Part 1

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THE TELEPHONE. A LECTURE

ENTITLED RESEARCHES IN ELECTRIC TELEPHONY,

BY PROFESSOR ALEXANDER GRAHAM BELL,

DELIVERED BEFORE The Society of Telegraph Engineers, OCTOBER 31ST, 1877.

PUBLISHED BY THE SOCIETY, AND EDITED BY LIEUT.-COL. FRANK BOLTON, C.E., HON. SECRETARY, AND WILLIAM EDWARD LANGDON, ACTING SECRETARY.

London: E. AND F. N. SPON, 46, CHARING CROSS.

New York: 446, BROOME STREET.

1878. _Price One Shilling and Sixpence._ The right of translation and reproduction is reserved

EXTRACTS OF PROCEEDINGS OF THE SOCIETY OF TELEGRAPH ENGINEERS.

Special General Meeting, held at 25, Great George Street, Westminster, on Wednesday, the 31st October, 1877. PROFESSOR ABEL, C.B., F.R.S., President, in the Chair.

The PRESIDENT: Gentlemen, the Council of the Society of Telegraph Engineers felt that they were sure of doing what the members would consider right in summoning a special meeting for the two-fold purpose of giving a welcome to Professor Bell to this country and affording the Members an opportunity of hearing from him an account, which he has been so good as to promise to give us, of the nature, history, and development of, what may well be called, one of the most interesting discoveries of our age. Our time is very precious this evening. We all desire to hear everything Professor Bell can tell us on this subject, and many gentlemen will probably desire afterwards to ask questions or discuss the subject, for I see present a great number of eminent scientific men. I will not waste another moment, but at once call upon Professor Bell to commence his discourse on the Electric Telephone.

RESEARCHES IN ELECTRIC TELEPHONY.

By PROFESSOR ALEXANDER GRAHAM BELL.

PROFESSOR BELL: Mr. President and Gentlemen of the Society of Telegraph Engineers. It is to-night my pleasure, as well as duty, to give you some account of the telephonic researches in which I have been so long engaged. Many years ago my attention was directed to the mechanism of speech by my father, Alexander Melville Bell, of Edinburgh, who has made a life-long study of the subject. Many of those present may recollect the invention by my father of a means of representing, in a wonderfully accurate manner, the positions of the vocal organs in forming sounds. Together we carried on quite a number of experiments, seeking to discover the correct mechanism of English and foreign elements of speech, and I remember especially an investigation in which we were engaged concerning the musical relations of vowel sounds. When vowel sounds are whispered, each vowel seems to possess a particular pitch of its own, and by whispering certain vowels in succession a musical scale can be distinctly perceived. Our aim was to determine the natural pitch of each vowel; but unexpected difficulties made their appearance, for many of the vowels seemed to possess a double pitch—one due, probably, to the resonance of the air in the mouth, and the other to the resonance of the air contained in the cavity behind the tongue, comprehending the pharynx and larynx.

I hit upon an expedient for determining the pitch which at that time I thought to be original with myself. It consisted in vibrating a tuning-fork in front of the mouth while the positions of the vocal organs for the various vowel sounds were silently taken. It was found that each vowel position caused the reinforcement of some particular fork or forks.

I wrote an account of these researches to Mr. Alex. J. Ellis, of London, whom I have very great pleasure in seeing here to-night. In reply he informed me that the experiments related had already been performed by Helmholtz, and in a much more perfect manner than I had done. Indeed, he said that Helmholtz had not only analysed the vowel sounds into their constituent musical elements, but had actually performed the synthesis of them.

He had succeeded in producing, artificially, certain of the vowel sounds by causing tuning-forks of different pitch to vibrate simultaneously by means of an electric current. Mr. Ellis was kind enough to grant me an interview for the purpose of explaining the apparatus employed by Helmholtz in producing these extraordinary effects, and I spent the greater part of a delightful day with him in investigating the subject. At that time, however, I was too slightly acquainted with the laws of electricity fully to understand the explanations given; but the interview had the effect of arousing my interest in the subjects of sound and electricity, and I did not rest until I had obtained possession of a copy of Helmholtz’ great work,[1] and had attempted, in a crude and imperfect manner it is true, to reproduce his results. While reflecting upon the possibilities of the production of sound by electrical means, it struck me that the principle of vibrating a tuning-fork by the intermittent attraction of an electro-magnet might be applied to the electrical production of music.

I imagined to myself a series of tuning-forks of different pitches, arranged to vibrate automatically in the manner shown by Helmholtz, each fork interrupting at every vibration a voltaic current; and the thought occurred, “Why should not the depression of a key like that of a piano direct the interrupted current from any one of these forks, through a telegraph wire, to a series of electro-magnets operating the strings of a piano or other musical instrument, in which case a person might play the tuning-fork piano in one place and the music be audible from the electromagnetic piano in a distant city?”

The more I reflected upon this arrangement the more feasible did it seem to me; indeed, I saw no reason why the depression of a number of keys at the tuning-fork end of the circuit should not be followed by the audible production of a full chord from the piano in the distant city, each tuning-fork affecting at the receiving end that string of the piano with which it was in unison. At this time the interest which I felt in electricity led me to study the various systems of telegraphy in use in this country and in America. I was much struck with the simplicity of the Morse alphabet, and with the fact that it could be read by sound. Instead of having the dots and dashes recorded upon paper, the operators were in the habit of observing the duration of the click of the instruments, and in this way were enabled to distinguish by ear the various signals.

It struck me that in a similar manner the duration of a musical note might be made to represent the dot or dash of the telegraph code, so that a person might operate one of the keys of the tuning-fork piano referred to above, and the duration of the sound proceeding from the corresponding string of the distant piano be observed by an operator stationed there. It seemed to me that in this way a number of distinct telegraph messages might be sent simultaneously from the tuning-fork piano to the other end of the circuit, by operators each manipulating a different key of the instrument. These messages would be read by operators stationed at the distant piano, each receiving operator listening for signals of a certain definite pitch, and ignoring all others. In this way could be accomplished the simultaneous transmission of a number of telegraphic messages along a single wire, the number being limited only by the delicacy of the listener’s ear. The idea of increasing the carrying power of a telegraph wire in this way took complete possession of my mind, and it was this practical end that I had in view when I commenced my researches in Electric Telephony.

In the progress of science it is universally found that complexity leads to simplicity, and in narrating the history of scientific research it is often advisable to begin at the end.

In glancing back over my own researches I find it necessary to designate, by distinct names, a variety of electrical currents by means of which sounds can be produced, and I shall direct your attention to several distinct species of what may be termed “telephonic” currents of electricity. In order that the peculiarities of these currents may be clearly understood, I shall ask Mr. Frost to project upon the screen a graphical illustration of the different varieties.

The graphical method of representing electrical currents here shown is the best means I have been able to devise of studying in an accurate manner the effects produced by various forms of telephonic apparatus, and it has led me to the conception of that peculiar species of telephonic current here designated as _undulatory_, which has rendered feasible the artificial production of articulate speech by electrical means.

A horizontal line (_g g´_) is taken as the zero of current, and impulses of positive electricity are represented above the zero line, and negative impulses below it, or _vice versâ_.

The vertical thickness of any electrical impulse (_b_ or _d_), measured from the zero line, indicates the intensity of the electrical current at the point observed, and the horizontal extension of the electric line (_b_ or _d_) indicates the duration of the impulse.

Nine varieties of telephonic currents may be distinguished, but it will only be necessary to show you six of these. The three primary varieties designated as “intermittent,” “pulsatory,” and “undulatory,” are represented in lines 1, 2, and 3.

Sub-varieties of these can be distinguished as “direct” or “reversed” currents according as the electrical impulses are all of one kind or are alternately positive and negative. “Direct” currents may still further be distinguished as “positive” or “negative,” according as the impulses are of one kind or of the other.

An _intermittent current_ is characterised by the alternate presence and absence of electricity upon the circuit;

A _pulsatory current_ results from sudden or instantaneous changes in the intensity of a continuous current; and

An _undulatory current_ is a current of electricity, the intensity of which varies in a manner proportional to the velocity of the motion of a particle of air during the production of a sound: thus the curve representing graphically the undulatory current for a simple musical tone is the curve expressive of a simple pendulous vibration—that is, a sinusoidal curve.

Telephonic currents of electricity may be:

{Direct {Positive 1 Positive intermittent current. Intermittent { {Negative 2 Negative ” ” { —— Reversed 3 Reversed ” ”

{Direct {Positive 4 Positive pulsatory current. Pulsatory { {Negative 5 Negative ” ” { —— Reversed 6 Reversed ” ”

{Direct {Positive 7 Positive undulatory current. Undulatory { {Positive 8 Negative ” ” { —— Reversed 9 Reversed ” ”

And here I may remark, that, although the conception of the undulatory current of electricity is entirely original with myself, methods of producing sound by means of intermittent and pulsatory currents have long been known. For instance, it was long since discovered that an electro-magnet gives forth a decided sound when it is suddenly magnetized or demagnetized. When the circuit upon which it is placed is rapidly made and broken, a succession of explosive noises proceeds from the magnet. These sounds produce upon the ear the effect of a musical note when the current is interrupted a sufficient number of times per second. The discovery of “Galvanic Music,” by Page,[2] in 1837, led inquirers in different parts of the world almost simultaneously to enter into the field of telephonic research; and the acoustical effects produced by magnetization were carefully studied by Marrian,[3] Beatson,[4] Gassiot,[5] De la Rive,[6] Matteucci,[7] Guillemin,[8] Wertheim,[9] Wartmann,[10] Janniar,[11] Joule,[12] Laborde,[13] Legat,[14] Reis,[15] Poggendorff,[16] Du Moncel,[17] Delezenne,[18] and others.[19] It should also be mentioned that Gore[20] obtained loud musical notes from mercury, accompanied by singularly beautiful crispations of the surface during the course of experiments in electrolysis; Page[21] produced musical tones from Trevelyan’s bars by the action of the galvanic current; and further it was discovered by Sullivan[22] that a current of electricity is generated by the vibration of a wire composed partly of one metal and partly of another. The current was produced so long as the wire emitted a musical note, but stopped immediately upon the cessation of the sound.

For several years my attention was almost exclusively directed to the production of an instrument for making and breaking a voltaic circuit with extreme rapidity, to take the place of the transmitting tuning-fork used in Helmholtz’ researches. I will not trouble you with the description of all the various forms of apparatus that were devised, but will merely direct your attention to one of the best of them, shown in fig. 2. In the transmitting instrument T, a steel reed _a_ is employed, which is kept in continuous vibration by the action of an electro-magnet _e_ and local battery. In the course of its vibration the reed strikes alternately against two fixed points _m_, _l_, and thus completes alternately a local and a main circuit. When the key K is depressed an intermittent current from the main battery B is directed to the line-wire W, and passes through the electro-magnet E of a receiving instrument R at the distant end of the circuit, and thence to the ground G. The steel reed A is placed in front of the receiving magnet, and when its normal rate of vibration is the same as the reed of the transmitting instrument it is thrown into powerful vibration, emitting a musical tone of a similar pitch to that produced by the reed of the transmitting instrument, but if it is normally of a different pitch it remains silent.

A glance at figs. 3, 4, and 5 will show the arrangement of such instruments upon a telegraphic circuit, designed to enable a number of telegraphic despatches to be transmitted simultaneously along the same wire. The transmitters and receivers that are numbered alike have the same pitch or rate of vibration. Thus the reed of T´ is in unison with the reeds T´ and R´ at all the stations upon the circuit, so that a telegraphic despatch sent by the manipulation of the key K´ at the station shown in fig. 3 will be received upon the receiving instruments K´ at all the other stations upon the circuit. Without going into details, I shall merely say that the great defects of this plan of multiple telegraphy were found to consist, firstly, in the fact that the receiving operators were required to possess a good musical ear in order to discriminate the signals; and secondly, that the signals could only pass in one direction along the line (so that two wires would be necessary in order to complete communication in both directions). The first objection was got over by employing the device which I term a “vibratory circuit-breaker,” shown in the next diagram, whereby musical signals can be automatically recorded.

Fig. 6 shows a receiving instrument R, with a vibratory circuit-breaker _v_ attached. The light spring-lever _v_ overlaps the free end of the steel reed A, and normally closes a local circuit, in which may be placed a Morse-sounder or other telegraphic apparatus. When the reed A is thrown into vibration by the passage of a musical signal, the spring arm _v_ is thrown upwards, opening the local circuit at the point 5. When the spring-arm _v_ is so arranged as to have normally a much slower rate of vibration than the reed A_{1}, the local circuit is found to remain permanently open during the vibration of A, the spring-arm _v_ coming into contact with the point 5 only upon the cessation of the receiver’s vibration. Thus the signals produced by the vibration of the reed A are reproduced upon an ordinary telegraphic instrument in the local circuit.

Fig. 7 shows the application of electric telephony to autographic telegraphy.

T, T´, &c., represent the reeds of transmitting instruments of different pitch, R, R´, &c., the receivers at the distant station of corresponding pitch, and, _r_, _r´_, &c., the vibratory circuit-breakers attached to the receiving instruments, and connected with metallic bristles, 21, resting upon chemically prepared paper P. The message, or picture, to be copied, is written upon a metallic surface, F__0_, with non-metallic ink, and placed upon a metallic cylinder 7, connected with the main battery B; and the chemically prepared paper P, upon which the message is to be received, is placed upon a metallic cylinder connected with the local battery B´ at the receiving station. When the cylinders at either end of the circuit are rotated in the direction of the arrows—but not necessarily at the same rate of speed—a _fac simile_ of whatever is written or drawn upon the metallic surface F__0_ appears upon the chemically prepared paper P.

The method by means of which the musical signals may be sent simultaneously in both directions along the same circuit is shown in our next illustration, figures 8, 9, and 10. The arrangement is similar to that shown in figures 3, 4, and 5, excepting that the intermittent current from the transmitting instruments is passed through the primary wires of an induction coil, and the receiving instruments are placed in circuit with the secondary wire. In this way free earth communication is secured at either end of the circuit, and the musical signals produced by the manipulation of any key are received at all the stations upon the line. The great objection to this plan is the extreme complication of the parts and the necessity of employing local and main batteries at every station. It was also found by practical experiment that it was difficult, if not impossible, upon either of the plans here shown, to transmit simultaneously the number of musical tones that theory showed to be feasible. Mature consideration revealed the fact that this difficulty lay in the nature of the electrical current employed, and was finally obviated by the invention of the _undulatory_ current.

It is a strange fact that important inventions are often made almost simultaneously by different persons in different parts of the world, and the idea of multiple telegraphy as developed in the preceding diagrams seems to have occurred independently to no less than four other inventors in America and Europe. Even the details of the arrangements upon circuit—shown in figures 3, 4, 5, and 8, 9, 10—are extremely similar in the plans proposed by Mr. Cromwell Varley of London, Mr. Elisha Gray of Chicago, Mr. Paul La Cour of Copenhagen, and Mr. Thomas Edison of Newark, New Jersey. Into the question of priority of invention, of course, it is not my intention to go to-night.

That the difficulty in the use of an intermittent current may be more clearly understood, I shall ask you to accompany me in my explanation of the effect produced when two musical signals of different pitch are simultaneously directed along the same circuit. Fig. 11 shows an arrangement whereby the reeds _a a´_ of two transmitting instruments are caused to interrupt the current from the same battery, B. We shall suppose the musical interval between the two reeds to be a major third, in which case their vibrations are in the ratio of 4 to 5, _i.e._, 4 vibrations of _a_ are made in the same time as 5 vibrations of _a^1_. A^2 and B^2 represent the intermittent currents produced, 4 impulses of B^2 being made in the same time as 5 impulses of A^2. The line A^2 + B^2 represents the resultant effect upon the main line when the reeds _a_ and _a^1_ are simultaneously caused to make and break the same circuit, and from the illustration you will perceive that the resultant current, whilst retaining a uniform intensity, is less interrupted when both reeds are in operation than when one alone is employed. By carrying your thoughts still further you will understand that when a large number of reeds of different pitch or of different rates of vibration are simultaneously making and breaking the same circuit the resultant effect upon the main line is practically equivalent to one continuous current.

It will also be understood that the maximum number of musical signals that can be simultaneously directed along a single wire without conflict depends very much upon the ratio which the “make” bears to the “break;” the shorter the contact made, and the longer the break, the greater the number of signals that can be transmitted without confusion, and _vice versâ_. The apparatus by means of which this theoretical conclusion has been verified is here to-night, and consists of an ordinary parlour harmonium, the reeds of which are operated by wind in the usual manner. In front of each reed is arranged a metal screw, against which the reed strikes in the course of its vibration. By adjusting the screw the duration of the contact can be made long or short. The reeds are connected with one pole of a battery, and the screws against which they strike communicate with the line-wire, so that intermittent impulses from the battery are transmitted along the line-wire during the vibration of the reeds.