Telegraph (Gr.τήλε, afar, and γράφειν, to write), an apparatus by which intelligence is communicated to a distance. It properly includes the various methods of signalling. The Roman generals, as described by Julius Africanus, spelled words by means of fires of different substances. The North American aborigines made use of regular stations over the western country for such signals; and the Indians of the northwest territory in this way made known the approach of Fremont, as he passed through their regions. Polybius describes two modes of telegraphing by means of torches; and Bishop "Wilkins, after giving an account of this in his book entitled " Mercury, or the Secret and Swift Messenger," describes a method of conversing at a distance with three lights or torches at night, which may be so used as to indicate the 24 necessary letters of the alphabet, these being divided into three classes of eight letters each, which are severally designated by one, two, or three torches, and the number of the letter by the number of times the torches are elevated or displayed.
Another method was also proposed by Bishop Wilkins, in which intelligible signals were conveyed by means of two lights attached to long poles; and for long distances he suggested the use of the then newly invented telescope. A variety of systems of telegraphic signals were brought into notice by different inventors in the 17th and 18th centuries, one of the earliest of which is that of Dr. Robert Hooke described in the " Philosophical Transactions" for 1684. It consisted of 24 symbols formed of blocks of wood, representing alphabetic characters, and six more formed of curved lines to be used as arbitrary signals. These were to be exposed in succession in an elevated frame at some conspicuous point, and, being observed at another station, were to be there repeated and sent forward to the next, and so on. At night torches or other lights were to be substituted for the wooden figures. The first working telegraph of much importance was that known as Chappe's, invented in 1792, which was brought into use during the wars of the French revolution. At the top of a tall post was attached a cross bar upon a pivot, so that it could be easily turned from a horizontal to an inclined position.
Each end of this cross bar carried a short arm, which could also be turned upon its pivot so as to stand in any position in relation to the bar. The movements were made by means of ropes which passed through the bar and down the post. This apparatus admitted of 256 distinct signals; but M. Chappe limited its use in great part to 16 signals, each one of which represented a letter of the abbreviated alphabet he had constructed. Chappe's method has been generally adopted, all the alleged improvements in it being of minor importance. Mr. R. Lovell Edgeworth about the same time brought before the public his plan of a telegraph, or as he called it telelograph or tellograph, by which the signals represented numbers, the meaning of which would be found in the dictionary prepared for this system. The signals were made by means of four pieces of wood, each one in the form of a long isosceles triangle, placed near together, each supported upon a pivot round which it could be turned in any direction. The movements of each were limited to eight, and indicated the first seven numerals and zero.
The first triangle or pointer represented units, the second tens, the third hundreds, and the fourth thousands, So that any number might be expressed that did not contain the figure 8 or 9. The admiralty telegraph proposed by Lord G. Murray was used in England from 1795 to 1816, when it gave place to that known as the semaphore (Gr. σήμα, a sign, and φέρειυ, to carry), which the French had adopted in 1803. This consisted of six conspicuous boards or shutters set in a frame, each of which could be turned upon its axis so as to present either its edge or its broad surface to the next station. The movements represented figures, and a series of numbers was indicated by their combinations. Some of these stood for the letters of the alphabet, and the others for arbitrary signals. The French semaphore (also known as signal posts) consisted of three or more arms attached by pivots to an upright post, admitting of motion in any direction, and indicating by their various positions either figures or letters. Many modifications of this apparatus were used.
For telegraphic communication at sea, flags of various colors have long been used. (See Signals, Naval.) In 1835 Gauss proposed to employ a small heliotrope or mirror for reflecting rays of light from the sun or an artificial source as a means of communicating signals. With a mirror so small that it may be carried in the waistcoat pocket, flashes of light may be clearly perceived for 12 m. or more, and, the mirror being gently moved on some established system, the appearance and disappearance of the flashes may indicate letters or words. By this device time can be saved, telescopes dispensed with, and the signals seen only by those for whom they are intended. Francis Galton, the African traveller, proposed a plan similar to this at a meeting of the royal geographical society, and described an optical arrangement he had devised by which the operator may know if the mirror is directed aright. Among the later publications upon the telegraphs adopted previous to the electric telegraph, are papers in the " Journal of the Society of Arts," vols, xxvi., xxxiv., xxxv., and xxxvi.; "A Treatise explanatory of a new System of Naval, Military, and Political Telegraphic Communications," etc, by John Macdonald (London, 1817); " Description of the Universal Telegraph for Day and Night Signals," by C. W. Pasley (London, 1823); and Edgeworth's "Essay on the Art of conveying Secret and Swift Intelligence," in the "Transactions of the Royal Irish Academy," vol. vi.
The advantage of all these methods of telegraphing, which may be described in general as the optical method, is, that they employ nature's great highways, which cost nothing; the disadvantages are, that the signals cannot record themselves, but require the constant attention of an observer, and can be used only for moderate distances and in favorable weather. Moreover, the expense is great compared with the meagre intelligence which is communicated. The semaphore between London and Portsmouth, 72 m., which could be used less than one fifth of the time, required an annual expenditure of £3,403. - Electric Telegeaph. The various kinds of electric telegraphs may be classified in two ways. In the first place, they differ in regard to the source from which the electricity is derived. In the present state of science, five independent sources of electricity are recognized: 1, friction; 2, chemical action; 3, magnetic induction; 4, heat; 5, physiological actions. The difficulty of insulation unfits frictional electricity for this work, except at short distances and in dry air. The fourth and fifth sources must be rejected as insufficient for practical use. Successful telegraphs must rely on electricity produced by chemical action or magnetic induction.
In the second place, electric telegraphs may be classified according to that one of the five special effects of electricity which is selected as the means of delivering the message when it arrives: 1. The statical attractions and repulsions would be impracticable except with frictional electricity. 2. The chemical effect of electricity is capable of making a visible sign and also a permanent record. 3. The magnetic effect is able to make a visible sign, as in the needle telegraph; it can also prick out its message in an artificial alphabet, or even print it in ordinary type. 4. The physiological effect can furnish a signal which may be felt. 5. The luminous and the calorific effects can be used for visible signals, but they cannot write or print. Of the manifold attempts at electric telegraphs, the best are now known to be those which employ the chemical or the magnetic effects. As the chemical telegraph works silently, an electro-magnet is required even in this case to attract the attention of the person who is to receive the message. The electro-magnetic telegraph can address the eye or the ear, and can also write or print. - Attempts have been made to prove that the electric telegraph was foreshadowed more than two centuries ago.
Prof. Mannoir puts in a claim for Dr. Odier on account of a letter which he wrote in 1773. But Addison, in No. 241 of the "Spectator," written in 1711, quotes from the Prolusiones Academical of Strada a description of essentially the same arrangement as that proposed by Dr. Odier. Moreover, Schwenter in 1636 had the same idea, but borrowed from a still earlier writer. How chimerical the scheme was in all these cases, and how unworthy of being regarded as an anticipation of the real discovery, will appear from the following brief description of the project: A magnetized needle is free to move over a graduated dial, the marks being the letters of the alphabet. One of these instruments stands in one place, and another in a remote city. If the needle of one is placed upon a particular letter, the needle of the other will move to the same letter by virtue of the magnetic forces. Du Fay, Winckler, Lemonnier, Gray, and Desaguliers made experiments, which showed that the effect of electricity could be transmitted to a distance.
The discovery made by Dr. Watson in 1747, that electricity would force its way through considerable lengths of wire, and that earth and water could take the place of wire in completing the circuit, furnishes the first facts of any significance in the history of the electric telegraph. He transmitted shocks across the Thames and the New river, in one instance at Shooter's Hill the circuit being composed of about 2 m. of wire and 2 m. of the earth; and ' he supported his wires upon posts. Franklin made similar experiments across the Schuylkill river in 1748, and De Luc afterward on the lake of Geneva. Signals were communicated by means of the electric shock from one apartment to another by Lesage at Geneva in 1774, and by Lomond in France in 1787 by the divergence of pith balls on some concerted plan; and in 1794 Reizen of Germany employed the electric spark for telegraphing, making use of interrupted strips of tin foil, so arranged that the form of the letter or figure was exhibited by the sparks. He employed 36 wires from one station to another, each one of them communicating with one of the letters or figures, and each one connecting with a return wire, thus making 72 in all.
This plan is described in vol. ix. of Voigt's Magazin. Cavallo in his "Treatise on Electricity " (1795) suggests the explosion of gunpowder to call attention, and then the transmission of signals by a succession of sparks at intervals and in numbers according to the system agreed upon. Don Francisco Salva of Madrid and Sr. Betancourt constructed similar telegraphs at Madrid in 1797 and 1798, one of them extending between Madrid and Aran-juez, about 26 m. (Voigt's Magazin, vol. xi.) Salva communicated his plans to the royal academy of sciences at Barcelona, and according to the journals of 1797 they were highly commended by the minister of state. Salva appears to have had a clear idea of the practicability of electric communication even beneath the sea, and in the last of his memoirs he proposed to substitute the voltaic pile for the electrical machine. Other attempts to employ frictional electricity were made by Francis Ronalds at Hammersmith, England, in 181G, on a line of 8 m.; and in 1827 by Harrison G. Dyar at the race course on Long Island, N. Y., on a line of 2 m. The latter made use of iron wire, glass insulators, and wooden posts, and employed for signalling the chemical power of the electric current to change the color of litmus paper.
Ronalds introduced the plan of employing a clock at each of the two stations, both of them running together exactly, and each bringing into view one after the other the letters of the alphabet arranged upon a disk which revolved behind a screen with an opening for one letter. Each clock was provided with two pith balls connected with an electrical machine at the other station; and their divergence called the attention of the other operator to the letter then in view. The voltaic pile, discovered in 1800, furnished in its continuous current a more promising agent for transmitting 'intelligence than the sudden and transient discharge of the friction machine. Sommering began his experiments in 1809, and devised a plan of telegraphing which was as perfect as was practicable at that time. He used 35 wires, terminating in gold points, set up vertically on a horizontal line at the bottom of a glass reservoir of water. In the other direction these wires, brought together in a tube, extended to the other station, where they again diverged, terminating in brass plates attached to a horizontal wooden bar.
The plates at one end and the points at the other were marked with corresponding letters, and whenever a momentary current was sent through any two of the plates, hydrogen was evolved at one of the gold points and oxygen at another, and thus two letters were indicated. Sommering found that the addition of 2,000 ft. of wire produced little or no sensible additional resistance, and that voltaic action was instantaneously developed at least for the distance of 3,000 ft. In 1810 Prof. Coxe of Pennsylvania suggested a method of telegraphing by means of the chemical effect of electricity. Schweigger described an improvement upon Sominering's arrangement, by which all the wires could be dispensed with except two. The batteries then known were insufficient for the transmission of currents through great distances, and besides were deficient in sustaining power; therefore no further progress was made in perfecting the electric telegraph until the principles of electro-magnetism had been developed. (See Electro-Magnetism.) In 1819 Oersted discovered the power which the current possesses of deflecting a magnetized needle out of the magnetic meridian. In 1820 Schweigger added the multiplier.
This was followed by Arago's discovery in the same year that a steel rod was magnetized when placed across a wire which was carrying a current. Ampere immediately substituted a helix for a straight wire. In 1825 Sturgeon used soft iron in place of steel, and the electromagnet was born. Between 1828 and 1830 Prof. Henry of Princeton, N. J., made great improvements in the construction of electromagnets by covering the wire and winding the coil compactly. In 1831 he devised an instrument which is essentially the same as the Morse register. Moreover, Ohm in 1827, and Fechner in 1831, published the results of their theoretical investigations into the laws of the voltaic current, which shed a flood of light on the subject of telegraphing at long distances. If these investigations had but little practical effect, it was because they were not generally known until the same results had been at a later day worked out empirically. Equally important was the invention of the constant battery by Daniell in 1836, and of various other constant batteries which have been contrived since that time. The discovery of magneto-electricity by Faraday in 1831, and the introduction at a much later date of the induction coil, supplied constant sources of intense electricity adapted to the telegraph.
Within a year after Oersted's discovery Ampere pointed out its applicability to telegraphic signals. His plan contemplated at least 30 needles and GO independent wires. In 1828 Ritchie gave an experimental illustration of such a device before the royal institution of London. In 1829 Fechner had a similar project for uniting Leipsic and Dresden by means of 24 sets of underground wires. In 1832 Schilling exhibited to the emperor Nicholas of Russia a needle telegraph in operation on a small scale. He used a needle provided with a multiplier of insulated wire for each letter or number to be indicated. The several wires were brought together beyond the multipliers into one cord, and thence passed to the first station. Eventually he succeeded in reducing the number of needles to one. He also introduced an alarum at the commencement of the passage of the current by causing a solid body to fall, on the same principle as had been already recommended by Prof. Henry in his lectures. These experiments were interrupted by his death, and the steps made were lost, without even a very accurate account of the results being preserved.
The next experiments of importance were those of Gauss and Weber of Gottingen in 1833 and 1834. They employed first voltaic electricity excited by numerous small elements, and afterward a magneto-electric machine to transmit signals from 9,000 to 15,000 ft. They caused a magnetic bar to be deflected to one side or the other, and interpreted its repeated movements into the letters of the alphabet. The vibrations of the magnet were checked by a damper, or by the use of currents alternating in direction. This telegraph was of practical value in comparing clocks and for other purposes. Gauss stimulated his pupil Steinheil to a bolder undertaking, in which he was assisted by the Bavarian government. Stein-heil's telegraph, completed in 1837, extended 12 m., employed but a single wire, and made use of the earth to complete the circuit. The signals were sounds produced upon a series of bells of different tones, which soon became intelligible to a cultivated ear; and the same deflections of the needle that caused the sounds were also made to trace with ink lines and dots upon a ribbon of paper moved at a uniform rate, the alphabet having a remote resemblance to that invented by Swaim in 1829. Steinleil used a magneto-electric machine, but with the magnets stationary and the multiplying coils revolving close to them. - Morse's telegraph, which is generally recognized in all parts of the world as the most efficient and simple, was first publicly exhibited in the university of New York in 1837. It had been gradually brought to a working condition by experiments and contrivances devised by the inventor since 1832, with the assistance of L. D. Gale and George and Alfred Vail. In October, 1837, Prof.* Morse filed a caveat in the patent office to secure his invention; and he obtained the patent in 1840, covering the improvements he had in the mean time made in the apparatus.
The telegraph was first brought into practical use, May 27, 1844, between Washington and Baltimore. An insulated wire buried in a lead pipe underground was first tried, and failing was replaced with one on posts. The power was derived from a voltaic battery, and an electromagnet was employed at the receiving station for developing its effects. When the current flowed, this magnet attracted an armature, by which, according to the duration of the current, dots or lines were marked upon a moving slip of paper with a pen or pencil. The apparatus furnished a simple and effective means of recording signals, which by the needle telegraph were only evanescent. The apparatus was improved by the substitution of a sharp point for the pen or pencil, which is attached to one end of a lever, at the other end of which is the movable armature. The following illustrations exhibit the several parts of the Morse instrument as now in use. The key, fig. 1, consists of a brass lever L, swung on pivots, and having on one end a button. When this button is pressed down, two platinum wires, a and b, are brought into contact, thus closing the circuit; when the pressure is removed, a spring lifts the lever, separates the wires, and breaks the circuit.
When the message is sent the operator permanently closes the circuit by springing to the left the lever S, which brings into contact the duplicate platinum wires a' b'. The relay magnet, fig. 2, is an electro-magnet wound with a long fine wire, which is introduced into the main line and becomes a part of the great conductor from city to city. When the key breaks and closes the circuit, the relay receives the voltaic current and becomes magnetized and demagnetized. The delicately poised lever L, having the armature of the magnet attached to it, vibrates forward and backward, bringing together the two platinum wires a b, and thus breaking and closing a secondary or local circuit, embracing a local battery and a strong electro-magnet. This magnet perforins various work, such as embossing or printing paper, or the liberation of machinery for the production of sounds. A screw B is used to move the magnet coils backward and forward so as to adjust the general magnetic power, and a spring S retracts the armature after magnetic attraction has drawn it forward.
The sounder, fig. 3, is an electro-magnet used in the local circuit.
Fig. 1. - Key.
Fig. 2. - Relay.
The armature, A, is attracted by the electromagnet M, causing the lever L to vibrate between the screws S S, which are so adjusted as to limit the vibrations. The backward and forward blows thus given, some of which are short and some long, correspond to the dots and dashes of the Morse alphabet. This is now more generally used than the Morse register or recording instrument, as experience has proved that fewer errors are made by the ear than by the eye. The Morse register, fig. 4, has also the electro-magnet M, the armature A, the lever L, and the adjusting screws S S; but instead of producing sounds merely, the lever L embosses on a fillet of paper P dots and dashes in precise accordance with the movements of the key and relay. The paper is carried between two rollers, moved by clockwork, in one of which is a groove, into which the steel point presses the paper. When successive blows are struck on the key, closing and opening the circuit quickly, corresponding dots appear on the paper; but if the key be pressed down for a longer or shorter time, keeping the circuit closed, a continuous line of any desired length may be produced on the paper.
The signs for the letters of the English alphabet (which are variously modified to adapt them to other alphabets), and for the numerals and punctuation marks, are as follows, those most used being the simplest:
Fig. 3. - Sounder.
Fig. 4. - Register.
The slightness of the difference, which cannot he avoided, between some of the signs, as in the C and S, I and O, L and T, etc, exposes to mistakes, which in case of writing in cipher cannot be corrected, and not always when the message is perfectly understood by the operator who sends it. Thus a merchant telegraphed from New Orleans to his correspondent in New York to protect a certain bill of exchange; the word "protect" was read as "protest," and involved serious consequences. - What is known as the English telegraph is the result of the investigations and inventions of William F. Cooke, whose attention was directed to this subject in March, 1836, when a student at Heidelberg, by witnessing an experiment performed by Prof. Moncke of causing the deflection of a magnetic needle by the electric current. In July of that year Cooke produced an experimental instrument, which he not long afterward took to England and sought to introduce on the Liverpool and Manchester railway. He there became associated with Prof. Wheatstone, and the two united their labors to perfect the instrument.
The first patent for an electric telegraph was issued to them on June 12, 1837. They employed five magnetic needles and coils, and either five or six wires, with a peculiar keyboard invented by "Wheatstone, upon which were arranged the letters, and these were designated in turn as any two of the needles arranged across the centre of the board pointed to one and another of them. The apparatus underwent various modifications in the hands of its inventors, and was much simplified by the use of only two needles, and finally of only one, different letters being designated by the deflection of the needle to the right or to the left one or more times in either or both directions. The swinging of the needle is checked by small pins fixed on the dial, so that the motions are rendered precise and clear. In this single-needle telegraph, each instrument has its own battery and wire. In case of accident to the wire of one instrument, that of the other serves to keep up the communication. With each apparatus was formerly connected an alarum bell, the clapper of which was moved by a weight or spring connected with clockwork, which was released by means of an electro-magnet. This is now generally abandoned, the sound made by the click of the needle against the pins being found sufficient.
Wheatstone introduced one very important feature in his electric telegraph, which is a local battery for working the alarum. It is brought into action by the deflection of a magnetic needle, the ends of which are thus placed in contact with the two wires of the second battery, and so close its circuit. The double-needle telegraph is often used upon the railways of Great Britain, each needle having its own wire. The different signs are made by the movements of one or both of the needles. The needles upon the dial are moved by the messages sent as well as by those received, so that each operator may see the signals he makes. In these needle telegraphs no record is made of the message by the instrument itself; the operator observes the signs, and notes them upon paper as they succeed each other. With the English double-needle telegraph, employing two wires and two batteries and other apparatus at each station, an expert operator can send as many as 150 letters a minute; but this is more than can be correctly read, the limit of which is about 100 letters a minute, and in actual practice the number is somewhat less than this, or from 17 to 24 words a minute.
Operators accustomed to the work do not require the lettered dial for reading the movements of the needle. - Of the numerous telegraphic inventions that soon succeeded those already named, Alexander Bain's are particularly worthy of notice. He was engaged in England as early as 1840 in producing a printing telegraph, and in 1846 patented what is known as an electrochemical and registering telegraph, the principle of which had been first applied to the purpose by Dyar in this country in 1827, and by Edward Davy in England in 1838. Mr. Bain brought his new telegraph to the United States in 1849, and it was brought into use on several important lines; but after a lawsuit involving chiefly the use of the local circuit, the Morse interests forced a consolidation, and the Bain system had afterward but a limited use. The local circuit gave to the Morse system its great importance and value. On long lines of telegraph the wire offers such resistance to the passage of the current that its presence is detected only by delicate instruments, which however are capable of vibrating levers whose office is to open and close secondary or local circuits; and these circuits being short, unlimited magnetic power may be obtained for recording or producing sounds.
The Bain telegraph was essentially the same as that now called the " automatic." The revival of the system is due to recent discoveries in the arrangement of circuits, by which the rapidity of recorded electrical impulses through very long conductors has been made almost infinite. For recording, dots and lines are produced on chemically prepared paper, which is moved while damp at a uniform rate over a metallic roller; a fine wire, through which the line current passes, rests on the surface of the paper and blackens it by decomposing the chemical. The current was formerly sent over the line by the key, as in the Morse system; but to call attention a bell was used, and this usually required the local circuit. Mr. Bain had at this time fully developed a plan for transmitting signals with a rapidity far greater than could be effected with the key, and this plan is the same as that now used in the revived system. In place of the key a fillet of paper . was punched with lines and dots representing a message. This was passed over a metallic roller with great speed, and a fine wire which rested on the paper entered each hole as it moved and completed the circuit through the roller.
The receiving machine was made to run at a speed corresponding with that of the transmitting machine, and the perforated dots and dashes were reproduced in blackened dots and dashes. The advantage of this system lies in the transmission of long messages, which are received and prepared by several operators, at great speed. Until recently this speed could be obtained only on short circuits, the marks on long circuits running into each other and becoming illegible. Later improvements have enabled messages to be sent from Brussels to Ostend and back at the rate of 450 words a minute; and the American instruments have sent between Washington and New York 5,250 letters a minute, requiring 10 perforators to feed it, 10 copyists, and two operators. - Facsimile Telegraphs. Electric copying or facsimile telegraphs are modifications of the automatic chemical. They originated with F. C. Bakewell of England in 1850, and have been improved by Caselli, Bonelli, and others. In them the message is written with a pen dipped in varnish upon a sheet of tin foil, which is then laid around a metallic cylinder, corresponding precisely in its size, rate of revolution, and longitudinal movement, with another cylinder at the receiving station, which is covered with chemically prepared paper and provided with a pointer like that of the Bain chemical telegraph.
These cylinders being set in motion at the same instant, the point of the registering apparatus makes a continuous colored line, running round the cylinder in a close spiral so long as the metal style at the other station presses upon the tin foil; but as this passes over the lines of varnish a break in the circuit occurs, causing an interruption of the colored line at the other station. The blank spaces thus produced will be found when the lines have been drawn over the whole paper to be a facsimile of those written in varnish upon the tin foil. The lines, though drawn as spirals upon the cylinder, appear as parallels when the paper is taken off. About 10 revolutions of the cylinder, making as many parallel lines, are sufficient to complete one line of writing; a cylinder 6 in. in diameter affords sufficient length for about 100 letters of the alphabet in one line; and as the rate of revolution is not less than 30 in a minute, 300 letters or more may be transmitted in this period. A message in cipher can be sent by this method without risk of error, and even invisible messages written in colorless varnish may be received and impressed in invisible characters upon prepared paper, to be afterward brought out by chemical means; thus, if the paper be moistened with diluted acid alone, no visible mark is left upon it until it is brushed over with a solution of prussiate of potash, when the lines appear in their blue color.
Great improvements in the autographic telegraph have been made by Caselli, who has succeeded in making dark letters upon a white ground. His instruments have been used on some of the French lines since 1862. - Printing Telegraphs. Royal E. House, of Vermont, received a patent in 1848 for an admirable long-line printing apparatus, which was first used in 1847, sending messages in Roman capitals between Cincinnati and Jef-fersonville, Ind., 150 m. The necessity of avoiding the peculiar features upon which other telegraphic systems were established, in order to give to it a distinctive and patentable character, added greatly to the difficulties of the undertaking, which after nearly six years of labor were overcome by the ingenuity and perseverance of Mr. House. The apparatus is very complicated, and little more can be attempted than to state its great powers of execution and its perfect accuracy. The mechanical movements of this machine are set in action by hand labor applied to a crank, which works an air pump for supplying a current of condensed air, which under the control of the electric current carries forward the movements of the composing and printing apparatus, so that each letter may be printed at the exact instant that it is struck upon the keyboard of the instrument.
This keyboard, which resembles that of a piano, is connected with the electric current, and as the keys are struck the circuit is opened and closed with the movements of a circuit wheel which controls the movements of the typo wheel. A complete revolution of the circuit wheel, coming round again to the same letter, breaks and closes the circuit 28 times, and other letters a less number according to their arrangement on the type wheel. The printing apparatus is quite distinct from the circuit, but the composing apparatus forms a part of it. The impression of the letter is produced by a blackened ribbon being pressed against the paper by the type. From the voltaic battery of one station, the current passes along the wire to the next station, then through the coil of an axial magnet to the insulated iron frame of the composing machine, and thence to a circuit wheel revolving in this frame. Through a spring that rubs on the edge of this wheel it passes into the return wire, and through another battery back to the first station to pursue the same course through the composing machine and magnet there, and all others upon the line.
In sending a message, the operator sets his machine in motion and gives a signal by breaks of the circuit, repeated a different number of times for different offices on the same wire. As. this is heard by the operator at the receiving station, he sets his machine in motion, and the type wheel at its starting point, and signals back that he is ready. No further attention is required on his part, while the machine goes on, printing the communication in Roman capitals upon the long strip of paper regularly supplied to the type wheel. From 250 to 2G0 letters as a maximum can be accurately printed every minute, and over 3,000 words an hour of press news, partly abbreviated, have been sent over the wires with a single instrument. The House printer was the parent of many others working on the same principle, the "step by step" movement, in which each break or close of circuit allows a tooth of an escape wheel to pass; a type wheel being on the same shaft, a new letter appears for each tooth that escapes. - On May 20, 1856, Mr. Hughes patented a telegraph, in which the feat of printing a letter with every impulse or wave of the electric current was accomplished.
In the other telegraphs, as already described, several impulses produced by successive makes or breaks of the circuit are required to form a single letter; this in House's telegraph varies up to 14 breaks, the maximum required for repeating the same letter, and averages about 7 impulses; and in the Morse system the average is about 3½ impulses, those which make lines being of longer duration than those which make dots. The saving of time thus effected by the Hughes instrument is of great importance, especially on long lines in which an appreciable amount of time is expended in the passage of the current. In long lines of submarine telegraphs, as will be noticed below, a greatly increased resistance is experienced in charging the wires with the electric current, and the impulses necessarily succeed each other with extreme slowness and diminution of force. The type wheel in the Hughes system is provided with 28 types; it is kept in rapid revolution during the whole time of operating, and is so perfect in its movement that, though the revolutions may be from 100 to 140 a minute, the variations of two machines at different stations do not exceed 1/20 of a second in several hours.
At the instant one of the 28 keys is depressed, the current entering the magnet at the distant station causes the strip of paper to be brought against the type opposite to it at the time, and receive the impression in ink while this is rapidly carried round with the wheel. The operator can send an average of two impulses with each revolution of the type wheel, thus making the capacity of the instrument 200 letters or 40 words a minute, and the maximum is much above this. The regulators or governors of the clockwork which carries the type wheels at the different stations are springs of the same musical tone, which consequently vibrate the same number of times a second, and which control by their vibrations the escapement of the apparatus. The power of the electric current required is reduced in a wonderful degree by the combination of the natural magnet and the electromagnet, making only so much electricity necessary as will neutralize the magnetism in the natural magnet by causing magnetism of an opposite polarity to be created in the poles of the electro-magnet. This extreme delicacy, however, renders the telegraph liable to be interrupted by atmospheric electricity, such as is developed previous to and during the continuance of the aurora borealis.
It is asserted that this instrument can work upon a longer line without the aid of repeaters than any other, and this with an extraordinarily low battery power. - In the winter of 1858 a new instrument was perfected by G. M. Phelps of Troy, combining the most valuable portions of both the House and Hughes patents, which has been introduced with great success on nearly all the lines formerly using those inventions. This has been termed the " combination" instrument, and has the advantage of being able to work through a much longer circuit than the House machine, with a smaller battery, as well as of being much simpler. The keyboard and transmitting machinery of this instrument are precisely like those of Hughes, as is also the printing apparatus, with the exception of the electro-magnet, which is of the ordinary form, and operates upon the type wheel through the medium of compressed air as in the House machine. The vibrating spring used by Hughes as a governor is superseded in the combination instrument by a most ingenious electro-magnetic governor, the invention of Mr. Phelps. It consists of a hollow iron drum, geared to the transmitting cylinder and type wheel of the instrument and moving with them, but much faster.
If the machinery has a tendency to revolve too rapidly, the increased centrifugal force, acting upon a detached section of the drum, actuates a series of levers inside, by which a spring is raised, closing the circuit of a local battery through an electro-magnet. A friction brake, which is applied to the revolving drum by the attraction of this magnet, instantly reduces the speed to the required limits, when the local circuit is again broken. The combination instrument is considered the most perfect printing telegraph for long lines yet produced. The Anders printing telegraph, patented in 1871, and worked by magneto-electricity, is designed for private lines, though capable of operating over distances of 45 m. - Dial Telegraphs. In these instruments the step by step movement is generally employed, but the escape wheel does not carry a type wheel, nor do the printing accessories enter into their construction. A light needle is carried around with the escape wheel and points at the successive letters. They are thus visual and not recording telegraphs. In England, the " Magnetic Telegraph Company "employed magneto-electricity, thus dispensing with voltaic batteries, the use of which involves much care and expense.
The apparatus is remarkably compact, without clockwork or complicated movements such as are common in other telegraphs. Though used double, with two sets of magnets, with a wire from each connecting with two needles upon the dial at the opposite station, the whole apparatus, including the tablet or dial, occupies but a few inches of space, and is always ready for instant use, however long it may have remained inactive. The magnets, of horse-shoe form, about 12 in number for each set, are 15 in. long and 1½ in. broad. They are laid one upon another in two piles near together, and fastened down to the table by screws. Opposite the ends of each pile, placed upon a rotating axis, is the soft iron armature, consisting of two cylinders wound around with long coils of fine copper wire covered with cotton. The wire of the two coils is connected together, and one end of each passes in a spiral through the axle to the platform upon which the apparatus rests. One end is thence carried into the earth, and the other goes to the electro-magnet of its own dial, thence to the distant station, and through the instrument there into the earth. The same arrangement is repeated with the other set.
The axis of each armature extends toward the operator, and is provided with a crank handle by which each is turned to generate the electric current. The effect is seen in the movement of the two needles placed upon the dial over the magnets. It is asserted that this telegraph is worked with the greatest economy, that it cannot be disturbed by electric storms in the atmosphere, and that its average celerity has been found to be 27⅓ words a minute, with a maximum of 37 1/6. In the United States the dial telegraph is largely used where operators are supposed to have but moderate skill, as in police and private telegraphy. The instruments are worked with a small battery. Primary signals are given by bells, and the letters are pointed out by the revolving needle. The transmitting part is the usual circuit wheel, which breaks and closes the circuit and produces the rotating movement of the needle of the distant instrument. This circuit wheel is arrested, in the process of telegraphing, by a series of pins, one of which is placed opposite each letter.
When the A pin of the transmitter is pressed down, the circuit wheel is arrested just as it has caused the needle of the other instrument to rotate to A. - Construction of Telegraph Lines. Telegraph wires are usually carried over the surface of the country upon poles standing from 25 to 30 ft. above the ground, and placed from 80 to 100 yards apart. As poles are objectionable in cities, many plans have been devised for carrying the wires under ground. In London they are covered with gutta percha and tape and put into lead or iron pipes, which are laid under the sidewalk, or into creosoted wooden troughs filled with bitumen, which are buried in trenches beside the roadway. In Paris the wires are carried in lead pipes through the sewers and catacombs. The "American Compound Wire Company " have introduced a wire, consisting of a core of steel and envelope of copper, with a tinned surface, which, with equal conductivity and greater strength, weighs less and requires fewer supports. Another insulated wire, called "kerite wire," the invention of Mr. A. G. Day of New York, has a covering compounded of rubber and hydrocarbons. It is said to offer great resistance to oxidation, and that it may be exposed in the air or buried in the earth for years without serious injury.
As, with batteries of the same intensity, the conductivity increases with the cross section of the wire, large wires are to be preferred to small ones upon long circuits. In working direct, a distance of over 400 or 500 m., the line is usually divided at some intermedi- . ate point into two distinct circuits, which are connected by means of a "repeater." If the circuit be broken on either side of the repeater, it will break the circuit on the other side also. The combined circuits can thus be operated from either end as if they were one continuous wire, while the current of each battery has to pass only half the distance between the terminal stations. A line can thus be extended indefinitely. Copper wire is a much better conductor than one of iron of the same size, and will carry the current from five to six times as far; but want of strength, and frequent breakage from its greater expansion and contraction by the changes of temperature, prevent its use except on important submarine lines. The insulation of the wires upon the posts is a matter of much importance, and is not easily effected, for any non-conductor interposed between the wire and the post becomes a conductor when its surface is wet with rain.
Glass knobs with grooves around them for securing the wire have been made in a great variety of forms, and secured to the posts, or to the cross bars where there are several wires, by pins of wood or iron. A great improvement upon this is a glass cap exactly fitting over a wooden pin 1¼ in. in diameter, and having an outer covering of wood, saturated like the pin with coal tar and pitch, to which the wire is fastened, and which, projecting below and entirely covering the glass, keeps it dry and makes the insulation complete. Batchelder's vulcanite insulators have been very extensively applied in the United States. In Europe, insulators of earthenware and porcelain are used. In forests the wires should be allowed to pass loosely through the supports, so that in case of a tree falling upon them they need not be broken; but in an open country they are usually fastened to each post. On some telegraph lines in Europe and in Asia, the wires, instead of being supported upon poles, are buried beneath the ground. Their first cost is always heavy, and many of them have soon proved failures through imperfection in the insulation.
The wires are best insulated by coating them with gutta percha, and they are protected from injury by laying them in pipes of lead or of earthenware, or in wooden boxes preserved by saturating the wood with a solution of sulphate of copper or chloride of zinc. Some of these lines have worked perfectly for many years, but when they fail it is a matter of great expense and difficulty to discover their defective points. - In the extent of its telegraphic lines the United States has exceeded every other country. In 18(50 it was estimated that there were over 50,000 m. in operation, and at present there is not less than 150,000 m. of wire. In the aggregate, 700,000 m. of wire spread their network over the earth for telegraphic purposes, including lines in Australia, India, China, and Siberia. Russia is engaged in extending an important line from Moscow to the Pacific so as to connect eastern Asia with Europe, and possibly hereafter with America by the way of Behring strait. This line was completed to Perm, on the borders of Siberia, and from that place across the Ural mountains to Omsk on the Irtish, in 1861. Thence it is continued to Tomsk, and S. E. to Irkutsk; next it passes the Altai mountains to Kiakhta on the Chinese frontier, thence to Cheta on the Amoor, and thence to Nertchinsk. From Orum, or some other point on the Amoor, one branch Mill go down the river and another southward to a Russian port on the Japan sea.
The project of extending these lines to Beh-ring's strait, and across to Alaska, Oregon, and California, which had been partially carried into effect on the American side, was abandoned after the Atlantic cables had been brought into working condition. - Submarine Telegraphs. The idea of a submarine telegraph appears to have been conceived by several of the earlier electricians. Salva is said to have proposed one as early as 1797 between Barcelona and Palma in the island of Majorca. Experiments were made in India by Dr. O'Shaughnessy in 1839 with this object, and he insulated his wires by covering them with tarred yarn, enclosing them in split rattan, and covering this again with tarred yarn. Wheatstone in 1840 gave it as his opinion before a committee of the house of commons that a submarine communication between England and France was practicable. Morse, on Oct. 18, 1842, laid a copper wire, insulated by means of a hempen strand coated with tar, pitch, and India rubber, from Governor's island to the Battery in New York, and the next morning was beginning to receive communications through it, when the wire was caught in the anchor of a vessel getting under way, and being hauled on board was stolen by the sailors.
Samuel Colt laid a submarine cable in 1843 from Coney island and Fire island, at the mouth of New York harbor, up to the city, and operated it successfully. The first submarine telegraph wire laid in Europe was across the Rhine from Deutz to Cologne, about half a mile; it was insulated with gutta percha, and laid by Lieut. Siemens of the royal Prussian artillery. This appears to have been the first application of gutta percha to this purpose, the substance about that time first beginning to attract attention. In 1850 a copper wire covered with gutta percha was laid between Dover and Calais by Brett, but its success was shortlived. The next year it was replaced by a cable of four wires, which has given complete satisfaction. In 1853 six cables (the longest of which, between England and Scotland, was about 100 m.) were successfully laid. In 1854 five other cables went into operation, the longest being only about 64 m. In 1855-'6 two more were added, that from Varna to Constantinople being about 160 m.
Besides these, two cables had been laid in deeper waters: one from Newfoundland to Cape Breton, and another from Spezia to Corsica. The grand attempts to connect the European and American continents by a cable across the Atlantic, commenced in 1857 and perfected Aug. 5, 1858, have been noticed in the article Field, Cyrus West. Before these were undertaken great encouragement was given to the enterprise by the successful experiments made on Oct. 9, 1856, in transmitting distinct signals at the rate of 210, 241, and even 270 a minute through a number of connected coils of wires, insulated with gutta percha, and making a total length of about 2,000 m., increased to a virtual circuit of 2,300 m. by the interposition of fine wires at the joinings of the coils. The wires were excited by the magneto-electric coils of "Whitehouse, and the signals were received upon the ordinary recording apparatus of Morse. But a great difference was afterward experienced in the working of the wires when submerged. Before the cable was laid it was ascertained that insulated wires acquire a new character when submerged, and that instead of transmitting the current as simple conductors, they are of the nature of the Ley-den jar, the gutta percha corresponding to the glass, the inner wire to the interior coating, and the iron covering or the water itself to the exterior coating; and that consequently the cable must be charged throughout the entire length before any current is produced.
Among other interesting phenomena, it was observed that the voltaic current is not transmitted so rapidly through such a conductor as the magneto-electric current; and that alternating positive and negative signals are transmitted more rapidly than successive signals of the same character. After being laid, the wires were first worked by the Ruhm-korff induction coils and a Smee battery, and afterward by a Daniell battery; but the current was for the most part so weak as scarcely to operate the most delicate relay, though susceptible to a current that can hardly be perceived on the tongue. The effect was indicated at the Newfoundland station by the deflection of a delicate galvanometer, and at Valentia in Ireland by that of the reflecting galvanometer of Thomson, in which a delicate magnet carries a small mirror from which a beam of light is reflected. This ray being thrown upon a surface at some distance, a movement of the magnet that is not directly perceptible may be even measured upon a graduated scale. The transmitted current was, much of the time that the cable continued in action, so weak that every expedient of this kind was necessary to render the signals perceptible.
From the first there was a defect in the part of the cable laid toward the Irish shore, which caused a temporary interruption of communications between the ships. Between Aug. 13 and Sept. 1 there were 129 messages of 1,474 words sent from Valentia to Newfoundland, and 271 of 2,885 words in the other direction. The message from Queen Victoria to the president of the United States, 99 words, occupied in its transmission 67 minutes. The rate of reception was very variable, the signals being often unintelligible and requiring several repetitions. Electricians were sent to Valentia, and the most powerful batteries, as well as the great magneto-electric machine of W. T. Henley, were applied to test the condition of the cable. The power thus employed was more than 1,000 times what would be required in an ordinarily well insulated conductor to give perfect signals to the mirror galvanometer. To the end of the cable a voltaic battery was connected by one of its poles, a galvanometer was placed in the circuit, the other pole was connected with the earth, and by these means the location of the defect in the cable was ascertained; but all attempts to recover it were unsuccessful.
The cost of the cable was as follows : for 2,500 m. at $485 per mile, $1,212,500; for 10 m. at $1,250 per mile, $12,500; and for 25 m. shore ends at the same price, $31,250; making altogether $1,256,250. The expenditures of the company up to Dec. 1, 1858, had amounted to $1,834,500. - After the failure of this great enterprise attention was directed to the practicability of extending a cable across the Atlantic from Labrador to Scotland, by way of Greenland, Iceland, and the Faroe islands. The route is about 1,800 m. long, and presents no continuous length of submarine cable for a greater distance than that between Labrador and Greenland, which is about 600 m. Mr. T. P. Shaffner, of the United States, had obtained in 1854 from the king of Denmark a concession of exclusive rights in Greenland, Iceland, and the Faroe islands for this purpose. He sailed from Boston, Aug. 29, 1859, and made the preliminary surveys at his own expense, and he induced the British government to send a steam vessel to take the deep-sea soundings; but the project was not consummated.
The failure of other deep-sea cables, as that between Sardinia, Malta, and Corfu, and the long cable from the Red sea to India, increased the distrust occasioned by the failure of the Atlantic cable of 1858. The result was that a committee, consisting of the most eminent electrical engineers, was appointed by the English chamber of commerce and the "Transatlantic Telegraph Company," to whom the duty was assigned of inquiring into the causes of these disastrous failures, and providing instructions for the future in regard to the manufacture, tests, and placing of cables. It appeared that the mechanical department of the subject was in a more advanced state than the electrical. The committee, after 18 months of hard work, published an elaborate report in 1863. Moreover, the theoretical researches of Thomson, Jenkins, and others, had thrown much light on the electrical requirements of submarine lines. Meanwhile, a cable was laid successfully between Malta and Alexandria in 1861, and the Persian gulf cable (about 1,330 m. long) in 1864. When Mr. Field visited England in 1862, to urge on a second attempt to establish telegraphic communications across the Atlantic, he found that the manufacturers, Messrs. Glass, Elliott, and co., were confident of their ability to make and place a good and durable cable between Great Britain and America, and were willing to incur a part of the risk.
The second Atlantic cable, made by the " Telegraph Construction and Maintenance Company," was tested with every precaution, and found to be unexceptionable in its electrical conditions, and was shipped on board the Great Eastern in 1865.) This cable (2,186 m. long) consists of seven copper wires (No. 18) twisted into a spiral, covered with four coats of gutta percha, between which are thin layers of Chatterton's compound. The external protection is made of ten iron wires, each surrounded by manila yarn. After about half of the cable had been paid out it broke, and the expedition was abandoned for the season. The total expenditure of money had been about $3,000,000. In 1866 a third cable, of similar construction to the second, but stronger, lighter, and more flexible, was placed on board the Great Eastern and successfully laid. The length between Trinity bay and Valentia is 2,134 m. Its first duty was to transmit a message of peace, viz., that a treaty had been signed by Prussia and Austria. Capt. Anderson returned with the Great Eastern to the place where the cable of 1865 had parted, and succeeded in splicing it and completing the line.
In 1869 the French Atlantic line went into operation between Brest and St. Pierre, and between St. Pierre and Duxbury, Mass., the total length being 3,857 m. In 1870 more than 15,000 m. of cable were laid, including the Indian cables (from Suez to Aden, from Aden to Bombay, and from Penang to Singapore), the China cable, and the North China from Hong Kong to Shanghai and from Shanghai to Posiet in the Littoral province of Siberia. In 1874 the work was begun by the "Direct Cable Company " of laying the new Atlantic line between Ballinskilligs bay, in Ireland, and Rye, New Hampshire, by the way of Nova Scotia. In spite of many obstacles and delays, the cable was put in position between Rye Beach and Torbay, N. S., and between Torbay and Newfoundland, also between Cahirciveen island and a point 200 m. E. of Newfoundland, before rough weather put an end to the work. The final splice of 200 m. was made early in the summer of 1875. In 1873 a cable was laid between Lisbon and Madeira; in 1874 Madeira was connected by cable with St. Vincent, one of the Cape Verd islands (1,200 m.), and St. Vincent with Per-nambuco (1,845 m). In 1875 cables were laid between Jamaica and Porto Rico, Constantinople and Odessa, Zante and Otranto, and Barcelona and Marseilles. In all, more than 200 cables have been laid, with a length of about 50,000 m. - The interval of time which must elapse between the sending of successive signals through similar cables increases as the square of their lengths; and in different cables of equal length, this time is the least when the thickness of the insulating coating is one third of the diameter of the compound conductor.
With the improved transmitting apparatus of Thomson and Varley, eight words can be sent in the time otherwise required for one. Seventeen words a minute have been sent through the French Atlantic cable. Thomson's syphon recorder quadrupled the speed of cable telegraphy. The current from the cable passes into a coil of wire suspended between the poles of magnets. The coil turns round in a direction depending upon the direction of the current. The motion of the coil is communicated by means of a thread and lever to a glass syphon which feeds itself with ink from a basin. The ink is electrified and. spurts out against a moving strip of paper, and draws an undulating curve which indicates the letters of the message. The speed of working with this recorder is about the same as with the reflecting galvanometer; and in either case it is much greater than could be attained by the moving armature, which requires that the current should rise and fall by large differences; and this would take more time. - Telegraphic Disturbance. The offices and operators of air lines of telegraph are exposed to accidents from lightning, either from the direct stroke or the induced electricity when a discharge occurs between two clouds. A great many lightning guards have been devised. Sabine mentions eleven.
In lines which follow the undulations of mountainous regions (as between Vienna and Milan), there is so great disturbance from atmospheric currents, even under a blue sky, that it is impossible to send messages at certain hours. The aurora sometimes acts powerfully upon the wires, interfering with the battery currents. On such occasions, if the battery be taken off, the messages may be sent by means of the current induced by the aurora. The action of cable lines is disturbed by earth currents. Generally, the difference of potential between different parts of the earth is small; but it is subject to sudden and capricious changes, and amounts sometimes to that of a battery of 140 of the Daniell elements. The direction of these earth currents is such as to derange particularly the Atlantic lines. The instruments are protected by the use of the condensers of Varley and others. These earth currents must not be confounded with those excited when plates of zinc and copper are buried in the earth, which Kemp, Fox, and Reich made the subject of numerous experiments, and which Bain, Palagi, and others put into the harness to work the telegraph. - Various Uses of the Telegraph. The electric telegraph has been applied to uses never contemplated by its originators.
In 1852 Channing and Farmer of Boston devised a system of telegraphic fire alarms, which was adopted in the city of Boston. Five so-called signal circuits were extended from the city hall to different parts of the city, and in connection with these were stationed 50 signal boxes attached to buildings at convenient points. The door of a box being opened, a crank is seen with directions for the number of times it is to be turned to convey to the central office the number of the station and district. From the central station five wires called alarm circuits connect with the different fire bells throughout the city, the hammers of which, run by weights, are set in action by the telegraph itself and strike the number of the district and station of the alarm. The electric current is excited by a magneto-electric machine which is set in motion by the pressure of the water with which the city is supplied, and the same power is employed to wind up the weights that move the bell hammers. The bells have been rung, as an experiment, from Portland through the telegraph wires extending to that place. The fire alarm also affords an incidental protection to the city from lightning.
Large metallic surfaces being placed near the wires at all the stations and connected with the ground, a stroke of lightning upon the wires will leap across to these conductors, and pass harmlessly to the ground, while the artificial current possesses too little intensity ever to overcome the intervening space, and continues in the circuit. Similar arrangements are provided upon many telegraph lines. The telegraphic fire alarm has now been introduced into all the larger cities. The fire alarm telegraph of Boston is employed to designate the exact, noon by a single stroke upon the bell of the Old South church, an exact chronometer being placed in the circuit and arranged so as to pass the current at 12 o'clock precisely. By a similar arrangement in London a large ball is made to drop exactly at 12 o'clock from a pole erected in the Strand by the action of a current from the royal observatory. The same tiling is also done at Nelson's monument, Edinburgh. In Paris a cannon is fired upon a similar plan. Chronometers in observatories are also made to run synchronously with a standard instrument by means of the electric current.
Recently, the Harvard college observatory has established a telegraphic connection with Boston, and thence with the lines which diverge from that city, so that a uniform time can be distributed to all the railroad stations in New England. In a similar way Greenwich time is given to the whole of Great Britain. The application of the telegraph to the determination of longitudes has been described in the article Coast Survey, vol. iv., p. 759. Upon some railroads the telegraph is used with great advantage for regulating the running of trains. In numer.-ous places telegraphs have been constructed for private purposes, and in London from the house of commons to the committee rooms. The transactions of the stock exchange in New York are telegraphed to the brokers' offices and the hotels, and are instantly and simultaneously made known in a thousand different places, where they are sometimes recorded by automatic printing instruments. For this purpose a very rapid printer has been devised. The usual type and escape wheels are made very light, and are rotated, not by electricity, but by a spring.
The current is reversed at every vibration, and the printing is effected by the power of a magnet, which is included in the same circuit with those that liberate the escape wheel; but it is made more sluggish in action so that it does not perform its work until the arrest of the circuit wheel at a letter gives time for it to be charged. This instrument, which occupies only one sixth of a cubic foot of space, will print 800 letters a minute. - A system of telegraphs for the use of large cities was devised by Wheat-stone, by which a company leases the use of a small wire by the year to individuals. For distances not exceeding 20 m. a copper wire no larger than a cotton thread is sufficient. Numbers of these, insulated by being wound with thread, may be brought together into one cord, and suspended from strong iron wires passed in different directions upon the houses. The latter, communicating with the ground at numerous points, will convey away all atmospheric discharges that might otherwise be troublesome. The "Law Telegraph Company" in the city of New York has established a complete system of communication by means of dial instruments between the leading law firms and the courts.
A rapid system of signalling is used, by which any member of the company can be put, through the agency of a central office, into direct private communication with any other member, or with the courts of New York or Brooklyn. The Chester *dial is employed by this company. In the automatic lire alarm, a circuit is closed by the expansion of metal under a rising temperature. The circuit closer, which is called a thermostat, is attached to the ceilings of stores or dwellings, and is adjusted to work at a fixed temperature. In the city of New York houses and stores furnished with these instruments are connected telegraphically with the fire patrol, the usual apparatus for indicating the locality of the fire being included in the system. The district telegraph system, which has been introduced in New York, Boston, and elsewhere, by which a messenger, policeman, or fireman can be summoned to any house that adopts it, is a still wider extension of Wheatstone's scheme. On a smaller scale, telegraphic communications may be kept up between the remote quarters of a ship or yacht; the electro-magnetic bell-ringer may be used for domestic purposes, and the burglar alarm for the protection of private dwellings.
By means of Batchelder's electro-magnetic tell-tale clock, the times are recorded when a watchman visits the different points of his beat. The most difficult piece of music may be punched out upon a moving strip of paper, and then played automatically by means of electro-magnetism. On the field of battle, telegraphic lines may be quickly extemporized, and an interchange of reports and orders may be maintained between the outposts of an army and headquarters. During the American civil war, telegraphic field trains were in use. A machine has been invented, operated by keys, which enables a reporter to secure a printed copy of the very words which come from the mouth of the orator. In some countries, as in England, where the lines have been purchased by the government, the telegraphs are associated with the postal service. For short distances the pneumatic telegraph is used, the written messages being driven through underground pipes by condensed air. For this purpose three engines of 50 horse power each are in constant service at the central post office in London. - Multiple Telegraphy. During the last quarter of a century various attempts have been made to contrive ways by which two messages should be sent at the same time, in the same or in opposite directions, over a single wire.
Gintl, Edlung, Wartmann, Frischen, Siemens, Halske, Duncker, Starke, Rouvier, Zante-deschi, Farmer, and Stearns have all experimented with this object, and some of them have invented ingenious instruments. In 1849 Siemens and Halske took out a patent in England for a method of transmitting simultaneously a plurality of messages. In 1855 Starke devised a method of sending two messages at the same time upon the same wire. By means of two keys, and two batteries of different intensities, two independent receiving magnets were worked at the other end of the line, either separately or together. In 1854 Siemens and Halske independently invented the differential method of sending two messages at the same time in opposite directions. About the same time Farmer devised a way of doing the same thing, using two auxiliary batteries in combination with two principal batteries. The essential conditions for successful duplex telegraphy are: 1, that neither key should put in action the receiving magnet at its own end of the line; 2, that in all positions of the key signals should he sent through a line of constant length and capacity.
This is done by dividing the current from the battery at each end of the. line equally between the line itself and an equivalent resistance coil and condenser, and winding the wire round the receiving magnets in such a way that the two parts of the current produce equal and opposite magnetism in the core of soft iron. The modifications made by Stearns in the arrangement of Siemens and Gintl have obviated all the practical difficulties, and made duplex and even quadruplex telegraphy a success in the United States. By means of Stearns's invention, known as the Franklin, the duplex system has gone into effect, not only between Boston and Washington, but also between Cape Breton and San Francisco, and has been introduced into England. The quadruplex system works well between Boston and New York. The phonetic system of Gray and Bell (which is still in its infancy) aims to increase indefinitely the number of messages which can be sent simultaneously over a single wire, by using tuning forks, moved by electro-magnets, for sending and receiving the signals. Only one fork at the receiving station is in unison with a particular fork at the sending station, and responds to it.
Experiments upon a similar system were made by Paul la Cour in Copenhagen on a line of 242 m. in 1874, an account of which was presented to the royal Danish academy of sciences. It was thought that by this arrangement not only many messages • could be sent at the same time on a single wire, but also a message could be received only by the station for which it was intended. - See Schellen, Der elektromagnetische Telegraph (Brunswick, 1850); Moigno, Traite de la telegraphie electrique (Paris, 1849); Highton, " The Electric Telegraph, its History and Progress," a number of Weale's series (London, 1852); Jones, " Historical Sketch of the Electric Telegraph " (New York, 1852); Turnbull, "The Electro-Magnetic Telegraph" (Philadelphia, 1853); Schaffner, "Telegraph Companion" (2 vols., New York, 1854-'5), and "The Telegraph Manual" (1859); Prescott, "History, Theory, and Practice of the Electric Telegraph" (Boston, 1859); Dumoncel, Telegraphie electrique (Paris, 1864); Field, "History of the Atlantic Telegraph " (New York, 1866); Griscom, "The Telegraph Cable " (Philadelphia, 1867); Sabine, "The Electric Telegraph" (London, 1867); Cully, "Handbook of Practical Telegraphy'.' (New York, 1870); Goklsmid, "Telegraph and Travel, a Narrative of the Formation and Development of Telegraphic Communication between England and India" (London, 1874); and Douglas, " A Manual of Telegraph Construction" (1875).