MODERN PRACTICE

OF THE

ELECTRIC TELEGRAPH

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By Frank L. Pope

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Back to Chapter 3

CHAPTER IV.

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THE MORSE, OR AMERICAN TELEGRAPHIC SYSTEM.

51. The Morse Telegraphic Apparatus consists of a signal key for breaking and closing the circuit, and an electro-magnet, the armature of which is attached to a lever carrying a steel point or style, which embosses a mark upon a narrow strip of paper, moved uniformly along by clock-work. As long as a current continues to flow through the coils of the electro-magnet the armature is attracted, and the mark is made upon the moving paper. As soon as the circuit is broken the armature ceases to be attracted, and is withdrawn from contact with the paper by means of a spring. The duration of the current, and consequently the length of the mark, depends upon the duration of the contact made by the key.

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Figure 10 (1200 dpi monochrome)

Figure 10 (1200 dpi 8 level)

52. The Morse Signal Key is shown in fig. 10.* It consists of a brass lever, A, four or five inches in length, which is hung upon a steel arbor, G, between adjustable set screws, D D, in such a manner as to allow it to move freely in a vertical direction. This movement, however, is limited in one direction by the anvil C, and in the other by the adjustable set-screw, F.

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* The drawings of the signal key, register and relay (figs. 10, 11 and 12), are from instruments manufactured by Bradley.

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One wire of the main circuit is connected to the metallic frame of the key, and the other to the anvil, C, which is insulated from the frame. These connections are made by screws passing up through the table from beneath. The lever is provided with a knob of vulcanite, B, by means of which it may be pressed down by the finger of the operator, bringing the lever in contact with the anvil, and thus closing the circuit, precisely as if the wires themselves had been brought together. The points of contact between the lever and the anvil are made of platina, as ordinary metals would be fused by the passage of the electric spark when the circuit is broken. A spring beneath the lever restores it to its original position when the pressure of the operator's finger is withdrawn. When the key is not in use the circuit is completed by bringing the lever of the circuit closer, H, into contact with the anvil, C.

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53. The Morse Register.--- Fig. 11 represents the recording apparatus, usually termed a register, which is made in several different forms, all involving the same principles. M is the electro-magnet, the two ends of the wire forming the coils being carried to the terminal binding screws on the base, one of which is shown at s, to which the conducting wires are attached. Above the electro-magnet is seen the armature attached to the lever L, which moves upon an arbor at d. The opposite extremity of the lever carries a steel point, p. The strip of paper passes through the guide g and between the grooved rollers r r, which are moved by a train of wheels driven by a weight attached by a cord to the drum, W.

When the armature is attracted by the magnet the style p is brought forcibly in contact with the paper, moving above it upon the grooved roller, and a raised line is embossed upon it corresponding in length to the time the armature remains attracted. A spring adjusted by the nut n withdraws the lever when the attractions ceases. The movement of the lever is limited by the adjustable screw, m. The screw c regulates the pressure of the rollers upon the paper, and the clock-work is started and stopped by the brake a. The weight is wound up occasionally, as required, by the operator.

54. The Morse instrument is worked either by the main line current or by relay. For a distance not exceeding 20 or 30 miles, a register, whose coils are wound with No. 30 copper wire, may be worked by the line current, if the line be well insulated (57).

55. When the insulation is defective, or the circuit so long that its resistance renders the current too weak to work a register direct, as is usually the case with telegraph lines, it becomes necessary to employ a receiving magnet or relay, which brings a local battery (11) into action at the receiving station, the current of which operates the register.

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56. The Relay Magnet.--- The construction of the relay is shown in fig. 12. M is the electro-magnet, which is placed in a horizontal position, and is movable by means of the screw a. The coils of the magnet are of fine wire, usually from No. 30 to No. 36 in size, of great length and closely wound.* The ends are connected to the line circuit by the binding screws, m m'. The armature lever b is connected with the binding screw l by a wire carried underneath the base of the instrument. A platina point, c, on the armature lever, is brought in contact with a similar point on the end of the screw d whenever the armature is attracted by the magnet, the screw being in metallic connection with the binding screw l', by means of the frame of the apparatus and a wire beneath the base. One of the screws, l l', is connected to one pole of the local battery (11), and the other to the other pole, embracing the register magnet in its circuit. Therefore, whenever the armature is attracted by the force of the main current acting upon the relay magnet, the circuit of the local battery is completed through the register. As the relay is constructed with great delicacy, a feeble line current is enabled to actuate a register powerfully through the intervention of a local battery.

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* In the instruments manufactured by Dr. Bradley the helices or coils of the electro-magnets, instead of being composed of silk

insulated copper wire, as described in sec. 34, are made of naked wire, ingeniously wound by accurate machinery in such a manner that the convolutions are separated from each other by a space of 1-600 to 1-800 of an inch, the several layers being insulated from each other by thin paper. It is claimed that, by this method of winding, a coil of a given length and gauge of wire, and, consequently, of a given resistance, can be made of much less diameter than is possible with silk insulated wire, while, at the same time, the number of convolutions will be increased as well as the power of the electro-magnet.

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The movement of the armature is regulated to correspond with the varying strength of the line current by means of the adjustable spiral spring f. The magnet may be also set at any required distance from the armature by means of the screw a, which is cut with a right and left hand thread, passing through the soft iron bar connecting the two cores, and also through the supporting post in the rear of the coils. The latter slide through openings in the upright metallic plate which supports the adjustable platina pointed screw d.

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Fig. 13 represents a Pocket Relay, as it is usually termed, although it is properly a main line sounder (57). This is provided with a key, as shown in the figure, the whole being conveniently and compactly arranged to fit into an oval case four or five inches long, which may be carried in the pocket. It is an extremely convenient apparatus for line repairers. The cut shows the arrangement manufactured by the Messrs. Chester.

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57. The Sounder.--- In many of the larger telegraph offices the recording apparatus is dispensed with, and the communications read by the sound of the armature lever. In that case the Sounder (fig. 14) is employed in the place of the register, the connections of the wires being arranged in precisely the same manner. The Sounder consists simply of the electro-magnet, armature and lever, fixed upon a base.* The coils are usually wound with No. 23 wire.

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* The instrument shown in the figure is from the manufactory of C. T. & J. N. Chester.

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Main Line Sounders are used in some offices, which enables the operator to dispense with the local battery. The coils are wound with fine wire, usually No. 30, and are frequently made somewhat larger than those of the relay. A common form of this instrument is known as the ``Box Sounder.'' The lever, striking upon a hollow wooden box containing the magnet gives a sound that may easily be distinguished by the operator under ordinary circumstances.

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Fig. 15 (S. F. Day & Co.) shows an excellent form of Main Line Sounder. The parts of the instrument are mounted upon a metallic plate, the centre of which is raised slightly above the base, so as to form a bridge, as shown in the cut. The armature lever is of steel, and the whole arrangement is well adapted to increase the sound of the lever as much as possible---a feature of great value in working with weak currents or on badly insulated lines. These instruments are also made in several other forms, and various devices for increasing the sound of the lever are made use of. On many lines they are found to answer as well as the usual arrangement, employing a relay and local battery.

For circuits of moderate length a Main Line Register (fig 16), manufactured by Day & Co., has been employed with excellent results.

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58. Arrangement of a Terminal Station.--- Fig. 17 is a diagram showing the arrangement of wires, batteries, and instruments for one of the terminal stations of a line. The line wire L first enters the lightning arrester X, and passes thence through the coils of the relay M by the binding screws, 1, 2, and thence to the key K, main battery E, and finally to the ground at G. The local circuit commences at the + pole of the local battery E' and through the platina points of the relay by the binding screws, 3, 4, thence through the register or sounder coils, S, and back to the other pole of the battery.

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59. Arrangement of a Way Station.--- Fig. 18 shows a plan of the instruments and connections at a way station. The line enters at L, passes through the lightning arrester X (70), and thence through the relay M, key K, and back to the lightning arrester, and thence to the next station by the line L'. The arrangement of the local circuit is the same as in the last figure. The button C, arranged as shown in the figure, is called a ``cut-out'' (62). When turned so as to connect the two wires leading into the office, it allows the line current to pass across from one to the other without going through the instruments. The instruments should always be cut out by means of this apparatus when leaving the office temporarily, or for the night, and also during a thunder storm, to avoid damage to the apparatus. Fig. 21 shows a better arrangement.

The Ground Switch, Q (63), is used to connect the line with the earth on either side of the instruments at pleasure. It is only used in case of accidents or interruptions on the lines, as will be hereafter explained.

60. Adjustment of the Apparatus.--- The principal difficulties which the operator is liable to meet with in working the Morse apparatus are as follows:

1. When the paper in the register does not run freely from the reel on which it is held, or sticks in the guides from irregularity in width, or if the style is adjusted to indent the paper too deeply, the paper moves irregularly, shortening dashes into dots, and causing dots to run together.

2. The style should be adjusted so as to move freely in the groove of the upper roller, or the marks will be more or less indistinct. If it is completely out of the groove, no marks will be produced. These faults generally arise from too much end play in the pivots of the lever, or from the pivot screws working loose. When the lever works too loosely in its bearings, irregular dashes, too deep at their commencement, and tapering off to nothing, will be produced.

Residuary magnetism sometimes causes the armature of the electro-magnet to stick. This will always happen if the armature is allowed to touch the poles of the magnet. The screw stop should therefore be adjusted so as to prevent the armature from approaching too closely to the poles of the magnet. The upper screw stop, which regulates the play of the lever, should be adjusted so that the movement is just sufficient to withdraw the style from contact with the paper.

3. If the paper runs between the rollers ``crooked,'' the pressure of the upper roller upon the paper is greater at one end than the other. This pressure is regulated by two springs, one on each side of the instrument, and they should be made as nearly equal in pressure as possible.

4. When the signs are confused the relay requires adjustment to suit the strength of the current.

5. If the relay moves by the action of the line current, and the register or sounder does not act, the fault is somewhere in the local circuit. If the register does not work when the relay is moved by the finger, the local circuit is certainly at fault, either from weakness of the local battery, a loose connection, a broken wire, or dirt between the platina points of the relay. The latter should, when too much corroded, be cleaned carefully with emery paper, taking care to remove as little of the platina as possible.

6. The sticking of the key, which sometimes occurs, is caused either by the platina points becoming oxidized and dirty, or by small particles of metal and dirt collecting behind the circuit closer and about the anvil, causing a partial connection when the key is open.

7. It is very important that all the connections about an office should be firmly screwed up. Neglect of this precaution is a very prolific cause of trouble upon a telegraph line.

8. In rainy weather, or when the insulation of the line is defective from any cause, the cores of the relay must be withdrawn to a greater distance from the armature, to avoid the influence of the residual magnetism, caused by the escape of the ``current'' from the line. This is called ``adjusting'' the instrument, and is one of the most important of an operator's duties, requiring great judgement and skill during unfavorable weather and on poorly insulated lines. The key should never be opened without carefully adjusting the relay, to be sure that no other offices are using the line.

SWITCHES OR COMMUTATORS.

61. These are employed for the purpose of connecting one circuit with another, for dividing a circuit into two parts, or in short, for any purpose where it is necessary to alter the connections of a line or circuit.

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62. Fig. 19 shows the simple Button or Circuit Closer, which is usually employed as a ``cut out'' (58). The base A is of wood or hard rubber. The brass lever, B, when in the position shown in the figure, forms an electrical connection between the metallic studs C C, which are continuous with the screws, D D, passing through the table and terminating in binding screws, to which the wires are attached. The spring F, pressing against the lever, insures a firm contact with the studs. This circuit closer is sometimes, for special purposes, made with four connections instead of two.

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63. Fig. 20 represents a Ground Switch (58). The lever A is attached to a wire leading to the earth, and the two studs, B, C, are connected to the line wire on each side of the instruments.

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64. The Plug Switch is shown in fig. 21. This arrangement consists of a brass spring, brought very firmly against a stationary pin. A wedge or plug made of two pieces of brass, separated by an insulating material, is made in the form shown, to admit of insertion between the spring and the pin. The wires leading to the instrument are attached to this wedge by flexible conductors. When the wedge is inserted, the line current is diverted through the instrument, but is not interrupted. The instrument may readily be withdrawn from the line by taking out the wedge, the spring instantaneously closing the main circuit. This arrangement is found extremely useful in connecting batteries as well as instruments. At a way station it is preferable to a simple cut- out, for the reason that the apparatus is entirely disconnected from the circuit when the wedge is withdrawn (59).

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* L. G. Tillotson & Co., New York.

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This switch may be made of any size and with any number of connections, depending upon the number of lines it is designed to accommodate. The wires may be attached to it in a number of different ways, the particular arrangement adopted in each case depending upon the nature of the changes required to be made.

66. Arrangement of the Connections.--- The switch shown in the figure, placed at a way station, could be arranged to accommodate three through wires, and an equal number of instruments, providing for all the necessary changes. The arrangements in this case would be as follows : Connect line wires Nos. 1, 2 and 3, east, with A, B and C ; 1, 2 and 3, west, with D, E and F. Instrument No. 1 to I and II, No. 2 to III and IV, No. 3 to V and VI. Turn the buttons so as to connect A with I and D with II. The circuit of No. 1 wire will then enter at A, go to instrument No. 1 via I, returning to II, and thence going out at D. The other instruments may be connected at pleasure in the same manner. If it is desired to connect a circuit through, for instance No. 1, leaving the instrument out of circuit, it is done by turning the buttons so as to connect both A and D to the same horizontal wire, either I or II. By a little study it will be seen that any wire east may be connected with any other wire west, with or without any desired instrument, at pleasure. The ground wire is attached at VII, and may be connected with any line wire east or west at pleasure.

67. The same switch, placed at a terminal station, would provide for six wires, by connecting them as before to the screws A, B, C, D, E, F, and the instruments to I, II, III, IV, V, VI. The wires of a loop (87) may be connected to I and II in place of the instrument, and may be put in circuit with any wire by turning the buttons connected with I and II both on to the corresponding strap, which is then divided by withdrawing the peg, forcing the current to pass through the loop. Extra sets of buttons for loops are usually provided when the switch is intended for a terminal station, which can be used without diminishing the capacity of the switch for other purposes.

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68. Jones' Lock Switch is employed for the same purposes, and connected in the same manner as the one last described, but the connection between the vertical and horizontal wires is made by a metallic peg, provided with a spring, as shown in fig. 23 (Chester). This arrangement entirely obviates the danger of imperfect connections, from the loosening of buttons, etc., which is sometimes a source of trouble in the Culgan Switch. It is also cheaper and much more compact ; a matter of some importance in arranging for the accommodation of a large number of wires.

69. There are other forms of switches designed for special purposes, which it is unnecessary to describe in a work of this kind. Those already referred to are all that are generally required in fitting up a telegraph station.

LIGHTNING ARRESTERS.

70. The danger of injury to the instruments and operators at a telegraph station, by atmospheric electricity, is usually guarded against by the use of an apparatus termed the Lightning Arrester, which is constructed in accordance with the well established fact that this kind of electricity, being possessed of enormous intensity, prefers a short route through a poor conductor to a longer one through a good conductor, while the comparatively low intensity of the voltaic current, used for telegraphic purposes, confines it to the conducting wires.

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71. The Plate Arrester.--- The arrester most usually employed upon the telegraph lines in this country consists of a flat plate of brass, about five or six inches in length, which is attached to the ``ground wire.'' Other plates of brass rest upon this, being separated from it by a thin sheet of insulating material. These last mentioned plates are provided with binding screws, for the attachment of the line wires. Any surplus charge of atmospheric electricity, entering by the line wires, forces its way through the insulating material into the ground plate, and is thus carried off to the ground without injuring the apparatus. The form of arrester supplied by the Messrs. Chester is shown in fig. 24. The plates in connection with the line wires are firmly held in their places by a wooden cross piece, secured by screws at each end, as shown in the cut. A thin sheet of gutta percha, or paper, is used to separate the plates. When paper is used it should be saturated with paraffine. Mica is, perhaps, better than either, as it is not carbonized by the passage of the spark, as paper sometimes is, so as to form a ground connection. The manner in which the arrester is connected with the wires leading into an office will be seen by reference to fig. 18, where the two line wires, L, and L', are attached to the two upper plates of the arrester, X, while a wire leading to the ground at G is attached to the lower plate.

72. Bradley's Arrester.--- Another form of arrester, designed by Dr. Bradley, is shown in fig. 25, and has recently been quite extensively employed, with excellent results.

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It depends for its action upon the well ascertained fact that lightning always passes from a point to a plate with great facility. The line wires leading into the office are attached to the metallic plates A and B by means of binding screws beneath, the ground wire being attached in the same manner to the plate C. Platina tipped screws, 1, 2, 3, 4, are fixed to each plate, and are adjusted so as to come nearly in contact with the opposite plate. As lightning occasionally passes from the earth to the clouds, as well as from the clouds to the earth, this arrester is so arranged as to facilitate its passage in either direction. The buttons, F F, are so arranged that the apparatus serves for a ``cut-out'' and a ``ground switch'' as well as an arrester. Its application to these purposes will be at once understood by an inspection of the cut. This form of arrester is peculiarly well adapted for the protection of cables, or any situation where it is exposed to accidental dampness, as it is much less apt to interfere with the working of the line in such cases than the plate arrester previously described.

73. Lightning arresters must always be kept free from dampness and dirt, as far as practicable. Much annoyance often arises from neglect of this precaution, as moisture between the plates will often cause a serious escape, greatly interfering with the working of the line. This difficulty is especially liable to occur where the arresters are used for the protection of submarine cables. A flash of atmospheric electricity also frequently carbonizes the paper between the plates, or fuses the metal, so as to permanently connect the ground and the line. Consequently, the lightning arresters should be frequently taken apart and examined. This should invariably be done after a thunder storm.

REPEATERS.

74. When the length of a telegraphic circuit exceeds a certain limit, depending upon the insulation, the size of the conductor, the number of instruments in circuit, etc., the line current becomes so enfeebled, even when large batteries are employed, that satisfactory signals cannot be transmitted. In such cases it was formerly customary to re-write the messages at some intermediate station, but this duty is now usually performed by an apparatus called a repeater. The principle of this arrangement consists in causing the sounder or register connected with one circuit to open and close the circuit of another line by an action similar to that of a relay (56). Repeaters are also often used for connecting one or more branch lines with a main line, for the purpose of transmitting press news, etc., simultaneously to different places. This enables all the stations in connection to write to each other as readily as if they were situated upon the same circuit.

Since the general introduction of repeaters it has become quite practicable to telegraph direct between places situated at very great distances from each other. It is not uncommon, at the present day, to work direct through four or five thousand miles of continuous line by the aid of these instruments with almost as much facility as if it were one continuous circuit. On one or two occasions the stations at Heart's Content, Newfoundland, and San Francisco, California, have been placed in direct communication with each other, the operators at these widely separated points conversing with each other across the entire breadth of the continent without the slightest difficulty.

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75. Wood's Button Repeater.--- This is the simplest arrangement of this kind now in use. Fig. 26 shows the most convenient and serviceable form in which the button or switch, and its connections can be arranged for the purpose of changing the circuits. The instruments, batteries, &c., are shown in outline, for convenience of explanation. M and M' are the eastern and western relays, S and S' the eastern and western sounders. The local connections are not shown, but are run as usual. The eastern and western main batteries are shown at B and B', and are placed with opposite poles to the ground, at the repeating station, so that when the line is put ``through'' the two batteries will coincide.

By means of this arrangement the following result may be obtained :

I. Two distinct and independent circuits. The lever L remaining in the position shown in the drawing (marked 1), and the button a 4, closed.

II. A through circuit. The lever L remains as before, but the button at 4 is opened, throwing off the ground connection between the two batteries, B and B'.

III. Two distinct circuits arranged for repeating. The button at 4 is closed. If the lever L be placed in the position indicated by the figures 2, 2, the eastern sounder repeats into the western circuit. If the lever is changed to 3, 3, the western sounder repeats into the eastern circuit. The operator in charge of a button repeater will find his duty very simple if he governs himself by the following

Rule.--- When either sounder fails to work coincident with the other, turn the button instantly.

In connecting up this apparatus, the arrangement of the poles of the main batteries above specified should be carefully borne in mind. It is also of the utmost importance that these batteries should be perfectly insulated from the ground, as the point at which the circuit is open and closed is between the battery and the ground. Therefore, an escape occurring from the battery to the ground will cause a residual current upon the main line, when the circuit is open at the repeating points of the sounder, and thus interfere with its working.

In cases where it is not required to work the two lines through in one circuit, the connections are arranged differently from the plan shown in fig. 26, the main battery being placed in the circuit between the lever L and the ground G, instead of at B and B', as shown. In this case the switch 4 may be dispensed with altogether.

76. The lever of the sounder moves through a certain space before closing the circuit of the second line, so that the duration of the current sent forward is shorter than that received from the transmitting station. A second repeater shortens it still more, so that the dots cease to be repeated, and are frequently lost altogether. The sending operator must therefore transmit the signals more firmly, as it is termed ; that is, increase the length of the key contact, especially when sending dots. For the same reason, the sounder levers in a repeating apparatus should be adjusted to have as little motion as possible.

77. Hicks' Automatic Repeater.--- This arrangement dispenses with the attendance of an operator for the purpose of changing the circuits while working, the only attention required being to keep the relays properly adjusted. The principle of the apparatus is shown in fig. 27.

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The main circuits pass through the relay magnets M and M', thence to the repeating points f g and f' g', attached to the opposite sounder levers respectively, and thence to the main battery and ground at G and G'. The platina points of the screws f and f' are placed upon U shaped springs, which, in a great measure, prevents the shortening of the signals referred to in the last paragraph. The local circuits are run through the relay points b and b' and the sounders R and R', on each side of the apparatus, in the ordinary manner, but to prevent confusion of lines, are omitted in the drawing. The ``extra local'' magnets, L and L' act upon armatures placed upon the relay levers a and a', opposite to the regular armature. (See figure.) These extra local magnets are movable by means of the screws d d', and the adjustment of the relays M M' is performed by means of these extra local magnets, the springs s s' not being used for this purpose.

In the figure the repeater is shown in its normal position, with both circuits closed. The circuits of the extra local batteries B B' (shown by dotted lines) pass through the sounder levers l l', the screws p p', and thence respectively to the extra local magnets on the opposite side of the apparatus. These magnets must be so adjusted that their attraction is not sufficient to draw the armatures away from M M' unless the main circuit is broken.

It will also be seen, by referring to the drawing, that when the main circuit is broken and the armature falls back on the point c, that the extra local magnet L is cut out. But the instant this happens the spring s draws the armature away again. As soon as the contact is broken at c there is a circuit through L, and the armature is again drawn back to c. The tension of the spring s being but just sufficient to draw the armature away from c, the armature vibrates on the point c through such a small space, and with such rapidity, that the motion is invisible to the eye. On account of the extreme rapidity of these vibrations, it is impossible to close the main circuit at a time when the extra local magnet L is not cut out, and the armature will consequently obey the slightest impulse caused by the attraction of the relay magnet.

The working of the apparatus requires but little further explanation. If the western main circuit be broken, for instance, the armature lever a falls back and vibrates on the point c, as above described. The sounder lever l first breaks the circuit of the eastern extra local magnet L', then that of the eastern main line, which passes through the relay M. The circuit through both L' and M' being thus broken, the slight tension of the spring s' will hold the armature in its place, and prevent the local circuit through R, and consequently the western main circuit, from being broken. When the western circuit is again closed the reverse of these operations takes place.

78. In using this repeater the springs s s' should be adjusted with the smallest possible amount of tension, just sufficient to hold the armature in place. When once adjusted they should be let alone. Care must be taken that none of the wires under or about the magnets touch any part of the brass. The extra local magnets, for example, may be cut out entirely in this way. The screws that adjust the extra local magnets should be oiled with fine oil to prevent wear and make their adjustment easy. The extra local batteries must be kept of a uniform strength ; if they are allowed to become weak the instrument will be thrown out of adjustment.

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79. Milliken's Repeater.--- In the general arrangement of its connections this repeater somewhat resembles that of Hicks', but is more simple in principle. Fig. 28 is a plan of its connections. The main line wire from the west passes through the relay magnet M and the repeating points f' g' of the opposite sounder, and thence to the battery and ground at G'. The eastern line passes through M', f and g to G, in a similar manner.

The extra local magnets L and L' are arranged, as shown in the figure, so that when either of their armatures is released it is drawn back by the spring attached to its lever, bringing the latter firmly in contact with the armature lever of the corresponding relay. The extra local batteries are shown at B and B' the circuit of each being indicated by dotted lines. The ordinary local circuit through the relay and sounder is omitted, to avoid confusion in the diagram.

If the main circuit be broken in the western wire, the relay M breaks the local circuit of the sounder R at b. The movement of the lever l of the sounder first breaks the extra local circuit at p, causing the magnet L' to release the armature d', which is drawn back by the spring s' against the top of the lever a', and, secondly, the eastern main circuit is also broken at f. g. The lever a' is prevented from falling back when the circuit of M' is broken by the tension of the spring s', which is so adjusted as to be greater than that of the spring h'. The apparatus on the right hand side of the repeater, therefore, remains quiet while the west is working, and vice versa, the current through M' being always restored before that through L' is broken, which is effected by the U shaped spring on the screw f.

One of the principal advantages in the construction of Milliken's repeater consists in the fact, that any slight variation in the strength of the extra local circuit, from weakness of the battery or other causes, does not affect the adjustment of the relay magnets, as in the case with Hicks' repeater. The adjustment and action of the two magnets are entirely independent of each other, as will be seen by reference to the diagram. The relay levers also move more freely, being unencumbered with extra armatures or other appliances.

In this, as in the Hicks repeater, buttons are provided, by means of which each line may be worked separately without interfering with the other, if desired.

These are omitted in the drawing, to prevent confusion, but are arranged so that, when closed, one button forms a permanent connection between f and g, thus preventing the movement of the lever l from breaking the eastern main circuit, and another connects p and l, thus keeping the extra local circuit constantly closed, and the armature lever d' withdrawn from interference with a'.

The same thing may be accomplished by causing the button to break the extra local circuit entirely, when the instruments are to be worked separately, and ``turning down'' the adjusting spring s' of the lever d'. It will, of course, be understood that the other side of the repeater is arranged in precisely the same manner.

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80. Bunnell's Repeater.--- The arrangement of the main circuits in this repeater is exactly the same as in the ordinary ``button repeater,'' and will be readily understood by reference to fig. 29. The eastern main wire enters at the right, passing through the repeating point, s', of the western sounder, S', and through the coils of the eastern relay, M, and thence to the main battery and earth at E. The western main wire is similarly connected on the opposite side of the instrument. In the button repeater (75) a switch is so arranged as to form a connection, cutting out the repeating points of the sounder on the opposite side, when either line is working, requiring a person to be constantly stationed at the instrument to make the necessary changes when two stations, on opposite sides of the repeater, are corresponding with each other. In Bunnell's repeater this duty is performed automatically by means of two ``governor'' or controlling magnets, G G, the action of which will be hereafter described.

The eastern and western main circuits both being closed and the apparatus at rest, the course of the local circuit of the eastern instrument is as follows : From the local battery, L, through the coils of the eastern sounder, thence passing through the closed relay points at M, and returning to the other pole of the battery. The resistance of the governor magnet, G, prevents any appreciable portion of the current from passing through its coils, as long as the closed points of the relay, M, afford it a shorter route. If the local circuit be broken by the relay points at M, it is forced to pass through the coils of the sounder, S, and also of the governor, G.

When a circuit of low intensity passes through the coils of two magnets, differing considerably in resistance, the attraction of the magnet having the least resistance is very small in comparison with that of the other. A practical application of this principle is made in this repeater, by forming the helices of the governor magnet of finer wire than that of the sounders. The effect of this is, that when the local circuit is thrown through both magnets by the opening of the relay, that the armature of the governor magnet is attracted with considerable strength, while the magnetism developed in the sounder is not sufficient to move its armature, although the same current passes through its coils. This arrangement is, of course, the same on each side of the repeater, and by bearing it in mind the action of the instrument may be readily comprehended.

When both main circuits are closed and the repeater at rest, the governor magnets remain open, being cut out by the points of the relays, which, as well as the sounders, are closed on both sides of the apparatus. If, now, we suppose the circuit to be opened by an operator on the western main line, the armature of the relay, M', falls back, opening the sounder, S', and closing the governor magnet, G', as previously explained. This breaks the eastern main circuit at s', and also at a', as well as the circuit of the opposite governor magnet, G, at the point b. The breaking of the eastern main circuit at S' opens the eastern relay, M, and consequently its sounder, S, but the circuit of the governor magnet, G, being broken at b', it remains inactive, and the western main circuit is complete through the points, a, although broken at the point, s, by the opening of the sounder, S. Upon the closing of the western main circuit this action is reversed, and the apparatus resumes its original position. If the eastern main circuit be opened the same action takes place, but on the opposite side of the repeater.

In most repeaters hitherto constructed one side of the apparatus remains silent while the opposite side is in action, but in this one the relays and sounders on both sides work together, the points, a, a', on the armature of the governor magnets acting automatically in the same manner as the switch of a button repeater, when moved by the hand of the operator.

81. An advantage claimed for this repeater is, that both sides of the apparatus work together, affording the operator in charge a better opportunity to know how both lines are working. The extra local batteries are dispensed with, and the relay levers are not encumbered with extra armatures and other appliances. The adjustments required are the same as in a simple relay and sounder.

82. Various other repeaters have been contrived, and to some extent adopted in this country, but as those we have described are much more extensively used than any others, it has not been deemed necessary to describe the others in a work of this kind.

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83. Combination Locals.--- In offices containing a number of instruments, a single local battery is frequently employed to operate all the sounders in the office. Such an arrangement is called a combination local. The best way of making the connections is shown in fig. 30, in which the instruments are represented at I, II, III, and IV. The local battery is shown at E. The common conductors, a and b, should be of large copper wire, say No. 12 or 14. If the ordinary Daniell's battery is used for this purpose, the cells should be connected for quantity, as shown in the diagram, and not in a single series. Every sounder in the combination should have the same size and amount of wire in its coils, as nearly as possible, in order to secure the best results.

84. Another plan is to use separate locals, a wire being run from one pole of each local to its corresponding instrument, the opposite poles of the batteries, and the instrument wires being all connected to a common return wire.

85. These combination locals are very objectionable, however, and their use should be avoided wherever possible. The iron cores in two different relays may happen to be in connection with the silk covered wire with which they are wound, a circumstance which frequently occurs. In such a case, if the two armatures chance to touch the poles of their respective relays, a metallic connection, technically called a cross, is made between the two main lines. Again, if these two relays are at a terminal station, and in connection with two main batteries, with opposite poles to the ground, the combined force of both batteries is thrown on short circuit, through the local return wire, burning the relays, exhausting the batteries, and interfering with the operation of every wire connected with them. The cause of these troubles being somewhat obscure, it might, for a considerable time, escape detection.

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86. Local Circuit Changer.--- In offices containing two sets of instruments on different circuits, it is often desirable to change them. A simple arrangement for this purpose is shown in fig. 31, in which the relays are represented at M and M' ; S and S' are the sounders or registers, E and E' are the local batteries. B is a simple button or circuit closer (62), having four connecting points, 1, 2, 3, 4. When the button is in the position 1, 2, as shown in the figure, the relay M works the sounder S, and the relay M' the Sounder S'. By changing the position of the button to 3, 4, S is worked by M' and S' by M. This simple arrangement is often very convenient in railway stations, where a sounder may be placed on one circuit and a register on the other, so that an operator who is unable to read by sound can instantly shift the register upon either line at pleasure.

TECHNICAL TERMS USED IN THE TELEGRAPH SERVICE.

87. Line.--- The wire or wires connecting one station with another.

Circuit.--- The wires, instruments, &c., through which the current passes from one pole of the battery to the other.

Metallic Circuit.--- A circuit in which a return wire is used in place of the earth.

Local Circuit.--- One which includes only the apparatus in an office, and is closed by a relay.

Local.--- The battery of a local circuit.

Loop.--- A wire going out and returning to the same point, as to a branch office, and forming part of a main circuit.

Binding Screws or Terminals.--- Screws attached to instruments for holding the connecting wires.

To Cross-connect Wires.--- To interchange them at an intermediate station, as in (sec) 117.

To put Wires straight.--- To restore the usual arrangement of wires and instruments.

To Ground a Wire, or put on Ground.--- To make a connection between the line wire and the earth.

To Open a Wire.--- To disconnect it so that no current can pass.

Reversed Batteries.--- Two batteries in the same circuit with like poles towards each other.

To Reverse a Battery.--- To place its opposite pole to the line ; or, in other words, interchange the ground and line wires at the poles of the battery.

Escape.--- The leakage of current from the line to the ground, caused by defective insulation and contact with partial conductors.

Cross.--- A metallic connection between two wires, arising from their coming in contact with each other, or from other causes.

Weather Cross.--- The leakage of current from one wire to another during rainy weather, owing to defective insulation.

On to Chapter 5

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