Alexander Graham Bell's Path to the Telephone
Introduction
Michael E. Gorman
Technology, Culture & Communications, SEAS
University of Virginia
To organize and depict, in abbreviated form, Alexander Graham Bell's
invention of the telephone, we [1] have created a series of flowchart "maps"
that include every sketch we have been able to locate from Bell's
experimental notebooks, patents, depositions in court and correspondence.
As the dates on the map indicate, time advances as on the maps from top to bottom.
Multiple boxes spreading from right to left at the same time indicate that
Bell was pursuing several lines of research at that point.
When we say that Bell followed a path to the telephone, it makes his
innovation process sound more linear and goal-directed than it really was,
though Bell tried very hard to be scientific in his approach [2] and
therefore was more linear than his competitors Edison and Gray. We refer
to this flowchart as a map because the term flowchart implies more logical structure
than does map, which may reflect the wanderings of an inventor.
This series of maps is arranged hierarchically. The top
level depicts the major experiments along Bell's path to a patent and to a
device that successfully transmitted speech. When you click on one of the
sketches in boxes on this top level, you will move to a lower-level map,
depicting a series of experiments that were subsumed under that
higher-level box. Some of these lower level maps will be combined with text
which describes the depicted experiments and/or sketches.
These maps were originally developed using a program called TopDown on the
Macintosh; exporting them to the World Wide Web has caused us to make
format changes that we think will result in improvements over the longer
term, but in the short term, may make them more difficult to use. We
welcome feedback as you attempt to explore Bell's path. What follows is a
narrative that will help you to understand the structure of the top-level map,
and will also provide references for further study.
When Bell started the early experiments depicted in the top level of the
map, he wasn't thinking about a telephone. Indeed, as the
parallelogram-shaped box on the upper right-hand part of our map suggests,
he was thinking about the cutting-edge technology of his day: the multiple
telegraph. Throughout the maps, this shape will indicate an inference about Bell's goals at a particular stage. When the goal is explicitly stated, we use a box with a wedge pointing toward the goal. At the time, everyone knew
that the inventor who could create a device that would send multiple
messages over the same wire would reap fame and fortune. A duplex that
could send two messages simultaneously was available by the early 1870s,
but Bell, Edison, and Gray were all in pursuit of a device that could send
four, six, eight, or more messages.
Bell's first idea for a multiple telegraph stemmed from his observations
of Helmholtz's apparatus for producing vowel sounds electromechanically.
The oval to the right of the "Mental Model for a Multiple Telegraph" box
suggests the Helmholtz influence; a sub-map under this oval suggests how
Bell found out about Helmholtz. Bell wanted to use Helmholtz's scientific
discoveries as the basis for a working device. Here we appear to have a
clear-cut case of an inventor borrowing his ideas from others. If Bell had
simply taken Helmholtz's apparatus and tweaked it a bit to create a
multiple telegraph, there would be no need for a cognitive map--one could
trace an invention path that required virtually no mental processing.
Bell, however, did more than modify the Helmholtz apparatus, he transformed
it. Indeed, he misunderstood it in a creative way. Helmholtz's device used a series of tuning forks and
resonance chambers to simulate vowel sounds. A single tuning fork
continually interrupted the circuit, which kept all the other forks in
constant vibration. Bell could not read Helmholtz in the original German;
instead, this apparatus was described to him by Alexander Ellis, and Bell
derived much of his understanding from complex diagrams. Therefore,
according to Robert Bruce,[3] he made an important error. He assumed the
lower interrupting fork was transmitting vowel sounds which were reproduced
by the other forks.[4] Bell assumed that if vowels could be transmitted over
wires, so could other sounds, including musical tones and consonants.
Therefore, this mapping method allows us to represent how an inventor
transforms knowledge from outside sources and contacts. An inventor's or
user's mental representation of a device is not always the same as--or
even similar to--the way the designer intended it to be represented. In
the case of invention, two kinds of representation are particularly
crucial.
Mental Models and Mechanical Representations
In terms of our cognitive framework,[5] the Helmholtz interrupting fork and
resonator served as mental models for Bell's harmonic multiple telegraph.
Mental models are dynamic visual representations of devices, objects, or
forces that an inventor or scientist can "run" in his or her "mind's eye."
There is a growing literature on mental models in cognitive psychology; the
term is not always used in the same way by different authors [6]. Our meaning
and use are best illustrated by examples.
Consider the interrupting fork and resonator. For Bell, these devices
served as mental pictures of how a multiple telegraph might be achieved.
The box below the goal statement on the upper right contains Bell's first
attempt to build a multiple telegraph transmitter and receiver. The
transmitter closely resembles Helmholtz's interrupting fork; it made or
broke contact with a dish of Mercury, which alternately completed and
interrupted the circuit. Similarly, the receiving end resembles
Helmholtz's upper resonator; the electromagnets attracted the tuning fork
every time the circuit was completed, causing the fork to vibrate. (see
lower level maps subsumed under the "Mental Model for a Multiple Telegraph"
box).
We have put boxes around the transmitter and receiver to indicate what we
call "slots",[7] or areas an inventor can concentrate on. For example, if
one divides Bell's multiple telegraph into transmitter and receiver slots,
one can then imagine putting different devices in place of the Helmholtz
fork and resonator.
Bell intended to set up a series of tuning forks which made or broke
contact with mercury cups, and match them with tuning forks on the other
end of the circuit that would vibrate at the same frequency. Four, six,
eight or more tuning forks could send separate tones over the same wire to
the same number of matching tuning forks, each of which would respond only
to the vibrations sent by its "twin" on the transmitting end.
In his subsequent experiments, he began with devices that looked like
Helmholtz's, but gradually developed alternatives that accomplished the
same goals. These alternate devices are what we call mechanical
representations; they can be inserted into slots like different values into
a variable or function. Experiments with different mechanical
representations often suggest alterations in the mental model, as we shall
see below.
Below the "Mental Model for a Multiple Telegraph" box is a conclusion,
marked by a box with a wavy line on the bottom. This indicates what Bell
learned from the line of experiments associated with the box: he now had a
clear idea how to transmit musical tones, though he had not mastered the
complexities of the circuits involved in turning this idea into a
successful multiple telegraph. Indeed, in response to his difficulties with
circuits and connections, Bell made an important decision about his
cognitive style: "It became evident to me, that with my own rude
workmanship, and with the limited time and means at my disposal, I could
not hope to construct any better models. I therefore from this time
(November, 1873) devoted less time to practical experiment than to the
theoretical development of the details of the invention."[8]
To show how Bell evolved a new mechanical representation, let us explore
one of the sub-maps associated with the box labeled "Mental Model for a
Multiple Telegraph." Figure 3* shows a lower-level, more detailed map of
how Bell developed his tuned reed relay, a mechanical representation he
used repeatedly as a kind of "transceiver" He began with two tuning fork
arrangements that were attempts to reproduce Helmholtz's apparatus and
effects as closely as possible. Then he switched to a steel plate,
vibrating over twin electromagnets, an idea he got from reading J. Baille"s
The Wonders of Electricity.[9] Finally, he left one end of the plate free
to vibrate. The result is displayed in the box labeled "Universal
Transceiver."
Here we think Bell alters his mental model to accommodate his insight that
the same device can be used as both transmitter and receiver. In effect, he
merges his transmitter and receiver slots into kind of a "transceiver"
slot.
The simplicity of this approach is appealing--and unique to Bell. Edison,
for example, recognized immediately that one had to perfect a distinct
transmitter. Gray also had a series of separate transmitters and
receivers, and only used a "transceiver" in one of his later attempts to
get around Bell's successful patent that included a speaking telegraph. [10]
Bell's experiments with reed relays and similar devices in complex
telegraph circuits continued throughout this period. Indeed, the line that
branches back to a circuit with two of these reed relays suggests how this
line of research played a critical role in Bell's first telephone--but we
will say more about that later (in the June 2nd Experiment section).
Inventors need not be limited to a single mental model; indeed, they can
consider several alternatives at one time. Bell was no exception. The
"Alternate Mental Model for a Multiple Telegraph" box shows that, in
addition to imagining a multiple harmonic telegraph in which the same
device served as both transmitter and receiver, Bell also thought about,
and experimented with, transmitters and receivers that could handle
multiple tones. In this particular sketch,[11] a cylinder of bar magnets is
rotated rapidly in front of a magnet and induces a current. This
intermittent, make-or-break current, is transmitted to a coil of wire in the
center of which a nail vibrates, making a crackling sound: "The sound
issuing from the helix is a kind of crackling noise, and cannot be called a
musical note although its pitch is quite apparent."[12]. The pitch of the
sound coming from the vibrating nail can be altered by rotating the
cylinder more rapidly or more slowly. Hence, multiple operators could send
distinct tones over the same wire simply by rotating their cylinders at
different rates, and the same kind of receiver could be used to translate
these different rotation-rates into distinct messages. This scheme
obviated the need for separately tuned forks on either end.[13]
Vibratory Analyzer Slot
How would a telegraph operator be able to distinguish different tones
reliably? Remember that the operator might have to distinguish eight or
more separate messages sent either to separately tuned forks or to a single
universal receiver. Both Bell and his competitor, Elisha Gray, confronted
this problem after they had established that the transmission of distinct tones
was possible. The box labeled "Vibratory Analyzer Slot" shows Bell's
solution, which he was able to patent.[14] The "P" inside a circle next to
the box indicates that the sketch is part of a successful patent and flags
patents in our mapping methodology.
The new slot is shown to the right of one of Bell's tuned reed relays. As
the steel reed vibrates, it makes contact with a lever, the other end of
which dips in and out of two cups of mercury, alternately making and
breaking a circuit. (See Figure 4*) Therefore, the harmonic vibrations of
the reed were translated into on-off impulses suitable for telegraphy. This
lever and twin cups resembled Morse's original telegraph portrule,
illustrating the way in which mechanical representations can readily be
borrowed from another source.[15]
The Morse device provided Bell with a mechanical representation that he
used in his March 6 application. But in his patent, Bell made it clear that it
was the principle he was after, not just a specific mechanical
representation: "Many forms of circuit breakers for the purpose may be
employed such as membranes &c., all that is required being that the circuit
breaker shall be capable of vibratory or oscillatory movement, and that its
normal rate of movement, when in oscillation or vibration, shall be slower
than that of the receiver by which it is actuated."[16] Indeed, Bell later
patented an improvement in this vibratory circuit-breaker.[17]
So, by the spring of 1875, Bell had a mental model for a complete system
of multiple telegraphy and had succeeded in patenting parts of it. A
significant part of this mental model was the idea that the goal in
multiple telegraphy was to transmit what Bell called an "undulatory
current" as opposed to the intermittent or make-or-break current used in
single telegraphy. To trace this important aspect of Bell's mental model,
we will have to go to the upper left-hand box of the Master Map.
The Ear Phonautograph
Bell lacked the electrical knowledge and expertise of other multiple
telegraph inventors like Edison and Gray. But he did posses a unique area
of expertise. He was a teacher of the deaf, and therefore understood the
importance of speech in communication. His father, Alexander Melville, had
invented a "Visible Speech" alphabet that would help the deaf learn to
speak. Bell was similarly interested in devices that would help the deaf
"see" speech, as is indicated by the goal box above "The Ear Phonautograph"
(see the top left-hand corner of the Master Map).
Bell's interest in teaching the deaf kindled his interest in devices used
to visualize sound; these devices are represented on sub-maps beneath the
ear phonautograph box. At MIT, he experimented with Koenig's manometric
flame and a version Scott's phonautograph that had been improved by Charles
Cross' pupil, Charles Morey. Bell planned to use the devices to give a
deaf child feedback. Bell would make templates of speech sounds and then
instruct the child to speak into one of the devices and reproduce the
template pattern. Since Bell could not physically record the manometric
flame patterns using photography and since the patterns were difficult to
discern, he concentrated on the phonautograph.
Controlled tests of the two devices revealed differences in curves
produced in response to the same sound. Bell concluded that the
phonautograph device needed extensive modification so that the tracings
would match the flame shapes of the manometric capsule. Considering the
phonautograph's geometry--with its thin, light membrane and the relatively
heavy wooden lever and style moved by the membrane--Bell was struck by the
resemblance between the device and the structure of the human ear. The ear
analogy suggested the sorts of modifications he might undertake to
successfully replicate the flame shapes in the tracings of this device.
The modifications aimed to make the analogy between technology and nature
more literal. Bell sought to duplicate "the shape of the membrane of the
human ear, the shapes of the bones attached to it, the mode of connection
between the two, etc."[18]
Bell built an ear phonautograph in 1874 following a suggestion from
Clarence Blake (a more detailed picture of this device can be found by
clicking on the top level phonautograph box and going to a lower level).
It consisted of the bones of an actual human ear, mounted on a wooden
frame. When one spoke into it, the bones vibrated; a bristle brush
descending from the bones traced the shape of the sound waves on a piece of
smoked glass, which could be rolled back and forth underneath..
The box with the wavy line below the phonautograph shows the conclusion
Bell drew from this experiment--that sound could be translated into visible
waves. From this phonautograph, Bell gained a tactual, "hands-on"
understanding of how speech is translated into sinusoidal or undulating
waves. From his multiple telegraph experiments, Bell gained a similar
understanding of how the vibrations of a reed could be translated intoelect
ric current, and reproduced as sound.
The Harp Apparatus
Bell's background in telegraphy and in the visible reproduction of sound
come together in the box labeled "Harp Apparatus", which represents a new
mental model of how undulating sound waves might be translated into
electric currents of the same form. Bell sketched, but never built, this
device in the summer of 1874. To understand its function, it is better to
refer to its precursor, stored in a sub-map (found by clicking on the top
level box). This device consists of two permanent horseshoe magnets with
two of Bell's steel reeds on each. Bell hoped such a device would serve as
a transceiver for two distinct signals, corresponding to each of the reeds.
Why had Bell decided to substitute a permanent magnet for the
electromagnets he had previously preferred in his multiple telegraph
experiments? In his own words, Bell realized that:
-
when a permanent magnet is moved towards the pole of an electromagnet, a
current of electricity appeared in the coil of the electro-magnet; and that
when the permanent magnet was moved from the electro-magnet, a current of
opposite kind was induced in the coils. I had no doubt, therefore, that a
permanent magnet, like the reed of one of my receiving instruments,
vibrating with the frequency of a musical sound in front of the pole of an
electro magnet, should induce in the coils of the latter alternately
positive and negative impulses corresponding in frequency to the vibration
of the reed, and that these reversed impulses would come at equal distances
apart.[19]
In other words, Bell postulates that if a magnet is moving away from a
coil half of the time and moving towards the coil the other half then the
induced current should imitate the vibrating magnet because the flux will
be increasing half of the time (magnet moving towards coil) and decreasing
half of the time (moving away). If the flux is increasing and decreasing
periodically (at discrete intervals in time) then so will the induced
current in the coil.
To accomplish this goal, Bell put two steel reeds, A and B on a
horseshoe-shaped permanent magnet M. A" and B" represent the same reeds
on a duplicate transceiver. When A is plucked, A" will sound, and
vice-versa. When A vibrated toward the coil under it, the current became
increasingly positive (or negative, depending on which pole of the magnet A
was and how the underlying coil was wound); when A vibrated away from the
coil, a current of the opposite kind was induced. The signal, therefore,
was sent across as a sinusoidal wave, exactly the same form of wave traced
by the phonautograph on smoked glass or reflected into a rotating mirror by
the manometric flame .
Bell referred to this as an "undulating current", and it became the focus
of his successful telephone patent two years later. Bell knew, from
Helmholtz, that this wave would "express in a graphical manner the
vibratory movement of the air while the reeds were producing their musical
tones."[20] Furthermore, the vibrations of the individual reeds on the
permanent magnet could be summed into a single undulating curve.
Therefore, the device could send A and B as distinct tones and also the sum
of A and B. (For a picture of this device, explore the levels below the
Harp Apparatus box on the top level box).
Bell realized that if one could combine the sounds from two reeds to
make a more complex wave, one could theoretically reproduce any sound by a
combination of reeds. This insight is derived from the Helmholtz
apparatus, in which multiple tuning forks were used to reproduce vowel
sounds.
The result, in Bell's case, was a new mental model for the transmission of
musical tones, vowel sounds, or even speech. This model is represented by
the harp apparatus, a device Bell sketched, but never built, in the summer
of 1874. (For a better picture of this device, explore the levels below
its top level box). It essentially involves placing a large number of
steel reeds on the poles of a horseshoe-shaped electromagnet long enough to
accommodate the reeds. Like the strings of a piano, these reeds would
theoretically reproduce any musical tone; like Helmholtz's tuning forks,
they could theoretically reproduce vowel sounds as well. For example, when
one spoke a vowel into the transmitting harp, a combination of reeds
representing the fundamental tone and its overtones would vibrate and this
exact combination would be transmitted to the other side, reproducing the
vowel sound. This principle had been clearly established by the Helmholtz
device which was Bell's original mental model; in this case, however, the
single interrupting fork and series of separate resonators were replaced by
a series of reeds combining to induce a current in a single electromagnet.
Bell knew he could never build such a device, owing in part to the
multiplicity of reeds that would be required, but it served as a new mental
model, showing him how the undulating waves traced by the phonautograph
could be turned into an undulating electric current and reproduced as
sound.
This undulating current was Bell's greatest innovation. Telegraphy
involved make or break connections well suited to dots and dashes, but
poorly suited to speech.[21] Bell called the current produced by these
"intermittent", because it was on or off; when several messages containing
dots and dashes were combined, Bell thought the result would be a
continuous "on" current, which could not transmit a message. But the
result of combining undulating currents would be a sinusoidal curve that
would be different for every combination of sounds, therefore allowing one
to discriminate among different messages.
Bell believed that a steel reed vibrating over a magnet could never
induce an undulating current of sufficient force to transmit over a
distance. Therefore, he continued to focus primarily on developing a
multiple telegraph, encouraged by his primary backer and future
father-in-law Gardiner Hubbard, who urged him constantly to perfect such a
device and abandon the pursuit of a speaking telegraph.[22]
The continuation of these efforts is suggested by the "alternate mental
model for a multiple telegraph" box. Bell turns to these experiments with
rotating magnets just after developing his horseshoe magnet transceiver.
The rotating magnets allowed him to induce a current far more powerful than
anything he could achieve with a reed vibrating over a permanent magnet.
The June 2nd Experiment
The lines from the Harp and the multiple telegraph come together on the
map in a box labeled "Experiment in which one reed relay induces a powerful
current in others", which shows two reed relays connected in a circuit.
This kind of circuit emerges from Bell's earliest mental model for a
multiple telegraph, based on substituting the reeds for Helmholtz's tuning
forks. But the harp mental model primes Bell to recognize the significance
of a serendipitous discovery he and Watson made on June 2, 1875. Bell had
set up three multiple telegraph stations, A, B and C, each with three
tuned-reed relays. He wanted to be able to pluck the first reed in A and
have the corresponding reeds in B & C vibrate. (For a diagram, explore the
levels below the "Experiment in which one reed relay induces a powerful
current in others" box). Naturally, these reeds were very difficult to tune
and required constant adjustment--shortening or lengthening.
When Bell depressed the telegraph key corresponding to one of the reeds
at A, the corresponding reed at B vibrated well, but Watson, who was in
another room with C, said it was stuck. To release it, Watson plucked it;
Bell noticed that this caused the corresponding reed at B to vibrate
powerfully. Bell then listened to each of the reeds at B in succession,
placing his ear right against them, and heard both the pitch and the
overtones of the tuned reed. "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
electro-magnet would be too feeble to produce audible effects that could be
practically utilized for the purposes of multiple telegraphy and of
speech-transmission."[23]
Here we arrive at one of those moments of creative insight that are often
referred to as "mysterious"[24], and, in this case, as heavily dependent on
serendipity. Consider Watson's dramatic description:
-
That undulatory had passed through the connecting wire to the distant
receiver which, fortunately, was a mechanism that could transform the
current back into an extremely faint echo of the sound of the vibrating
spring that had generated it, but what was still more fortunate, the right
man had that mechanism at his ear during that fleeting moment, and
instantly recognized the transcendent importance of that faint sound thus
electrically transmitted. The shout I heard and his excited rush into my
room were the result of that recognition. The speaking telephone was born
at that moment...All the experimenting that followed that discovery, up to
the time the telephone was put into practical use, was largely a matter of
working out the details.[25]
Here we have a classic account of the Eureka moment. There is no doubt
that this was a very important experiment, but its significance is somewhat
exaggerated by Watson: extensive work remained to be done afterwards, and
the current insight was grounded in earlier work. Although his early
experiments combining two transmitters and receivers in an attempt to build
a multiple telegraph were not successful, Bell noticed a particular
phenomenon that prepared him to appreciate the serendipitous discovery of
June 2nd. When Bell tried to use two of his steel reed relays as
transmitters and pressed his ear against one of the receiving reeds, he
heard "two musical tones, corresponding in pitch to the two transmitters
employed, but different in pitch from the sound produced when the reed of
the receiver at [the] ear was plucked with the finger."[26] Bell had, of
course, hoped to hear only a single tone corresponding to the pitch of one
of the sending reeds; the extra tone was a kind of interference effect that
another inventor might have dismissed as noise or error to be removed. Bell
knew that this effect depended on dampening the vibrations of the reed, in
this case by pressing his ear against it.[27]
So, by June 2nd Bell knew that a single one of his reed relays could
receive complex sounds. He also knew that a reed could generate sufficient
current to transmit a tone over a distance. What he learned from the
serendipitous error involving the stuck reed was that a single reed, when
dampened or stuck, could also induce a current sufficient to transmit
complex sounds over a distance--at this point, no greater than from one
room to another, but the potential for longer transmission was clearly
there. The multiple reeds of the harp were not necessary.
Cognitive psychologists have recently begun to study the effect of
various kinds of error on scientific reasoning.[28] Typically, the concern
in such studies is with how people can be taught to recognize and remove
sources of error. But one of the characteristics of genius is recognizing
when an apparent "error" is in fact a phenomenon of great significance.
Serendipity lies in the beholder. The little mold on one of Alexander
Fleming's petri dishes is an oft-cited example.[29] Similarly, Bell confronts
an error--a single reed stubbornly produces multiple tones when
plucked--and realizes that this apparent problem is in fact an opportunity.
Bell immediately asked Watson to build a working telephone in which a reed
relay was attached to a diaphragm or membrane with a speaking cavity over
it. As one spoke into the cavity, the membrane would vibrate; these
vibrations would be translated into an electrical current by the dampened
reed, which would send them to a similar device on the other end.
Unfortunately, this device did not produce intelligible speech, though Bell
and Watson heard a kind of mumbling that suggested they were on the right
track (see the box labeled "Gallows Telephone").
Sound and Electricity as Sinusoidal Waves
Bythe 20th of January,1876, in a patent application, Bell states his
mental model of how mechanical motion is translated into electrical
current:
-
Electrical undulations, induced by the vibration of a body capable of
inductive action, can be represented graphically, without error, by the
same sinusoidal curve which expresses the vibration of the inducing body
itself, and the effect of its vibrations upon the air; for, as above
stated, the rate of oscillation in the electrical current corresponds to
the rate of vibration of the inducing body---that is, to the pitch of the
sound produced. The intensity of the current varies with the amplitude of
the vibration--that is, with the loudness of the sound; and the polarity of
the current corresponds to the direction of the vibrating body--that is, to
the condensations and rarefactions of air produced by the vibration.[30]
The "body" he uses to illustrate these vibrations is his standard reed
relay mechanical representation. Even though the Gallows telephone does
not work, he knows he has discovered the theoretical principle behind a
telegraph or telephone. The above passage from his patent application
describes a one-to-one correspondence between characteristics of sound and
electricity as well as the belief that sound and electricity will form the
same sinusoidal curve when transmitted.
The Ear Mental Model
On February 21, 1876, Bell made a statement and a sketch of the mental
model that represented the synthesis of the phonautograph and his multiple
telegraph experiments.[31] Bell draws an ear with two different mechanical
representations next to the bones. On the left is an electromagnet,
suggesting that the bones will serve a function similar to the armature on
his familiar reed-relay mechanical representation. On the right an iron
cylinder is attached to the bones and this vibrates in the center of a
magnetized helix with an iron core. Again, Bell had conducted experiments
with such an arrangement, verifying that it could produce an undulatory
current; he would later develop this mechanical representation into a
telephone receiver. Beside the sketch, Bell wrote, "Make transmitting
instrument after the model of the human ear. Make armature after the shape
of the ossicles. Follow out the analogy of nature."[32]
What Bell first does in this remarkable statement is outline two goals.
Cognitive scientists have done extensive work on goals, especially the
differentiation between goals and sub-goals.[33]
The statement "Make
armature after the shape of the ossicles" is a sub-goal under "Make
transmitting instrument after the model of the human ear" because the
former suggests what needs to be done in a particular slot in order to
accomplish the latter. (Note that we use a wedge-shaped box to denote
stated, as opposed to inferred, goals).
The statement that he was "following the analogy of nature" illustrates
another component of our framework. Inventors and scientists often employ
heuristics, or "rules of thumb", to reach their goals.[34] Bell's strategy
of "following the analogy of nature" is one such strategy: when in doubt,
try to copy nature. Note that heuristics depend heavily on mental models;
in order for Bell to copy nature, he has to have both a clear understanding
of the ear and a set of mechanical representations that he can employ.
Bell's Gallows telephone followed this mental model--it is a kind of
electromechanical ear. If so, why does Bell state his mental model a year
later? Actually, it is rare for an inventor or scientist to state their
underlying assumptions explicitly.[35] Bell is a theoretical inventor;
therefore, he pays careful attention to developing and articulating a
mental model. He might have had the rough outlines of this mental model
long before the February 22nd date on which he wrote it in his notebook,
and merely noted it as both a reminder to himself and in preparation for
future patent litigation.[36] Or this entry might have represented a moment
in which he synthesized earlier insights into a conscious statement .
By now, the reader may be somewhat bewildered by the variety of uses to
which we have put the term mental model. We used it to describe Bell's
understanding of the Helmholtz apparatus for reproducing vowel sounds,
Bell's own harp apparatus, his understanding of how sound and electricity
could be visualized in terms of sinusoidal waves, and finally, this sketch
of the bones of the ear next to two different mechanical representations.
Mental model is a 'scruffy" term, which means it cannot (to the dismay of
philosophers) be defined precisely. But the term draws our attention to
the way Bell imagines devices and how they work. Some of his mental models
seem very close to practical devices; others, like the harp and the ear,
are flights of the imagination that could never be built. But they allow
him to carry out thought experiments, to visualize and manipulate the
relationships between sound, electricity and magnetism. Given his limited
electromechanical skills, mental modeling is especially important to Bell.
A Slot Diagram Based on a Patent Drawing
Below the mental model on our main map is a slot diagram based on Bell's
patent signed on January 20, 1876 and submitted on February 14th . The
oval in it connected to this slot diagram reflects the fact that Gardiner
Hubbard actually submitted the patent for his son-in-law. Bell was waiting
for a possible British patent when Hubbard decided it was time and they
could afford to wait no longer. As it turned out, Hubbard's timing was
very tight--a few hours later, Elisha Gray submitted a caveat for a
speaking telegraph.[38]
The oval, in this case, reflects an important change of heart that we
need to explain more fully. Hubbard had gone from being suspicious of
Bell's telephonic researches to becoming a backer. Indeed, it was Hubbard
who built the corporation that bears Bell's name and made the inventor a
millionaire. This oval will eventually include a sub-map that sketches
Hubbard's path from telegraph to telephone backer, and records the early
details of the agreements that lead to the Bell corporation. The map can
serve as a reminder of areas that need work.
Generally speaking, we find that patent drawings make the best basis for
slot diagrams, although--given the limited number of patents filed by
Bell--we often have to use his notebook sketches. Patent applications
provide the best sketches and most articulate description of the goals and
sub-goals reached by inventors.
In Bell's case, the "Ear and Membrane" slot indicates that Bell could use
a number of different devices to realize the same function as the
anatomical parts. The "Ossicles Slot" has the same meaning; the patent
diagram shows one of his steel reed armatures serving the function of the
bones, but the ear diagram in his notebook makes it clear he considered
alternate mechanical representations. Bell's ear mental model suggests
nothing about how he is going to accomplish long-distance transmission, so
we have introduced a "Line" slot. Note that this slot overlaps with the
Ossicles slot; this is deliberate, to indicate the obvious--that improving
the relationship between the armature and the induction coil is one of the
keys to long-distance transmission. Slots are not necessarily mutually
exclusive. We have also noted slots for "power source", to indicate that he
could remove the battery or increase its strength, and a "motion into
current" slot, to indicate that he could experiment with different ways of
translating the motion of the armature into an undulating electric current.
Finally, there is a "receiver" slot, to denote the fact that Bell will try
a variety of substitutions to improve reception, including devices which do
not look exactly like the transmitter. Again, whatever he learns about
armatures in the Ossicles slot could be applied to the receiver.
In Bell's case, we could possibly have determined his slots simply from
looking at his ear diagrams. But we do not determine slots solely on an a
priori basis; instead, we also look closely at the experiments an inventor
does,to see what areas he is concentrating on. In other words, we could
have divided the ear up very differently, but we have tried to stick hard
to Bell's divisions. Slots, then, become an important tool for mapping the
invention process.
Bell's patent was eventually granted, and became the focus of endless
litigation, but that lies beyond our story. Part of the frustration
experienced by other inventors like Edison and Gray comes from the fact
that when Bell filed, he had no working telephone. But he did have a
mental model, as our slot diagram illustrates. In his subsequent
experiments, Bell opened certain of these slots and tried to insert or
develop different mechanical representations to improve performance.
The First Transmission of Speech
When Bell obtained his patent, he still did not have a working device.
The line of experiments that led to the first successful transmission of
speech is depicted in the two boxes below the "Slots in Bell's Ear Mental
Model" box (by below, in this case, we mean lower on the same page in
Mosaic, connected by arrows). To see a detailed rendition of the actual
experiments, one needs to click on these two boxes. The upper box
describes experiments with devices that look much like the ear mental
model.
The box that is lower and to the right is connected by a minus and a plus
sign with devices next to each. This is a short-hand way of indicating
that to get from one box to the other, Bell removes an electromagnet and
substitutes a dish of water. The box called 'spark arrester" above it is
connected by an arrow, to indicate that Bell had previous experience using
water as a medium of resistance in a device that prevented sparks in a
telegraph rely. The liquid experiments led to the famous "Watson--come
here--I want you" result obtained on March 10th. Text describing these
experiments in detail can be obtained by clicking on the detailed
representations of the experiments themselves.
The upper level map needs to be continued to Bell's second patent,
obtained in January of 1877. This second patent includes devices that look
much like those in his first patent; he abandoned the liquid transmitter
variations, which is why they are depicted off to the side. The story of
why he did this is told elsewhere,[38] and will be incorporated in future
versions of the map.
Endnotes
"We" refers to a team of faculty and students that included my colleague
W. Bernard Carlson and several recent graduates of the University of
Virginia, including Tamar Lieberman, Matthew M. Mehalik, Christy Nilsen and
Charles Twardy.Back
D.A. Hounshell makes the case that Bell deliberately sought to establish
strong links to the scientific community of the day, whereas Elisha Gray
did not. Bell's careful attention to science and scientists was one of the
reasons for his success. See "Bell and Gray: Contrasts in Style,
Politics, and Etiquette", IEEE Proceedings 64 (1976) :1305-14; and "Two
Paths to the Telephone", Scientific American 244 (January 1981) : 156-63.Back
R. Bruce (1973). Alexander Graham Bell and the Conquest of Solitude.
Boston: Little, Brown & Co., p. 51. Bruce cites a source from 1879-- much
later than the actual event. This is not a reliable source because a later
reconstruction has great potential for distorting the original events. We
have not been able to find more reliable sources with earlier dates to
describe this event. In an account from 1877 Bell indicates that he
understood Helmholtz by describing that the Helmholtz apparatus "produce[s]
vowel sounds artificially." (George B. Prescott. (1972) Bell's Electric
Speaking Telephone: Its Invention, Construction, Application, Modification
and History. New York: Arno Press. pp.66-67) So, we must be careful in
interpreting this bit of information, since it does not come to us directly
from primary sources written at the time of the event.
What is clear is that Bell saw his early multiple telegraph experiments as
similar to Helmholtz's experiments with vowel sounds--"My knowledge of
Helmholtz's apparatus for the artificial production of vowel sounds incited
me to experiments of a similar character..." (The Bell Telephone: The
Deposition of Alexander Graham Bell in the Suit Brought by the United
States to Annul the Bell Patents. (1908) Boston: American Bell Telephone
Company. p. 12)--whereas, in fact, Bell's and Helmholtz's experiments were
quite different.Back
See R. Bruce (1973). Alexander Graham Bell and the Conquest of Solitude.
Boston: Little, Brown & Co., pp. 50-51.Back
R. D. Tweney (1989) makes a distinction between framework and theory:
-
Truth claims in a theory are based on the familiar strategies of scientific
practice, while truth claims in a framework rely on interpretive
procedures more akin to the methods of historical scholarship,. A theory
is an attempt to construct a model of the world which meets certain
criteria of testability; it makes predictions, is potentially
disconfirmable, and has interesting consequences. A framework is an
attempt to re-construct a model of the world which meets criteria other
than testability as such. An adequate framework is one that is consistent
with the details of the process, is interestingly related to our theories
of the world, and reduces the apparent complexity of the real world process
in a way which permits anchoring the framework to the data. In effect, an
adequate framework must allow us to see order amid chaos ("A Framework for
the Cognitive Psychology of Science," in B. Gholson, W.R. Shadish, R.A.
Niemeyer & A.C. Houts (Eds.) Psychology of Science. Cambridge: Cambridge
University Press, p. 344).
Our framework and maps allow us to perceive order among the chaos of the
inventor's sketches, artifacts, caveats and notes, Our framework might
eventually evolve into a more formal, theoretical model, but at the very
least, it provides us with a rigorous basis for comparing inventors.Back
For good reviews, see D. Gentner & A.L. Stevens, Mental Models.
(Hillsdale, N.J.: Lawrence Erlbaum Associates, 1983), 99-129 and W.B.
Rouse & N.M. Morris, "On Looking Into the Black Box: Prospects and Limits
in the Search for Mental Models," Psychological Bulletin, Vol. 100 (1986)
: 349-363.Back
This term is borrowed from R.J. Weber & D.N. Perkins (1989) "How to Invent
Artifacts and Ideas," New Ideas in Psychology, 7:49-72.Back
A.G. Bell, The Multiple Telegraph Boston: Franklin Press, Rand, Avery &
Co., 1876, p. 8. Klahr and Dunbar, in an experimental simulation of
scientific reasoning, found that college students adopted either a
theoretical or experimental style; Bell obviously leaned more toward the
former, which in Klahr and Dunbar's artificial task was more effective.
See D. Klahr and K. Dunbar, "Dual Space Search During Scientific
Reasoning," Cognitive Science, 1988, Vol. 12, 1-48.Back
J. Baille. The Wonders of Electricity. New York: Charles Scribner, 1872),
pp. 140-143.Back
Bell's sucessful patent was number 174,465. Gray's rejected patent
application was filed on 29 October 1877.Back
The sketches of transmitter and receiver here are not juxtaposed in this
way in the original documents; we have done so to illustrate Bell's
alternate mental model. For the rotating magnet, see Bell, The Multiple
Telegraph, p. 14. Bell eventually patented the general principle of using
rotating magnets to induce a continuous current in a closed circuit; see A.
G. Bell, "Generating Electric Currents," U.S. Patent No. 181,553, (filed
August 12, 1876, granted August 29, 1876). For the nail in a helix, see
letter from A.G. Bell to Gardiner Hubbard on November 27, 1874. Bell Family
Papers, Library of Congress, Box 80.Back
Bell to Hubbard, op cit.Back
For more details on Bell's multiple telegraph experiments, see M.E.
Gorman, M. Mehalik, W.B. Carlson & M. Oblon, "Alexander Graham Bell, Elisha
Gray and the Speaking Telegraph: A Cognitive Comparison", History of
Technology, Vol. 15, 1993. For example, in the case of the nail in a
helix, Bell was re-discovering a principle used by Philip Reis in the first
device labeled a telephone. Bell claims he made the discovery
independently, without knowing Reis' work. Those wishing to receive
preprints of this paper can write to the senior author of this chapter.Back
Bell filed an application for this patent on March 6, 1875. The
patent "Improvement in Transmitters and Receivers for Electric Telegraphs"
was granted on April 6, 1876 as Patent No. 161,739. The patent shows the
circuit-breaker as part of an autograph or facsimile telegraph. Bell
attached this mechanical representation to the autograph telegraph, in
part, to avoid an interference with Gray; as he said in a letter to his
mother and father, March 5th, 1875:
- My lawyers were at first doubtful
whether the examiners would declare an interference between me and Gray as
Gray's apparatus had been there for so long a time.
They feared I had but a poor chance--and my spirits at once fell to
zero. They said it would be difficult to convince them I had not copied.
When however they saw the "Autograph Telegraph" developed from the multiple
telegraph --they at once said that was a good proof of independent
invention as Gray had no such idea.Back
Brooke Hindle, Emulation and Invention, New York: W. W. Norton & Co., 198=
1.Back
A. G. Bell, "Improvement in Transmitters and Receivers for Electric
Telegraphs," op cit.Back
A. G. Bell, "Telephonic Telegraph Receiver," Patent No. 178,399, filed
April 8, 1876, granted June 6, 1876.Back
The Bell Telephone (1908), 23-29.Back
A.G. Bell, "Telephonic Telegraph Receiver," 21.Back
The Bell Telephone (1908), 34. Bell is reporting his understanding at
a later date, during patent testimony (date 4 April 1892). Bell claims to
have arrived at this understanding in the summer of 1874.Back
Bell felt that the the first "telephone", developed by Philip Reis, in
Germany, worked on this make-or-break principle; as a result, it could
reproduce the pitch of a vowel, but not the complex overtones represented
by the multiple resonators in the Helmholtz apparatus. see The Telephone
Appeals. Boston: Alfred Mudge & Son Law Printers, 1887. pp. 104-110.Back
Gardiner Hubbard eventually decided to support his son-in-law's
telephonic researches, and ended-up being the principle founder of the
Bell Telephone Corporation. It was Hubbard who made Bell a millionaire
(see Bruce, 1973).Back
The Bell Telephone (1908), p. 59Back
See D. N. Perkins, The Mind's Best Work Cambridge: Harvard UP, 1981; and
M. Boden, The Creative Mind: Myths & Mechanisms. New York: Basic Books,
1990, for a summary of the literature on creativity and insight that
includes arguments about how these "mysterious" processes can be unpacked
and studied.Back
T.A. Watson (1913) "The Birth and Babyhood of the Telephone" Address
delivered to the 3rd Annual Convention of the Telephone Pioneers of America
at Chicago. Reprinted by the American Telephone and Telegraph Co., pp
10-11.Back
A.G. Bell, The Bell Telephone, p. 16.Back
Bruce, op cit, p. 147.Back
See chapters 4-6 of M.E. Gormans Simulating Science: Heuristics and
Mental Models in Technoscientific Thinking. Bloomington: Indiana University
Press, 1992, for a description of this research.Back
G. MacFarlane (1984). Alexander Fleming: The Man and the Myth.
Cambridge, MA: Harvard U. Press.Back
A. G. Bell, "Improvement in Telegraphy," Patent No. 174,465, witnessed
20 Jan 1876, submitted 14 Feb 1876, granted 7 March 1876. Reproduced in The
Bell Telephone: The Deposition of Alexander Graham Bell in the Suit
Brought by the United States to Annul the Bell Patents. Boston: American
Bell Telephone Company, 1908, p. 455-56.Back
Experiments Made by Alexander Graham Bell, vol. I, p. 13.Back
Ibid. Exptl Notebook vol. 1, p. 13.Back
See, for example, R. Wilensky, Planning and Understanding: A
Computational Approach to Human Reasoning. Reading, MA: Addison-Wesly,
1983.Back
There is a long literature on scientific heuristics in cognitive
psychology; see, for example, D. Kulkarni & H.A. Simon, "The Processes of
Scientific Discovery: The Strategies of Experimentation", Cognitive
Science. Vol.12 (1989) 139-175; and M.E. Gorman & W.B. Carlson , "Can
Experiments Be Used to Study Science?" Social Epistemology 3(1989)
:89-106.Back
Edison describes his mental model based on Reiss in patent testimony:
"My sketches were rough ideas of how to carry out that whch was necessary
in my mind, to turn the Reiss transmitter into an articulating transmitter.
They were notes for future use in experimentation." (from Edison
testimony, "The interferences on Telephones between Thomas A. Edison, A. E.
Dolbear, Elisha Gray, A.G. Bell, J.W. McDonough, G.B. Richmond, W.L.
Voelkers, J.H. Irwin, and Francis Blake, Jr.," deposition taken November 8,
1880, p. 9 paragraph 26).Back
Indeed, Bell's notebook was started in response to Gardiner Hubbard's
reminder that he ought to write everything down.Back
See Bruce, op cit, pp. 165-168.Back
See M.E. Gorman, M. Mehalik, W.B. Carlson & M. Oblon, "Alexander Graham
Bell, Elisha Gray and the Speaking Telegraph: A Cognitive Comparison",
History of Technology, Vol. 15, 1993, 1-56.Back
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