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The Early Telephone At the beginning of the nineteenth century several simple devices such as speaki8ng tubes and Sega phones had been used for conveying speech to a distance. Transmission of musical sounds through solid rods had also been tried with success, notably by Wheatstone, who in 1831 described his experiments with the optimistic prediction: ‘could any conducting substance be rendered perfectly equal in density and elasticity so as to allow the undulations to proceed with a uniform velocity without any reflections and interferences, it would be as easy to transmit sounds through such conductors from Aberdeen to London as it is now to establish a communication from one chamber to another.’ There is some uncertainty as to the exact date on which the word telephone was firs employed, but it was well before the time of the electric telephone, for in the famous arbitration case on the electric telegraph involving Cooke and Wheatstone, in 1841, the word was frequently used in connection with the transmission of speech. The inventor of the telephone, as we know it, using an electric current for the transmitting medium, was Alexander Graham Bell, and his fundamental discovery was made on 2 June 1875. Bell did not stumble over the secret of the telephone in the traditional manner of many discoveries but arrived at it after years of patient study and deliberate step by step progress to the ultimate goal. Not only did he, himself, devote nearly twenty ears of his adult life in pursuance of his objective, but the foundations on which he built had been laid during two previous generations. Bell’s grandfathers had been a professor of elocution, who wrote books on the subject which in the 1830’s became a very popular branch of self-education. His father, following the same line, had specialized in the mechanism of speech. As a professor at University College, London, he in turn wrote books on the subject aiming at the analysis of sounds for such purposes as teaching the deaf and dumb to speak, and , by a system which he called ‘visible speech’ expressing sounds graphically. In 1870the family moved to Brantford, Ontario, Canada, where Bell continued his activities and he was soon absorbed in experiments in electric telephony employing groups of electrically controlled tuning forks. The vibration of a fork was made to operate a wire-in-mercury contact by which an interrupted current was transmitted to a similar tuning fork at a distance, operated by means of an electromagnet. Thus he produced what was virtually an electric telegraph based on a musical code of signals. The next step in the development of the telephone idea came when Bell recalled that a permanent magnet when moved towards the poles of an electromagnet produced a current in the coils of the latter and that on withdrawing the magnet a current was generated in the reverse direction. If, therefore, a permanent magnet was fixed to one of his vibrating reeds and held in front of an electromagnet a current would be induced of the same frequency as that of the red. He wrote, ‘in this arrangement voltaic batteries, current interrupters and induction coils became unnecessary and I was fascinated by the simplicity of the arrangement of circuit.’ In 1874 Bell conceived the idea of the electric harp, which consisted of a large number of reeds operating alongside one another in front of the common core of an electromagnet. In describing the proposal he said: ‘utter a sound in the neighborhood of the harp H and certain of the rods would be thrown into vibrations with different amplitudes. At the other end of the circuit the corresponding rods of the harp H would vibrate with their proper relations of force and the timber of the sound would be reproduced.’ In his account of the matter later Bell explained that the expense of constructing the apparatus deterred him form making the attempt. In spite of this explanation the electric harp has frequently been referred to in the literature as a practical achievement and as the real invention of the speaking telephone, but to be historically accurate we must await Bell’s next step in the development. Studying the form and construction of the human ear and noticing the disparity in size between the membrane and the small bones moved by it, Bell then conceived the idea of making a telephone with a large membrane carrying a small piece of still, but this time it was lack of confidence, not of finance, which held him back. He had no faith in the power of the small induced currents to transmit the necessary amount of energy. One day Bell and his assistant were conducting their experiments with vibrating reeds fitted with coils wire in an attempt to send more than one telegraphic message on the same circuit by means of different frequencies. On one of these occasions Bell, at the receiving end, noticed something peculiar; his own armature was vibrating in unison with the remote plucked reed. In his famous deposition later he said, ‘I called out to Mr. Watson to pluck his reed again. At every pluck I could hear a musical tone of similar pitch to that produced by the instrument in Mr. Watson’s hands and could even recognize the peculiar quality or timber of the pluck. These experiments at once removed the doubt that had been in my mind since the summer of 1874, that magneto electric currents generated by the vibration of an armature in front of an electromagnet would be too feeble to produce audible effects that could be practically utilized fro the purpose of multiple telegraphy, and of speech transmission. In spite of personal financial difficulties Bell persisted in development of more effective receivers and the form and size of the electromagnet went through various stages. A thin iron plate was adopted for the diaphragm and the coils were carried as extended pole pieces on a permanent magnet of which both rod-type and u- shaped were used. Within a few months the equipment had been assembled in a long box with a mouthpiece at one end. A fundamental difference then developed between transmitter and receiver. In the former the box shape persisted but the pole pieces of the magnet were turned at right angles to the permanent magnet so that the box with the long magnet could lie flat against a wall with the mouthpiece standing out convenient for speaking into. The receiver, on the other hand, soon took the form of a tube for convenience in holding to the ear. Early in 1877 the telephone had created a world-wide interest. Speech and been transmitted over the existing telegraph lines and the time had come for commercializing the invention. Bell offered pairs of instruments on lease for social purposes at $20 a year, and ‘for business purposes’ at twice this rent. Before following the steady course of Bell’s progress it is appropriate at this stage to refer to another name in the history of the telephone. Philip Reis, a Berman school teacher, invented a telephone in 1863, which was exhibited at the British Association. It depended on the magnetic tick occurring in an iron rod standing on a sounding board when the current in a surrounding coil is interrupted. This device took the form of a receiver and the transmitter was a diaphragm to which was connected a mercury contact. Reis seem to have followed very much the same line of reasoning on the analysis of sounds as Bell did. The idea of a central switch room by which subscribers could be interconnected was suggested in October 1877 by an enterprising journalist in Boston and quickly took practical shape based on the telegraph system which had already operated to a limited extent in the united states, England and France. The first telephone exchange on a commercial basis was installed at New Haven, Connecticut, in January 1878. Drop indicators were used with a call bell and two- way lever switches enabled the operator to connect his own telephone to any line and obtain instruction. Another switch enabled him to send out a signal in the form of a loud buzzing sound on the subscriber’s receiver. Edison knew that if a metallic point was drawn over a chalk surface moistened with potassium iodide the passage of small currents between the point and the chalk affected the amount of drag. He therefore made a chalk cylinder which could be rotated by hand and arranged a mica diaphragm with a platinum point connected rigidly to its center. When the received undulating telephone currents passed through the moving contact they caused a vibration of the diaphragm which reproduced the speech. He gave the name microphone to the instrument he was using because it magnified weak sounds. As was pointed out by Wheat-stone and others it did not in fact respond to sounds in the surrounding air but only when in contact with a vibrating body. Thus at the Royal Society meeting the members ‘heard’ the tramp of a fly: in reality what they heard was the effect of a fly walking about on a loose contact, a rather different thing from reception of airborne sound waves. Nevertheless the use of a loose contact between granules of carbon stemming from Hughes’ discovery led to a host of types of transmitter, one of which was attributed to Hunnings, a Yorkshire clergyman, and another to Blake, an American, Hunnings was the first to use particles of carbon loosely assembled between two conducting electrodes, but he did not carry his idea forward to a commercial transmitter. Blake, on the other hand, in association with the Bell Co., hand his design accepted and it was used extensively by early telephone subscribers for many years. The first transmitter of the granular form to be brought into common use in this country was the Deckert in which carbon granules were disposed between a carbon diaphragm and carbon block. The surface of the block had pyramidal projections, the tips other pyramids having tufts of cotton wool to prevent ‘packing’ of the grains. The construction replaced Blake’s transmitter and was assembled I its place in the same wooden cabinets. The Deckert transmitter was found to be so efficient that the speech currents resulting soon caused intolerable interference between the lines of separate subscribers and double-wire working had to be resorted to. So important was this that in the case of the National Telephone Co., the former Blake transmitters were retained for some time to avoid the expense of doubling the circuits. The outstanding step made in transmitter development was in the invention in 1892 of the ‘solid back’ instrument by White for the American Bell Telephone Co. A cell, partially lined with carbon, was carried on the front side of a rigid support and the front side of the cell was closed with a small mica diaphragm lined with carbon and attached at the center to a large acoustic diaphragm facing the mouthpiece. By careful selection of the carbon for the granules and screening for uniformity in size, as well as by the introduction of precision in the manufacture, the White solid-back transmitter quickly established itself. It could handle larger currents than previous designs of transmitter and enabled satisfactory conversation to be carried out on longer lines. In 1880 the instruments standardized for subscribers’ use were Telephone No. 1 and Telephone No. 2. The former, the wall type, was made of wood having a projecting ebonite mouthpiece on the transmitter with the tubular receiver and switch hook at the side and a double magneto bell in front. The desk type, contracted mostly of metal, carried the transmitter with its ebonite mouthpiece on a tubular pillar with the receiver and switch hook on the side, but the bell was accommodated in a separate wooden box. Solid back transmitters were adopted for both types of instrument. Today’s receiver has a sensitivity twenty times that of the instrument used fifty years ago with a magnet weighing only one-hundredth that of the Bell receiver been increased but greater purity of tone achieved so that the voices of different speakers can be clearly distinguished through a more uniform response over the frequency range. This improvement, in addition to giving better service to the telephone user, has had an important effect on the overall economy of the system: it has made possible the use of much smaller wires in the subscriber’s circuit: conductors only 0.012 in. diameter may become standard. When the first telephone exchanges were projected the telegraph system with its ramification of circuits was already established, and it was natural tat practice should follow precedent. There was, however, a basic difference in the requirements of the two services; telegraphs were usually long-distance circuits with lines from town to town, whereas in telephony, initially at any rate, the main problem was to connect many subscribers in a congested urban area with one another through a local exchange. Consequently bare wires strung over rooftops became the usual practice. To prevent corrosion in industrial towns and large cities the wires were often protected with an impregnated cotton covering. Although the high electrical resistance of iron wire was a great disadvantage it required many years of testing and consideration before its place was taken by copper. Because of their increased tensile strength phosphor bronze and silicon bronze were favored by some but hard- drawn copper held the field until the brittleness of bronze was overcome. Soft copper binding wires were introduced for holding the wire to the insulator of porcelain of various shaped, and gutta-percha covered wire was used fro leading into premises. The congestion resulting from the large number of wires leaving the structure over an urban telephone exchange soon called for a bunching of the circuits into groups and this was done by the use of multi-core aerial cables. Early forms consisted of a number of gutta-percha insulted wires bound together with tape and associated with a stranded galvanized wire to give supporting strength. Later rubber was substituted for the gutta-percha which cracked when exposed to air and sunlight. A problem which faced the early telephone engineer was the prevention of overhearing between circuits when so many had to be carried in close proximity to one another. The impracticability of the single-wire earth circuit which had been suitable for telegraphs was soon appreciated and in 1892 expensive schemes of doubling, or making the circuit ‘metallic’ as it was called, were carried out. Even then induction effects were found to be serious and twists were introduced. One of the most important improvements in the prevision of circuits between subscribers and exchange and between one exchange and another was the invention of the dry-core paper cable. In the discussions of a special conference of specialists held in New York in 1887, the importance of keeping the electrostatic capacity at a low value was emphasized and at a similar conference two years later, John A. Barrett, electrician, American Telephone and Telegraph Co., announced that he had ‘been engaged in a effort to reduce specific inductive capacity of the wrapping used upon the conductors of as to secure a considerably lower limit for static capacity while still using the same dimensions for the cable. We have had an almost unlooked for success into his direction in the employment of Manila paper in the place of cotton as the wrappings of the conductors. Dry-core cable was thus established and has held the field for telephone work both on short subscribers’ circuits and for long-distance transmission right up to recent times, when its supremacy has been challenged by the coaxial cable. For long distances the multi-twin, i.e. one pair twisted round another, and the star quad, i.e., four wires laid up together with diagonal wires forming pairs, were adopted. The cables were at first drawn into cast-iron pipes and later earthenware single and multiple ducts. The heavy overhead long-distance lines continued to grow in number and size until the First World War but, as even then they failed to met the demand, more and more cables were laid. After the war much attention was given to the production of a star quad cable with improved symmetry. This was achieved by the use of a spiral thread under the paper and a thread down the center of the quad assembly. Throughout the period already covered in the possibilities of automatic switching of lines. As early as 1879 the brothers Connolly of Philadelphia proposed an automatic telephone which in which pulses of current were transmitted by the rotation of a letter pointer on the principle of the Foment telegraph. The possibilities of this system were strictly limited and others were suggested, but in 1889 Strowger, an undertaker of Kansas City, U.S.A., dissatisfied with his telephone service, made the first tentative step towards what has become a practical system applied on a world-wide basis. The basis of the Strowger system was the operation of ratchet and pawl by means of current impulses sent out by the subscriber on a counting system. To send the figure 1 he pressed a key once, to send 5, five times, and so on. Several keys were provided, one for units, one for tens, one for hundreds, and soon, and each was connected by a separate wire to the central exchange. The contacts were contained within a hollow cylinder and a radial arm, moved step by step by incoming impulses, could rotate over the contacts. It could also rise and fall. Various modifications were followed in 1895 by a design very similar to that which has survived i.e. Ten rows each of ten contacts arranged in the form of an arc. The upright shaft had both vertical and rotary movement. In 1896 the subscribers’ dial- sending apparatus was invented and with modifications has become the standard equipment.
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