Bell received his patent on March 7, 1876. He had not yet successfully transmitted speech. From March 7 to 10, 1876, Bell did a series of experiments which culminated in the first transmission of speech. To show this process, I have employed protocol analysis, a technique used to record and analyze the problem-solving processes of participants in cognitive tasks (Ericsson & Simon, 1984). These participants are asked to speak aloud as they work, saying whatever comes into their minds. This is not the same as introspection--they are not being asked to reflect on the causes of their behavior, only report whatever mental steps they are going through. Their statements are used by the psychologist to create a problem behavior graph which documents their progress towards a solution.
We cannot protocol Bell for obvious reasons, but his notebook gives us a good record of his thoughts--he tries to record the steps in detail, pauses to consider alternatives and remind himself of goals. Tweney and Gooding have pioneered the use of protocol analysis with historical data; they conducted fine-grained studies of Faraday's cognitive processes (Gooding, 1990; Tweney, 1989). Like Bell, Faraday left extensive records--detailed notebooks, correspondence and artifacts. In fact, his notebook was seen as the model for other scientists and inventors.
Tweney and Gooding used Faraday's notebook to create graphical representations of his progress--we saw a brief example of this in Chapter 1. Gooding graphed each result, or hypothesis, and the manipulations that led Faraday to move from one state to another (see Figure 3 from Chapter 1). States were represented by boxes and operators by lines that went horizontally rightward for results that changed Faraday's knowledge state and vertically downward for results that did not. The problem-behavior graphs I created to document Bell's process differ in at least three respects from the conventions established by Gooding and Tweney :
(1) Instead of relying solely on symbols like squares for observations and triangles for shifts in goals, the components and the resulting combinations created by Bell are actually shown inside the symbols, to make it more transparent to a reader and to reveal the mechanical representations used by the inventor. Bell spends much of his time during this sequence of experiments substituting components in slots; these substitutions are illustrated with sketches, marked with plusses and minuses, to indicate whether a component was added or removed. (2) The line moves to the right in Gooding's graphs if there is a change in Faraday's knowledge state. In the Bell graphs below, the line moves right if Bell thinks the result is positive--he is generally quite explicit about whether he thought a result was positive, in terms of the current state of his research. Where he indicates that a result is somewhat positive, but less so than previous ones, the arrow will move rightward and downward, indicating some progress. This emphasis on positive and negative results comes out of Bell's notebook. He will occasionally pause to tell us what hypothesis he is working on, but mostly he wants to record configurations that do and don't produce a strong signal.
There is an alternate way of determining whether a result is positive or not. Barney Finn at the Smithsonian replicated a number of Bell's key experiments, using an oscilloscope to determine how strong a signal resulted (Finn, 1966). Bell did not have an oscilloscope, and relied on his own ear. Naturally, his perceptions were colored by his hopes, but what I intend to reconstruct is this pattern of perceptions and hopes, thereby avoiding the criticism that I might have simply imposed some post-hoc rational scheme on Bell's actual problem-solving process. This emphasis on viewing problem-solving in its actual context is characteristic of new work in what is called situated cognition (Bredo, 1994). We will have more to say about this work later.
(3) A slot diagram is also provided for each chain of experiments, to show the areas Bell was concentrating on and to suggest connections to his overall mental model. At the top of Figure 16 is a slot diagram, based on the circuit with which Bell began this sequences of experiments. The primary purpose of the slot diagram is to indicate the places where Bell made substitutions or changes; in this sense, the slot diagram also serves to define the problem space in which the inventor was working.
Figure 16: Slot diagram(at top left) and problem-behavior graph showing Bell's first series of experiments on March 8th.
The slot into which Bell substituted tuning forks, reeds and other armatures is labeled 'ossicles' to remind us that his goal was to find an armature which would 'follow the analogy of nature' and function like the ossicles, translating sound into an undulating electric current. The 'electromagnetic induction' slot indicates the place in his mental model where Bell had to solve the problem of how to translate the vibrations of an armature into an undulating current. Pushing the nature analogy, we might have referred to this as the 'organ of corti' slot; Bell knew roughly how this organ translated the vibrations of the bones into electrical impulses (Feist, 1993). Finally, there is a slot for 'power source', which in this chain of experiments meant a battery-- Bell could vary the number of cells.
On March 8th, Bell began by trying to transmit, clearly and distinctly, a tone using a familiar assemblage of components that had worked in the past: his steel reed mechanical representation as a receiver and a tuning fork, a la Helmholtz, as his transmitter (Gorman, Mehalik, Carlson, & Oblon, 1993). This experiment is really a replication of work done earlier. It was almost as though Bell were trying to establish a baseline, reminding himself of the quality of the results he could achieve with his familiar mechanical representations. He achieved the expected positive result--a clearly audible sound from the receiver.
Bell next tried adding an electromagnet of 'very high resistance'. This result was partially successful: a faint sound was heard from the receiver. This result was in line with expectations--increased resistance should produce a reduced signal. He may have been exploring what would happen if he tried to transmit over long distances, where the resistance of the line is a major factor, or he may simply have wanted to assess how strong the signal was by checking how much resistance it could overcome.
Next, he tried removing the electromagnet altogether, simply vibrating the fork over the wire. There was no sound--no surprise, because without the electromagnet, there was no mechanism for translating mechanical motion into undulating current. Bell in this case was probably checking to make certain he could distinguish the sound of the fork from that of the receiving reed. He had to listen to the reed by pressing his ear against it while vibrating the fork a short distance away. He knew how easy it would be to fool himself.
Next, he put the original electromagnet back in and removed the armature from the receiver, to listen directly to the coil. Here, he was working within the ossicles slot to see exactly what modifications would produce the strongest signal. Again, no sound. In this case, it was less clear that he expected a negative result. Bell had done previous experiments in which he heard sounds from a coil without an armature, but certainly not the kinds of tones he heard when he used a reed. Still, he probably wanted to check and make certain the tones he heard were really produced by the reed.
When he put an armature of soft iron on the receiver, he obtained a positive result.
Next, he shifted to the power source slot, removing it altogether. Bell had noted that the battery he was using was 'almost run down'--this experiment was probably an effort to make sure it was necessary. Bell was obsessed with simplicity: if he could transmit a clear signal without a battery in the circuit, so much the better. This attempt produced a negative result, as indicated by the arrow pointing to the right.
Robert Bruce, the distinguished Bell biographer, has described the set of experiments in Figure 16 as 'random' (Bruce, 1973). But Figure 16 shows they were anything but random: Bell moved systematically from slot to slot, removing or substituting one component at a time. Bruner called this heuristic 'conservative focusing' to distinguish it from another heuristic, 'focused gambling' (Bruner, 1956). The former involves a careful, systematic search through the problem space, varying only one thing at a time; the latter involves making a leap to a new part of the problem space by altering several variables at once. The two heuristics can be used in combination: an inventor could gamble by trying a radically different configuration of components, get a positive result, then return to a conservative focusing heuristic to see which changes were most important.
Bell's conservative focusing in this case was also a form of replication. He had already done versions of most of these experiments before. Bell had to review his mental model in his notebook before embarking on a new program of research; it seems he also needed to see if he could reproduce results obtained with familiar mechanical representations. He was in effect establishing a base-line for further experimentation.
At this point on March 8th, Bell made what in hindsight was a significant change, although it was still consistent with his conservative focusing heuristic. He inserted a dish of water into what had been the electromagnetic induction slot, which leads to a change in the slot diagram (see Figure 17).
This device was never patented, and we have no record of experiments Bell may have conducted with it. But the spark arrester may have served as a mechanical representation, reminding Bell how water could be used as medium of higher resistance in a circuit, one that would conduct induced currents of sufficient strength. The idea of turning this mechanical representation into a telephone transmitter probably came from his conversation with the examiner about the interference with Gray. This kind of opportunistic reasoning often occurs in design: a suggestion about another possible solution path is mated with previous work to produce an alternative approach (Simina & Kolodner, 1995).
The upper left-hand corner of Figure 17 shows a new slot diagram, in which the electromagnetic induction slot is replaced by a 'resistance medium' slot and the ossicles slot is replaced by 'contacts'. This new slot diagram is a reminder that the shift to liquids represents a transformation of the problem space, opening up new alternatives to explore. The 'resistance medium' slot indicated that Bell could alter the resistance of the water by adding acid, or substituting other materials for water: in his spark arrester application, he mentioned "carbon, plumbago, animal and vegetable tissues, and other substances offering a high resistance" (Bell, 1908). The 'contacts' slots represented the fact that Bell focused on the relative sizes and depths of the contacts in the water.
Figure 17: Slot diagram and problem-behavior graph after Bell introduces water as a resistance medium
If this approach were successful, it would apparently eliminate one of Bell's sub-goals: to make an armature after the shape of the ossicles. A contact dipping in water is not shaped like the ossicles! But it would still serve the same function: to translate the undulations of speech into electrical impulses. Bell seems to have blurred the traditional distinction between form and function: for him, form often suggested function. But once he had the function clearly in mind, he was willing to relax the constraints of the original form, in this case the shape of the ossicles, focusing instead on any arrangement which would translate sound waves into undulating electrical currents. Bell began with the experiment shown in the slot diagram in Figure 17; when one tine of the vibrating fork was placed in the water, a 'faint sound' resulted. The diagonal arrow to the next experiment indicates that this was a somewhat positive result. Next, he added a bit of acid to the water. This produced a much louder sound. Increasing the distance between the tuning fork and the conducting wire had no effect, which meant that Bell could ignore distance between contacts at this point. He then added a strip of brass to the conducting wire; this made the sound 'much louder' and completely immersing this wire in the liquid made the sound 'very loud' (Bell, 1876b, p. 37). Next, he decided to increase the size of the vibrating contact; to do this, he substituted a bell for the tuning fork. No sound resulted, nor was transmission improved when he substituted a steel wire for the brass one to see if the key was the difference in metals. When he replaced the bell with a piece of steel, the sound was again loud.
Note how Bell in this sequence of experiments employed the conservative focusing heuristic he had used in his earlier experiments on the same day, systematically altering one variable at a time to improve transmission. After acidulating the water, he quickly focused on the contacts slot. His heuristic was similar to what Platt (Platt, 1964) has called a strong inference strategy; he designed experiments that discriminated among hypotheses. He eliminated distance between contacts, which Gray regarded as the key to transmission, and also difference in the metals used in the contacts.
At this point, Bell paused, apparently at the end of his working day, and wrote down a new hypothesis under the heading "Thoughts", which can be paraphrased as follows: the best results could be obtained when the vibrating contact was smallest and the contact on the other end of the circuit was largest. This is shown in Figure 17 by a trapezoidal box, with a sketch in it that is based on the sketch Bell drew in his notebook. The vibrating contact was a small needle; the other contact was a large, flat ribbon which lay underneath the vibrating contact. The sketch included a speaking tube and membrane, borrowed from devices Bell had constructed earlier. The receiver was his familiar steel reed mechanical representation.
On the next day (March 9th), Bell and Watson built a version of this apparatus, using a sounding box instead of a speaking tube, a cork to attach the needle to the membrane, and a brass ribbon as the other contact. These substitutions are shown on the left-hand side of Figure 18. One of Bell's reed receivers was placed in another room. Bell listened while Watson sang, and was able to hear the pitch of Watson's voice. When Watson spoke, Bell heard "a confused muttering sound like speech but could not make out the sense. When Mr. Watson counted--I fancied I could perceive the articulations 'one, two, three, four, five'--but this may have been fancy--as I knew beforehand what to expect. However that may be I am certain that the inflection of the voice was represented" (Bell, 1876, p. 39). As far as Bell was concerned, this was a positive result--a similar result had convinced him that the Gallows telephone represented a patentable idea. Hence, the horizontal arrow to the next experiment, conducted on the next day.
Figure 18: Experiments by Bell and Watson on March 9th and 10th leading up the first transmission of speech
On March 10th, the two substituted a platinum pipe for the brass ribbon and a speaking tube for the sounding box. Bell spoke the famous words "Mr. Watson--Come here--I want to see you." (Bell, 1876, 40).
Here is the moment when the hero had reached his goal. It is even enshrined in a myth--that Bell spilled acid on his pants, and that is why he asked Watson to "come here." But this moment of heroic triumph is more apparent in hindsight. Arguably, the June 2nd experiment was more important, because it led to the patent.
Furthermore, Bell and Watson did not break out the champagne. Indeed, they continued to experiment. The two switched places and Watson read to Bell from a book: Bell could make out only a few words, but heard Watson say "Mr. Bell, do you understand what I say?" (Bell, 1876, 41). They continued to experiment, trying to figure out the exact circumstances which had produced the positive result, and also how to improve it. Adding cells to the battery produced a violent hissing. Bell realized that the transmitter was in effect operating as a battery, because one contact was brass and the other platinum. A black deposit quickly formed on the platinum contact.
To avoid these problems, Watson and Bell went back to their experiments with tuning forks, in effect replicating earlier work. Bell noted that the more deeply the prong of the fork was immersed in the water, the less the sound.
This page was last edited: Wednesday, July 14, 1999