W. Bernard Carlson, "Banishing Prometheus?"

Banishing Prometheus? Edison, Invention, and Representation

W. Bernard Carlson (University of Virginia)

A chance sketch--a rude combination of carelessly considered pencillings--the jotted memoranda of a contemplative brain, prying into the corners of contrivance--often form the nucleus of a splendid invention. An idea thus preserved at the moment of its birth, may become of incalculable value, when rescued from the desultory train of fancy, and treated as the sober offspring of reason.

--Jacques Eugene Armendgaud (1883)[1]

Of all the parts of technoscience, the engineers' drawings and the organisation and management of the traces generated similtaneously by engineers, draughtsmen, physicists, economists, accountants, marketing agents and managers are the most revealing.

--Bruno Latour (1987)[2]

The soul never thinks without an image.


One of the central challenges in the history and sociology of technology today is understanding the role of visual materials. Engineers, inventors, skilled workers--all types of technologists--live in a world brimming with blueprints, patents, sketches, exploded-view diagrams, flowcharts, photographs, and videos. Even for average consumers, much of our experience with technology is mediated through visual representations of the technology found in instruction manuals and advertisements; these images introduce us to the technological artifact and help us decide what meanings we wish to ascribe to it.

Although prominent technological historians such as Eugene Ferguson, Brooke Hindle, and Steven Lubar have called our attention to the importance of visual materials, we know little about how and why pictures play such a prominent role in technology and engineering.[4] With the exception of a short study by Bert S. Hall and Ian Bates on how Leonardo sketched several alternative designs for epicyclical gearing, most historians have not analyzed in detail how technologists employ visual materials in their work.[5] Like Ferguson, most historians of technology have tended to say that visual images are generated in the "mind's eye" and let it go at that.

The reasons for this gap in technology studies are undoubtedly numerous and complex, but two factors deserve mention. First, like most scholars trained in the humanities and social sciences, historians study written records and frequently lack the intellectual preparation to tackle nonverbal records such as artifacts or pictures. In my own case, I began research on the inventor Elihu Thomson by carefully reading his daily business correspondence, only to gradually realize that he regarded letter-writing as an unpleasant chore that distracted him from the creative act of invention.[6] For Thomson, sketching and model-building were the invention process, but how does one study these activities? To some extent, I balanced my reading of the business records with an investigation of Thomson's surviving test models, but my work on Thomson left me with the feeling that I had not fully probed the process of invention.

Underlying this tendency in historical scholarship to privilege written over visual records is a deeper and more problematic assumption. Since the Enlightenment, intellectuals in the West have tended to treat words as rational and objective and pictures as personal and emotional. Language, it is assumed, can be used with a degree of precision not possible with visual materials. Pictures, even blueprints, are subject to interpretation and discussion. For many scholars, visual materials are too close to the senses of seeing and feeling to be considered "pure" rational thought.[7] At the same time, some of the professions who produce and use visual materials--artists and architects--have tended to accentuate the link between visual materials and mysterious genius. Much of the Romantic myth of genius invoked by artists centers on the notion that artists are a special group because their ability to represent emotions and ideas visually permits them to capture more profound insights than are possible with mere words. Unfortunately, this tendency to equate words with thinking and pictures with feeling has had a profound impact on the character of twentieth century engineering, leading to an overemphasis in engineering education on science and mathematics to the almost complete exclusion of anything relating to the art and practice of engineering.[8]

Contrary to these powerful tendencies which discourage one from studying visual materials, this paper shows how it is possible to analyze one type of visual materials, sketches, and to learn something about how technologists use visual materials in thinking about and manipulating material objects. For the purposes of this paper, sketches are the quick drawings made by inventors in the course of their work. Because they are highly personal and hence seemingly highly subjective, sketches constitute a formidable challenge to the analyst intent on recovering the purposeful thinking that the sketches may represent. However, drawing on the ongoing project I have been pursuing with Michael Gorman on comparing how Alexander Graham Bell, Elisha Gray, and Thomas Edison, I will demonstrate how the analysis of sketches can be done with care and precision.[9] For this demonstration, I will discuss how Edison drew three sketches of the Reis telephone in 1875. In analyzing these sketches, I will show why it is important to evolve new language to talk about how an inventor thinks and works. I will next suggest that one can move beyond the analysis of individual sketches to studying how an inventor works through dozens of sketches by using a representational technique which Gorman and I call mapping. By using maps to organize and study an inventor's sketches, one can recover the nonverbal purposeful acts by which an inventor creates new artifacts.[10] Moreover, mapping permits us to characterize with greater precision what we mean by inventor's method. To illustrate this, I will present an overview of Edison's work on the telephone in 1877, followed by detailed examples from the Edison maps we have developed. Borrowing from this paper's epigram, then, I wish to rescue sketches "from the desultory train of fancy" and instead treat them "as the sober offspring of reason."

Using Sketches to Communicate and Generate Ideas

If we are going to treat an inventor's sketches "as the sober offspring of reason," then one place to start is to think about the functions that they may play in the invention process. Like other documents, sketches are used by inventors both to generate and communicate ideas.[11]

To date, historians of technology have highlighted the importance of sketches as a form of communication.[12] In several biographies of inventors, historians have discussed how inventors make sketches in notebooks to record experiments on the benchtop.[13] In order that their sketches can be used to objectively communicate an experiment to audiences removed in time and place (audiences such as patent examiners and judges in patent courts), inventors frequently explain their sketches to individuals who then sign and date the sketch. Inventors also use sketches to communicate their ideas to assistants who in turn build and test the invention. One famous example of this is the purported first sketch of the phonograph on which Edison scribbled instructions to his chief machinist, "Kreusi-make this-Edison."[14] Likewise, Edison's assistants made sketches to communicate their work to their boss. For example, several of Edison's machinists documented their time on the telephone project by sketching the patent models Edison asked them to build and by noting on the sketch how much the model cost (Figure 1). And of course, inventors often use sketches or drawings to explain their ideas to investors, journalists, and other individuals outside their immediate circle of associates[15] For example, many of Bell's earliest telegraph devices are illustrated by small sketches in his frequent letters to his parents.

In focusing on how sketches may be used to communicate ideas between the inventor and several social groups, historians and sociologists have been able to help us see invention as a social process. Rather than being simply the act of creating a new machine, most scholars would agree with Thomas P. Hughes and John Law that invention involves the linking of ideas, artifacts, capital, skilled labor, and manufacturing and marketing capabilities.[16] To link these human and nonhuman components together, inventors must communicate and negotiate with investors, assistants, and consumers, and sketches are documents which allow us to trace how information moves between these groups.

However in their discussions of the role of documents and visual materials in technoscience, Bruno Latour and some sociologists have pushed the notion of documents to a phenomenological extreme. Latour and his followers would argue that sketches and other documents created in the production of knowledge exist only for the purpose of facilitating social transactions between individuals and groups. A sketch or picture is an inscription used by an actor to strengthen and enhance his or her intellectual and social power. In taking this position, Latour argues that cognition--the notion that ideas exist in the mind of an individual--is irrelevant or impossible to study.[17] We can only study that which is communicated and that which becomes part of the social discourse. Viewed from this perspective, sketches are only of interest when they are communicated by the inventor to various audiences.

I do not think it is appropriate to go to this phenomenological extreme. Inventors certainly use sketches to communicate ideas, but they also use them to generate and manipulate ideas.[18] One hint that sketches and notebooks are used for the generation of ideas can be seen in the private and personal nature of an inventor's notebooks. A famous example of this are the notebooks in which Leonardo da Vinci made entries using his mirror writing to ensure that his ideas could not be easily read by assistants or rivals. As another instance, Bell began keeping a notebook in January 1876 at the behest of his father-in-law Gardiner Hubbard; as an attorney, Hubbard knew well the importance of having good documentation for use in future litigation. While Bell dutifully made entries in his notebooks, he failed to have the entries witnessed, and hence limited the value of his notebooks as evidence in patent cases.[19] Instead, we suspect that Bell found the notebooks far more valuable as a place for representing his ideas using both sketches and written descriptions. To some extent, Bell developed his notebook for himself as the audience, and not for sharing his ideas with anyone else. In this sense, an inventor's notebook--and the sketches it contains--may be documents primarily for generating ideas, not communicating them.

In studying an inventor's notebooks and sketches, we believe it is important to recognize that these documents are used both to generate and communicate ideas. One should certainly be sensitive to how sketches communicate ideas between and among individuals and groups, and we are glad that other scholars are studying this function. However, in our work, we are focusing on the other function, on comprehending how inventors use sketches to generate and refine their ideas. To illustrate this, let us examine a specific sketch produced by Edison in 1875.

Edison and the Reis Telephone

Although Bell is credited with the invention of the telephone in 1876, he was not the only inventor investigating the possibility of a telephone in the early 1870s. Both Edison and Gray were also studying the relationship between sound and electricity. Like Bell, Edison and Gray were fascinated with the problem of multiple message telegraphy. But unlike Bell who struggled in vain to create a working multiple system, Edison successfully patented a number of multiple message schemes, including several duplex (two-message) and quadruplex (four-message) systems. Edison sold his duplex patents to Western Union who used the patents to block the development of rival telegraph systems, including the postal telegraph scheme proposed by Bell's father-in-law Hubbard.[20] Edison also helped create one of these rivals to Western Union by initially selling his quadruplex to Jay Gould and the Atlantic & Pacific Telegraph Company in 1875.[21]

Because multiple telegraphy had proven to be central to his livelihood, Edison carefully monitored developments in this field. In the summer of 1874, Edison learned that Gray was demonstrating a new harmonic telegraph scheme which might use several acoustic tones to send multiple messages. Anxious to protect his quadruplex patents, Edison began studying acoustics and thinking about how sound and electricity might be integrated in future telegraph systems.[22]

In the course of his thinking about acoustics and telegraphy, Edison became familiar with the electromechanical apparatus devised by Hermann von Helmholtz to reproduce vowel sounds.[23] However, Edison was even more intrigued by an idea proposed in a popular account of electricity. In The Wonders of Electricity, J. Baile speculated about the possibility of using electricity to transmitting the human voice.[24] Would it not be possible, suggested Baile, for a person's voice to vibrate a plate on one end of an electrical wire, to have the vibrations carried along the wire by an electric current, and to somehow have these transmitted waves vibrate a plate on the other end? Based on his experience with electricity, Edison sensed that this was possible, but he thought that the real challenge would be to reproduce both loud and soft sounds. To do this, he decided that it would be necessary to vary the current in the telegraph circuit proportional to the volume of the sound. Edison thought that the best way to accomplish this was to vary the resistance in the circuit, and he had already patented a variable resistor which functioned by having a electrode move up and down in a small vial of water (Figure 2)[25].

Although Edison thought about how sound and electricity might be used together in a telegraph system sometime in 1874, he did nothing with these observations until July 1875. By then the president of Western Union, William Orton, had become sufficiently concerned about the acoustic telegraph schemes of Gray and Bell that he proposed that Edison investigate the field for Western Union. Orton had let Edison's quadruplex slip through his fingers, and he was now anxious not to have a rival company gain a competitive edge through acoustic telegraphy. Consequently, Orton offered Edison a contract which paid Edison $200 a week for experiments. Edison accepted the contract, and as a starting point, Orton sent him an English translation of a German report of a curious electroacoustic device, a telephone invented by Philipp Reis.[26]

Reis was a school teacher at a private school outside Frankfurt who learned physics by attending lectures at the Physical Society of that city. In the early 1860s, he became interested in understanding the functioning of the human ear, and to do so, he invented a series of instruments "by which it is possible to make clear and evident the functions of the organs of hearing, but with which also one can reproduce tones of all kinds at any desired distance by means of the galvanic current."[27] Reis called his instruments "telephones," and he appears to have employed them to understand how the human ear processes complex sounds such as the voice or musical notes. In demonstrating his telephones before several audiences in Germany, Reis mentioned the possibility of using them to conduct conversations at a distance, but it is unclear how well his instruments were at transmitting speech.[28]

In 1862, Reis demonstrated his telephone for Inspector Wilhelm von Legat of the Royal Prussian Telegraph Corps. Legat published a report of the demonstration in the journal of the Austro-German Telegraph Society, and it was this report that was translated and given to Edison in July 1875.[29] In his paper, Legat explained how complex sounds were the result of the superposition of individual tones and how the Reis telephone could be used to study this phenomenon. In the Reis telephone, the transmitter consisted of a cone, membrane and sensitive switch (Figure 3). As one spoke or sang into the cone, the collodion membrane vibrated. Resting on the membrane was a metal lever, pivoted in such a way that a small motion of the membrane produced a large motion at the opposite end of the lever. At its end opposite the membrane, the lever formed a switch in the telegraph line. Normally, this switch was closed, but when one spoke into the cone, the vibrations interrupted the current, creating a series of pulses. These pulses were then sent to Reis' receiver or analyzer Here the intermittent current energized and de-energized an electromagnet which in turn attracted and repelled a metal reed. Properly adjusted, the reed reproduced the basic tone of the voice or musical note sounded at the transmitter.

Upon reading the translation of Legat's report, Edison quickly sized up Reis' telephone and sketched several alternatives (Figure 4). These sketches are Edison's "notes" on the Legat report.[30] To us, these sketches may seem surprising because Edison used very few words to assess Reis telephone, but Edison probably found it easier to summarize his thinking in terms of pictures and not words.

In the top sketch, Edison compared Reis' device with Helmholtz' apparatus for reproducing vowel sounds (Figure 5). Instead of using a delicate (and probably temperamental) pivoted lever as Reis had, Edison proposed substituting a tuning fork and a needle-in-a-cup switch which used "mercury like Helmholtz." Drawing on his earlier thinking about sound waves and electricity, however, Edison decided that if one wanted to produce both loud and soft sounds, one did not want to interrupt the current; rather, one wanted to vary the current in the circuit proportional to the sound. Accordingly, Edison re-represented the Reis telephone as a variable current device. In the center sketch, Edison replaced Reis' switch with the liquid variable resistor he had patented in 1873 (Figure 2). Because the liquid resistor required one electrode to move vertically in a vial of water, Edison bent Reis' lever ninety degrees at the pivot, but he still proportioned the lever so that a small motion at the membrane produced a large motion in the vial. For this second transmitter, Edison added a receiver which modelled after the receivers in the Helmholtz apparatus.

In the bottom sketch, Edison did away with the vial and introduced a high-resistance liquid directly into Reis' switch. In this design, Edison positioned a funnel with a drip wick over the switch. Drops of water would fall from the funnel between the switch's two contacts and create a path of high-resistance for the current. Because of electrolysis, the passage of current would cause the drop to evaporate, thus it making it necessary for the funnel to create a new drop. Finally, because it would be difficult to have a drop fall precisely between two points (as in Reis' original switch), Edison stretched the points of the electrodes into lines and hence sketched two small plates or knife-edges as the electrodes in this transmitter.

In describing these three sketches, we can see that Edison re-represented Reis' telephone by making a series of specific "moves." On one level, Edison made several substitutions. Deciding that the switch in the Reis transmitter should be changed, Edison tried using a combination of a tuning fork and mercury cup, then a liquid rheostat, and finally a novel arrangement using knife-edges and drops of a high-resistance liquid. In the center sketch, Edison dropped the Reis receiver and substituted a Helmholtz receiver. Significantly, with the exception of the droplet scheme, Edison substituted devices which already existed; in the first and second sketch, he borrowed items from the Helmholtz apparatus while in the second sketch he carried over a device from one of his own patents.

In studying a large number of sketches made by Edison, Bell, and Gray, we have found that inventors frequently make these sort of substitutions. The inventor takes something that he has seen in another machine and places it in a new design. Frequently, the components used in the substitution are relatively stable, in the sense that the inventor carries them over from one machine to next without making significant changes to them. Further, as one surveys a number of sketches for one inventor, one notices that an inventor favors some components, and uses them repeatedly. For instance, Edison frequently used a special telegraph device, a polar relay, in many of his inventions, ranging from his multiple telegraph schemes to his motion picture machines.[31] Because these stable components or building blocks seem to play a prominent role in the invention process, we have chosen to give them a specific name, mechanical representations, and we are trying to identify and trace them through the sketches of each inventor.

In the process of making substitutions, it is important to note not only what an inventor substitutes (the mechanical representations) but also where he chooses to make the substitution. In these three sketches, Edison wanted to convert the Reis transmitter from an intermittent current device to a variable current device and he chose to do so by focusing his attention on a particular part of the Reis transmitter, the sensitive switch. To highlight what the inventor chooses to problematize in a particular invention, we refer to the place or zone he or she studies as a slot.[32] Not surprisingly, in comparing Bell, Gray, and Edison, we see that they focus on different aspects of their telephone-like devices, thus making it possible to compare their activities in terms of their choices of slots. In using the word slot, we are construing the process of substitution in terms of the imagery of a inserting an object (like a square peg) into a space (like a square hole). However, for inventors, the mechanical representation does not always fit precisely in the slot, and a poor fit between object and analytical space may lead an inventor to try substituting new mechanical representations and identifying new slots in his or her design.

While substitution is one kind of "move" or operation that an inventor can perform in a sketch, a second kind of "move" involves spatial manipulation. An example of this sort of manipulation can be seen in Edison's bottom sketch of the Reis transmitter. In this sketch, Edison converted Reis' switch into a liquid rheostat by having droplets fall between the contacts. Because it would be very tricky to get the droplets to fall and rest between two points, Edison replaced the points with two horizontal plates. In doing so, one could say that he created the plates by stretching the two points into two horizontal lines. Viewed in the isolation of a single sketch, this sort of spatial manipulation may seem far-fetched, but as one scrutinizes many sketches, one finds that an inventor tends to make some spatial manipulations and not others. Moreover, in comparing inventors, one finds that different inventors manipulate their ideas in different ways. For instance, Bell generated several different multiple telegraph devices by rotating and positioning the reed in different ways in relation to the pole of the electromagnet. Although Bell frequently rotated devices as he moved from one sketch to another, Edison appears to have never recast a device by rotating one component relative to another. Conversely, we have yet to see Bell stretch a point into a line.

We know as much as we do about these three sketches because Edison discussed them in his testimony during the telephone litigation in 1880. Edison used the sketches in the testimony to establish that he had possessed the idea of using variable resistance to convert sound waves into electric current waves in 1875, months before Bell filed the patent application for his telephone. However, in the testimony, Edison did not enter this page of sketches as a regular exhibit because the sketches were not witnessed or dated at the time they were created. Indeed, Edison's chief assistant, Charles Batchelor, testified that he had seen his chief make these sketches in the summer of 1875 but they had not been explained to him and so he did not sign and witness them.[33]

Rather than serving to communicate Edison's interpretation of the Reis telephone to his assistants in 1875, these sketches were part of the process of generating ideas, and Edison himself testified to this:

I have spoken as if these devices were made. I do not mean to say they were made. . . . My sketches were rough ideas of how to carry out that which was necessary in my mind, to turn the Reiss [sic] transmitter into an articulating transmitter. They were notes for future use in experimentation.[34]

In calling these sketches "rough ideas" and "notes for future use in experimentation," Edison signals that these sketches were not handed over to a machinist or experimenter to build and test. Instead, these sketches embody something more general in Edison's thinking about a possible invention. In sketching these variations, Edison transformed the Reis telephone (which was not very useful or interesting to him) into an idea or vision he could use in future experiments. Edison was trying to capture on paper his vision of how sound waves could be converted into electric current waves. Because aspects of this vision were hazy and uncertain, Edison could only attempt to capture it by representing and re-representing it, using devices with which he was familiar. As a telegrapher, manufacturer, and inventor skilled in manipulating objects on the benchtop, Edison had found that the best way to track a hazy vision was to sketch it; although he was aware of how physicists and engineers were using words (theories) and mathematical statements to represent electrical phenomena, Edison had little use for words and equations. And although this vision seems painfully elusive and fleeting to us (especially if we expect Edison to put it into words), we would nonetheless argue that this sketch embodies a key component of the invention process, a mental model.

As an inventor thinks and sketches, he or she does not simply manipulate mechanical representations using specific moves or heuristics in some random fashion; instead these manipulations are an attempt to capture, to flesh out, a mental model. On one level, a mental model is a goal, as in Edison's desire "to turn the Reiss transmitter into an articulating transmitter." Yet on another level, a mental model is an incomplete picture or image of how the inventor thinks his new invention should function. Mental models are frequently the "rough ideas" which the inventor converts into a smooth-running invention only by representing and re-representing his or her mental models in a variety of ways.

For Edison, these sketches from the summer of 1875 represent a powerful mental model that he used through much of his research on the telephone from 1876 to 1878. Many of Edison's sketches for the telephone were based on the idea of variable resistance secured by either the notion of moving an electrode through a high-resistance medium (as in the center sketch where the vertical electrode moves through the vial of water) or the idea of securing variable resistance by introducing a high-resistance medium between electrodes (as in the bottom sketch).[35] Significantly, I would emphasize that while Edison derived this mental model from the Reis telephone, the Reis telephone (as Reis or Legat or anyone else conceived it) did not constitute Edison's mental model. Rather, Edison's mental model was his transformation of the Reis telephone, illustrated in these sketches.

Though seldom articulated by historical actors and elusive to the historical analyst, mental models play a central part in the thoughts and actions of inventors. Along with the "moves" and mechanical representations, they are a bright thread that runs through the tapestry of an inventor's work. Although one can partly illustrate a mental model by pointing to key sketches such as these made by Edison in the summer of 1875, one does not fully appreciate a mental model until one traces the bright thread through the entire tapestry. To accomplish this, one needs to look not at how an inventor transforms one sketch into another, but at how he or she transforms dozens of sketches in sequence. To capture this sequence, we must turn now to looking how sketches can be arrayed in the form of a map of the invention process.

From Individual Sketches to a Visual Discourse

Before discussing in detail aspects of the maps which depict our interpretation of how Edison worked on the telephone, I must explain a key assumption underlying our mapping techniques. We believe an inventor does not draw sketches one-by-one without reference to any other sketches. Rather, an inventor generates sketches in a stream or discourse. As the editors of the Edison Papers remind us, one "cannot fully appreciate Edison's genius without poring over the entire glorious variety of his ideas as they unfold in his drawings and writings."[36]

At first glance, this assumption may not seem problematic, especially if one is studying an inventor's notebooks. Everything about a notebook--its chronological entries, the similarities one can see in several sketches on a given page, the very fact that it is bound--all these features encourage us to view the work in a notebook as a continuous stream of thought and action. Furthermore, inventors and scientists may also reveal to us that they see the notebook as a continuous, evolving stream of ideas when they add features such as cross-references between entries. For example, Bell made periodic cross-references between experiments, and Ryan Tweney has described Michael Faraday used extensive cross-referencing in his notebooks in order to develop new theories and concepts.[37]

However, the assumption that an inventor's sketches should be viewed as a continuous discourse does become problematic when the inventor's sketches are disparate and not bound in a notebook. Edison, for example, produced over 500 telephone sketches between 1875 and 1878, some of which he drew in notebooks but others were simply on loose sheets of paper. As Paul Israel and Robert Friedel noted in their study of Edison's invention of the incandescent light, Edison and his associates did not use their notebooks in sequence; instead, Edison placed notebooks on the various worktables in his Menlo Park laboratory, and he and his experimenters made entries in whatever notebook was handy.[38] Although Edison signed and dated many sketches (and many were also witnessed), he generally did not include a written explanation which can be used to place his sketches in context.

In handling large numbers of sketches with little written information, one temptation is to treat each individual sketch as a solitary act of creation. It is easy to think that each sketch was the product of a specific time and place, and that the number of factors possibly influencing an inventor at a given moment is infinite. Who is to say that the content of a particular sketch was not influenced by what an inventor has read, what his associates told him, what his patron needed, or by what the inventor had for lunch? Thus, because one cannot sort out the multiple influences, some would argue that we cannot analyze a sketch except as a momentary creation. Hence each sketch should be treated individually, and not as part of a continuous discourse.

However, as tempting as these conclusions are, I prefer to see sketches as part of a larger whole. While I would agree that the number of contextual factors influencing an inventor is nearly infinite, one of the few ways to cope with the staggering number of possible influences is to shift one's analytical gaze away from the context to the content of individual sketches. For the moment we need to look more closely at what is in each sketch produced by an inventor; what ideas and objects does it represent? Are there similarities and differences between sketches? And if there are similarities in the content of sketches, can we use these similarities to establish the individuals and ideas influencing an inventor? Hence can we use the content of sketches to sort through the myriad contextual factors? It is my contention that we will only make progress in understanding how different contextual factors inform the invention process by understanding first the intimate details of the documents produced in the heat of invention.

Significantly, as one begins to look closely at dozens of sketches, one notices that there are similarities in style and content.[39] Inventors represent their creations in consistent ways and use some devices over and over. To see these similarities requires immersion in the visual materials, but once noticed, these similarities suggest that sketches can be seen as a continuous stream of thoughts and actions, a visual discourse.

The Art of Mapping

In order to reconstruct the visual discourse of inventors, Gorman and I have been evolving a set of representational techniques we call mapping.[40] Our maps depict hundreds of Edison's sketches of the telephone and we use a system of lines and special boxes to identify links between the different sketches (See Figure 8 for a key to the Edison maps). These maps are generated on a Macintosh computer system by a team of undergraduate engineering students.[41]

On an initial level, our maps are simply a visual "spreadsheet." Wishing to stay close to the visual materials and not reduce them to verbal descriptions, we use the computer to bring all of the sketches together in a single space. Just as financial analysts and engineers employ spreadsheet programs to array numbers in rows and columns in order to identify relationships and trends in quantitative data, so we use our maps to arrange the sketches and look for links and patterns.[42]

In looking for patterns, we test various hypotheses about what constitutes a group of related sketches or a line of research. For some portion of the Edison corpus, it is fairly obvious how sketches may be connected; for instance, in May 1877, Edison drew a series of sketches of different arrangements for plumbago contacts (see Figure 6). In other areas, it can be quite tricky to determine how to group the sketches as Edison sometimes changed several different components in each successive sketch. For instance, in March 1877, Edison sketched several telephone transmitters with four diaphragms and he subsequently submitted a patent for this device. While it is tempting to lump all of these four-diaphragm telephones together, we have mapped them on separate lines (Figure 7). This is because on closer inspection, one can see that some have switches and others have plumbago contacts. In grouping the sketches we move by trial-and-error, testing different mapping arrangements and evaluating them on the basis of how well each arrangement does in accounting for all of the sketches from a given time period. Eventually, these mapping experiments lead us to arrange the sketches by date horizontally across the page and new lines of research by moving down the page (figure 8).

My students and I spend a great deal of time wrestling with grouping sketches in sequential lines of research on the map because the overall layout of the lines helps us reconstruct what Edison's mental models may have been at different times in developing the telephone. In trying to identify Edison's mental models, we continually review Edison's letters and legal testimony for clues as to what might have been the central idea, image, or goal guiding his efforts. We then test these different potential mental models by using them to organize the lines of research into a coherent pattern. As a mental model seems to account for more of the visual and written evidence, so my students and I gain confidence that we are on the right track.

As we array the sketches in lines of research changing over time, our maps begin to take on the features of a genealogical or family tree. In this phase, we puzzle about the moves or heuristics Edison used to convert one sketch to another and how he shifted from one line of research to another. To document the specific changes from one sketch to another, we add a "wing" or group of small boxes on the right side of the sketch box (Figure 8). We also use boxes with rounded corners to provide commentary on the significance of a particular sketch. As we find cases where Edison borrowed a mechanical representation from an earlier sketch, we insert small cross-reference boxes. Likewise, as we create explanations about how Edison moved from one sketch to another, we connect the sketch boxes with lines and add a parallelogram-shaped box. If we find that Edison shaped a sketch in response to an idea or need of an individual outside his circle at Menlo Park, then we note this external influence with an oval. Proceeding in this way, the map becomes a family tree in the sense of depicting how each sketch has various antecedents or parents and how each gives rise to new offspring or children.

An Overview of Edison's Work on the Telephone in 1877

At the present time, my students and I have concentrated our efforts on mapping Edison's efforts to perfect the telephone in 1877.[43] In doing so, we have created eighteen large maps which depict the connections for over 150 sketches from January to August 1877.[44] Rather than discuss each of these large maps completely, I will present an overview map of Edison's efforts to develop a telephone in 1877 and then "zoom in" on interesting features of the detailed maps. It is important to note that the overview map presented below is based on the eight highly detailed maps and provides a summary of the major trends of those maps. To use a cartographic analogy, if the detailed maps depict provinces or states, then the overview map is a map of an entire country.

After sketching his alternatives to the Reis telephone in July 1875, Edison focused on developing several acoustic, multiple-message telegraphs for Western Union. Some of these devices were based on Reis receivers, others used vibrating reeds similar to those employed by Gray, and a few had metal diaphragms.[45] While working with the vibrating reed version in November 1875, Edison thought he had a detected how electric energy could be transmitted without wires and he dubbed this discovery the "etheric force."[46] Encouraged by Western Union's continuing support of his inventions, Edison decided in the spring of 1876 to move his laboratory from his telegraph instrument factory in downtown Newark to a new building in rural Menlo Park. At Menlo Park, Edison continued to pursue his experiments in acoustic telegraphy along with several other projects.[47]

By the fall of 1876, however, both Edison and Western Union had learned of Bell's telephone patent (issued in April 1876). After considering the possibility of purchasing Bell's patent, Orton decided that he preferred to have Edison develop a series of patents for the telephone which could be used to block Bell's efforts and permit Western Union to set up its own telephone systems.[48]

As a starting point, Edison went back to his three sketches of how to improve the Reis telephone and pursued three lines of research (Figure 9). First, in the fall of 1876 Edison had his assistant James Adams investigate a telephone in which the diaphragm was connected to an electrical contact sitting in a dish filled with a high-resistance liquid or powder.[49] As one spoke into this telephone, the sound waves "dragged" or pulled the contact in and out of the resistance (Box a, Figure 9). Next, in February 1877, Edison drew telephones which varied the total resistance by having small contacts on the diaphragm which "switched" different resistances into the circuit (Box b, Figure 9) Finally, inspired by his knife-edge design, Edison devised a telephone in which he replaced the knife edge with two parallel disks and he tried using both plumbago[50] as well as felt soaked in various high-resistance liquids as the resistance medium (Box c, Figure 9). In these designs, the resistance was varied as the disks "squeezed" the resistance medium.

Edison pursued these three lines of research and secured limited results until March 1877. At the end of that month, he substituted plumbago or platinum points for the disks on his "squeeze" telephone (Box d, Figure 9). These telephones seemed to work better, leading Edison to think more carefully about using points. In particular, he now considered using four high-resistance points pressing on the diaphragm with varying degrees of force (Box e, Figure 9). Edison noted an inverse relationship between the mechanical force and the electrical resistance--that the resistance increased as the force decreased--and drew on this observation to construct his pressure relay telephone in April 1877 (Box f, Figure 9).

Once he realized that he could use mechanical pressure to vary the resistance of plumbago, Edison experimented both with improved versions of his pressure relay and small blocks of plumbago pressing against the diaphragm.(Box g, Figure 9) At the end of May, Edison tested the effectiveness of using plumbago blocks by replacing the receiver with a series of Helmholtz-like tuning forks (Box h but see also figure 13). With this test arrangement, Edison wanted to see if his transmitter was fully capturing all of the tones comprising speech, and he found that while the plumbago seemed to be working alright, he needed to pay more attention to the acoustic components of his telephone--the diaphragm and mouthpiece or resonant cavity. Consequently, in June and July of 1877, Edison and his associates made a series of changes to the diaphragm (such as replacing the metal membrane with a mica one) and they tested double resonant cavities. Because sounds such as "s" (sibilants) were not being transmitted (they failed to vibrate the diaphragm sufficiently), Edison tried adding a vibrating reed to his telephone. Mounted on the top of the resonant cavity, the reed vibrated in response to sibilants, opened and closed an electrical circuit, and hence added additional current at the appropriate frequency to the signal. Eventually, however, Edison decided that the slight improvement from using the reed did not offset the extra circuitry that it required and so he abandoned this line of investigation.

As is often the case, changing one component in system often creates new and unexpected problems; once Edison began employing thin mica diaphragms in his telephone in June 1877, he had to solve the problem that they tended to shatter with repeated use. To dampen some of the vibrations on the diaphragm, Edison tried a variety of springs which held the plumbago close to diaphragm while also serving as a shock absorber (Box i, Figure 9). Dissatisfied with the volume and articulation of these telephones, Edison briefly went back to using metal diaphragms (which added a musical ring to the transmission) and he undertook a brief search for an alternative to either metal or mica in late July.

However, because he could not find a material that worked as well as mica, Edison continued using mica and he instead modified the resistance medium. Reasoning that he could reduce the amount mechanical force by replacing the solid blocks of plumbago with some some soft version, Edison began mixing powdered plumbago with silk fibers or fluff.[51] By carefully forming the plumbago and fluff into the shape of a tiny cigar and by using ingenious spring arrangements to hold the fluff cigar next to the diaphragm, Edison was able to improve the volume of his telephone. Nevertheless, the fluff telephones required frequent adjustment and Edison felt that their articulation was no better than that of Bell's magneto telephone.[52]

In late October and early November 1877, Edison overcame these difficulties by developing a new mental model of how the carbon functioned in his telephone. According to Batchelor, "Mr. Edison . . . found out that plumbago does not alter its resistance by pressure as we at first thought; but the increased pressure made better contact."[53] On the basis of this new mental model, Edison now decided to employ a hard button made of lampblack. Because a button of pure lampblack would have a high resistance, Edison lowered its resistance by mixing in ground rubber and he reduced the force on the button by placing a small rubber tube between the button and the diaphragm (Figure 10).

To his dismay, Edison found that the rubber tube quickly lost its shape and failed to conduct the vibrations. He replaced the rubber tube with a platinum spring, but even a delicate spring added an extra musical tone to the signal. Consequently, he tried progressively thicker springs, which gave better results. These experiments led Edison to place an aluminum button and a glass disk between the carbon button and a thick iron diaphragm (Figure 11). This new arrangement gave superior results on tests conducted in April 1878 on the Western Union lines between New York and Philadelphia. The company chose this 90 mile line because it was one of the busiest in the network[54] Even on this heavily used line, Edison's carbon transmitter was capable of transmitting even whispers loudly and distinctly, and it became the standard configuration for Edison's telephone.

By the spring of 1878, both Edison and Western Union were satisfied with the carbon telephone, and Edison assigned the patents to Western Union for $100,000.[55] To complement Edison's patents, Western Union purchased Gray's harmonic telegraph as well as a patent from Amos Dolbear who had developed an improved version of Bell's telephone.[56] Armed with these patents, Western Union organized the American Speaking Telephone Company, and this firm began installing telephones and setting up exchanges.[57] In many cities, American Speaking Telephone raced with the local Bell agents to open the first telephone exchange. Within a year, American Speaking Telephone had installed 56,000 telephones in 55 cities.[58]

Faced with vigorous competition, the Bell interests were forced to play their trump card. In August 1878, Bell Telephone sued Western Union for infringing Bell's patent. Specifically, Bell telephone accused Peter Dowd, a Western Union agent of illegally installing telephones which used Bell's patented principle. Over the next fourteen months, both sides amassed a huge amount of evidence.[59] The actual court hearing for the case was scheduled for the fall of 1879, but as the starting date drew near, the attorneys for Western Union elected to settle with Bell Telephone out of court. Western Union apparently chose to settle the dispute because Jay Gould had mounted a hostile takeover attempt, and the firm needed to marshall its resources to fend off Gould.[60] Western Union agreed to withdraw from the telephone field and sell its existing telephone exchanges to American Bell; in return Bell agreed to pay Western Union a royalty of 20 percent for seventeen years on the telephone rentals in their former exchanges.[61] With his corporate patron satisfied, Edison turned his attention to new projects concerning the phonograph and the electric light.

What do the Maps Reveal?

Armed with this overview of Edison's work on the telephone in 1877, let us turn now to examining several features of the maps. In doing so, I will move from general things the maps suggest about Edison's method of invention to more specific aspects of his work. To highlight what was distinctive about Edison's method, I will in some cases compare what we are learning about Edison with what we have discovered about Bell's method of invention.[62]

A major feature of the maps is that they reveal what we think were Edison's mental models and the lines of research he established to investigate them. Significantly, our maps suggest that inventors may have different kinds of mental models. For instance, in studying Bell's notebooks, Gorman has found that Bell's key mental model was the human ear; Bell designed several of his crucial early telephones by thinking about how the eardrum and bones of the inner ear worked.[63] In contrast, I have concluded that for the first few months of 1877 Edison was guided by the different functions by which he could secure variable resistance.[64] The maps suggest that he investigated how to secure variable resistance by (a) "dragging" a contact through a resistance medium; (b) "squeezing" the resistance medium between two contacts (either knife-edges, disks, or plates); and (c) "switching" in different resistances. Hence, the maps illustrate how Edison's mental model for the telephone may have been a family of functions, of alternative ways of securing variable resistance.

Another striking feature of Edison's method revealed by the maps is that he did not systematically pursue one line of research but rather investigated several lines at once. As the map in Figure 12 reveals, Edison jumped from one line of research to another, sketching several ideas for one kind of telephone and then shifting to another. This eclectic approach by Edison is very different from the approach used by Bell who tended to work through one particular set of modifications before investigating another area.

Edison probably maintained multiple lines of inquiry because of the potential benefits of cross-breeding the results of one line with another. Edison sometimes generated a new line of investigation by combining results from two previous lines. For instance, Edison arrived at the idea of using plumbago under pressure in his telephone by combining ideas from his switching telephones with his "squeeze" telephones (see overview map). We also know from later projects that Edison maintained multiple lines of inquiry and switched his experimenters from one line to another to keep up their enthusiasm and interest in a project.[65] While we suspect the same might be true in the telephone, we have not yet been able to identify any lines which Edison assigned to one assistant or another.

While it is sometimes unclear why Edison started or stopped a particular line of research, we have found in one case that change came about as a result of a new test instrument. At the end of June 1877, Edison shifted his attention away from investigating the resistance medium and its contacts to improving the acoustic components of his telephone--the diaphragm and resonant cavity. Edison made this change as a result of conducting experiments using new devices for testing the acoustic fidelity of his transmitters and receivers. In one experiment, Edison connected three Helmholtz tuning forks to his transmitter and then listened at the receiver to see if the transmitter introduced any distortion to the frequencies generated by the turning forks (Figure 13). On the basis of this test, Edison shifted his attention to a systematic investigation of the diaphragm, adding weights or rubber disks to dampen the motion of the diaphragm and he also tried changing the material in the diaphragm from parchment to mica.[66] In deciding to use a test instrument, Edison seems to be not only seeking to validate the results of a line of investigation but also looking for new areas to study.

The maps have also led us to continue to investigate how Edison moved from sketch to sketch. For example, Edison often tried changing from a parallel to a series circuit. While experimenting in late May 1877 with small blocks of plumbago (as part of his investigation of how to take advantage of plumbago under pressure), Edison drew two sketches of how to position two blocks behind the diaphragm (Figure 14). In the first version, Edison arranged the blocks so that they created two separate and parallel paths between the batteries and the transmission line. In the second sketch, Edison had the current pass from the battery through both plumbago blocks.

Another move used by Edison was to compare electrical and mechanical means of achieving the same end. For instance, in a sketch dated 21 May 1877, Edison investigated how he might amplify the signal in his plumbago telephone. In the top sketch he used an induction coil or transformer to boost the signal and in the lower sketch he used an L-shaped lever. By making the horizontal arm of this lever longer than the vertical arm, Edison was able to convert relatively small movements of the diaphragm into a strong force on the plumbago (Figure 15). Edison was quite familiar with using an L-shaped lever in this manner since he used this sort of lever in his one of his transformations of the Reis telephone (Figure 3). Hence, this sketch provides another example of how Edison borrowed a mechanical representation from an older sketch.

The maps do not by any means provide all of the answers but frequently raise new questions. As we puzzle over each sketch and try to find an appropriate place for it on a map, we are often forced to investigate where Edison got specific mechanical representations. In a sketch dated 27 June 1877, we have discovered that Edison conducted further acoustic tests of his transmitter by employing the manumetric capsule of Rudolf Koenig (Figure 16). This capsule was an airtight container with a flexible diaphragm on one side and a small orifice on the other side. The capsule was then filled with flammable gas which was ignited as it escaped from the orifice. If one spoke into the membrane while the gas was burning, then flame would vary proportionally to the sound waves.[67] As he did in his other acoustic tests, Edison placed a manumetric capsule on the transmitter and receiver, and compared the flames produced by each in order to determine whether there was any distortion.

While this is certainly a bizarre way to test his telephone, this sketch raises questions about where Edison learned about the manumetric capsule since Edison did not employ this device previously. We suspect that Edison learned about this device by attending a lecture and demonstration given by Bell in New York in May 1877.[68] Bell was fascinated by the manumetric capsule, used it throughout his experiments on the telephone, and may very well have included it in his lecture.[69] Thus, in our efforts to understand the contents of each sketch and locate it in the inventor's visual discourse, we are forced to ask new questions about where an inventor secures new ideas and devices.

Another type of question posed by the maps comes when we compare the general character of Edison's work on the telephone during the winter and spring of 1877 with the summer of that year. During the first few months Edison worked on the telephone, he regularly sketched complete telephones which functioned in significantly different ways. After June, Edison shifted his attention to perfecting individual components (such as the diaphragm, resonant cavity, and carbon holder) of the plumbago or carbon telephone. Notably, Edison changed notebooks around this time, moving from doing most of his sketches in notebook 11 to notebook 12. Obviously, once Edison had settled on using plumbago in his telephone, it seems reasonable to shift from "conceptual" sketches to "engineering" drawings. Nevertheless, we still wonder as to why the shift came when it did and why it seems so sudden and thoroughgoing. We know that Edison spent much of June in court testifying in the quadruplex cases, and while he was away, he may have made up his mind about how he wanted to develop the carbon telephone. We also know that Edison's chief experimenter, Charles Batchelor, spent June testing hundreds of carbon compounds and that he discovered that lampblack worked better than plumbago.[70] Nevertheless, this major shift has led us to consider what was going on at Western Union and if Edison was being pressured by Orton at this time to produce a telephone quickly. Again, an important characteristic of the maps is that they permit us to see interesting developments in how Edison thinks and works and this forces us to ask new and more precise questions about who or what may be influencing the invention process.


In this paper, I have tried to show how it is possible to analyze the sketches produced by inventors. Although most historians of technology have assumed that inventors generate and manipulate sketches using the mysterious faculty of the mind's eye, I would suggest that it is possible to reconstruct the series of moves used by an inventor in sketching alternative devices. To illustrate this, we looked first at how Edison transformed the Reis telephone during the summer of 1875. Notably to develop a fine-grained analysis of sketching, one needs to be explicit about how one is conceptualizing the thoughts and actions of the inventor, and so I introduced the concepts of mechanical representation, slot, heuristic, and mental model.

Inventors do not simply produce a few sketches; if they are like Edison, they produce hundreds. To get intellectual control of a large number of sketches, I suggested next that we view an inventor's sketches as constituting a visual discourse in which an inventor borrows and modifies different ideas and devices. One can examine this visual discourse by creating a map in which one links the sketches together and looks for patterns.

These maps are valuable because they give us a new and detailed picture of how an inventor may think and work. In the maps, we are able to identify not only the general contours of an inventor's method--how he conceptualizes an invention and the lines of research he undertakes--but also some of the specific ways he generates new devices. As examples, we saw how Edison transformed different versions of the telephone by substitutions, spatial manipulation, changing from a parallel to a series circuit, or comparing different means of achieving the same end. Furthermore, the maps raise new questions about who or what may be influencing the content of the sketches (through, say, the sudden appearance of a new device) or the timing of changes in an inventor's strategy.

Taken together, the application of these cognitive concepts and the representational technique of mapping to Edison's sketches suggests a new definition of invention: Invention is a process by which an individual represents and re-represents ideas and objects until he achieves a stable configuration that more or less matches his mental model or goals. Although I have concentrated here on one type of representation, sketches, inventors use other kinds of representation including test models, written descriptions (such as patent applications), and public announcements (such as advertisements) to create, shape, and hone their ideas.

In putting forward this definition, I do not wish to deny that invention is also a social process. Individuals represent ideas and objects employing information, techniques, and resources they have acquired from other people. Frequently, the definition of what constitutes a stable configuration is determined not only by the inventor himself but by what he is able to demonstrate to his assistants and backers. And likewise, the goals of an inventor often include either having some sort of impact on society or reaping some sort of reward.

Instead, what I am saying with this definition is that invention process is both social and cognitive. As an inventor talks and works with other people, he is also thinking and acting. And rather than make a series of unexamined assumptions about what this thinking and acting is, it is preferable to be explicit about how we interpret how inventors think and act. Hence, Gorman and I have found it necessary to create new conceptual categories to describe how inventors work. In part, we have undertaken this cognitive venture not to undermine the social history of technology but rather to enhance it. I sincerely believe that we can only expand our understanding of the dynamic interaction of technology and society by first making sense of how technologists think and act. To put it in concrete terms, if we wish to understand fully Edison's laboratory at Menlo Park (context), then we must master what he produced there (content) and the process by which these sketches and artifacts were created. We must investigate not only social negotiations but mental processes as well. Invention, or more broadly how individuals transform knowledge, is neither social nor cognitive; it is always both.

In employing these concepts and maps to reconstruct an inventor's visual discourse and identify elements of his method, one is not engaged in a frivolous or arcane enterprise. Rather I feel I am completing a challenge posed by Thomas Hughes in his biography of Elmer Sperry: Do we want to view invention as a random, mysterious process or we do we want to see it as a sequence of purposeful acts?[71] If we choose the first course, that invention is mysterious, then we are conceding that technological change is truly autonomous, beyond our ability to understand, guide, or control. If, however, we choose the second course (as I suspect most historians of technology do), then we are creating the theory and cases studies that can be used to guide and control technology. But to accomplish this we must develop concepts and techniques which permit us to recover the purposeful acts constituting invention and technological change. Just as historians and sociologists studying technology have found it necessary to develop explicit concepts for describing and analyzing the interaction of social groups and technological artifacts, so it is necessary to be clear about the categories one is using to study the process of invention.[72] Unless we are explicit about the theoretical ideas we are using to study the invention process, then we are likely to see only the simplest reflections of our cultural biases in the historical source materials.

[1][Jacques Eugene] Armengaud and Mme. Armengaud, The Practical Draughtsman's Book of Industrial Design, and Machinist's and Engineer's Drawing Companion..., trans. W. Johnson (Philadelphia: Henry Carey Baird, 1883), p. iii.

[2]Bruno Latour, Science in Action: How to Follow Scientists and Engineers Through Society (Milton Keynes: Open University Press, 1987), p. 253.

[3]Quoted in Rudolf Arnheim, Visual Thinking (Berkeley: University of California Press, 1969), p. 12.

[4]Eugene S. Ferguson, Engineering and the Mind's Eye (Cambridge: MIT Press, 1992); Brooke Hindle, Emulation and Invention (New York: Norton, 1981); and Steven Lubar, "Representing Technological Knowledge," Proceedings of Joint Meeting of the History of Science Society and Society for the History of Technology, Madison, October 1991. See also Henry Petroski, "On the Backs of Envelopes," American Scientist, January-February 1991, 15-7.

[5]Bert S. Hall and Ian Bates, "Leonardo, the Chiarvelle Clock, and Epicyclic Gearing: A Reply to Antonio Simoni," Antiquitarian Horology 9:910-17 (1976). I am grateful to Edwin Layton for calling this paper to my attention.

[6]W. Bernard Carlson, Innovation as a Social Process: Elihu Thomson and the Rise of General Electric, 1870-1900 (New York: Cambridge University Press, 1991).

[7]Barbara Stafford develops these themes in "Voyeur or Observer? Enlightenment Thoughts on the Dilemmas of Display," Configurations 1:95-128 (Winter 1993).

[8]Ferguson, 153-94.

[9]We have published several reports on this research; see W. Bernard Carlson and Michael E. Gorman, "Thinking and Doing at Menlo Park: Edison's Development of the Telephone, 1876-1878" in W.S. Pretzer, Ed., Working at Inventing: Thomas A. Edison and the Menlo Park Experience (Dearborn: Henry Ford Museum & Greenfield Village, 1989), 84-99; Michael E. Gorman and W. Bernard Carlson, "Interpreting Invention as a Cognitive Process: The Case of Alexander Graham Bell, Thomas Edison, and the Telephone," Science, Technology, and Human Values 15:131-64 (Spring 1990); W. Bernard Carlson and Michael E. Gorman, "A Cognitive Framework to Understand Technological Creativity: Bell, Edison, and the Telephone in R. J. Weber and D. N. Perkins, Eds., Inventive Minds: Creativity in Technology (New York: Oxford University Press, 1992), 48-79; Michael E. Gorman, Matthew M. Mehalik, W. Bernard Carlson, and Michael Oblon, "Alexander Graham Bell, Elisha Gray, and the Speaking Telegraph: A Cognitive Comparison," History of Technology, 15:1-56 (1993); W. Bernard Carlson and Michael E. Gorman, "La Methode Edison: Le Cas du Telephone," Les Cahiers des Science & Vie No. 32 April 1996), pp. 40-9.

[10]Several historians of science have emphasized the importance of recovering the experimental and benchtop work of scientists; see David Gooding, "Mapping Experiment as a Learning Process: How the First Electromagnetic Motor Was Invented," Science, Technology, and Human Values 15:165-201 (Spring 1990) and Peter Galison, How Experiments End (Chicago: University of Chicago Press, 1987); Frederick Lawrence Holmes, Lavoiser and the Chemistry of Life: An Exploration of Scientific Creativity (Madison: University of Wisconsin Press, 1985).

[11]I am grateful to Margaret B.W. Graham for suggesting that I consider how sketches may serve both these functions.

[12]Steven Lubar explored this theme in "Representing Technological Knowledge." For an example of how engineering drawings constituted a system of communication and control in a nineteenth century factory, see John Kennedy Brown, "The Baldwin Locomotive Works, 1831-1915: A Case Study in the Capital Equipment Sector," Ph.D dissertation, History, University of Virginia, 1992, 160-9.

[13]See for example, Thomas P. Hughes, Elmer Sperry: Inventor and Engineer (Baltimore: Johns Hopkins University Press, 1971); Peter L. Jakab, Visions of a Flying Machine: The Wright Brothers and the Process of Invention (Washington: Smithsonian Institution Press, 1990).

[14]Edward Jay Pershey reports that this famous sketch only became the "first" drawing of the phonograph when in 1927, on the fiftieth anniversary of the invention, Edison pulled it out of a drawer and added his line of instructions. See "Drawing as a Means to Inventing: Edison and the Invention of the Phonograph," in Pretzer, Working at Inventing,, 100-15.

[15]Charles Bazerman is exploring this theme in his current study, "The Languages of Edison's Light: The Emergence of the Electrical Light into the Discursive Worlds of the Late Nineteenth Century."

[16]See Thomas P. Hughes, Networks of Power: Electrification in Western Society, 1880-1930 (Baltimore: Johns Hopkins University Press, 1983) and John Law, "Technology and Heterogeneous Engineering: The Case of Portuguese Expansion" in Wiebe E. Bijker, Thomas P. Hughes, and Trevor Pinch, Eds., The Social Construction of Technological Systems: New Directions in the Sociology and History of Technology (Cambridge: MIT Press, 1987), pp. 111-34. This theme is also developed in Carlson, Innovation as a Social Process.

[17]Bruno Latour, Science in Action: How to Follow Scientists and Engineers Through Society (Milton Keynes: Open University Press, 1987).

[18]For further discussion of how our position differs from Latour's see W. Bernard Carlson and Michael E. Gorman, "Socio-technical Graphs and Cognitive Maps: A Comment on Latour, Mauguin, and Teil." Social Studies of Science 22:81-91 (1992).

[19]See "Experiments made by A. Graham Bell, Vol. 1," notebook, Bell Family Papers, Box 258, Library of Congress, Washington, DC. Although Bell and his lawyers introduced these notebooks as evidence in their first major patent case, Bell Telephone v. Peter A. Dowd, Bell's lawyers found it preferable to document Bell's development of the telephone using letters Bell had sent home to his parents.

[20]W. Bernard Carlson, "Entrepreneurship in the Early Development of the Telephone: How did William Orton and Gardiner Hubbard Conceptualize this New Technology?" Business and Economic History 23:161-92 (Winter 1994), pp. 171-3.

[21]See Agreement with Jay Gould, 4 Jan. 1875 in The Papers of Thomas A. Edison, ed. Robert A. Rosenberg et al. (Baltimore: Johns Hopkins University Press, 1991), Vol. 2, pp. 378-80. Hereafter cited as Edison Papers, Vol. 2. Edison's business relationship with Gould is outlined in Edison Papers, Vol. 2, pp. 313-4 and 372-5 as well as in Paul Israel, From Machine Shop to Industrial Laboratory: Telegraphy and the Changing Context of American Invention, 1830-1920 (Baltimore: Johns Hopkins University Press, 1992), 138 and 147.

[22]Testimony of Thomas A. Edison in The Speaking Telephone Interferences. United States Patent Office. Evidence on behalf of Thomas A. Edison , 2 vols., (hereafter cited as Edison Evidence), vol. 1, p. 4. Reproduced in The Thomas A. Edison Papers: A Selective Microfilm Edition (Frederick, Md.: University Publications of America, 1985- ), Reel 11, (hereafter cited as TAEM).

[23]For a description of this apparatus, see Hermann L. F. Helmholtz, On the Sensations of Tone as a Physiological Basis for the Theory of Music, trans. A. J. Ellis (London: Longmans, Green, 1875), 174-82 and 604-7.

[24]J. Baile The Wonders of Electricity , trans. J.W. Armstrong, (New York: Charles Scribner, 1872).


Thomas A. Edison, "Relay Magnets," U.S Patent No. 141,777 (executed 7 March 1873, granted 12 Aug. 1873).

[26]Testimony of Edison, Edison Evidence, Vol. 1, pp. 4-5; Contract between Edison and Western Union, 14 Dec. 1875, Edison Testimony, Vol. 2, pp. 600-2; Israel, 138-40.

[27]Silvanus P. Thompson, Philipp Reis: Inventor of the Telephone (London: E.&F.N. Spon, 1883), p. 5

[28]See Philipp Reis, "On Telephony by the Galvanic Current," [1861], and "On the Transmission of Tones to a Distance as Far as Desired, by the Help of Electricity (Telephony)," [1863], both translated in Thompson, pp. 50-66. See especially pp. 51 and 65.

[29]See "Translation by WU Translator of `Reiss Telephone,'" Edison Evidence, vol.2, pp. 509 ff. Legat's report (with its original illustrations) is also translated in Thompson, pp. 70-8 and 182-3.

[30]Edison discussed these sketches in his testimony, Edison Evidence, Vol. 1, pp. 6-9.

[31]W. Bernard Carlson and Michael E. Gorman, "Understanding Invention as a Cognitive Process: The Case of Thomas Edison and Early Motion Pictures, 1888-91," Social Studies of Science 20:387-430 (1990), pp. 405-6.

[32]Our concept of slot is a modification of a concept developed by Robert J. Weber and David N. Perkins in "How to Invent Artifacts and Ideas," New Ideas in Psychology 7:49-72 (1989).

[33]Testimony of Charles Batchelor, Edison Evidence, Vol. 1, p. 224.

[34]Testimony of Edison, Edison Evidence, Vol. 1, p. 9.

[35]For a summary of Edison's telephone experiments in 1877, see Carlson and Gorman, "A Cognitive Framework to Understand Creativity," 65-72.

[36]The Papers of Thomas A. Edison, ed. Robert Rosenberg et al., (Baltimore: Johns Hopkins University Press, 1994), Vol. 3, p. xxviii.

[37]Ryan D. Tweney, "Faraday's Notebooks: The Active Organization of a Creative Science," Physics Education 26:301-6 (Sept. 1991).

[38]Robert Friedel and Paul Israel, Edison's Electric Light: Biography of an Invention (New Brunswick: Rutgers University Press, 1986), 233-8. Edison described his notebook scheme in his testimony, Edison Evidence, Vol. 1, p. 60.

[39]As one example of similarities, I have noticed that Bell and Edison have pronounced drawing styles. Almost all of Bell's sketches are two-dimensional, elevations of his devices while Edison generally sketched his devices in an isometric projection which provided the illusion of a third dimension to his drawings.

[40]David Gooding has developed a different mapping system for recovering the nonverbal, purposeful acts embedded in Michael Faraday's experiments, and we have profited greatly from studying Gooding's work; see his "Mapping Experiment as a Learning Process."

[41]The maps are prepared by first scanning into the computer the sketches from xerox copies made from the Edison microfilm. Next the scanned sketches are "pasted" into a commercial software package, Topdown@. Topdown then permits the students to draw boxes around the sketches, connect the boxes by lines, and add interpretative apparatus. Additional information about each sketch is also stored in an electronic notecard connected to each sketch box. This mapping technique has been tdeveloped and perfected by a number of students who have worked with us over the last five years. The maps discussed in this paper were prepared by Jeff Gallimore and Chip Littlepage in 1992-3.

[42]I am using the notion of a "spreadsheet" here to emphasize the qualitative aspects of spreadsheets--that one often sees patterns once the numbers are arrayed in rows and columns. There is, of course, no quantitative aspect to our maps, in the sense that numerical spreadsheets have equations for calculating the values of certain cells. My thanks to JoAnne Yates for pointing out this distinction.

[43]We have been studying Edison's 1877 sketches for two reasons. First, although Edison and his experimenters did investigate the telephone in the fall of 1876 and in the winter and spring of 1878, the bulk of their work on this invention took place in 1877. Second, most of the 1877 sketches were entered as evidence in the 1880 telephone litigation and hence are conveniently available on a single reel of the Edison microfilm. At the present time, we are collecting additional Edison sketches of the telephone from other portions of the microfilm and we will eventually include them on our maps. Of course, we will revise our maps as these sketches reveal new information.

[44]For an example of one these maps, see Figure 12.

[45]As examples, see Edison Papers, V. 2, 631-2, 664-6, and 699.

[46]Carlson, Innovation as a Social Process, , 69-82.

[47]Edison's activities in the fall and winter of 1875-76 are summarized in Edison Papers, Vol. 2, pp. 580-3 and 704-6.

[48]Carlson, "Entrepreneurship in the Early Development of the Telephone," pp. 174-6; Robert Bruce, Bell: Alexander Graham Bell and the Conquest of Solitude (Boston: Little, Brown, 1973), p. 229; Frederick L. Rhodes, Beginnings of Telephony (New York: Harper & Brothers, 1929), p. 51.

[49]Edison, "Speaking Telegraph" sketch, 12 Oct. 1876, TAEM 11:[238].

[50]Plumbago is an archaic term, typically used to describe graphite or the lead in pencils. In his telephone, Edison appears to use this term to describe several different types of carbon, and so the reader should be warned that when plumbago is mentioned in the text, we are simply employing Edison's term and they should not necessarily assume that Edison is using graphite.

[51]Batchelor diary, entry for 30 July 1877, TAEM.

[52]George B. Prescott, Bell's Electric Speaking Telephone: Its Invention, Construction, Application, Modification, and History (New York: D. Appleton, 1884' reprinted Arno, 1972), p. 224.

[53]Batchelor diary, entry for [9 Nov. 1877], TAEM,

[54] Presott, pp. 224-'6 ; "Edison's Carbon Telephone," Journal of the Telegraph, 16 April 1878, p. 114.

[55]For a discussion of the business history of the telephone from 1877 to 1879, see Carlson, "Entrepreneurship in the Early Development of the Telephone," pp. 179-85.

[56]Michael F. Wolff, "The Marriage That Almost Was," IEEE Spectrum, 13 (Feb. 1976), 40-51, on p. 50.

[57]"The American Speaking Telegraph Company," Journal of the Telegraph, 10:357 (1 Dec. 1877).

[58]The number of telephones and exchanges is based on the terms of the Dowd settlement; see Brooks, 1975, 71.

[59]American Bell Tel. Co. v. Peter A. Dowd; A Bill (No. 1040) in equity filed 12 September in the U.S. District Court, District of Massachusetts. Part I, Pleadings and Evidence; Part II, Exhibits (Boston, 1880).

[60]Gould ultimately gained control of Western Union in 1881; see Edwin N.Asmann, "the Telegraph and the Telephone: Their Development and Role in the Economic History of the United States: The First Century, 1844, 1944," Ph.D Dissertation, History, Northwestern University, 1980, pp. 97-8 and Israel, 1992, 147-9.

[61]Details of the settlement can be found in Rhodes, 1929, 52-3. Estimates of this royalty income vary, but Western Union earned between $3.5 and 7 million on this agreement; see Matthew Josephson, Edison: A Biography (New York: McGraw-Hill, 1959), p. 148 and Wolff, p. 51.

[62]Several historians of technology have investigated how inventors may have distinctive ways of working or a "method." Perhaps the historian who has written most persuasively on this topic is Thomas P. Hughes; see his article, "Edison's method," in W.B. Pickett, Technology at the Turning Point (San Francisco: San Francisco Press, 1977); Sperry: ; Networks of Power: ; and American Genesis: A Century of Invention and Technological Enthusiasm (New York: Viking, 1989). For additional interesting discussions, see Carlson, Innovation as a Social Process; David A. Hounshell, "Elisha Gray and the Telephone: On the Disadvantages of Being an Expert," Technology and Culture 16:133-61 (1975); and Steven Lubar, "Culture and Technological Design in the 19th-century pin industry: John Howe and the Howe Manufacturing Company," Technology and Culture 28:253-82 (1987).

[63]Michael E. Gorman and W. Bernard Carlson, "Mapping Invention and Design." Chemtech , October 1992, 584-91.

[64] With Edison, we have considered a variety of potential mental models; at times, we have thought that Edison may have been guided in his investigations by testing different materials or by certain circuit configurations. However, we have increasingly come to the conclusion that for the first few months of 1877 Edison was guided by the function by which he could secure variable resistance. Again, mapping is in part a way of visually thinking through and testing alternative hypotheses of what an inventor's mental model might be.

[65]See W. Bernard Carlson, "Thomas Edison as a Manager of R&D: The Development of the Alkaline Storage Battery, 1899-1915." IEEE Technology and Society 12:4-12 (December 1988), and Carlson and Gorman, "Understanding Invention as a Cognitive Process:"

[66]See Edison sketches from 24-27 June 1877, TAEM, reel 11, frames [347, 350, 352, 358, 361, and 363-4].

[67]For a description of the manumetric capsule, see Catalogue des Appareils d'Acoustique Construits par Rudolph Koenig (Paris, 1865), pp. 43-6 in the Trade Catalog Collection, National Museum of American History and James E. Homans, ABC of the Telephone (New York: Theodore Audel, 1901), pp. 16-7.

[68]Batchelor Diary, 19 May 1877, TAEM.

[69]On Bell's interest in the manumetric capsule, see his "Researches in Electric Telephony," Journal of the Society of Telegraph Engineers 6:385-421 (1877), on p. 404.

[70] Batchelor's test notes from 13-25 June 1877 can be found on TAEM, reel 11, frames 306-357.

[71] Hughes, Sperry, 63.

[72]Wiebe E. Bijker, Thomas P. Hughes, and Trevor Pinch, Eds., The Social Construction of Technological Systems: New Directions in the Sociology and History of Technology (Cambridge: MIT Press, 1987) and Wiebe E. Bijker and John Law, Eds., Shaping Technology/Building Society: Studies in Sociotechnical Change (Cambridge: MIT Press, 1992).