The New International Encyclopædia/Telephone
TELEPHONE (from Gk. τῆλε, tēle, afar + φωνή, phōnē, voice, sound). An instrument for the transmission of speech or musical or other sounds by means of electrical vibrations corresponding to the original sounds. The first use of the word telephone is in a description of experiments by Wheatstone where sound was transmitted through wooden rods. In 1837 Page, of Salem, Mass., noticed that an iron rod suddenly magnetized and demagnetized would emit certain sounds which were due to a rearrangement of the molecules, and this phenomenon has since been known as Page's effect. Bourseul of France in 1854 conceived the fundamental idea of the telephone, but did not, however, put it into actual practice. He proposed a device in which a current interrupted by a vibrating disk under the influence of the voice would produce a similar vibration of a disk at the end of a conductor through the agency of an electro-magnet. In 1860 Philipp Reis, of Frankfort, invented an apparatus which he named ‘Telephone,’ with which he was able to reproduce sound at a distance. Reis's telephone, about which there has been much controversy, in his hands at least was able to transmit articulate speech, and he is entitled to credit for the principle of the instrument. For the practical development of the idea and the invention of an actual working telephone the honor must be given to Alexander Graham Bell, who, March 7, 1876, received letters patent for new and useful improvements in telegraphy in which a method for the transmission of vocal sounds is one of the most important of the claims. Few patents for inventions have been subject to more litigation than the telephone, and the literature on the subject is quite exhaustive; but Bell's rights have been sustained by the highest courts, and though he was closely followed by other inventors, notably Elisha Gray, he may fairly be entitled to the honor of the invention.
SECTION OF RECEIVER WITH COMPOUND UNIPOLAR MAGNET.
The Bell telephone, which has survived as the modern receiver, served both as transmitter and receiver in the early apparatus. A reference to the accompanying diagram showing a cross section of a modern unipolar receiver will make clear its action. There is a hard rubber case hollowed at its upper extremity and containing the soft iron diaphragm about 1 inch thick and two and a quarter inches in diameter, with free part one and three-fourths inches across, which is tightly held at its circumference, but its centre is free to vibrate. A bar magnet, either single or compound, carries at its upper end a coil of fine silk-covered wire (No. 38 B. & S. gauge generally) with resistance of about 75 ohms, whose terminals connect with the binding posts. A more powerful receiver can be constructed by employing instead of a single magnet a horseshoe magnet with coils on each pole. In the Ader bipolar receiver, used extensively in Continental Europe, the horseshoe magnet is ring-shaped and outside of the diaphragm, and in front of the pole pieces a soft iron ring is placed with the object of strengthening the field of force between the poles. The diaphragm of a telephone receiver is in close proximity to the pole or poles of the magnet, but not in contact. When used as a transmitting instrument this diaphragm will vibrate under the influence of the voice, its movement being caused by the movement of the air known as sound waves. The diaphragm rapidly approaching and receding from the magnet consequently produces currents by induction in the wire of the coil. These currents will be transmitted over the line wire, and, flowing through the coil of the receiving instrument, will cause its magnet to become more strongly magnetized and the diaphragm to be attracted. The diaphragm of the receiver will accordingly move in unison with that of the transmitter, and consequently the sound wave which impinges on the latter will be reproduced. The ground can be used as a return or the circuit can be of wire throughout. The currents of electricity that were transmitted in this way were too feeble to produce satisfactory sounds at the receiving instrument when there was a line of any considerable length, and it was necessary to find a better transmitter. Accordingly there followed the carbon transmitter, where the change of resistance of carbon under pressure produces pulsations in the current corresponding to the vibration of the sound waves.
Previous to this, however, came Elisha Gray's transmitter, consisting of a needle mounted at the centre of a vibrating diaphragm and dipping into a liquid of rather low conductivity. The current passed through the needle and the liquid and the resistance of the circuit varied with the vibration of the diaphragm. This transmitter allowed variable but continuous currents to pass, and did not interrupt them entirely, as did the transmitter of Reis's telephone. The next transmitter was that of Berliner (1877), based on the variation of resistance with pressure, a diaphragm vibrating in contact with a metal knob; and then came that of Edison, where a button of compressed carbon was in contact with a small disk of platinum on the diaphragm. The microphone of Hughes (1878), where two bodies are in loose contact, has furnished the type of modern transmitters, where the carbon is in the form of finely divided granules held between two conducting plates, one of which is the diaphragm on which the voice strikes. The Edison form was, however, used for a number of years, but the Hunnings form or some modification was found necessary when long-distance telephoning came into practice. With such transmitters it was found necessary to introduce a secondary circuit instead of having the varying currents flow in the main circuit as was the case originally. The change in resistance then was small in comparison with the total resistance of the circuit and the effect on the receiver was not as marked as desired. Accordingly Edison conceived the idea of using an induction coil in the circuit with the transmitter. This induction coil consists of a primary coil with a few layers of coarse copper wire wound around a bundle of soft iron wire and a secondary coil of a large number of turns of fine wire. The diagram below, where the receiver has been removed from the hook (hook up), shows the general arrangement of the circuit. The current from the battery flows through the transmitter and the primary of the induction coil. Any difference of intensity in current caused by a change of resistance in the transmitter will give rise to induced currents in the secondary, which will affect the receiver correspondingly, and the original vibration of the sound waves will be reproduced. The addition of the coil renders the apparatus far more sensitive and the increase in voltage caused by the many turns of the secondary enables the sound to be transmitted to a much greater distance. The Blake transmitter, the invention of Francis Blake, of Boston, was used in the United States almost universally until the adoption of the transmitter with the granulated carbon, and is familiar in the older instruments, being incased in a wooden box. Its action depends upon the pressure on a button of a compressed carbon by a point in connection with a metal diaphragm. The transmitter in most general use at present is the White or solid back transmitter, illustrated in the accompanying diagram. The construction of the transmitter will appear from the diagram. Between two disks of carbon is placed granular carbon. One disk is in contact with the solid back of the instrument, while the other is in contact with the diaphragm on which the sound waves impinge. The back of the transmitter forms one electrode, while the front plate is insulated from the rest of the apparatus and is connected with the other conductor. There are numerous other forms of transmitter which are constantly increasing with the extending use of the telephone for interior use and by independent companies. These transmitters require batteries, of which the Leclanche, some form of dry cell, or the Fuller bichromate of potash cell are generally employed, while for central stations and wherever possible storage cells are very desirable and useful.
WHITE SOLID BACK TRANSMITTER.
With the telephone must be included some sort of call-bell, and for this purpose a magneto-bell is usually employed. This consists of a small magneto-generator in which the armature is revolved by a few turns of a crank and a current of considerable voltage (that is, compared with the battery) is transmitted to the distant station, where there is what is known as a polarized bell. The current transmitted is alternating and the bell used is of the polarized ringing form, where the armature is alternately attracted by one pole and the other, depending on the polarity of the passing current. In the older form of circuit still in use in many exchanges where the central station must be called up by turning the crank the magneto machine and bell are in circuit as long as the receiver hangs on a hook which forms a switch. The circuit is shown below. When the handle of the magneto is turned a current is sent out through the bell and hook to the line. Then the receiver is taken down and placed at the car and the bell circuit is broken, merely the telephone circuit being in connection with the line wire. With a number of subscribers an exchange or central station is necessary where the wires connecting the various subscribers or other stations can be joined at will. At these stations an annunciator, which may be either a falling flap with the appropriate number or an incandescent lamp, informs the operator of the call and by means of the switchboard to which all the wires are led the connections desired by the subscriber are made. Improvements in switchboards and their increased size to meet the growing demands of cities have been most marked, and this form of apparatus is now so complex as to be quite unintelligible except to a telephone engineer, as almost every part of the apparatus has been subjected to important improvements.
|TELEPHONE CIRCUIT WITH HOOK DOWN AND WITH HOOK UP.|
a and c binding posts connecting with the line. The post b forms the ground connection for lightning. The dotted lines indicate that part of the circuit cut out by the hook switch.
The use of a common battery at the central station has been one of the most important developments of recent years, as it does away with the magneto call at the subscriber's instrument, a saving of no small dimensions, as the magneto machine was the most expensive part of the equipment, the mere removal of the receiver informing the central operator of the subscriber's presence at the telephone. In the Hayes system, which is extensively employed in the United States, a device known as a repeating coil is used, and the battery is bridged across the circuit at the central station. The repeating coil consists of a transformer or induction coil formed by two coils of wire of equal length and size, it being customary to wind the four coils required for two repeating coils on the same core. There are two sets of windings in each circuit and the current of the battery divides and passes through a single coil before reaching the line or main circuit wires. In other words, the negative pole of the battery connects with the two sets of windings of one repeating coil, one of which joins the wires leading to each station, while the positive pole is similarly connected on the other side. Any variation in the current caused by the action of the sound waves on the transmitter of one circuit will produce similar effects in the other circuit by inductive action. Such is the case when the line is arranged for talking. To signal the central station the subscriber removes his receiver from the hook, thus closing a circuit which acts upon a relay and causes a small incandescent lamp to glow. This gives the signal to the central operator, who immediately completes the talking circuit first with her own transmitter and receiver, and then with that of the desired subscriber. The attention of the latter has been attracted by a call bell energized by an alternating current. This bell is in series with a condenser which has been bridged across the main circuit. Another central energy system is that of Stone, where impedance coils, or wire windings of considerable self-induction, are placed in the circuit instead of the repeating coils of the Hayes system. The effect of these coils is to prevent the rapidly alternating current in the telephone circuit flowing through the battery and to have it travel along the line to the other station where the impulses are reproduced. In the Dean-Carty System an impedance coil is employed bridged across the main circuit at the plugs and to the centre of it is connected one pole of a battery whose other terminal is grounded. There is also an impedance coil at each station connected with both sides of the circuit and its centre point is connected with the transmitter and the primary of the induction coil which are connected with the ground. All of the various systems for central energy in actual practice are necessarily exceedingly complex and are subject to important modification and improvement, but the foregoing are the more important. There are also methods where storage cells are used at the subscriber's station and where a thermopile is employed in connection with an ordinary lighting circuit.
Long-distance telephony was first made possible in 1885, when the American Bell Telephone Company organized the American Telephone and Telegraph Company. For several years previously experimental lines with metallic circuits of hard drawn copper were operated between New York and Boston. In 1885 a regular line between New York and Philadelphia was constructed, and so great was its success that within two years long-distance lines were established between New York and Boston, Albany and Buffalo, Chicago and Milwaukee, Boston and Providence, and New York and New Haven. The New York and Chicago circuit, 950 miles distance, 1900 miles of wire, was opened October 18, 1892, and long-distance telephoning between New York and Milwaukee and Saint Louis is also carried on. The American Bell Telephone Company in 1900 acquired the rights of patents of M. I. Pupin, by which the limits of long-distance telephony are greatly increased and conversation over circuits where there are submarine conductors of considerable length is possible. This is accomplished by inserting coils of self-induction at regularly recurring intervals along the line obtained by calculation.
The American Bell Telephone Company practically controls the telephone business of the United States, though a number of strong independent companies have been organized, whose business is increasing.
Statistics of the American Bell Telephone Company from 1894 (January 1st) to 1901
|Miles of wire on poles||214,676||232,008||260,324||286,632||327,315||396,503||509,036||627,897|
|Miles of wire on buildings||16,492||14,525||12,861||12,594||13,776||15,329||15,087||16,833|
|Miles of wire underground||120,675||148,285||184,515||234,801||282,634||358,184||489,250||705,269|
|Miles of wire submarine||1,637||1,856||2,028||2,818||2,675||2,973||3,404||4,203|
|Total miles of exchange service wire||353,480||396,674||459,728||536,845||626,400||772,989||1,016,777||1,354,202|
Public Ownership of Telephones. In Europe public ownership of telephones exists to a certain extent and there has been agitation in this direction in the United States. For the most part, such public ownership of telephones is national, rather than municipal, and is chiefly confined to countries where private ownership of franchises is far less common than public ownership. Actual statistics are not readily available, and are constantly changing, but an admirable summary of the ownership of telephones in various countries, made by U. N. Bethell, general manager of the New York and New Jersey Telephone Company (see Bibliography below), is as follows:
“All over Europe, with a few exceptions, the industry at present [early in 1903] is controlled and owned by States or municipalities. In Belgium, France, Switzerland, Germany, Austria, and Hungary the central Government operates the industry. In Holland the State operates the trunk lines; in the two principal cities, Amsterdam and Rotterdam, the municipalities operate the local systems; and at The Hague a private company operates. In Denmark and Norway private enterprise under Government control operates the industry, while in Sweden the State operates it, except that in Stockholm and vicinity a private company since 1890 has been in active competition with the State. In Great Britain, in most places, private enterprise operates the local systems under license from the State; in a few places municipalities operate or are preparing to operate local systems; the State operates the trunk lines. In the United States private enterprise, under Government control, operates both the local systems and the trunk lines.”
Among the municipal telephone systems in use or under construction in Great Britain early in 1893 were those at Glasgow, Portsmouth, Swansea, Brighton, and Hull. The general movement for municipal telephones in Great Britain followed a Parliamentary act of 1899, authorizing municipal construction. Tunbridge Wells and Glasgow, in 1901, were the first to install and operate systems under the act, but after an active campaign against public ownership in Tunbridge Wells the municipal plant was sold to its private competitor, in the latter part of 1902. There were conflicting reports as to the financial success of the plant, but apparently the advice of the engineer was not followed during construction, while subsequently the plant suffered from poor management. It is said that the municipal plant resulted in a marked reduction of rates and that when sold it yielded a profit. It should be added that in 1911 all telephone licenses granted to private companies in Great Britain will expire, and that all such companies pay 10 per cent. of their gross receipts to the Post-Office Department, which has had a monopoly of the telegraph business since 1869. The policy of the Post-Office Department is to monopolize the telephone as well.
The general question of municipal ownership has been discussed at length under that head. The public interests demand that the business, shall be conducted as a monopoly, under public control. The latter does not exist in the United States to the extent that might be inferred from the closing sentence of the above quotation, but that is largely the fault of the legislative and executive departments of the several States, and to some extent of the municipalities also. Finally, the long-distance lines would be a troublesome factor in municipal ownership in America, unless they, as in some countries abroad, were owned by the general Government.
Bibliography. The following list contains some of the more important works on the telephone to which the reader is referred for further information: Miller, American Telephone Practice (New York, 1899); Alsopp, Telephones, Their Construction and Fitting (London, 1900); Houston and Kenelly, The Electric Telephone (New York, 1896); Webb, Telephone Hand-hook (Chicago, 1894; new ed. 1901); Hopkins, Telephone Lines and Their Properties (New York, 1898); Prescott, Bell's Electric Speaking Telephone (New York, 1884; 2d ed. 1890); Thompson, Philipp Reis, Inventor of the Telephone (London, 1883). For discussion of the public ownership of telephones consult some of the references under Municipal Ownership; also papers by Bethell (against), Parsons (for) and Bennett (as to Great Britain) in “Proceedings of National Convention upon Municipal Operation and Public Franchises,” published in Municipal Affairs (New York, vol. vi., No. 4, 1902-3); also Hemenway on “Municipal Telephones,” Proceedings Seventh Annual Convention League of American Municipalities (Des Moines, Iowa, November, 1903).