Tel′e-graph.
In a general sense, the word
telegraph includes all modes of communicating intelligence to a distance.
The modes may be classified as, —
1. Visible.
2. Audible.
3. Tangible.
1. Of the first are:—
a. Semaphores; moving or posturing arms (
Chappe's; Pasley's; Popham's).
b. Arrangement of disks, triangles (
Edgeworth's), lanterns, arbitrary characters (
Hook's).
c. Waving flags or torches (
Polybius) by day or night.
d. Various flags disposed on signal halyards (
Marine Code).
e. Colored lights.
f. Rockets varying in number or variety.
g. Intermittent flashes of light, from a mirror (
heliotrope), or a lantern.
h. Puffs of smoke, according to a code.
i. A moving pointer acting by electric impulse (
Wheatstone and Cooke's telegraph).
j. An adjustable column of liquid (
Percival's hydraulic telegraph).
k. The printing (
House, Hughes), dotting, and marking a traveling ribbon (
Morse), chemical paper (
Bain), and autographic (
Caselli, Bonelli, telegraphs, which imprint or impress visible characters on paper.
l. The electric telegraph, read by the passage of sparks to a conductor (
Bain).
2. Of the
audible may be enumerated:—
a. The clicking (
Morse apparatus) and its imitations.
b. A bell actuated by electric connections (
Bell). (
The telegraphic sounder.)
c. Mechanical, noisy devices; horns, gongs, drums, trumpets, whistles, clappers; some actuated by machinery, as alarms, especially for marine
fog-alarms. See siren.
d. Firing of guns; varied as to intervals or rapidity.
3. Among the
tangible may be stated:—
a. The Morse instrument read by the pulsations of the armature.
b. An electric telegraph read by the shock transmitted.
The subject of telegraphs is considered under various special titles, and detailed description of each at this place would involve repetition.
See under the following heads:—
| Acoustic telegraph. | Needle-telegraph. |
| Alphabet-telegraph. | Optical telegraph. |
| Annunciator. | Pantelegraph. |
| Astatic needle. | Paragrandine. |
| Autographic telegraph. | Paragrele. |
| Bank-alarm. | Pneumatic telegraph. |
| Battery. | Printing-telegraph. |
| Beacon. | Receiving-magnet. |
| Bell-telegraph. | Recording-telegraph. |
| Chemical-printing telegraph. | Reel-telegraph. |
| Circuit. | Relay-magnet. |
| Circuit-breaker. | Repeater. |
| Circuit-closer. | Resistance-box. |
| Commutator. | Resistance-coil. |
| Copying-telegraph. | Semaphore. |
| Current-regulator. | Signal. |
| Disk-telegraph. | Solar telegraph. |
| Duplex telegraph. | Sounder. |
| Earth-battery. | Submarine cable. |
| Earth-plate. | Submarine telegraph. |
| Electric bridge. | Switch. |
| Electric cable. | Symbol-printing telegraph. |
| Electro-chemical telegraph. | Telegraph-alarm. |
| Electro-magnetic telegraph. | Telegraph-cable. |
| Field-telegraph. | Telegraph-clock. |
| Fire-alarm telegraph. | Telegraph-dial. |
| Galvanic battery. | Telegraphic keyboard. |
| Galvanometer. | Telegraph-indicator. |
| Galvanometric multiplier. | Telegraph-key. |
| Heliotrope. | Telegraph-pole. |
| Hydraulic telegraph. | Telegraph-reel. |
| Indicator. | Telegraph-register. |
| Indicator-telegraph. | Telegraph tariff-indicator. |
| Insulator. | Telegraph-wire. |
| Line-wire. | Terminal. |
| Magneto-electric telegraph. | Type-setting telegraph. |
| Manipulator. | Writing-telegraph. |
| Mechanical telegraph. |
A brief summary of the principle and general
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method of operation of the electro-magnetic telegraph may not be out of place here.
The parts common to all the various forms are :—
1, a
battery for generating the electricity; 2, a
wire for conducting the current; 3, a
transmitting instrument, by which the circuit is made and broken to cause the intermittent impulses which make the signals; 4, a
receiving instrument, having a needle or armature which vibrates under the influence of the pulsations of the current.
Various forms of constant battery are used; one is required at each station for transmission, a pole of each being connected by the wire with the opposite pole of the other; the other poles are connected with the earth, which completes the circuit.
When so arranged, the batteries are said to be reversed.
When connection is made between the line wire and the battery at the transmitting station by means of key, lever, or other contrivance, the current flowing through the electro-magnetic coil at this station passes through the wire to another coil at the receiving station, by which it is intensified, regaining a portion of the force which it had lost by the resistance of the wire, and acquires sufficient power to operate the indicating or recording device, having done which it is conducted away to the earth.
A current may thus be transmitted to any distance by having
relay magnets at proper intervals to restore the strength of the current when it becomes enfeebled.
The receiving apparatus at any or all intermediate stations may be included in the circuit, so that the dispatch will be repeated at those points, or it may be thrown out of the circuit, so that it will be received only at the extreme end of the line.
When the transmitting apparatus is out of connection with the battery, the current passing from the pole of one battery to the opposite pole of the other is conducted away to the earth.
In some forms of telegraph, however, as the fire alarm, the circuit is continuous through the signaling instrument, the signals being made only when this circuit is broken.
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Arrangement of a terminal station. |
Fig. 6236 shows the arrangement of wires, batteries, and instruments for one of the terminal stations of a line.
The linewire
a first enters the lightning-arrester
b, and thence passes by the binding-screws
c d through the relay-coils
e to the key
f, main battery
g, and finally to the ground at
h. The local circuit commences at the + pole of the local battery
i, and through the platinum points of the relay by the binding-screws
j k, thence through the register or sounder coils
l, and back to the other pole of the battery.
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|
Arrangement of a way-station. |
Fig. 6237 is a plan of the instruments and connections at a way-station.
The line-wire
a passes through the lightningar-rester
b to the relay
e, key
f, back to the lightning-arrester, and thence to the next station.
The local circuit is arranged similarly to the preceding.
m is a
cut-out, which may be turned so as to directly connect the wires leading into and out of the office, allowing the line-current to pass without going through the office.
The
ground-switch n 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.
Various as are the forms of telegraphs, and the appliances used in their working, they may be divided into a few general classes, dependent on the manner in which their indications are made.
1. The
indicator or
needle telegraph, in which the signals are read from the deflections of a needle to the right or left of a median line; such is
Wheatstone and
Cooke's. The submarine telegraph, where the reflecting galvanometer of
Thomson is employed, is a variety of this class.
2. The
disk, dial, or “step-by-step” telegraph, having the letters of the alphabet arranged near the periphery of a disk, which is rotated
step by
step until each letter of a word is brought opposite an index.
The magneto-electric telegraph of this kind is very convenient for local purposes in cities, requiring no battery and no skill in manipulation.
3. The
recording telegraph, in which dots and dashes, representing the various letters and numbers, are marked by appropriate mechanism upon a strip of paper, as in the original
Morse telegraph.
The
electro-chemical telegraph of
Bain and others belongs to this class.
4. The
printing-telegraph, by which the letters are printed in ink upon a strip of paper, each from its appropriate key at the other end of the line.
Such are those of
Hughes,
House, and others.
5. The
autographic telegraph, which makes an exact facsimile of the message sent upon a prepared sheet of paper, as those of Caselli and Bonelli.
This is a peculiar modification of the electro-chemical telegraph.
6. The
automatic telegraph was invented by
Wheatstone in 1858.
In the modern automatic telegraphic process, telegrams, by a device founded on the idea of the Jacquard loom, may now be committed to a roll of paper, punched with holes instead of letters, and dispatched automatically.
The punched roll delivers its message to the instrument without attendance, and the message is printed at the other end of the line at the same time.
The advantage claimed for this system is a gain of time, and the liberty to send messages when the line is in the most favorable condition without the assistance of the operator.
A larger number and greater variety of ideas can be conveyed with greater exactness in fewer words in the
English language than in any other.
Its advantage over French or German, for instance, is said to be from 25 to 33 per cent.
The telegraphs of the world are estimated (
Hawkshaw) at 400,000 miles, at $500 per mile=$200,000,000.
The wire is now in all cases, except those of submarine cables, and sometimes in cities, conveyed upon poles.
In this country any kind of available wood is used, and in passing through forests the wire is frequently attached to living trees.
The poles seldom undergo any treatment for the purpose of preserving them.
In
England more pains is taken.
The timber generally employed is larch treated with sulphate of copper, or red fir creosoted by the Bethel process.
When not sulphated or creosoted, they are well seasoned and then painted, the but-ends being slightly charred to a foot above the ground line and tarred.
Each pole is provided with an earth-wire or conductor for conveying electricity escaping from the wires in wet weather to the earth.
These sometimes project above the tops of the poles, and serve as lightning-arresters.
The poles are also stayed by wire ropes connected to rods inserted in the ground, and in exposed positions double stays are employed.
On railway lines the Varley double-cone brown-ware insulator is employed, and on canals and highways the single-cone white-ware or porcelain insulator.
The wires are attached to the insulators at every post.
What is known as the
Britannia joint is exclusively employed for uniting the lengths of wire.
This is made by bending the ends of the two wires, placing them side by side for a distance of three inches, binding them together with No. 19 wire, and soldering them.
The
domestic or
district telegraph is designed to connect stores, private dwellings, or other houses in cities with a central station, where there is an observer to attend to the messages received.
The transmitting instrument is attached to the wall at a convenient place in the house, and connected by a wire leading to the roof, with a wire leading to the station; it is provided with three knobs or levers, one for sounding an alarm of fire, another for summoning a policeman, and a third for indicating that a messenger is wanted.
On either of these signals being transmitted, the requirement is at once indicated and attended to at the central office.
Fig. 6238 is a magneto-electric dial-telegraph adapted for railroads and private business purposes.
The electricity is generated by working the treadles which rotate the armatures of the magnets.
When the crank at the front of the machine is in upright position, as shown, the alarm from a distant station may be received; it is turned to the right when desired to transmit a message; in either diagonal position the circuit is
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broken, and when turned to the left the circuit is through the indicator only.
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Magneto-electric dial-telegraph. |
The automaticalarm telegraph is constructed for “thieves” and for “fire.”
In one case, the shutters, windows, and doors are so connected with an alarm in an office or the bedroom as to spring an alarm if any of the said objects are tampered with.
In the other case, thermostats are placed at all necessary points, and when at any of these the heat of the room or passage rises a degree or two above the point for which it is set, an electric contact is made and the alarm is sprung.
The following patents of
Watkins may be consulted: March 10, 1863; May 10, 1870; January 31, 1871 (six patents); March 28, 1871; October 27, 1874.
The system of
fire-alarm telegraphs, now so general in large American cities, is referred to on page 849, and the devices on page 1913, register; page 1918, repeater.
One important application of the telegraph is for determining differences of longitude.
For this science is largely indebted to
Dr. Locke, of
Cincinnati, by whom it was successfully practiced as far back as 1848.
Cambridge Observatory, Mass., has thus been brought into direct communication with
San Francisco by connecting the wire with the pendulum of a clock at
Cambridge, so that the main circuit is broken and instantly closed at each oscillation; the moment at which the circuit is broken is noted by the observer at
San Francisco, by a clock regulated to local time there, which, being compared with the local time at
Cambridge, gives the difference of longitude between the two places.
Many other stations, both in
Europe and
America, have been connected, and their longitudes determined in this way.
The moments of breaking and closing the circuit are practically the same at both places, the velocity with which the current traverses the wire being comparable only to that of light, though
Professor O. M. Mitchell determined that a minute though appreciable interval of time elapsed during its passage between two widely separated stations.
The telegraph was first used for military purposes during the Crimean war, 1854-55.
Its application for this purpose was greatly extended during our recent civil war, and has now become systematized in the armies of
Europe.
In the
French army the whole apparatus is carried in a covered carriage, divided into two compartments, one for an office, and the other containing a reel of wire.
In the office is a table for supporting the instrument, two accumulators, one for the batteries, and the other for the signal-bells, and a seat for two persons.
The reel is supported on its axis in the rear compartment, so that the wire unwinds as the carriage proceeds; it contains 3 kilometres (nearly 2 miles) of wire, and extra reel carriages are provided, each carrying 21 kilometres (over 13 miles) of wire on 7 reels.
The wire is composed of 4 copper threads twisted together, and protected by an insulating coating of fiber and india-rubber, so that when laid on the ground it will sustain the passage of vehicles without injury.
Poles are used in special cases.
Each telegraph-carriage is in charge of a sergeant, two corporals, and twelve men divided into three squads, the first of which goes ahead with the sergeant, traces the line, cuts a trench for the wire, or makes the poles; the second has charge of the reels, and makes the necessary splices, and the third lays the wire or fixes it on the poles.
In mountainous countries mules are substituted for the carriage; one carries a small tent, a tripod table, stake, the battery, and tools; another two reels of wire; a third draws a barrow which serves as a reel-frame, which is guided by two men, who carry it in difficult places.
See telegraph-carriage.
