-wires and coil round the magnetic abundance of signals. It does not, however, form needles on the other. The gap thus made is left part of our present purpose to explain these—as vacant when no message is to be sent. When a their employment to represent letters, numerals,

!

The party

[ocr errors]

words, paragraphs, or the like, is quite arbitrary, fring. Electric currents not only deflect permanent and involves nothing electrical. We give a speci- magnets, such as the compass-needle, but confer men, however, of one of the telegraph alphabets :- magnetism upon non-magnetic iron. If a copper

wire, therefore, be coiled round a rod of malleable A, one movement to the left. N, one right.

iron, and a current of voltaic electricity be sent B, two left.

O, two right.
C, three ieft.
P, three right.

along the wire, the rod becomes a magnet so long D, four left. Qu, four right.

as the current passes ; and loses magnetism when E, one left, one right. R, one right, one left.

the current ceases. This magnetizing power of F, one left, two right. S, two right, one left. G, one left, three right, T, three right, one left. electricity is turned to account in the telegraph. H, two left, one right. U, one right, iwo left.

An ordinary alarum, or the striking machinery of I, two left, two right. V, two right, two left. J, two left, three right. W, three right, two lest.

a common clock, wound up so that the hammer K, three left, one right. X, one righi, three left. would strike and ring the bell if one of its wheels L., three left, two right. Y, iwo right, three left.

were not locked, is placed at every station. But M, four left, one right. 2, one right, four lefi.

this wheel is only locked by an iron rod which is We have provided hitherto only for messages balanced on a centre, and so arranged that one end being despatched from London. To secure Edin- falls into one of the notches between the teeth on burgh the same privilege, it is only requisite to the circumference of the wheel. The other extremdeposit a battery there also, and to attach one of ity of the rod is placed opposite, and close to the the wires from the battery (controlled by the han- ends of a horse-shoe of malleable iron, which is dle for reversing and arresting the current) to the surrounded by a coil of covered copper wire closely coil round the magnetic needle, and the other wire twisted round it, and connected by its ends with to the telegraph-wire with which the coil is not one of the telegraph-wires. And now, if a current connected, as more fully de cribed with reference of electricity be sent along the telegraph-wire, it to the London arrangement. If intermediate sta- circulates round the horse-shoe, and converts it, tions are to receive messages, then one of the tele- for the time, into a powerful magnet, which acgraph-wires is cut across opposite the station, and cordingly pulls towards it the free extremity of the an insulator of porcelain inserted between the iron rod, and thereby shifts the other end out of divided surfaces. A thin wire is then soldered to the notch in the toothed wheel. The bell immethe main wire on one side of the insulator, led into diately begins to ring, as the unlocked wheels the station, covered with thread wound round the revolve by the action of a spring or a weight; but magnetic index-needle, and led out again and sol- as soon as the current is stopped, the horse-shoe dered to the main wire on the other side of the ceases to be a magnet; the rod is no longer insulator. This arrangement is equivalent to a attracted, but falls back into the notch and stops loop on the telegraph-wire; and it must be bent so the bell. Under this arrangement, the bells at that the current shall flow in the same direction, every station would ring simultaneously, although round the intermediate station-needles as it does only one was intended to be warned; and the curround the terminal ones, otherwise the indices will rent that rings the bells would also move the not be moved to the same side by the same elec- index-needles, though only for a moment. On trical current. A battery at each station, with most telegraph-lines, however, a separate set of wires connected in the way already described, wires is now provided for the bells, so that they enables it to send messages in its turn.

are rung without affecting the needles. A sepa. From what has been said, it will be understood rate wire, also, is sometimes furnished for every that signals telegraphed from any one station to station, so that each bell can be rung independently any one other, will be contemporaneously exhibited of the others; but such arrangements necessarily at every station. For the whole of the stations are add much to the cost of the entire telegraph. included in one circle of conductors, which carry The magnetizing power of electricity is also the electricity round all the indicating apparatus applied to produce visible as well as audible sig. within its circuit; and the current cannot move nals. The following is one of many such arrangeone index without moving all. It is impossible, ments. A horse shoe which becomes alternately therefore, if a common alphabet be used along the magnetic and non-magnetic, as an electrical curline, to conceal from the whole of the stations rent does, or does not, circulate round a copper what may be intended only for one. All that can wire coiled about it, alternately lifts and lets fall be done, unless a separate series of wires or other an iron lever, which, like the beam or piston of a conductors were supplied for every station, is to steam-engine, gives a rotatory motion to a wheel. signify what place the message is directed to, so This wheel carries an index which travels over a that other stations need not be at the trouble of de- dial, round which the letters of the alphabet are ciphering the signals.

engraved. The current must be alternately inIn addition to the arrangements for producing terrupted and continued to keep the wheel revolrand interpreting signals, it is plainly necessary ing. When the current passes along the wire, that we should also have some contrivance for call- the index moves from the letter at which it is ing the attention of the parties in attendance to the pointing, to the next. The current is then cut dials, when a message is about to be sent. For off'; and, when it is restored, the index moves on this purpose, warning is given by a bell, which a to the succeeding letter. A key, like those of very ingenious application of electricity is made to the organ or piano--alternately depressed and

next.

[ocr errors][ocr errors][merged small][ocr errors][ocr errors][merged small][ocr errors]

allowed to ascend-furnishes the means of inter- | and back again. In actual practice, however, one rupting and renewing the current. This arrange- half of the wire is now commonly dispensed with, ment has been called the step by step telegraph ; and its place supplied-by the earth!

A cenas for each touch of the key the index makes only tury has elapsed since the very curious discovery one step; namely, from the letter it is at, to the was made, that the electricity of a charged Ley

It has the convenience, too, of using the den jar or battery will pass instantaneously through old familiar alphabet, instead of arbitrary deflec- a great length of moist earth. Voltaic electricity tions of needles, and is alleged to possess other has more recently been discovered to possess the advantages, which will presently be referred to. same power; and advantage has been taken of it

A third method of electric signalling, which in the following way. A wire is led from the promises well, but has not as yet been fully tried, last copper plate of a battery placed, let us supis to effect chemical decompositions by the cur- pose at London, along the telegraph posts, in the rent. One such electro-chemical process is the way already described, to Edinburgh, and is there following. A ribbon of paper, soaked in an acid bent backwards towards London. Instead, howsolution of the yellow prussiate of potash, and ever, of being carried along the posts a second pressed upon by two metallic springs placed side time, the wire is now cut short and soldered to a by side-which are in connection with the tele- large plate of metal, which is buried in the graph-wires—is wound off a roller by a piece of ground at some little depth. A comparatively clockwork. When the current circulates, it short wire is also attached to the last zinc of the passes, according to the direction in which it is London battery, and soldered to a metallic plate sent, by the one spring or the other, across the which is likewise buried in the ground. The wet ribbon, and decomposes the salt with which arrangement is equivalent to a great gap or breach it is impregnated, producing blue marks at either several hundred miles long, in the double wire, of the points where the spring touches the paper. filled up by moist earth. When the battery is in The blue spots or lines thus produced are longer action, the electricity (positive) flows from the or shorter, in proportion to the period during which copper along the wire to Edinburgh, descends the current flows, and at the one side or the other there to the one earth-plate, (as it has been called,) of the ribbon, according to the spring by which passes from it through the earth to the similar the electricity passes ; and these blue marks or plate near the London station, and from it reaches lines may be made to represent letters, according the zinc of the London battery. The circulation to their length and position on the paper. Their of the electricity in this way is found to be even variations in both respects are determined either more rapid than when the double wire is furnished by the movements of a handle at the station send- for its passage. ing messages, by means of which the current Good people have perplexed themselves with from a battery is interrupted, renewed, or reversed speculations as to why the electricity never wanat pleasure ; or by a mechanical arrangement of ders, misses its road, or fails to find its way back. great ingenuity, which we have not left ourselves But, as has been implied already, in the case of room to describe.

the double wire, electricity, like a prudent genLastly, it may be mentioned, on this topic, eral, always takes care that a retreat be provided that, from the first, much attention has been di- for before it begins its march. Till an unbroken rected to the arrangement of an apparatus which circuit of conductors connect the terminal plates should print as well as signal its messages. of the battery, no electricity can be set free. It Many beautiful contrivances for this purpose have is not essential, however, that those conductors been devised and tried-and in no long time we should be metallic ; a column or stratum of moist may expect to see some of them in use. Descrip- earth, we have seen, will do quite as well as an tions of them, however, would scarcely be intel- iron or zinc wire. One half in length of the conligible without drawings; and their consideration necting conductors must, however, be insulated ; may be deferred till their adoption is ratified by so that the electricity may be compelled to travel public approval. The question, What is the best to the farthest point to which messages are to be method of applying electricity to produce signals ? telegraphed. But the other half of the conductis at present undergoing the keenest discussion ; ors need not be insulated, and cannot be too large. nor will it be speedily settled. The telegraph The quicker the current can pass the better; and has not been long enough in use to enable us to it will pass most quickly when conveyed by one decide what arrangement is best ; but all compe- or other of the two great electrical conductors tent parties are satisfied that, wonderful as its which man has at his disposal—the solid mass of achievements are, they will yet be greatly ex- the globe, and the ocean with its tributary waters. ceeded. Our immediate object, however, is to The last allusion leads us directly to the Marecord its present condition, not to speculate on its rine Telegraph. It requires, however, no defuture improvements.

tailed description—as it differs from the Land In the preceding description we have purposely Telegraph only in having the space between the referred to the simplest and most easily under- buried plates occupied by water instead of by stood form of electric telegraph, where there is a earth. Broad estuaries or channels do not perwire reaching from the terminus at the one end mit the insulated wire to be carried across by of the telegraph-line, to the terminus at the other, bridges. The wire therefore proceeding from the

[ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][merged small]

water.

copper end of the battery is embedded in gutta per- | and in fogs or snow-storms, it was confidently cha, or any other water-proof insulator, and sunk in anticipated that the system of electric signals the waters to a depth sufficient to secure it against would be available in all states of the weather. fishing-nets, ships, anchors, or large sea animals. But this expectation has proved fallacious. For

In this way it is conveyed from one shore to hours together the telegraph will not work. This the other, and bending backwards after beng con- failure is sometimes owing to the insulation of nected with the index needles, terminates in a the wires along the poles having for the tire broad plate of metal sunk in the waves, close to been destroyed by moisture. The porcelain insuthe further shore. A second uninsulated wire lating tubes, however, are now made of such a proceeds from the zinc end of the battery to a shape, and so well protected from rain by sloping metal plate sunk below low water mark, at the covers, that non-insulation from moisture occurs side from which the insulated wire set off. Be- much more rarely than might be expected. There tween the immersed plates on the opposite shores are certain damp fogs, however, or mists, which the mass of water, though ever changing, acis in penetrate everywhere ; and so thoroughly wet the relation to electricity as if it were an undisturbed porcelain tubes, that they become conductors of gigantic metallic wire. Theoretically, there is electricity. In those circumstances it travels no limit to the ocean spaces which electricity from the baitery no further than the first wet post, may traverse in this way. Already, accordingly, down which it passes to the earth, and returns, te schemes for telegraphing across the Atlantic and infecto, to the battery. the Pacific have been triumphantly expounded to But a much more troublesome cause of inaction, the wonder-loving public.

or of irregular action, in telegraphs, is the influence One of these, whether hopeless or not for im- of atmospheric electricity upon them. The door mense distances, is so very ingenious, and so left open that the friend may enter, stands open likely to succeed across limited spaces, that we also for the foe. The insulated wires stretched cannot pass it unnoticed. It dispenses, except along the telegraph-posts for hundreds of miles, in to a very trifling extent, with wires, and carries order that a special current of electricity evolved the current both ways through moist earth and by a battery shall travel only in one directioa,

It is desirable, for example, to telegraph cannot, like a private road, be barred against elecfrom the right to the left bank of a broad river. tricity evolved from other sources. Nor is this From the copper end of a battery on the right all. When the electrician wishes to collect atmasbank, a wire is carried to the shore (on the same pheric electricity, he insulates a metallic wire, side) and soldered to a plate buried in the river and suspends it in the air. In other words, he below water mark. A wire is also led from the acts exactly as the constructer of the telegraph zinc end to a long coil of wire which ends in a does, though with a very different object in view. metallic plate. This likewise is buried in the The latter, much against his will, finds that his river below water mark on the same right bank wires not only permit, but invite, atmospheric elec-but at a distance from the battery considerably tricity to employ them as a highway. They act, greater than the breadth of the river across which in short, as lightning-conductors; and lead the signals are to be sent. On the left bank two formidable meteor into every station, where it plates are immersed opposite those on the right deranges or destroys the coils and magnets, and bank, and connected by a wire. The electricity, occasionally menaces buildings, and eren life, with on leaving the battery, has therefore the choice of destruction. two paths. It may either keep entirely on the To guard against these serious evils, lightningright bank, passing from the one buried plate on rods, descending to the ground, are fixed at interthat side to the other, and so back to the battery vals to the telegraph-posts, and at the station. by the long coiled wire; or it may cross to the houses. The sharp spikes in which these rods left bank through the water, traverse the wire on terminate above, being elevated considerably bethat side, return across the water to the right yond the telegraph-wires, present points of atirarbank, and regain the battery by the shorter coiled tion to the electricity of the clouds, so that it is wire. The Thames, as we learn, has been act- deterinined to them rather than to the less exaltid ually crossed by electric currents in this way; and unprojecting wires. It is thus transferred the resistance to their passage by the water be- from the atmosphere to the earth without affecting tween the banks being less than that between the the telegraph. The rods in question, however, ends of the wires on the right and left bank only protect the wires in their immediate neighborrespectively. A wire stretched from Land's End hood, and that ineffectually. to John O'Groat's House, would indeed measure An additional and more effectual mode of probut a small portion of the breadth of the Atlantic tection is to place a knob of metal on each wire --but by twisting the wire into coils, we might where it crosses the posts. A second and lower include in a short space an enormous length. knob is then placed close to the first, but without

It remains to consider some of the imperfec- touching it, and connected with a wire led down tions which attend the electric telegraph, and the post to the ground. If the lightning discharge considerably limit its useful application. When ran along the wire, it would be cut off at the first it was first suggested as a substitute for the opti- knob it reached on the line, on reaching which it cal telegraph, which was useless in dark nights would leap across to the lower knob, and descend

[ocr errors]
« PreviousContinue »