IB. HISTORY OF THE TELEPHONE
History of the Telephone
In 1831 Wheatstone by his "magic lyre" experiment showed [Footnote 127-2] that when the sounding-boards of two musical instruments are connected together by a rod of pine wood, a tune played on one will be faithfully reproduced by the other. This only answers, however, for telephoning musical sounds to short distances. Another and somewhat similar example is furnished by what has been variously designated as the "string," "toy," "lovers," and "mechanical" telephone. Two disks of thin metal, or two stretched membranes, each furnished with a mouthpiece, are connected together by a thin string or wire attached at each end to the centres of the membranes. A good example may be made with two cylindrical tin cups ; bottoms form the membranes and the cups the mouthpieces. When the connecting string is held taut and sounds, such as those of ordinary speech, are produced in front of one of the membranes, pulses corresponding to the fluctuations of the atmospheric pressure are transmitted along the string and communicated to the other membrane, which in its turn communicates them to the air, thus reproducing the sound. In both these examples all the three characteristicspitch, relative intensity, and qualityof sound are reproduced.
Let us now return to the development of the application of electricity to telephony. In July 1837 Dr C. G. Page of Salem, Mass., drew attention to the sound given out by an electromagnet at the instant when the electric circuit is closed or broken, and in October of the same year he discussed, in a short article [Footnote 127-3] entitled "Galvanic Music," the musical note produced by rapidly revolving the armature of an electromagnet in front of the poles. Experiments bearing on this subject were subsequently made by a great number of investigators. [Footnote 127-4] Pages discovery is of considerable importance in connexion with the theory of action of various forms of telephone, and was a very important feature in the early by Reis to transmit music and speech. On 26th August 1854 there appeared in LIllustration (Paris) an interesting article by Charles Bourseul on the electric transmission of speech. [Footnote 128-1] The writer recommended the use of a flexible place at the source of sound, which would vibrate in response to the varying pressure of the air, and thus open and close an electric circuit, and of a similar plate at the receiving station, which would be acted on electromagnetically and thus give out as many pulsations as there are breaks in the current. These suggestions were to some extent an anticipation of the work of Reis; but the conditions to be fulfilled before the sounds given out at the receiving station can be similar in pitch, quality, and relative intensity to those produced at the transmitting station are not stated, and do not seem to have been appreciated.
In Reiss lecture an apparatus was described which has given rise to much discussion as to priority in the invention of the telephone. The instrument was described in over fifty publications [Footnote 128-2] in various countries, and was well known to physical previous to Bells introduction of the electric telephone as a competitor with the electric telegraph. Reis caused a membrane to open and close an electric circuit at each vibration, thus transmitting as many electric pulses through the circuit as there were vibrations in the sound. These electric pulses were made to act on an electromagnet at the receiving station, which, in accordance with Pages discovery, gave out a sound of a pitch corresponding to the number of times it was magnetized or demagnetized per second. Reiss object was to reproduce at a distance not only music but also human speech ; but that he died not wholly succeed is clear from the following extract from his lecture : "Hitherto it has not been possible to reproduce human speech with sufficient distinctness. The consonants are for the most part reproduced pretty distictly, but not the vowels as yet in an equal degree." Considering the time at which he wrote, Reis seems to have understood very well the nature of the vibrations he had to reproduce, but he failed to comprehend how they could be reproduced by electricity. His fundamental ideathe interruption of the currentwas a fatal mistakes, which was not at the time properly understood. The suggestion of Bourseul and the experiments of Reis, are founded on the idea that a succession of currents, corresponding in number to the successive undulations of the pressure on the membrane of the transmitting instrument, could reproduced at the receiving station sounds of the same character as those produced at the sending station. Neither of them seemed to recognized anything as important except was to some extent obtained by the varying length possibly be to a small extent he used and the nature of his receiving instrument, it is hardly probable that duration of contact sensibly influenced the result. The quality of the sounds was to some extent also reproduced ; but, judging from the results of recent telephone investigation, it is highly probable that this was due, not to the varying duration, but to the varying firmness of the contact. Since the effect of the degree of contact has, through the researches of Bell, Berliner, Edison, Hughes Elisha Gray and others, become generally understood, it has become easy to make instruments very similar to those of Reis ; and even his instruments, with slight modification, can be made to speak fairly well. The accidental transmission of words by Reis, the occasional recognition of ht voice of a singer, and other instances of the transmission of quality were no doubt due to this element, the existance of or the necessity for which was never, so far as the present writer knows, hinted at by Reis.
The next worker at the telephone, and the one to whom the present great commercial importance of the instrument is due, was Bell. His aim was the production, by means of the undulations of pressure on a membrane caused by sound, of an electric current the strength of which should at every instant vary directly as the pressure varied. [Footnote 128-3] His first idea seems to have been to employ the vibrations of the current in an electric circuit, produced by moving the armature of an electromagnet included in the circuit nearer to or farther from the poles of the magnet. He proposed to make the armature partake of the vibrations of the atmosphere either by converting it into a suitable vibrator or by controlling its vibrations by a stretched membrane of parchment. In the early trials the armature had the form of a hinged lever of iron carrying a stud at one end, which pressed against the centre of a stretched membrane. The experiments with this form were not successful, and, with the view of making the moving parts as light as possible, he substituted for the comparatively heavy lever armature a small piece of clock spring, about the size of sixpence, glued to the centre of the diaphragm. The magnet was mounted with its end carrying the coil opposite, and very close to, the centre of the piece of clock spring. This answered sufficiently well to prove the feasibility of the plan, and subsequent experiments were directed to the discovery of the best form and arrangement of the parts. An increase in the size of the iron disk attached to the membrane augmented both the loudness and the distinctness of the sounds, and this finally led to the adoption of the thin iron disk now in use, which is supported round its edge, and acts as both membrane and armature. Again, the form of the opening or mouthpiece in front of the membrane exercised considerable influence on the efficiency of the instrument, and it was ultimately ascertained that a small central opening, with a thin air space extending across the face of the membrane, was best. It was also found that comparatively small magnets were sufficient, and that there was no particular virtue in the closed circuit and electromagnet, but that a small permanent having one pole in contact with the end of the core of a short electromagnet, the coil of which was in circuit with the line, but which had no permanent current flowing through it, answered the purpose quite as well. [Footnote 128-4] In fact the effect of keeping a permanent current flowing through the line and the coils of the electromagnet was to keep the core of the electro-magnet magnetized. This seems to have been almost simultaneously pointed out by Bell and others who were working in conjunction with him and by Professor Dolbear. Many experiments were made for ascertaining the best length of wire to use in the coil of the transmitting and the receiving instrument; but this is clearly a question dependent to a large extent on the nature of the line and the system of working adopted.
After Bells success a large number of experimenters entered the fields, and an almost endless variety of modifications have been described. But few possess any real merit, and almost none have any essentially new principle. [Footnote 128-5]
A telephone transmitter and a receiver on a novel plan were patented in July 1877 by Edison, shortly after the introduction of Bells instruments. The receiver was based on the change of friction produced by the passage of an electric current through the point of contact of certain substances in relative motion. In one form a drum, mounted on an axis and covered by a band of paper soaked in a solution of caustic potash, is turned under a spring the end of which is in contact through a platinum point which the paper. The spring is attached to the centre of a diaphragm is such a way that, when the drum is turned, the friction between the point of the spring and the paper deflects the diaphragm. The current from the line is made to pass through the spring and paper to the cylinder. Now it had been previously shown by Edison that, when a current is made to pass through an arrangement like that just described, the friction between the paper and the spring is greatly diminished. Hence, when the undulating telephonic currents are made to pass through the apparatus, the constant variation of the friction of the spring causes the deflexions of the diaphragm to vary in unison with the variation of the electric currents, and sounds are given out corresponding in pitch, and also to some extent in quality, with the sounds produced at the transmitting station. A cylinder of chalk was used in some of Edisons later experiments with this receiver the transmitter is illustrated (see fig. 10) and described (p. 132) below.
Experiments very similar to these of Edison were made by Elisha Gray of Boston, Mass., and described by him in papers communicated to the American Electrical Society in 1878. In these experiments the electric current passed through the fingers of the operators hand, which thus took the place of the spring in Edisons apparatus. The diaphragm was itself used as the rubbing surface, and it was either mounted and rotated or the fingers were moved over it. When the current passed, the friction was felt to increase, and the effect of sending a rapidly undulating current through the arrangement was to produce a sound. The application of this apparatus to the transmission of music is described by Gray. [Footnote 129-1]
In another form of telephone, brought prominently forward by Professor Dolbear, [Footnote 129-2] the effects are produced by electrostatic instead of electromagnetic forces, as in the Bell telephone. Sir W. Thomson observed in 1863 [Footnote 129-3] that when a condenser is charged or discharged a sharp click is heard, and a similar observation was made by Cromwell F. Varley, who proposed to make use of it in a telegraphic receiving instrument. [Footnote 129-4] In Dolbears instrument one plate of a condense is a flexible diaphragm, connected with the telephone line in such a way that the varying electric potential produced by the action of the transmitting telephone causes an increased or diminished charge in the condenser. This alteration of charge causes a corresponding charge in the mutual attraction of the plates of the condenser ; hence the flexiable plate is made to copy the vibrations of the diaphragm of the transmitter. It is obvious that this apparatus may be used either as a transmitter or as a receiver, but that the effects must under ordinary circumstances be in either case extremely feeble.
In the Reis instruments the transmitter and receiver are separate parts, which are not interchangeable. The Bell telephone can be used either as a transmitter or as a receiver. The Edison receiver and the Dolbear condenser were only intended to be used as receiving instruments.
It was very early recognizedand, indeed, is mentioned in the first patents of Bell, and in a caveat field by Elisha Gray in the United States patent office only some two hours after Bells application for a patentthat sounds and spoken words might be transmitted to a distance by causing the vibrations of a diaphragm to vary the resistance in the circuit. Both Bell and Gray proposed to do this by introducing a column of liquid into the circuit the length or the resistance of which could be varied by causing the vibrations of the diaphragm to vary the depth of immersion of light rod fixed to it and dipping into the liquid (see figs. 8, 9 below). This idea has been perhaps the most fruitful of any modification of telephonic apparatus introduced.
On 4th April 1877 Mr Emile Berliner field a caveat in the United States patent office, in which he stated that, on the principle of the variation with pressure of the resistance at the contact of two conductors, he had made an instrument which could be used as a telephone transmitter, and that, in consequence of the mutual forces between the two parts of the current on the two sides of the point of contact, the instrument was capable of acting as a receiver. The caveat was illustrated by a sketch showing a diaphragm with a metal patch in the centre, against which a metal knob was lightly pressed by an adjusting screw. This seems to have been the first transmitter in which it was proposed to use the resistance at the contact of two conductors.
Almost simultaneously with Berliner, Edison conceived the idea of using a variable resistance transmitter. [Footnote 129-5] He proposed to introduce into the circuit a cell containing carbon powder, the pressure on which would be varied by the vibrations of a diaphragm. He sometimes held the carbon powder against the diaphragm in a small shallow cell (from a quarter to half an inch in diameter and about an eighth of an inch deep), and sometimes he used what he described as a fluff, that is, a little brush of silk fibre with plumbago rubbed into it. In another form the plumbago powder was worked into a button cemented together with syrup and other substances. In the specification of the patent applied for on 21st July 1877 he showed a sketch of an instrument consisted of a diaphragm, with a small platinum patch in the centre for an electrode, against which a hard point, made of plumbago powerder cemented together with india-rubber and vulcanized, was pressed by a long spring, the pressure of the carbon against the platinum disk being adjusted by a straining screw near the base of the spring. Subsequently he filed an application for a patent in which various forms of springs and weights assisted in maintaining the contacts and otherwise improved the instrument.
In the early part of 1878 Professor Hughes, while engaged in experiments upon a Bell telephone in an electric circuit, discovered that a peculiar noise was produced whenever two hard electrodes, such as two wired, were drawn across each other, or were made to touch each other with a variable degree of firmness. Acting upon this discovery, he constructed an instrument which he called a microphone. [Footnote 129-6] and which consisted essentially (see fig. 11) of two hard carbon electrodes placed in contact, with a current passing through the point of contact and a telephone included in the same circuit. One of the electrodes was attached to a sounding board capable of being vibrated by sound-waves, and the other was held either by springs or weights in delicate contact with it. When the sounding board was spoken to or subjected sound-waves, the mechanical resistance of the loose electrode, due to its weight or the spring, or both, served to vary the pressure at the contact, and this gave to the current a form corresponding to the sound-waves, and it was therefore capable of being used as a speaking-telephone transmitter. [Footnote 130-1] The best transmitters now in use are modifications of Hughess apparatus. A microphonic apparatus very similar to it is described in the specification of German patent taken out by Robert Lutdge on 12th January 1878. In this patent the actin of the microphone is also described. [Footnote 130-2]
The next transmitter of note, introduced by Mr Francis Blake, U.S. (see fig. 13 below), although it does not, like the first microphones, embody anything intrinsically new, is one of the most perfect and convenient forms of microphone ; It is at present almost universally used in the United States.
It appears to be pretty well established that carbon in one form or another is the best material for one or both of the contacts of a microphone transmitter. When both the contacts are of the carbon and the surfaces have considerable area, say from a quarter to half an inch in diameter, the sounds are loud, but have a tendency to harshness. When, as in the Blake transmitter, one of the contacts is a piece of polished gas carbon and the other a small sphere of platinum about the twentieth of an inch in diameter, the articulation is clear, but less loud. For most purposes, however, the increased clearness more than compensates for the diminished loudness. Many transmitters in actual useas, for instance, the "Gower," largely employed in the United Kingdomhave a number of contacts. Some of these when properly adjusted are both loud and clear in their action. Although the Blake instrument is most in vogue in America, in the United Kingdom and on the Continent multiple contact microphones have found more favour. Carbon powder instruments have been to some extent used, and in one or two casesas, for examples, the Hunnings transmitterwith considerable success. The fault in most of them is the tendency of the powder to "pack," which causes the instrument to rapidly lose sensibility. In the Hunnings transmitter this difficulty is to a large extent overcome by the use of a course granular powder large extent cell (about an inch in diameter and from one-eighth to one-fourth of an inch deep). The front face of the cell is piece of platinum foil, which serves both as an electrode and as a diaphragm. The cell is placed either on edge or in inclined position when in use, the action being precisely similar to that in other transmitters. In addition to its freedom from packing, the carbon, in consequence of the inclined position of the cell, is also less liable to fall away from the electrode and break the circuit. Some packing of the powder, however, does occur, and several modifications have been proposed by Blake and others for making the sound vibrations stir the powder and keep it loose. Good results appear to have been got by placing the cell mouth downwards, the carbon powder lying on the platinum foil, and by forming the upper electrode either of wire gauze or of a perforated plate completely immersed in the powder. The sound vibrations are conveyed to the bottom of the cell by a bent tube communicating with a mouthpiece. Instruments of this class are very loud-speaking, and therefore very serviceable for long or disturbed circuits.
The radiophone is an instrument proposed by A. G. Bell and Summer Tainter in 1880 for utilizing radiant energy, such as light or radiant heat, for the transmission of sound. The apparatus forms a telephone transmitter of a particularly interesting kind. In the earlier papers describing it and the experiments which led to its invention it is called photophone, because at that time the effects were supposed to be wholly due to light. Afterwards, in order to avoid ambiguity, Bell changed the name to radiophone and suggested that, to distinguished between instruments depending on the different kinds of radiation, the means photophone, thermophone, &c., should be employed. He also proposed the name spectrophone for an application of this instrument to spectrum investigation. [Footnote 130-3] The apparatus is founded on the discovery, made by Mr May while carrying out experiments is exposed to light its electrical resistance is very different from what it is in the dark. This discovery led to a great many interesting experiments by the other investigators. [Footnote 130-4] In the thinking over this discovery in 1878 Bell conceived the idea that, if a beam of light proceeding from one station could be made to fall on a selenium plate at another station, and if its intensity could be varied by the voice of a speaker, then by connecting a telephone and a battery in circuit with the selenium plate the words spoken at the distant station would be heard in the telephone. This was found to be the case. At first, to vary the intensity of the beam, it was through a small opening, the width of which could be varied by the vibrations of a diaphragm against which the speech was directed. But better results were afterwards obtained when the diaphragm formed a mirror from which the beam of light was reflected. The spreading of the beam, due to the vibrations of the mirror diaphragm, served to vary its intensity (see fig. 18 below).
Edisons phonograph (see fig. 19 below) is an instrument whose action somewhat resembles that of a telephone transmitter and which has been much talked of in the regard to its possible applications in telephony. It was invented shortly after the introduction of the telephone for the purpose of recording sounds, and was included in some Edisons telephone patents as a means of working a telephone transmitter, and thus telephoning sounds which had been previously recorded on the phonograph sheets.
127-2 See his Scientific Papers, p. 47.
127-3 See Sillimans Journ., xxxii. p. 396 and xxxiii. p. 118.
127-4 Marrian, Phil. Mag., 3d ser., xxv. p. 382 ; Beatson, Arch. de lÉlect., v. p. 197 ; De la Rive, Treatise on Electricity, vol. i. p. 306, also Phil. Mag., 3d ser., vol. xxxv.p 422, and Comp. Rend., xx.p. 1287, xxii. p.432 ; Matteucci, Arch. de lÉlect., v. 389 ; Guillemin, Comp. Rend., xxii. p. 264 ; Wertheim, Comp. Rend., xxii. pp. 336, 544, xxvi. p. 505 also Ann. de Chim. et de Phys., xxiii. p. 302, and Phil. Mag., 3d ser., xxviii. P.544 ; Jannair, Comp. Rend., xxiii. p. 319 ; Joule, Phil. Mag., 3d ser., xxv. pp. 76, 225 ; Laborde, Comp. Rend., 1.p. 692 ; Poggendorff, Pogg. Ann., lxxxvii. p. 139, xcviii. p. 198 ; Du Moncel, Exp. de lÉlect., vol. ii. p. 125, iii. p. 83 ; and Delesenne, Bibl. Univ., 1841, xvi. p.406.
128-1 See also Didaskalia: Blätter für Geist, Gemüth, u. Publicität, Frankfort, No. 232, 28th September 1854 ; Du Moncel, Exposé des Applications de lÉlectricité, Paris, vol. ii. p. 25, ed. 1854, vol. iii. p. 110, ed. 1856, and Comp. Rend., 26th November 1877.
128-2 The English reader may consultJourn. Soc. Tel. Eng., March1883; British Assoc. Rep., 1863; Civ. Eng. and Arch. Journ., vol.xxvi. p. 307 ; R. M. Ferguson, Electricity, London, 1866, p. 257 ; S. P. Thompson, Philip Reis, the Inventor of the Telephone, London, 1883.
128-3 See A. G. Bell, "Telephone Researches," in Journ. Soc. Tel. Eng., 31st October 1877.
128-4 The extreme smallness of the magnets which might be successfully employed was first demostrated by Professor Peirce of Brown University, Providence, R. I.
128-5 For a detailed description, in a collected form, of a large number of the modification, see Du Moncel, "Le Téléphone," in Bibliothèque des Merveilles, Paris, 1882.
129-1 See George B. Prescott, The Speaking Telephone, London, 1879, pp. 151-205.
129-2 Scientific American, 18th June 1881.
129-3 Electrostatics and Magnetism, p. 236.
129-4 See Tel. Journ., 1st August 1877, p. 178 ; also Adams, Journ. Soc. Tel. Eng., 1877, p. 476.
129-5 See Journal of the Telegraph, New York, April 1877; Philadelphia Times, 9th of July 1877; and Scientific American, August 1877.
129-6 This term was used by Wheatstone in 1827 for an acoustic apparatus intended to convert very feeble into audible sounds ; see his Scientific Papers, p. 32.
130-1 See Proc. Roy. Soc., vol. xxvii. p. 362; Proc. Phys. Soc., vol. ii. p. 255; Phil. Mag., 5th ser., vol. vi. p. 44 ; Preece, Journ. Soc. Tel. Eng., vol. vii. p. 270.
130-2 Although this patent is dated prior to Hughess publications, it does not follow that the descriptions were filed before these.
130-3 On this subject see A. G. Bell, Phil. Mag., 5th ser., vol. xi. p. 510, and Journ. Soc. Tel. Eng., vol. ix p. 404 ; Mercadier, Phil. Mag., 5th ser., vol. p. 78; Tyndall, Proc. Roy. Soc. vol. xxxi. p. 307; Routgen, Phil. Mag., 5th ser., vol. xi. p. 308 ; Preece, Proc. Roy. Soc., vol. xxxi. p. 506; Rayleigh, Nature, vol. xxiii. p. 274, and Proc. Roy. Soc., 1877 ; Bidwell, Phil. Mag., 5th ser., vol. xi. p. 302 ; S. P. Thompson, Phil. Mag., 5th ser., vol. vi. p. 276.
130-4 See W. Smith, Journ. Soc. Tel. Eng., vol. v.p. 183, and vol. vi. p.423; M. L. Sale, Proc. Roy. Soc., vol. xxi. p. 283, and Phil. Mag., 4th ser., vol. xlvii. p. 216 ; Draper and Moss, Proc. Roy. Irish Acad., vol. i. p. 529 ; Rosse, Phil. Mag., 4th ser., vol. xlvii. p. 161; W. G. Adams, Proc. Roy. Soc., vol. xxiii. p. 535 and vol. xxiv. p. 163; W. G. Adams and B. E. Day, ibid., vol. xxv. p. 113; Werner Siemens, Monatsber. kön. Preuss. Akad. der Wissensch. zu Berlin, 1875, p. 280, and Phil. Mag., 4th ser. vol. i. p.416 ; Sabine, Phil. Mag., 5th ser., vol v. p. 401.
Read the rest of this article:
Telephone - Table of Contents