at this stage when Bell’s telephone was shown at the Philadelphia
Exhibition of 1876. Sir William Thompson did not hesitate to call
it ‘the wonder of wonders,’ and it instantly attracted universal
attention, although there was at first much incredulity as to its
genuineness. This telephone, in fact, reproduced articulate words, a
result which surpassed all the conceptions of physicists. In this case
it was no longer a conception, to be treated as visionary until there
was proof to the contrary: the instrument spoke, and even spoke so
loudly that it was not necessary to apply the ear. Sir William Thompson
spoke to this effect on the subject at the meeting of the British
Association at Glasgow in September 1876:--
‘In the department of telegraphs in the United States I saw and heard
Mr. Elisha Gray’s electric telephone, of wonderful construction, which
can repeat four despatches at the same time in the Morse code, and,
with some improvements in detail, this instrument is evidently capable
of a fourfold delivery. In the Canadian department I heard “To be or
not to be? There’s the rub,” uttered through a telegraphic wire, and
its pronunciation by electricity only made the rallying tone of the
monosyllables more emphatic. The wire also repeated some extracts
from New York papers. With my own ears I heard all this, distinctly
articulated through the slender circular disk formed by the armature
of an electro-magnet. It was my fellow-juryman, Professor Watson, who,
at the other extremity of the line, uttered these words in a loud
and distinct voice, while applying his mouth to a tightly stretched
membrane provided with a small piece of soft iron, which executed
movements corresponding to the sound vibrations of the air close to an
electro-magnet introduced into the circuit. This discovery, the wonder
of wonders in electric telegraphy, is due to a young fellow-countryman
of our own, Mr. Graham Bell, a native of Edinburgh and now naturalised
in New York.
‘It is impossible not to admire the daring invention by which we have
been able to realise with these simple expedients the complex problem
of reproducing by electricity the tones and delicate articulations of
voice and speech; and it was necessary, in order to obtain this result,
to find out the means of varying the intensity of the current in the
same proportion as the inflections of the sound emitted by the voice.’
If we are to believe Mr. Graham Bell, the invention of the telephone
was not due to a spontaneous and fortunate conception: it was the
result of his long and patient studies in acoustic science, and of
the labours of the physicists who preceded him.[2] His father, Mr.
Alexander Melville Bell, of Edinburgh, had studied this science
deeply, and had even succeeded in representing with great ingenuity
the adaptation of the vocal organs for the emission of sound. It was
natural that he should instil a taste for his favourite studies into
his son’s mind, and they made together numerous researches in order to
discover the relations which exist between the different elements of
speech in different languages, and the musical relations of vowels. It
is true that several of these researches had been made by M. Helmholtz,
and under more favourable conditions; but these studies were of great
use to Mr. Bell when he was afterwards occupied with the telephone, and
Helmholtz’s experiments, which he repeated with one of his friends,
Mr. Hellis of London, concerning the artificial reproduction of vowels
by means of electric tuning-forks, launched him into the study of the
application of electricity to acoustic instruments. He first invented
a system of an electric harmonica with a key-board, in which the
different sounds of the scale were reproduced by electric diapasons of
different forms, adapted to different notes, and which, when set in
motion by the successive lowering of the keys, could reproduce sounds
corresponding to the notes touched, just as in an ordinary piano.
He next, as he tells us, turned his attention to telegraphy, and
thought of making the Morse telegraphs audible by causing the
electro-magnetic organ to react on sounding contacts. It is true
that this result had already been obtained in the sounders used
in telegraphy, but he thought that by applying this system to his
electric harmonica, and by employing such an intensifying instrument as
Helmholtz’s resonator at the receiving station, it would be possible to
obtain through a single wire simultaneous transmissions which should be
due to the action of the voice. We shall see presently that this idea
was realised almost at the same time by several inventors, among others
by M. Paul Lacour, of Copenhagen, Mr. Elisha Gray, of Chicago, and
Messrs. Edison and Varley.
Mr. Bell’s study of electric telephones really dates from this time,
and he passed from complex to simple instruments, making a careful
study of the different modes of vibration which arise from different
modes of electric action. The following is an abstract, with the
omission of more technical details, of the paper read by Mr. Bell to
the Society of Telegraphic Engineers, London, October 31, 1877.
If the intensity of an electric current is represented by the ordinates
of a curve, and the duration of breaks in the current by the abscissæ,
the given curve may represent the waves of the positive or negative
current respectively, above and below the line of X, and these waves
will be more or less accentuated, just as the transmitted currents are
more or less instantaneous.
If the currents which are interrupted to produce a sound are quite
instantaneous in their manifestation, the curve represents a series of
isolated indentations, as we see in fig. 7; and if the interruptions
are so made as only to produce differences of intensity, the curve
is presented under the form of fig. 8. Finally, if the emissions of
current are so ordered that their intensity alternately increases
and diminishes, the curve takes the form represented in fig. 9. In
the first case, the currents are _intermittent_; in the second,
_pulsatory_; in the third case, they are _undulatory_.
[Illustration: FIG. 7.]
[Illustration: FIG. 8.]
[Illustration: FIG. 9.]
These currents are necessarily positive or negative, according to their
position above or below the line _x_, and if they are alternately
reversed, the curves present the form given in fig. 10, curves which
essentially differ from the first, not merely in the different form
of the indentations, but especially in the suppression of the extra
current, which is always found in the pulsatory and undulatory
currents.
[Illustration: FIG. 10.]
The two former systems of currents have long been in use for the
electric transmission of musical sounds, of which we have an
interesting example in Reiss’s telephone already described. But Mr.
Bell claims to have been the first to employ the undulatory currents,
which made it possible to solve the problem of transmitting speech.[3]
In order to estimate the importance of this discovery, it will be
enough to analyse the effects produced with these different systems of
currents when several notes of varying pitch are to be combined.
Fig. 7 shows a combination in which the styles _a_, _a′_, of two
sending instruments cause the interruption of the current from the same
battery B, so that the given vibrations should be between them in the
relation of a tierce major, that is in the relation of four to five.
Under such conditions, the currents are intermittent, and four contacts
of _a_ are produced in the same space of time as the five contacts of
_a′_, and the corresponding electric intensities will be represented
by the indentations we see in A^2 and in B^2: the combination of
these intensities A^2 + B^2 will produce the indentations at unequal
intervals which may be observed on the third line. It is evident that
although the current maintains a uniform intensity, there is less time
for the breaks when the interrupting styles act together than when they
act separately, so that when there are a number of contacts effected
simultaneously by styles working at different degrees of velocity, the
effects produced will have the effect of a continuous current. The
maximum number of distinct effects which can be produced in this way
will, however, greatly depend on the relation which exists between
the durations of the make and break of the current. The shorter the
contacts are, and the longer the breaks, the more numerous will be the
effects transmitted without confusion, and _vice versâ_.
By the aid of pulsatory currents the transmission of musical sounds is
effected in the way indicated in fig. 8, and it is seen that when they
are produced simultaneously, the result A^2 + B^2 is analogous to that
which would be produced by a continuous current of minimum intensity.
In the case of undulatory currents the result is different, but in
order to produce them it is necessary to have recourse to inductive
effects, and fig. 9 indicates the manner in which the experiment should
be made. In this case, ‘the current from the battery B is thrown into
waves by the inductive action of iron or steel reeds M, M, vibrated in
front of electro-magnets _e_, _e_, placed in circuit with the battery:
A^2 and B^2 represent the undulations caused in the current by the
vibration of the magnetised bodies, and it will be seen that there are
four undulations of B^2 in the same time as five undulations of A^2.
The resultant effect upon the main line is expressed by the curve A^2
+ B^2, which is the algebraical sum of the sinusoidal curves A^2 and
B^2. A similar effect is produced when reversed undulatory currents are
employed, as in fig. 10, where the current is produced by the vibration
of permanent magnets united upon a circuit, without a voltaic battery.
‘It will be understood from figs. 9 and 10 that the effect of
transmitting musical signals of different pitches simultaneously along
a single wire is not to obliterate the vibratory character of the
current, as in the case of intermittent and pulsatory currents, but to
change the shapes of the electrical undulations. In fact, the effect
produced upon the current is precisely analogous to the effect produced
in the air by the vibration of the inducing bodies M, M′. Hence it
should be possible to transmit as many musical tones simultaneously
through a telegraph wire as through the air.’
[Illustration: FIG. 11.]
After applying these principles to the construction of a telegraphic
system for multiple transmissions, Mr. Bell lost no time in making use
of his researches to improve the vocal training of deaf mutes. ‘It is
well known,’ he said, ‘that deaf mutes are dumb merely because they are
deaf, and that there is no defect in their vocal organs to incapacitate
them from utterance. Hence it was thought that my father’s system of
pictorial symbols, popularly known as visible speech, might prove a
means whereby we could teach the deaf and dumb to use their vocal
organs and to speak. The great success of these experiments urged upon
me the advisability of devising methods of exhibiting the vibrations
of sound optically, for use in teaching the deaf and dumb. For some
time I carried on experiments with the manometric capsule of Koenig,
and with the phonautograph of Léon Scott. The scientific apparatus in
the Institute of Technology in Boston was freely placed at my disposal
for these experiments, and it happened that at that time a student of
the Institute of Technology, Mr. Maurey, had invented an improvement
upon the phonautograph. He had succeeded in vibrating by the voice
a stylus of wood about a foot in length which was attached to the
membrane of the phonautograph, and in this way he had been enabled to
obtain enlarged tracings upon a plane surface of smoked glass. With
this apparatus I succeeded in producing very beautiful tracings of
the vibrations of the air for vowel sounds. Some of these tracings
are shown in fig. 11. I was much struck with this improved form of
apparatus, and it occurred to me that there was a remarkable likeness
between the manner in which this piece of wood was vibrated by the
membrane of the phonautograph and the manner in which the _ossiculæ_
of the human ear were moved by the tympanic membrane. I determined
therefore to construct a phonautograph modelled still more closely
upon the mechanism of the human ear, and for this purpose I sought
the assistance of a distinguished aurist in Boston, Dr. Clarence J.
Blake. He suggested the use of the human ear itself as a phonautograph,
instead of making an artificial imitation of it. The idea was novel,
and struck me accordingly, and I requested my friend to prepare a
specimen for me, which he did. The apparatus, as finally constructed,
is shown in fig. 12. The _stapes_ was removed, and a stylus of hay
about an inch in length was attached to the end of the _incus_. Upon
moistening the _membrana tympani_ and the _ossiculæ_ with a mixture of
glycerine and water, the necessary mobility of the parts was obtained;
and upon singing into the external artificial ear the stylus of hay
was thrown into vibration, and tracings were obtained upon a plane
surface of smoked glass passed rapidly underneath. While engaged in
these experiments I was struck with the remarkable disproportion in
weight between the membrane and the bones that were vibrated by it. It
occurred to me that if a membrane as thin as tissue paper could control
the vibration of bones that were, compared to it, of immense size
and weight, why should not a larger and thicker membrane be able to
vibrate a piece of iron in front of an electro-magnet, in which case the
complication of steel rods shown in my first form of telephone, could
be done away with, and a simple piece of iron attached to a membrane be
placed at either end of the telegraphic circuit?
[Illustration: FIG. 12.]
‘For this purpose I attached the reed A (fig. 13) loosely by one
extremity to the uncovered pole _h_ of the magnet, and fastened the
other extremity to the centre of a stretched membrane of goldbeaters’
skin _n_. I presumed that upon speaking in the neighbourhood of the
membrane _n_, it would be thrown into vibration and cause the steel
reed A to move in a similar manner, occasioning undulations in the
electrical current that would correspond to the changes in the density
of the air during the production of the sound; and I further thought
that the change of the intensity of the current at the receiving end
would cause the magnet there to attract the reed A′ in such a manner
that it should copy the motion of the reed A, in which case its
movements would occasion a sound from the membrane _n′_ similar in
_timbre_ to that which had occasioned the original vibration.
[Illustration: FIG. 13.]
[Illustration: FIG. 14.]
‘The results, however, were unsatisfactory and discouraging. My friend
Mr. Thomas A. Watson, who assisted me in this first experiment,
declared that he heard a faint sound proceed from the telephone at
his end of the circuit, but I was unable to verify his assertion.
After many experiments attended by the same only partially successful
results, I determined to reduce the size and weight of the spring as
much as possible. For this purpose I fastened a piece of clock spring,
about the size and shape of my thumbnail, firmly to the centre of the
diaphragm, and had a similar instrument at the other end (fig. 14);
we were then enabled to obtain distinctly audible effects. I remember
an experiment made with this telephone, which at the time gave me
great satisfaction and delight. One of the telephones was placed in my
lecture-room in the Boston University, and the other in the basement
of the adjoining building. One of my students repaired to the distant
telephone to observe the effects of articulate speech, while I uttered
the sentence, “Do you understand what I say?” into the telephone
placed in the lecture-hall. To my delight an answer was returned
through the instrument itself, articulate sounds proceeded from the
steel spring attached to the membrane, and I heard the sentence, “Yes,
I understand you perfectly.” It is a mistake, however, to suppose
that the articulation was by any means perfect, and expectancy no
doubt had a great deal to do with my recognition of the sentence;
still, the articulation was there, and I recognised the fact that the
indistinctness was entirely due to the imperfection of the instrument.
I will not trouble you by detailing the various stages through which
the apparatus passed, but shall merely say that after a time I produced
the form of instrument shown in fig. 15, which served very well as
a receiving telephone. In this condition my invention was exhibited
at the Centennial Exhibition in Philadelphia. The telephone shown in
fig. 14 was used as a transmitting instrument, and that in fig. 15 as
a receiver, so that vocal communication was only established in one
direction.
[Illustration: FIG. 15.]
‘The articulation produced from the instrument shown in fig. 15 was
remarkably distinct, but its great defect consisted in the fact that it
could not be used as a transmitting instrument, and thus two telephones
were required at each station, one for transmitting and one for
receiving spoken messages.
‘It was determined to vary the construction of the telephone, and I
sought by changing the size and tension of the membrane, the diameter
and thickness of the steel spring, the size and power of the magnet,
and the coils of insulated wire around their poles, to discover
empirically the exact effect of each element of the combination, and
thus to deduce a more perfect form of apparatus. It was found that a
marked increase in the loudness of the sounds resulted from shortening
the length of the coils of wire, and by enlarging the iron diaphragm
which was glued to the membrane. In the latter case, also, the
distinctness of the articulation was improved. Finally, the membrane
of goldbeaters’ skin was discarded entirely, and a simple iron plate
was used instead, and at once intelligible articulation was obtained.
The new form of instrument is that shown in fig. 16, and, as had been
long anticipated, it was proved that the only use of the battery was to
magnetise the iron core of the magnet, for the effects were equally
audible when the battery was omitted and a rod of magnetised steel
substituted for the iron core of the magnet.
‘It was my original intention, and it was always claimed by me, that
the final form of telephone would be operated by permanent magnets in
place of batteries, and numerous experiments had been carried on by Mr.
Watson and myself privately for the purpose of producing this effect.
[Illustration: FIG. 16.]
‘At the time the instruments were first exhibited in public the results
obtained with permanent magnets were not nearly so striking as when a
voltaic battery was employed, wherefore we thought it best to exhibit
only the latter form of instrument.
‘The interest excited by the first published accounts of the operation
of the telephone led many persons to investigate the subject, and I
doubt not that numbers of experimenters have independently discovered
that permanent magnets might be employed instead of voltaic batteries.
Indeed one gentleman, Professor Dolbear, of Tufts College, not only
claims to have discovered the magneto-electric telephone, but I
understand charges me with having obtained the idea from him through
the medium of a mutual friend.
[Illustration: FIG. 17.]
‘A still more powerful form of apparatus was constructed by using a
powerful compound horseshoe magnet in place of the straight rod which
had been previously used (see fig. 17). Indeed the sounds produced by
means of this instrument were of sufficient loudness to be faintly
audible to a large audience, and in this condition the instrument was
exhibited in the Essex Institute, in Salem, Massachusetts, on February
12, 1877, on which occasion a short speech shouted into a similar
telephone in Boston, sixteen miles away, was heard by the audience in
Salem. The tones of the speaker’s voice were distinctly audible to an
audience of 600 people, but the articulation was only distinct at a
distance of about 6 feet. On the same occasion, also, a report of the
lecture was transmitted by word of mouth from Salem to Boston, and
published in the papers the next morning.
[Illustration: FIG. 18.]
‘From the form of telephone shown in fig. 16 to the present form of
the instrument (fig. 18) is but a step. It is in fact the arrangement
of fig. 16 in a portable form, the magnet N S being placed inside the
handle, and a more convenient form of mouthpiece provided.
‘And here I wish to express my indebtedness to several scientific
friends in America for their co-operation and assistance. I would
specially mention Professor Peirce and Professor Blake, of Brown
University, Dr. Channing, Mr. Clarke, and Mr. Jones. It was always my
belief that a certain ratio would be found between the several parts of
a telephone, and that the size of the instrument was immaterial; but
Professor Peirce was the first to demonstrate the extreme smallness of
the magnets which might be employed. The convenient form of mouthpiece
shown in fig. 17, now adopted by me, was invented solely by my friend
Professor Peirce.’
[Illustration: FIG. 19.]
Another form of transmitting telephone exhibited in Philadelphia,
intended for use with the receiving telephone (fig. 15), is represented
by fig. 19.
A platinum wire attached to a stretched membrane completed a voltaic
circuit by dipping into water. Upon speaking to the membrane,
articulate sounds proceeded from the telephone in the distant room.
The sounds produced by the telephone became louder when dilute
sulphuric acid, or a saturated solution of salt, was substituted for
the water. Audible effects were also produced by the vibration of
plumbago in mercury, in a solution of bichromate of potash, in salt and
water, in dilute sulphuric acid, and in pure water.
Mr. Bell goes on to say:
‘I have found also that a musical tone proceeds from a piece of
plumbago or retort carbon when an intermittent current of electricity
is passed through it, and I have observed the most curious audible
effects produced by the passage of reversed intermittent currents
through the human body. A rheotome was placed in circuit with the
primary wires of an induction coil, and the fine wires were connected
with two strips of brass. One of these strips was held closely against
the ear, and a loud sound proceeded from it whenever the other slip was
touched with the other hand. The strips of brass were next held one in
each hand. The induced currents occasioned a muscular tremor in the
fingers. Upon placing my forefinger to my ear a loud crackling noise
was audible, seemingly proceeding from the finger itself. A friend who
was present placed my finger to his ear, but heard nothing. I requested
him to hold the strips himself. He was then distinctly conscious of a
noise (which I was unable to perceive) proceeding from his finger. In
this case a portion of the induced currents passed through the head of
the observer when he placed his ear against his own finger; and it is
possible that the sound was occasioned by a vibration of the surfaces
of the ear and finger in contact.
‘When two persons receive a shock from a Ruhmkorff’s coil by clasping
hands, each taking hold of one wire of the coil with the free hand, a
sound proceeds from the clasped hands. The effect is not produced when
the hands are moist. When either of the two touches the body of the
other, a loud sound comes from the parts in contact. When the arm of
one is placed against the arm of the other, the noise produced can be
heard at a distance of several feet. In all these cases a slight shock
is experienced so long as the contact is preserved. The introduction
of a piece of paper between the parts in contact does not materially
interfere with the production of the sounds, but the unpleasant effects
of the shock are avoided.