Other articles in the series:
- History of the relay
- History of electronic computers
- History of the transistor
- Internet history
The phone came about by accident. If Thanks to a century of research into the possibilities of transmitting messages using electricity, people stumbled upon the telephone in search of an improved telegraph. It is therefore fairly easy to assign a plausible, though not entirely certain, date for the invention of the telephone to be the year of the centenary of the founding of the United States, 1876.
And it cannot be said that the phone did not have predecessors. Since 1830, scientists have been looking for ways to turn sound into electricity, and electricity into sound.
electric sound
In 1837 year , a physician and experimenter in the field of electromagnetism from Massachusetts, stumbled upon a strange phenomenon. He placed an insulated coiled wire between the ends of a permanent magnet, and then lowered each end of the wire into containers of mercury connected to a battery. Each time he opened or closed the circuit by raising or lowering the end of the wire from the container, the magnet emitted a sound audible from a distance of a meter. Page called it galvanic music, and suggested that it was all about the "molecular disorder" going on in the magnet. Page launched a wave of research into two aspects of this discovery: the strange property of metallic materials to change shape when magnetized, and the more obvious sound generation by electricity.
We are particularly interested in two studies. The first was conducted by Johann Philipp Reis. Reis taught mathematics and exact sciences to schoolchildren at the Garnier Institute near Frankfurt, but in his spare time he was engaged in electrical research. By that time, several electricians had already created new versions of galvanic music, but Reis was the first to master the alchemy of the two-way translation of sound into electricity and vice versa.
Reis realized that a diaphragm, resembling a human eardrum, could close and open an electrical circuit when it vibrated. The first prototype of the "telephon" ["long-speaker"] device, built in 1860, consisted of an "ear" carved from wood with a membrane made from a pig's bladder stretched over it. A platinum electrode was attached to the lower part of the membrane, which, when vibrated, opened and closed the circuit with the battery. The receiver was a coil of wire wound around a knitting needle attached to a violin. The body of the violin intensified the vibrations of the shape-changing stylus as it alternately magnetized and demagnetized.
Reis' late model phone
Reis came up with many improvements to the early prototype, and along with other experimenters, found that if you sang or hum something into it, the transmitted sound remained recognizable. The words were harder to distinguish and often became distorted and incomprehensible. Many reports of successful voice transfers used common phrases such as "good morning" and "how are you", and they could be easily guessed. The main problem remained that Reis's transmitter only opened and closed the circuit, but did not regulate the volume of the sound. As a result, only a frequency with a fixed amplitude could be transmitted, and this could not imitate all the subtleties of the human voice.
Reis believed that his work should be recognized by science, but never achieved this. His device was a popular curiosity among the scientific elite, and copies appeared in most of the centers of this elite: in Paris, London, Washington. But his scientific work was rejected by Professor Poggendorff's Annalen der Physik [Annals of Physics], one of the oldest scientific journals and the most influential journal of the time. Reis's attempts to advertise the telephone through telegraph companies also failed. He suffered from tuberculosis, and his worsening illness kept him from further serious research. As a result, in 1873, the disease took his life and ambitions. And this is not the last time this disease will hinder the development of the phone's history.
While Reis improved his phone, put the finishing touches to his fruitful study of auditory physiology: "The doctrine of auditory sensations as a physiological basis for the theory of music" [Die Lehre von den Tonempfindungen als physiologische Grundlage für die Theorie der Musik], published in 1862. Helmholtz, at that time a professor at the University of Heidelberg, was a giant of science in the XNUMXth century, working on the physiology of vision, electrodynamics, thermodynamics, etc.
Helmholtz's work refers only in passing to our history, but it is a pity to miss it. In The Teaching of Auditory Sensations, Helmholtz did for music what Newton did for light - he showed how a seemingly single sensation can be disassembled into its component parts. He proved that differences in timbres, from violin to bassoon, come only from differences in the relative strength of their overtones (tones at double, triple, etc. frequency in relation to the base note). But for our story, the most interesting thing about his work lies in the remarkable tool he developed for demonstration purposes:
Helmholtz synthesizer variant
Helmholtz ordered the first device from a workshop in Cologne. Simply put, it was a synthesizer capable of producing sounds based on the composition of simple tones. His most amazing ability was the inexplicable ability to reproduce vowel sounds that everyone is accustomed to hearing only coming from the human mouth.
The synthesizer worked from the beating of the main tuning fork, vibrating on the base note, closing and opening the circuit, immersing the platinum wire in a container with mercury. Eight magnetized tuning forks, each of which vibrated with its own overtone, rested between the ends of an electromagnet connected to the circuit. Each closing of the circuit turned on the electromagnets, and kept the tuning forks in a vibrating state. Next to each tuning fork was a cylindrical resonator capable of amplifying its buzzing to an audible level. In the normal state, the lid on the resonator was closed, and muffled the sound of the tuning fork. If you move the cover to the side, you can hear this overtone, and thus "play" the sound of a pipe, piano or vowel "o".
This device will play a small role in creating a new kind of phone.
Harmonic telegraph
One of the lures for inventors of the second half of the 1870th century was the multitelegraph. The more telegraph signals could be crammed into one wire, the more efficient the telegraph network was. By the early XNUMXs, several different methods were known to organize duplex telegraphy (sending two signals in opposite directions at the same time). Shortly thereafter, Thomas Edison improved upon them by creating a quadruplex, combining duplex and diplex (transmitting two signals at the same time in the same direction), so that the wire could be used four times more efficiently.
But was it possible to further increase the number of signals? Organize some kind of octoruplex, or even more? That sound waves could be converted to electrical current and vice versa offered an interesting possibility. What if you use tones of varying pitch to create an acoustic, harmonic, or, poetically speaking, musical telegraph? If physical vibrations of different frequencies can be converted into electrical vibrations, and then re-disassembled into their original frequencies from the other side, then it would be possible to send many signals at the same time without mutual interference. The sound itself would then be only a means to an end, an intermediate medium shaping currents so that several signals could exist in one wire. For the sake of simplicity, I will refer to this concept as the harmonic telegraph, although various variations of the terms were used at the time.
It was not one way to create multiplexed signals. In France [after whom the unit of symbol rate is named - baud / approx. transl.] by 1874, he came up with a machine with a rotating distributor that alternately collected signals from several telegraph transmitters. Now we would call it a time multiplex, not a frequency multiplex. But this approach had a drawback - it would not lead to the creation of telephony.
By then, American telegraphy was dominated by Western Union, which had formed in the 1850s in an attempt to eliminate disadvantageous competition between a few large telegraph companies—before the advent of antitrust laws, such an explanation could easily be used to justify such mergers. One of the characters in our story described it as "probably the largest corporation that ever existed." With thousands of miles of wire and spending huge sums to build and maintain networks, Western Union followed developments in multiplex telegraphy with great interest.
Another player was also waiting for breakthroughs in the telegraph business. , a Boston lawyer and businessman, was one of the main advocates for bringing the American telegraph under the control of the federal government. Hubbard believed telegrams could be as cheap as letters and was determined to undermine what he saw as the cynical and extortionate monopoly of Western Union. Hubbard's bill did not propose the complete nationalization of existing telegraph companies, as almost all European powers did, but would establish a government-sponsored telegraph service under the auspices of the Post Office. But the result would most likely be the same, and Western Union would have gone out of business. By the mid-1870s, the legislation's progress had stalled, but Hubbard was confident that control of the critical new telegraph patent would give him the edge to push his proposal through Congress.
Gardiner Green Hubbard
There are two unique factors in the US: first, the continental scale of Western Union. None of the European telegraph organizations had such extended lines, and, consequently, no reason to develop multiplex telegraphy. Second, the open question of government control over the telegraph. The last European stronghold was Britain, which nationalized the telegraph in 1870. After that, there were no places left anywhere except the United States where the tempting prospect of making a technological breakthrough and undermining the monopoly loomed. Perhaps because of this, much of the work on the harmonic telegraph was done in the USA.
There were basically three contenders for the prize. Two of them were already venerable inventors - и . The third was a professor of rhetoric and teacher for the deaf named Bell.
Gray
Elisha Gray grew up on a farm in Ohio. Like many of his contemporaries, he played with telegraphy as a teenager, but at age 12, when his father died, he began to look for an occupation that could provide him. For a time he was a blacksmith's apprentice, then a ship's carpenter, and at 22 he learned that he could get an education at Oberlin College without stopping carpentry. After five years of study, he plunged into a career as an inventor in the field of telegraphy. His first patent was a self-adjusting relay, which, by using a second electromagnet instead of an armature-returning spring, eliminated the need to adjust the relay's sensitivity based on the current in the circuit.
Elisha Grey, ca. 1878
By 1870 he was already a partner in an electrical equipment company and worked there as chief engineer. In 1872, he and a partner moved the company to Chicago and renamed it the Western Electric Manufacturing Company. Western Electric soon became Western Union's main supplier of telegraph equipment. As a result, it will leave a noticeable mark in the history of telephony.
In early 1874, Gray heard a strange sound from his bathroom. It sounded like the howl of a vibrating rheotome, only much louder. The rheotome (literally "flow breaker") was a well-known electrical device that used a metal tab to rapidly open and close a circuit. Looking into the bathroom, Gray saw his son holding an induction coil connected to a rheotom in one hand, and rubbing the zinc coating of the bath with the other hand, which buzzed with the same frequency. Gray, intrigued by the opportunity, retired from his daily job at Western Electric to return to inventing. By the summer, he had developed a full-octave musical telegraph, with which it was possible to play sounds on a diaphragm made of a metal basin by pressing the keys of the keyboard.
Transmitter
Receiver
The musical telegraph was a novelty with no apparent commercial value. But Gray realized that the ability to transmit sounds of different tonalities over a single wire gave him two possibilities. With a transmitter of a different design, capable of picking up sound from the air, it was possible to create a voice telegraph. With another receiver capable of splitting the combined signal into its components, it was possible to make a harmonic telegraph—that is, a sound-based multiplex telegraph. He decided to concentrate on the second option, since the telegraph industry had obvious demands. He was confirmed in his choice after learning about Reis's phone, which seemed to be a simple philosophical toy.
Gray made the harmonic telegraph receiver from a set of electromagnets mated to metal strips. Each bar was tuned to a specific frequency and sounded when the corresponding button on the transmitter was pressed. The transmitter worked on the same principle as the musical telegraph.
Gray improved his apparatus for the next two years and took it to the exhibition. The official title of the event was". It was the first world's fair to be held in the United States and coincided with the nation's centenary celebrations, in connection with which the so-called. Centenary Exposure. It took place in Philadelphia in the summer of 1876. There, Gray demonstrated an "octruplex" connection (that is, the transmission of eight messages at the same time) on a specially prepared telegraph line from New York. This achievement was highly praised by the judges of the exhibition, but it was soon overshadowed by an even greater miracle.
Edison
, the president of Western Union, learned of Gray's progress rather quickly, which made him very nervous. At best, with Gray's success, the situation will turn into a very expensive patent licensing. In the worst case, Gray's patent will become the basis for the creation of a rival company that will shake the dominance of Western Union.
So in July 1875, Orton pulled an ace out of his sleeve, namely Thomas Edison. Edison grew up side by side with telegraphy, spent several years as a telegraph operator, and then became an inventor. His highest triumph at the time was a quadruplex connection, funded by Western Union a year earlier. Now Orton hoped that he would improve his invention and surpass what Gray had managed to do. He provided Edison with a description of Reis' phone; Edison also studied the work of Helmholtz, recently translated into English.
Edison was at the peak of his form, and innovative ideas poured out of him like sparks from an anvil. In the following year, he showed two different approaches to the acoustic telegraph - the first was similar to Gray's telegraph, and used tuning forks or vibrating reeds to create or perceive the desired frequency. Edison failed to get such an apparatus to work at an acceptable level.
The second approach, which he called "acoustic transmitter", was completely different. Instead of using vibrating reeds to transmit different frequencies, he used them to transmit pulses at different intervals. He divided the use of wire between transmitters by time rather than by frequency. This required perfect vibration synchronization in each receiver-transmitter pair so that the signals did not overlap. By August 1876, a quadruplex worked on this principle, although the signal became useless at a distance of more than 100 miles. He also had ideas for improving Reis's phone, which he temporarily put aside.
And then Edison heard about the sensation created at the Centennial Exposition in Philadelphia by a man named Bell.
Bell
was born in Edinburgh, Scotland, and grew up in London under the strict guidance of his grandfather. Like Gray and Edison, in adolescence he developed an interest in the telegraph, but then followed in the footsteps of his father and grandfather, choosing human speech as his main passion. His grandfather, Alexander, made a name for himself on the stage, and then began to teach oratory. His father, Alexander Melville, was also a teacher, and even developed and published a phonetic system he called "visible speech." The younger Alexander (Alek, as he was called in the family), chose to teach the deaf to speak as his occupation.
By the end of the 1860s he was studying anatomy and physiology at University College London. A student, Marie Eccleston, whom he was going to marry, studied with him. But then he abandoned both learning and love. Two of his brothers died of tuberculosis, and Alec's father demanded that he and the rest of his family emigrate to the New World in order to preserve the health of his only son. Bell complied, though he was reluctant and resentful about it, and set sail in 1870.
After a small hack in Ontario, Alexander, not without his father's connections, found a job as a teacher at a school for the deaf in Boston. There, the threads of his future began to be woven.
First, he had a student, Mabel Hubbard, who lost her hearing at the age of five due to scarlet fever. Bell tutored privately even after becoming professor of vocal physiology and oratory at Boston University, and Mabel was among his first students. She was just under 16 at the time of training, ten years younger than Bella, and within a few months he fell in love with this girl. We will return to her story later.
In 1872, Bell renewed his interest in telegraphy. A few years earlier, while still in London, Bell had learned of Helmholtz's experiments. But Bell misunderstood Helmholtz's achievement, believing that he not only created, but also transmitted complex sounds using electricity. So Bell became interested in harmonic telegraphy - the sharing of a wire by several signals transmitted at several frequencies. Perhaps inspired by the news that Western Union had acquired the idea of a duplex telegraph from Joseph Stearns, his fellow Bostonian, Bell revisited his ideas and, like Edison and Gray, began to try to implement them.
Once, while visiting Mabel, he touched the second thread of his fate - standing next to the piano, he showed her family a trick that he had learned in his youth. If you sing a clear note on the piano, the corresponding string will ring and play it back to you. He told Mabel's father that a tuned telegraph signal could achieve the same effect, and explained how this could be used in multiplex telegraphy. And Bell would not have found a listener better tuned to his story: he resonated with joy and instantly understood the main idea: “there is one air for everyone, and only one wire is needed”, that is, the wave propagation of current in a wire can copy the distribution in miniature air waves generated by a complex sound. Bell's listener was Gardiner Hubbard.
Phone
And now the story is getting very confusing, so I'm afraid to test the patience of the readers. I will try to track the main trends without getting bogged down in details.
Bell, supported by Hubbard and the father of another of his students, diligently worked on the harmonic telegraph without publicizing his progress. He alternated furious work with periods of rest when his health failed him, while trying to fulfill his university duties, promote his father's "visible speech" system, and work as a tutor. He hired a new assistant , an experienced mechanic from the Boston mechanical workshop of Charles Williams - people interested in electricity gathered there. Hubbard urged Bell, and did not even hesitate to use his daughter's hand as an incentive, refusing to marry her until Bell improved his telegraph.
In the summer of 1874, while on vacation near the family home in Ontario, Bell had an epiphany. Several thoughts that existed in his subconscious merged into one - the phone. His thoughts were not least influenced - the world's first sound recording device that painted sound waves on smoked glass. This convinced Bell that sound of any complexity could be reduced to the movements of a point in space, such as the movement of current through a wire. We will not dwell on the technical details, because they are not related to actually created phones and the practicality of their application is doubtful. But they took Bell's thinking in a new direction.
Concept sketch for Bell's original "harmonics" phone (not built)
Bell put this idea aside for a while, in order, as his partners expected him to, to pursue the goal of creating a harmonic telegraph.
But the routine of fine-tuning instruments soon bored him, and his heart, tired of the many practical obstacles that stood in the way from a working prototype to a practical system, gravitated more and more towards the telephone. The human voice was his first passion. In the summer of 1875, he discovered that vibrating reeds could not only quickly close and open a circuit in the manner of a telegraph key, but also create a continuous wave-like current while moving in a magnetic field. He shared his idea for a telephone with Watson, and together they built the first model of a telephone on this principle - a diaphragm vibrating in the field of an electromagnet excited a wave-like current in the magnet circuit. This device was capable of transmitting some muffled sounds of a voice. Hubbard was unimpressed with the device and ordered Bell to return to real work.
Bell's rudimentary gallows telephone in the summer of 1875
But Bell nevertheless convinced Hubbard and the rest of the partners that the idea should be patented, since it could be used in multiplex telegraphy. And if you already apply for a patent, no one will forbid mentioning in it the possibility of using a device for voice communications. Then in January, Bell added a new wave current generation mechanism to the patent draft: a variable resistance. He wanted to connect a vibrating diaphragm that received sound with a platinum contact that rose and fell from a container of acid that contained another, fixed contact. As the moving contact sank deeper, a larger surface area contacted the acid, which reduced the resistance to current flowing between the contacts—and vice versa.
Bell's sketch of the fluid variable resistance transmitter concept
Hubbard, knowing that Gray was on Bell's heels, submitted a wave current patent application to the patent office on the morning of February 14 without waiting for final confirmation from Bell. And in the afternoon of the same day, Gray's lawyer arrived with his patent. It also contained a proposal to generate a wave current using liquid variable resistance. It also mentioned the possibility of using the invention for both the telegraph and voice transmission. But he arrived several hours late in order to interfere with Bell's patent. If the order of arrival had been different, there would have been lengthy hearings about priorities before the patent was granted. As a result, on March 7, Bell was granted patent number 174, "Improvements in Telegraphy", which laid the cornerstone for the future dominance of the Bell system.
But this dramatic story was not without irony. For on February 14, 1876, neither Bell nor Gray built a working model of the telephone. No one has even tried it, except for Bell's short attempt last July, in which there was no variable resistance. Therefore, you should not consider patents as milestones in the history of technology. This critical moment in the development of telephony as a business enterprise had little to do with the telephone as a device.
It was not until the patent was sent that Bell and Watson were able to return to the telephone, despite Hubbard's constant demands to continue work on the multiplex telegraph. Bell and Watson spent months trying to get the idea of liquid variable resistance to work, and a telephone built on this principle was used to transmit the famous phrase: "Mr. Watson, come here, I want to see you."
But the inventors constantly had problems with the reliability of these transmitters. So Bell and Watson began to work on new transmitters using the magneto principle they had experimented with in the summer of 1875, using the movement of a diaphragm in a magnetic field to directly excite a current. The advantage was simplicity and reliability. The disadvantage was that the low power of the telephone signal was the result of air vibrations created by the speaker's voice. This limited the effective working distance of the magneto transmitter. And with a device with variable resistance, the voice modulated the current created by the battery, which could be made arbitrarily strong.
The new magnetos worked much better than the last summer's, and Gardiner decided there might be something to the idea of a telephone after all. Among other pastimes, he was a member of the Massachusetts Education and Science Exhibition Committee in the forthcoming Centenary Exposition. He used his influence to give Bell a place in an exhibition and in a competition where judges judged electrical inventions.
Bell/Watson magneto transmitter. The vibrating metal diaphragm D moves in the magnetic field of the magnet H and induces a current in the circuit
Receiver
The judges arrived at Bell immediately after studying Gray's harmonic telegraph. He left them at the receiver and moved to one of the transmitters located a hundred meters further down the gallery. Bell's interlocutors were amazed to hear his singing and words coming out of a small metal box. One of the judges was Bell's countryman, a Scot (who was later given the title of Lord Kelvin). Excitedly, he ran across the hall to Bell to inform him that he had heard his words, and later declared the telephone "the most amazing thing he had seen in America." The emperor of Brazil was also present, who first pressed the box to his ear, and then jumped up from his chair shouting: “I hear, I hear!”
The buzz caused by Bell at the exhibition led Edison to pursue his previous telephone transmission ideas. He immediately pounced on the main drawback of Bell's device - a frail magneto transmitter. He knew from his experiments with the quadruplex that the resistance of the coal chips changed with pressure. After many experiments with various configurations, he developed a variable resistance transmitter operating on this principle. Instead of the pressure waves moving in the contact liquid, the voice of the speaker squeezed the coal “button”, changed its resistance, and, consequently, the current strength in the circuit. It was far more reliable and easier to implement than the liquid transmitters conceived by Bell and Gray, and was a decisive contribution to the telephone's long-term success.
Still, Bell was the first to make the telephone, despite the obvious advantages in experience and skills that his rivals had. He was the first not because he was visited by an insight that others did not reach - they also thought of the telephone, but they considered it insignificant compared to the improved telegraph. Bell was the first because he liked the human voice more than the telegraph, so much so that he resisted the wishes of his partners until he could prove the working of his phone.
And what about the harmonic telegraph, on which Gray, Edison and Bell spent so much effort and thought? So far nothing has worked. Keeping the mechanical vibrators at both ends of the wire perfectly tuned proved very difficult, and no one knew how to amplify the combined signal so that it worked over long distances. It wasn't until the middle of the XNUMXth century, after the electrical technology that began with the radio enabled fine-tuning frequencies and low-noise amplification, that the idea of superimposing multiple signals to be transmitted over a single wire became a reality.
Farewell to Bell
Despite the telephone's success at the show, Hubbard was not interested in building a telephone system. The following winter, he offered to William Orton, president of Western Union, to purchase all rights to the telephone under Bell's patent for $100. Orton refused, influenced by a combination of dislike of Hubbard and his postal telegraph schemes, self-confidence, and Edison's work on the telephone, and also the belief that the telephone, compared with the telegraph, meant very little. Other attempts to sell the telephone idea have failed, largely due to fears of the huge costs of litigating over patent rights if commercialized. Therefore, in July 000, Bell and partners founded the Bell Telephone Company to organize telephone service on their own. That same month, Bell finally married Mabel Gardiner at her family's home, becoming successful enough to win her father's blessing.
Alec with wife Mabel and two surviving children - two of his sons died in infancy (c. 1885)
The following year, Orton changed his mind about the telephone and created his own company, the American Speaking Telephone Company, hoping that the patents of Edison, Gray and others would protect the company from Bell's legal attacks. She became a deadly threat to Bell's interests. Western Union had two main advantages. First, large financial resources. Bell's company was in need of money because it leased equipment to its customers, which required many months for it to pay off. Secondly, access to an improved Edison transmitter. Anyone who compared his transmitter to Bell's device could not fail to note the better clarity and volume of the former's voice. Bell's company had no choice but to sue a competitor for patent infringement.
If Western Union had unequivocal rights to the only high quality transmitter available, it would have powerful leverage to reach an agreement. But Bell's team unearthed a previous patent for a similar device from a German immigrant. and bought it out. It wasn't until many years of legal battles that Edison's patent was given priority. Seeing that the proceedings were not successful, in November 1879, Western Union agreed to transfer all patent rights to the telephone, equipment, and existing subscriber base (55 people) to Bell's company. In exchange, they asked for only 000% of the telephone lease for the next 20 years, and also that Bell should not get into the telegraph business.
The Bell company quickly replaced Bell's devices with improved models based first on the Berliner patent and then on patents obtained from Western Union. By the time the litigation was over, Bell's main occupation was testifying in patent litigations, of which there were plenty. By 1881 he had completely retired. Like Morse, and unlike Edison, he was not a systems builder. Theodore Vail, an energetic manager poached from the postal service by Gardiner, took over the company and led it to national dominance.
Initially, the telephone network did not grow in the same way as the telegraph network. The latter evolved by hopping from one commercial center to another, covering 150 km at a time, looking for the highest concentration of high-value customers, and only then supplementing the network with links to smaller local markets. Telephone networks grew like crystals from small points of growth, from several customers located in independent clusters in each city and neighborhood, and slowly, over decades, merged into regional and national structures.
There were two obstacles to large-scale telephony. First, there was the problem of distance. Even with amplified transmitters of variable resistance, created on the basis of Edison's idea, the range of the telegraph and telephone was incomparable. The more complex telephone signal was more prone to noise, and the electrical properties of fluctuating currents were less known than those of the direct current used in the telegraph.
Secondly, there was a communication problem. Bell's phone was a one-on-one communication device, it could connect two points with a single wire. For the telegraph, this was not a problem. One office could serve many clients, and messages could easily be routed from the central office to another line. But there was no easy way to transfer a telephone conversation. In the first embodiment of the phone, the third and subsequent people could only connect to the two people who were talking through what would later be called a "paired phone". That is, if all subscribers' devices were connected to one line, then each of them could talk (or eavesdrop) with the others.
We will return to the problem of distance in due time. IN we will delve into the problem of connections and its consequences, which had an impact on the development of the relay.
What to read
- Robert V. Bruce, Bell: Alexander Graham Bell and the Conquest of Solitude (1973)
- David A. Hounshell, “Elisha Gray and the Telephone: On the Disadvantages of Being an Expert,” Technology and Culture (1975).
- Paul Israel, Edison: A Life of Invention (1998)
- George B. Prescott, The Speaking Telephone, Talking Phonograph, and Other Novelties (1878)
Source: habr.com