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upon the stud b, the poles of the magnet shall clear the armature without actually touching it. A thin streak of light should be seen between the armature and the poles. Screw C is used to adjust the spiral spring above, by which, on the cessation of the electric current, the armature is drawn back and the disk ceases to mark the paper. In the first Morse instruments the marks were made on the paper with a pointed style (the instrument being thus known as the embosser); but by the invention of the ink-writing arrangement of Siemens, which we are now consider ing, the legibility and permanence of the record were secured, besides the advantage that a very light current will serve to make the marks. The case containing the clock-work, the arrangement of wheels by which the paper tape is unwound and carried forward, and the switch, by which the running of the tape is stopped, are not shown in the figure. The passage of a current draws down the armature, and elevates the disk, causing a straight mark on the tape so long as the current flows. When it ceases, the spring S draws back the armature as already described, and the mark is discontinued. Thus the duration of the current determines the nature of the mark, a momentary passage causing a dot, a longer depression of the key a dash; and as the alphabet invented by prof. Morse consists of dots or dashes, or a combination of the two, the above figure and explanation disclose the whole mystery of this system of telegraphy to those who have mastered the phenomena of electricity.

The Morse Alphabet.-Before going further, the details of this alphabet, universally recognized as a masterpiece of cryptography, may be given. The signals, as given below, are arranged in the groups, and accompanied by the mnemonic phrases, adopted by the British post-office when, in 1870, the transfer of the telegraphs to the government rendered necessary the rapid training of thousands of telegraphists throughout the kingdom:

Group 2.

T, Turnips
M, make

O, oxen

Ch, cheerful.

Group 4.

N, No

D, difficulty
B, baffles
G, great
Z, zeal.

Group 6.

K, Kindness

C, conciliates

Y, youth

X, extremely
Q, quickly.

The arrangement for the numerals is equally ingenious. Each figure is represented by five signals, thus:

2, 3,

4,

5,

6,

7,

8,

9,

0,

These are the numerals printed long, but on busy circuits expert clerks adopt the practice of "sending short," omitting all after the first dash in 1, 2, and 3, four of the dots in 5, and all before the last dash in 7, 8, 9, and 0. It is stated that prof. Morse founded his alphabet upon information given him by his brother, a journalist, as to the numerical relation of the letters in the English alphabet, the simplest signal (a dot) being given to E, and the next simplest (a dash) to T, those letters occurring most frequently in our language.

The Transmitting Key.-The "key" or hammer by which signals are transmitted from the operator at the sending office, is shown in fig. 2, in one of its earliest and most simple forms. The lever 1, 7 turns on its

axis A, and has on its under side two platinum nipples, m and n. L is the line-wire, connected with the axis; E, the "earth"-wire (passing through the Morse on its way to earth, and producing its signal there); and C, a wire connecting the stud a with the battery. As the key stands in the figure, it is in the position to

receive a current from the distant station, the E

course of the current being L, A, l, n, b, and

thence to the electro-magnet of the Morse en

FIG. 2.

route to earth. When it is desired to send a current, the handle H is depressed, and the

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current, generated in the battery, then comes by the wire C, and passing through a, m, and A, proceeds by the line-wire to the distant station. Various modifications of this key are in existence, but in all the principle remains the same, that the electric circuit is closed or completed by the depression of the key. The length of time during which the handle is depressed determines the length of the mark produced at the other end. Thus, if the clerk presses down the handle while he says "one-one two three," the inkdisk at the other end gives the mark. (dot dash) or the letter A, and so on through the various letters of the alphabet.

The Battery.-For the generation of power in the electric telegraph, Daniell's batteries (see GALVANISM) are chiefly employed in this country. Various forms of the Bunsen battery are also used, especially on the continent. The power employed varies with the length of line, the condition of the wires as regards insulation, and the nature of the instruments used.

The Circuit. The mode of joining up two stations by means of earth-wires, batteries, instruments, and line-wires, is shown in fig. 3. Assuming S and S 1 to be telegraph stations, P and P 1 are the "earth"-plates (see subsequent paragraph), B and B 1 the batteries, n and n 1 the electro-magnets and armatures, and b, k, g the transmitting keys and galvanometers. L, L show the line-wire, supported on poles and insulated. The key at station S is shown depressed, so that a current of electricity may be supposed to be passing from the battery B through the key and galvanometer along the

line-wire, and thence through k 1 and n 1 to the earth-plate P 1. Supposing, then, that the clerk at S desires to send a message to S 1, he depresses the key k several times so as to send a series of dots and dashes corresponding to the name (or rather the code signal representing the name) of the distant station. The attention of the clerk being gained by the clicking of the Morse, he turns the switch to set his paper tape in motion, gives the signal that he is ready, and the message is then sent.

The Line. From fig. 3 some idea may be gained as to the mode of carrying a wire or series of wires over posts, these posts being carried along the sides of a road or railway. In towns, wires are carried "over-house," or by underground pipes, the wires in the latter case being insulated by means of a gutta-percha or other suitable covering. The subterranean method is being applied to extended lines, especially in Germany. and is found to answer as well as the over-head system, while it avoids many of the casualties to which the latter is liable. In pole and over-house lines, the wires are kept from each other and from contact with the earth by insulators of various kinds. White porcelain and brown stoneware are the chief materials used. The former, when of good quality, well glazed and well burned, is perhaps the most perfect of all insuating materials, and does not deteriorate with age. The fewer the poles are in number on which the wires are suspended, the better is the insulation and the less the cost, but the liability to accident is probably greater. The number of poles used varies from 16 to 30 per mile, and is governed by the number of wires carried, the configura tion of the track, and other considerations. On road lines, the number of poles is generally larger than in the case of telegraphs carried alongside railways, the greater levelness and straightness of the latter reducing the number of supports required. The wire chiefly used for inland telegraph purposes is of iron, galvanized, and of No. 8(in.) gauge. The conductivity of a wire increases in the ratio of the square of its diameter (the resistance decreasing in the inverse ratio), and the advantage of using a thicker wire on the longer lines is thus seen. No. 4 wire is, for this reason, used on some of the longer lines.

The Earth-Earth Currents.-Mention has been made of the "earth," in the preceding description. This is the technical expression used in relation to the fact discovered by Steinheil in 1838, that the earth itself serves the purpose of completing the circuit,

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and renders the employment of a second or return wire unnecessary. The "earth" may consist of a buried plate of metal connected with the battery or line-wire, and of suffi cient surface to afford the necessary diffusion. The gas or water pipes of a town form excellent earths," care being taken that the connection is made with the pipe itself, and not with a branch, where a badly made joint might spoil the connection. Where dissimilar "earths" are in use, as for instance, a copper plate at one end, and an iron pipe at the other, a quasi battery is created, and vexatious currents pass along the line. Hence the "earths" on a circuit should be made alike. The earth, being regarded as a large reservoir of electricity, offers no sensible resistance to the passage of the current, in the same way as the ocean would receive or supply at any point an indefinite quantity of water. While this quality of the earth is one of the most valuable aids to telegraphy (reducing so materially the cost of wire erection), it presents at times those embarrassing interruptions known as earth currents. These currents, at all times unwelcome visitors to a telegraph office, are very variable, changing rapidly at times from positive to negative, altering their direction with the hour of the day, and leaving one circuit to appear ou another in a manner not explainable. The lines most liable to such disturbances are those running n.e. and s.w.; that is, connecting places separated in a straight line in those directions, and without reference to the actual direction of the wires. The easiest remedy for earth currents, when they are of sufficient strength to affect the lines, is to dispense with the earth connection, and revert to the original plan of using two wires. Thus between places where there are two wires, both may be disconnected from "earth," and used as a complete metallic circuit. Another remedy has been found in extending the circuit by joining to it a further wire, the terminal point of which lies beyond the direction or line in which the earth current is flowing. We must refer to the larger treatises on telegraphy for information regarding lateral induction, velocity of electric discharge, the tests for resistance, insulation, etc., and also for notices of some of the less prominent pieces of apparatus now found in the instrumentroom of the electrician.

The Relay. We now proceed to notice several methods by which the transmission of signals is facilitated or accelerated. First among those may be placed the relay. Siemen's polarized relay is now in very extensive use in this country. In the previous description of the Morse, we have assumed the instrument to be worked directly by the current sent along the line. On long circuits, however, direct working could only be

accomplished by great battery power, as, owing to inevitable loss by leakage, a current loses greatly before it reaches its destination. It is found to be a much better arrangement to have the instrument worked by a "local current," derived from a local battery at the receiving station. The mode by which this is accomplished will be seen from the diagrams. In the figures, NS is a hard steel permanent magnet, whose s. end S has a slit, in which the soft iron armature, a, is pivoted. To this armature a thin aluminium tongue, b, is attached, which, by making contact at the point c (fig. 4), completes the local circuit. To the n. end, N, of the permanent magnet the soft iron cores of the electro-magnet are fixed, as shown in the sketch. When the armature is equidistant from the poles of the electro-magnet, it is equally attracted by both; but if it be brought nearer to one than to the other, it will be held there, because it is under the influence of a more powerfully attracting force. Since the relative distance between the armature and the two pole-pieces may be increased at will, the attraction between either pole and the armature may be regulated with any degree of nicety. The electrical contacts for

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the local circuit are seen in fig. 4, which is shown with the local circuit completed. When two stations far apart are to be connected by telegraph, it is usual to transmit the signal to a half-way station, and thence to re-transmit it to its destination. The retransmission is not effected by manipulative skill, but by mechanical contrivance, so that, while the half-way station may read the message sent, no time is lost in the transmission. This is effected by making the intermediate instrument act as a relay in transmitting a message to the next station. The system, to be fully explained, would require more detail than we can here give to it. We shall only show how it is effected, leaving out of account how all the stations can communicate as in one circuit. The current C1, (fig. 5), from the sending-station enters the coil M, and goes thence to earth P, and returns as shown by arrow C1. The instrument may record or not as required, but its doing so in no way interferes with translation. The copper pole C, of the battery CC, is connected with the lever ' of the register, and the zinc pole is to earth. When the lever is drawn down by the current C1, it strikes against the point at the top of the pillar p, that checks its motion. The pillar p is joined to line La, running to the further station, and when the lever falls, a second circuit-viz., that of the battery CZ-is closed, in which C, the lever, the pillar L2, the further station, the earth, P, and Z are all included. Thus, as ' prints at the inter mediate station, it at the same time sends a new printing-current to the next. When it ceases to print, so does the instrument at the distant station.

Wheatstone's Automatic Transmitter.-The speed of the ordinary Morse instrument is limited to the rapidity with which the hand of the operator can move the key, so as to preserve the proper spacing between the marks at the receiving instrument. We are indebted to sir Charles Wheatstone for an apparatus which trebles, and in some cases quadruples the carrying capacity of a wire, securing, at the same time, mechanical accuracy in the relative size of the dots, dashes, spaces, etc. To effect this, three different instruments are required: First, there is a perforator, by which holes are punched in a paper slip to correspond with the signals required. The operator strikes three disks, the central one producing a central hole, which is of no avail electrically, only carrying forward the paper; the left-hand disk producing two holes, directly opposite to each other, on the sides of this central row; and that on the right producing two holes, placed diagonally to each other. The passage of the electric current is regulated by the position of the outer holes. Those opposite each other admit of a momentary passage of the current through the "transmitter"-used in sending the message-while the holes diagonally placed produce a lengthened mark, corresponding to the dash. The following diagram represents the word "and," as shown on the punched slip:

The third portion of this instrument is the "receiver," in which the currents sent by the action of the punched slips in the transmitter are reproduced in the dots and dashes of the Morse code-the printing being, moreover, done with a mathematical accuracy which keying by hand cannot attain. The speed of transmission depends on the length of line and state of the atmosphere; but the movement of the clock-work, both of transmitter and receiver, is capable of adjustment to any speed below 120 words per minute. When the post-office took possession of the telegraphs in this country, the Wheatstone automatic instrument was in use at only four stations in the kingdom. It has since come into extended use; and one of its most successful applications is in the simultaneous transmission of news from London to a large number of towns. The punched ribbon is carried from one transmitter to the other, the circuit to Birmingham, Manchester, and Liverpool (on which the highest speed is attained) sending it first, and from that instrument it passes to several others, each serving several towns. The adjustment of "resistance," by which a message is run off simultaneously at Edinburgh, Glasgow, Dundee, and Aberdeen by one sending from London (and so through the various transmitters where this system of "express news circuits" is adopted), forms one of the most interesting objects of study in the practical working of the telegraph in this kingdom. By combining the automatic transmission with Bain's principle of producing marks on chemically prepared paper, an American inventor has accomplished still higher speed, the lever action of the inking disk (fig. 1) being saved.

Other Instruments.-All that has been said as to the battery, the earth insulation, etc., is applicable to nearly every instrument now in use; the exception being several magneto electric instruments, such as Wheatstone's "ABC," in which the use of a battery is dispensed with, power being generated o bobbins coiled upon an armature rotating continuously over the two poles of a permanent magnet. On the upper surface

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of this instrument is seen a circle of buttons corresponding to the letters of the alphabet, by means of which levers, arranged vertically in a circle, may be pressed down. These levers press a pitch chain into a series of indentations on the periphery of a metal disk, the chain having sufficient slack, so that, when a second lever is depressed, the first must be raised. A series of currents, corresponding to the number of letters between each lever pressed down, is sent into the line, and operating on two little bent magnets, moves forward a ratchet wheel, having a pointer on the same axis which shows the letter on a dial card. In this way the message is spelled out letter by letter, and as the instrument gives not an arbitrary sign, but the letter itself, it is much used in private telegraphs and for the smaller post-offices throughout the kingdom. The non-recording instrument most used in this country (excluding private telegraphs) is the single-needle instrument of Cooke and Wheatstone. It consists of an upright galvanometer, with astatic needles, one of which moves within the coil, and the other upon the front of the dial. The needles are loaded at the lower end, to maintain them perpendicular when no current is passing. The instrument is worked by means of two keys, like those of a piano, a deflection of the needle to right or left being effected by depressing one or other of the keys. The signal is shown both on the sending and receiving instrument. The Morse alphabet is used, a deflection to the left corresponding to the dot, and one to the right representing the dash.

Acoustic Telegraphy.-Before the introduction of high speed automatic instruments for the more important circuits, expert telegraphists in many cases dispensed with the reading of the printed slip, reading by the sound, which, by long practice, became a language perfectly intelligible to them. The great advantage of this was, that the use of the eye was obtained exclusively for the task of writing down the message. In sir Charles Bright's "bell" instrument, most admirable results, in point of speed, have been attained. The bells, different in sound, are placed at the two sides of an upright instrument, so that the clerk, bending forward to write, may concentrate his attention on that duty, translating in his mind the tinkle of the hammers as they ring out their messagc. The bells are now worked in the Morse code-the left bell a dot, and the right bell a dash; but when first introduced, the instrument had a code of its own, based on the desire to complete each letter as much as possible on one bell, A simpler acoustic telegraph has been brought into use in America (hence called the "American sounder") and in this country. This instrument is, shortly stated, the Morse without its wheel-work and ink-printing apparatus; and its whole construction is shown in fig. 1, omitting the inking disk. The use of the "sounder" has greatly increased in this country owing to its cheapness and efficiency. For a description of the type-printing and fac simile instruments, on which great advances have been made of late years, we must refer our readers to the larger treatises on the telegraph and its history.

Duplex Working.-The fact that two currents may be sent simultaneously (one from each end) has been long recognized by electricians, but the principle of the duplex was revived and patented by Stearns, an American, in 1872. At first the duplex-working was only tried on short circuits of 40 to 60 m.; but it has now become a matter of daily use on every busy circuit, long or short, both in this country and abroad. The principle of the duplex system is that the current sent on the depression of the key is divided into two parts, one-half being carried through one pair of coils in a differential galvanometer to the line, and the other half through the other pair of coils to a resistance coil, and thus to earth. The resistance of the latter is made exactly equal to that of the line-wire, and the instrument of the sender being so placed that this divided current presses equally in each direction, this instrument remains unaffected, while the armature at the other end responds to the signal sent. At the same time a telegraphist at the other end is sending a current, which is divided in like manner, and leaves his own instrument unaffected while operating on the armature of the first instrument. The two currents on the linewire assist or oppose each other in such a way as to affect the equilibrium in the differential galanometer, but each operates only on the distant instrument. Duplex-working led to dip, that is, two messages passing over a wire in the same direction at once, and to this has followed quadruplex and multiplex telegraphy. Quadruplex working was first perfected in 1876 by Prescott, Edison, and Gerritt Smith, but the possibility of its being accomplished was suggested by Stark of Vienna, in 1855. It was introduced into Britain as a practical branch in 1878, and is now used from London to Liverpool, Dublin, and other towns. An illustration of the value of these additions to the wire power is afforded by a wire from Chicago to Pittsburg, 550 m., which is quadruplexed, and at Pittsburg branches off in two duplex circuits to Baltimore and Philadelphia, giving Chicago duplex communication with these two places. In the same way Middlesborough and West Hartlepool have been duplexed to London, on separate wires as far as Leeds, and quadruplex on one wire thence to London.

Multiplex Telegraphy and "Phantom" Circuits.-The most original feature of the telegraph section of the Paris exhibition of 1878 was the harmonic telegraph of Haskins and Gray, based on principles laid down by Cromwell Varley in 1870. In one application it occupies a place midway between duplex and multiplex telegraphy, namely in the "way duplex." or as it was felicitously termed by the late Mr. Orton, the phanton circuit." A wire may be occupied by the ordinary business of a series of intermediate