Invention of the telephone

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The history of the invention of the telephone is a confusing morass of claims and counterclaims, further worsened by the huge mass of lawsuits which hoped to resolve the patent claims of individuals. It is important to note that there is no one "inventor of the telephone", though Alexander Graham Bell is often credited as such, and the Italian Antonio Meucci was recognized as the true inventor by US Congress on 11th June 2002. The modern telephone is the result of work done by many people, all worthy of recognition of their contributions to the field. Bell was merely the first to patent the telephone, an "apparatus for transmitting vocal or other sounds telegraphically", 16 years after Antonio Meucci, who did not have sufficient funds to file a patent, demonstrated his "teletrofono" in New York in 1860.

Contents 1 Non-electric 'telephones' 2 Electro-magnetic transmitters (telephone) 2.1 Antonio Meucci 2.1.1 Chronology of Meucci's invention 2.2 Charles Bourseul 2.3 Johann Philipp Reis 2.4 Innocenzo Manzetti 2.5 Cromwell Varley 2.6 Poul la Cour 2.7 Elisha Gray 2.8 Thomas Edison 2.9 Bell's invention and claims 2.9.1 Bell's background 2.9.2 Bell's success 2.9.3 Public demonstrations 2.9.3.1 Earliest public demonstration of Bell's telephone 2.9.3.2 Later public demonstrations 2.9.4 Summary of Bell's achievements 2.10 Later developments 3 Controversy 4 Patents 5 See also 6 References

[edit] Non-electric 'telephones'

There is a sense in which a telephone is any mechanism capable of conducting sound for a great distance. The very earliest telephones were mechanical devices based on sound transportation through air or other physical media rather than electrical devices depending on electro-magnetic signals.

According to a letter in the Peking Gazette, in 968, the Chinese inventor Kung-Foo-Whing invented the thumtsein, which probably transported the speech through pipes. Speaking tubes remained common and can still be found today.

The lover's telephone (or string telephone) has also been known for centuries, connecting two diaphragms with string or wire which transmits the sound from one to the other by vibrations along the string and not through electric current. The classic example is the children's toy made by connecting the bottoms of two paper cups (or metal cans) with string.

[edit] Electro-magnetic transmitters (telephone)

[edit] Antonio Meucci

The telephone was invented around 1860 by Antonio Meucci who called it teletrofono (telectrophone).

From ^[1] Despite a public statement by the then Secretary of State that "there exists sufficient proof to give priority to Meucci in the invention of the telephone," and despite the fact that the United States initiated prosecution for fraud against Bell's patent, the trial was postponed from year to year until, at the death of Meucci in 1896, the case was dropped.

The first American demonstration of Meucci's invention took place in NYC, USA in 1854. In 1860, a description of it was published in New York's Italian language newspaper. Meucci invented a paired electro-magnetic transmitter and receiver, where the motion of a diaphragm modulated a signal in a coil by moving an electromagnet. This resulted in a good fidelity, but a very weak signal. Meucci is also credited with the early invention of inductive loading of telephone wires to increase long-distance signals. Unfortunately, serious burns, lack of English and poor business abilities resulted in Meucci failing to develop his inventions commercially in America. Meucci demonstrated some sort of instrument in 1849 in Havana, Cuba, but the evidence is unclear if this was an electric telephone or a variant on the string telephone using wires.

(Meucci has been further credited with invention of an anti-sidetone circuit. However, examination shows that his solution to sidetone was to maintain two separate telephone circuits, and thus twice as many transmission wires. The anti-sidetone circuit later introduced by Bell Telephone instead cancelled sidetone with a feedback process.)

Meucci was recognised as the first inventor of the telephone by the United States Congress, in its resolution 269 dated 11 June 2002 ("if Meucci had been able to pay the $10 fee to maintain the caveat after 1874, no patent could have been issued to Bell").

[edit] Chronology of Meucci's invention

An Italian researcher in telecommunications Basilio Catania and the Italian Society of Electrotechnics "Federazione Italiana di Elettrotecnica" have devoted a Museum to Antonio Meucci making a chronology of his inventing the telephone and tracing the history of the two trials opposing Antonio Meucci and Alexander Graham Bell [1] [2]. They both support the claim that Antonio Meucci was the real inventor of the telephone. What follows, if not otherwise stated, is a resumé of their historic reconstruction.^[2]

• In 1834 Meucci constructed a kind of acoustic telephone as a way to communicate between the stage and control room at the theatre "Teatro della Pergola" in Florence. This telephone is constructed on the model of pipe-telephones on ships and is still working.^[3]
  
• In 1848 Meucci developed a popular method of using electric shocks to treat rheumatism. He used to give his patients two conductors linked to 60 Bunsen batteries and ending with a cork. He also kept two conductors linked to the same Bunsen batteries. He used to sit in his laboratory, while the Bunsen batteries were placed in a second room and his patients in a third room. In 1849 while providing a treatment to a patient with a 114V electrical discharge, in his laboratory Meucci heard his patient's scream through the piece of copper wire that was between them, from the conductors he was keeping near his ear. His intuition was that the "tongue" of copper wire was vibrating just like a leave of an electroscope; which means that there was an electrostatic effect. In order to continue the experiment without hurting his patient, Meucci covered the copper wire with a piece of paper. Through this device he heard inarticulated human voice. He called this device "telegrafo parlante" (litt. "talking telegraph").^[4]
  

On the basis of this prototype, Meucci worked on more than 30 kinds of telephone. At the beginning he got inspiration from the telegraph model. Differently from other pioneers of the telephone, such as Charles Bourseul, Philipp Reis, Innocenzo Manzetti and others, he did not think about transmitting voice by using the principle of the telegraph key (in scientific jargon, the "make-and-break" method), but he looked for a "continuous" solution, which means without interrupting the electric flux.

• In 1856 Meucci constructed the first electromagnetic telephone, made of an electromagnet with a nucleus in the shape of a horseshoe bat, a diaphragm of animal skin, stiffened with potassium dichromate and keeping a metal disk stickened in the middle. The instrument was hosted in a cylindrical carton box.^[5] He constructed this as a way to connect his second-floor bedroom to his basement laboratory, and thus communicate with his wife who was an invalid.
  

Meucci separated the two directions of transmission in order to eliminate the so-called "local effect", adopting what we would call today a 4-wire-circuit. He constructed a simple calling system with a telegraphic manipulator which short-circuited the instrument of the calling person, producing in the instrument of the called person a succession of impulses (clicks), much more intense than those of normal conversation. As he was aware that his device required a bigger band than a telegraph, he found some means to avoid the so-called "skin effect" through superficial treatment of the conductor or by acting on the material (copper instead of iron). He successfully used an insulated copper plait, thus anticipating the litz wire used by Nikola Tesla in RF coils.

• In 1864 Meucci's realized his "best device", using an iron diaphragm with optimized thickness and tightly clamped along its rim. The instrument was housed in a shaving-soap box, whose cover clamped the diaphragm.
  
• In August 1870, Meucci obtained transmission of articulate human voice at a mile distance by using as a conductor a copper plait insulated by cotton. He called his device "telettrofono". According to an Affidavit of lawyer Michael Lemmi drawings and notes by Antonio Meucci dated September 27, 1870 show that Meucci understood inductive loading on long distance telephone lines 30 years before any other scientists. The painting made by Nestore Corradi in 1858 mentions the sentence "Electric current from the inductor pipe"
  
• About 1873 a certain Bill Carroll from Boston, who had news about Meucci's invention, asked him to construct a "telephone for scuba divers". This device should allow divers to communicate with people on surface. In Meucci's drawing, this device results to be an electromagnetic telephone, capsuled for it to be waterproof.
  

All these informations have been published on the Scientific American Supplement No. 520, December 19, 1885 .

[edit] Charles Bourseul

In 1854 in the magazine L'Illustration de Paris Charles Bourseul, a French telegraphist, published a plan for conveying sounds and even speech by electricity. “Suppose”, he explained, “that a man speaks near a movable disc sufficiently flexible to lose none of the vibrations of the voice; that this disc alternately makes and breaks the currents from a battery: you may have at a distance another disc which will simultaneously execute the same vibrations.... It is certain that, in a more or less distant future, speech will be transmitted by electricity. I have made experiments in this direction; they are delicate and demand time and patience, but the approximations obtained promise a favourable result.”

[edit] Johann Philipp Reis

In 1860 Johann Philipp Reis produced a device which could transmit musical notes, and even a lisping sentence or two. The first sentence spoken on it was "Das Pferd frisst keinen Gurkensalat" (the horse eats no cucumber salad). The motives for stating such a sentence is currently in dispute. See Reis' telephone for a detailed description. The Reis transmitter was a make-break transmitter. That is, a needle attached to a diaphragm was alternately pressed against, and released from a contact as the sound moved the diaphragm. This make-or-break signaling was able to transmit tones, and some vowels, but since it did not follow the analog shape of the sound wave (the contact was pure digital, on or off) it could not transmit consonants, or complex sounds. The Reis transmitter was very difficult to operate, since the relative position of the needle and the contact were critical to the device's operation at all. This can be called a "telephone", since it did transmit sounds over distance, but is hardly a telephone in the modern sense, as it failed to transmit a good copy of any supplied sound. Reis' invention is best known then as the "musical telephone".

[edit] Innocenzo Manzetti

Innocenzo Manzetti mooted the idea of a telephone as early as 1844, and may have made one in 1864, as an enhancement to an automaton built by him in 1849.

[edit] Cromwell Varley

Around 1870 Mr. Cromwell Fleetwood Varley, F.R.S., a well-known English electrician, patented a number of variations on the audio telegraph based on Reis' work. He never claimed or produced a device capable of transmitting speech, only pure tones.

[edit] Poul la Cour

Around 1874 Poul la Cour, a Danish inventor, experimented with audio telegraphs on a line of telegraph between Copenhagen and Fredericia in Jutland. In this a vibrating tuning-fork interrupted the current, which, after traversing the line, passed through an electromagnet, and attracted the limbs of another fork, making it strike a note like the transmitting fork. Moreover, the hums were made to record themselves on paper by turning the electromagnetic receiver into a relay, which actuated a Morse code printer by means of a local battery. Again, la Cour made no claims of transmitting voice, only pure tones.

[edit] Elisha Gray

Mr. Elisha Gray, of Chicago also devised a tone telegraph of this kind about the same time as Herr La Cour. In this apparatus a vibrating steel reed interrupted the current, which at the other end of the line passed through an electromagnet and vibrated a matching steel reed near its poles. Gray's 'harmonic telegraph,' with the vibrating reeds, was used by the Western Union Telegraph Company. Since more than one set of vibrations — that is to say, more than one note — can be sent over the same wire simultaneously, the harmonic telegraph can be utilised as a 'multiplex' or many-ply telegraph, conveying several messages through the same wire at once; and these can either be read by the operator by the sound, or a permanent record can be made by the marks drawn on a ribbon of travelling paper by a Morse recorder.

Gray's harmonic telegraph apparatus follows in the track of Reis and Bourseul — that is to say, the interruption of the current by a vibrating contact. Gray recognized the lack of fidelity of the make-break transmitter, and reasoned by analogy with the lovers telegraph that if the current could be made to model more closely the movements of the diaphragm rather than simply turning the circuit on and off, a greater fidelity might be achieved. Gray filed a "caveat" with the US patent office on February 14, 1876 for a liquid microphone, where a needle was placed just barely in contact with a liquid conductor such as a water/acid mixture, and as the diaphragm vibrated, the needle dipped more-or-less into the liquid, resulting in more-or-less current passing to the receiver. Gray did not convert his caveat into a patent until after the caveat had expired and hence left the field open to Bell. Bell used a Gray liquid transmitter in his famous 10 March 1876 experiment "Mr. Watson, come here, I want to see you", but avoided the liquid transmitter for his public demonstrations. The liquid transmitter had the problem that waves formed on the surface of the liquid, resulting in interference.

[edit] Thomas Edison

Thomas Alva Edison took the next step in developing telephonic fidelity with his invention of the carbon grain transmitter. Edison discovered that carbon grains, squeezed between two metal plates, had a resistance that was related to the pressure. Thus, the grains could vary their resistance as the plates moved in response to sound waves, and reproduce sound with good fidelity, without the problems associated with a liquid contact. This transmitter produced a strong signal that could be used for long-distances and the carbon microphone remained standard in telephony until the 1980s, and is still produced.

[edit] Bell's invention and claims

Alexander Graham Bell is commonly credited as the first inventor of the telephone. The classic story of his crying out "Watson, come here! I want to see you!" is a well known part of American history.^[6]. But Graham Bell was more an acute business man with far reaching friends rather than an inventor.

[edit] Bell's background

As Professor of Vocal Physiology at Boston University, Bell was engaged in training teachers in the art of instructing deaf mutes how to speak, and experimented with the Leon Scott phonautograph in recording the vibrations of speech. This apparatus consists essentially of a thin membrane vibrated by the voice and carrying a light stylus, which traces an undulatory line on a plate of smoked glass. The line is a graphic representation of the vibrations of the membrane and the waves of sound in the air.

This background prepared him for work with sound and electricity. He claimed to have began his researches in 1874 with a musical telegraph, in which he employed an on-off-on-off make-break circuit driven by a vibrating iron reed which created interrupted current to vibrate the receiver, which consisted of an electro-magnet causing an iron reed or tongue to vibrate, exactly the same as Bourseul, Reis and Gray. However Antonio Meucci's telettrofono was demonstrated publicly in New York earlier in 1860 and published on a New York's newspaper published in Italian language. During a 2 June 1875 experiment by Bell and his assistant Watson, a reed failed to respond to the intermittent current supplied by an electric battery. Bell told Watson, who was at the other end of the line, to pluck the reed, thinking it had stuck to the pole of the magnet. Mr. Watson complied, and to his astonishment Bell heard a reed at his end of the line vibrate and emit the same overtones of a plucked reed, although there was no interrupted on-off-on-off current to make it vibrate. A few experiments soon showed that his reed had been set in vibration by the magneto-electric currents induced in the line by the mere motion of the distant reed in the neighbourhood of its magnet. The battery current was not causing the vibration but was needed only to supply the magnetic field in which the reeds vibrated. Moreover, when Bell heard the rich overtones of the plucked reed, it occurred to him that since the circuit was never broken, all the complex vibrations of speech might be converted into undulating (alternating) currents, which in turn would reproduce the complex frequencies of speech at a distance.

After Bell and Watson discovered on June 2, 1875 that movements of the reed alone in a magnetic field could reproduce the frequencies of spoken sound waves, Bell reasoned by analogy with the mechanical phonautograph that a skin diaphragm would reproduce sounds like the human ear when connected to a steel or iron reed or hinged armature. On 1 July 1875, he instructed Watson to built a receiver consisting of a stretched diaphragm or drum of goldbeater's skin with an armature of magnetised iron attached to its middle, and free to vibrate in front of the pole of an electromagnet in circuit with the line. A second membrane-device was built for use as a transmitter. This was the "gallows" phone. A few days later they were tried together, one at each end of the line, which ran from a room in the inventor's house in Boston to the cellar underneath. Bell, in the work room, held one instrument in his hands, while Watson in the cellar listened at the other. Bell spoke into his instrument, “Do you understand what I say?” and Mr. Watson answered “Yes”. However, the voice sounds were not distinct and the armature tended to stick to the electromagnet pole and tear the membrane.

[edit] Bell's success

The first successful bi-directional transmission of clear speech by Bell and Watson was made on 10 March 1876 when Bell spoke into his device, “Mr. Watson, come here, I want to see you.” and Watson answered. The first long distance telephone call was made on 10 August 1876 by Bell from the family homestead in Brantford, Ontario, to his assistant located in Paris, Ontario, some 10 mi (16 km) distant.

A finished instrument was then made, having a transmitter formed of a double electromagnet, in front of which a membrane, stretched on a ring, carried an oblong piece of soft iron cemented to its middle. A mouthpiece before the diaphragm directed the sounds upon it, and as it vibrated with them, the soft iron “armature” induced corresponding currents in the coils of the electromagnet. These currents after traversing the line were passed through the receiver, which consisted of a tubular electromagnet, having one end partially closed by a thin circular disc of soft iron fixed at one point to the end of the tube. This receiver bore a resemblance to a cylindrical metal box with thick sides, having a thin iron lid fastened to its mouth by a single screw. When the undulatory current passed through the coil of this magnet, the disc, or armature-lid, was put into vibration and the sounds evolved from it.

The primitive telephone was rapidly improved, the double electromagnet being replaced by a single bar magnet having a small coil or bobbin of fire wire surrounding one pole, in front of which a thin disc of ferrotype is fixed in a circular mouthpiece, and serves as a combined membrane and armature. On speaking into the mouthpiece, the iron diaphragm vibrates with the voice in the magnetic field of the pole, and thereby excites the undulatory currents in the coil, which, after traveling through the wire to the distant place, are received in an identical apparatus. [This form was patented 30 January 1877.] In traversing the coil of the latter they reinforce or weaken the magnetism of the pole, and thus make the disc armature vibrate so as to give out a mimesis of the original voice. The sounds are small and elfin, a minim of speech, and only to be heard when the ear is close to the mouthpiece, but they are remarkably distinct, and, in spite of a disguising twang, due to the fundamental note of the disc itself, it is easy to recognize the speaker.

[edit] Public demonstrations

[edit] Earliest public demonstration of Bell's telephone

The apparatus was exhibited at the Centennial Exhibition, Philadelphia, in 1876, where it attracted the attention of Brazilian emperor Pedro II, and at the meeting of the British Association in Glasgow, during the autumn of that year, Sir William Thomson revealed its existence to the European public. In describing his visit to the Exhibition, he went on to say: 'In the Canadian department I heard, "To be or not to be . . . there's the rub," through an electric wire; but, scorning monosyllables, the electric articulation rose to higher flights, and gave me passages taken at random from the New York newspapers: "s.s. Cox has arrived" (I failed to make out the s.s. Cox); "The City of New York", "Senator Morton", "The Senate has resolved to print a thousand extra copies", "The Americans in London have resolved to celebrate the coming Fourth of July!" All this my own ears heard spoken to me with unmistakable distinctness by the then circular disc armature of just such another little electro-magnet as this I hold in my hand.'

To hear the immortal words of Shakespeare uttered by the small inanimate voice which had been given to the world must indeed have been a rare delight to the ardent soul of the great electrician.

The surprise created among the public at large by this unexpected communication will be readily remembered. Except one or two inventors, nobody had ever dreamed of a telegraph that could actually speak, any more than they had ever fancied one that could see or feel; and imagination grew busy in picturing the outcome of it. Since it was practically equivalent to a limitless extension of the vocal powers, the ingenious journalist soon conjured up an infinity of uses for the telephone, and hailed the approaching time when ocean-parted friends would be able to whisper to one another under the roaring billows of the Atlantic. Curiosity, however, was not fully satisfied until Professor Bell, the inventor of the instrument, himself showed it to British audiences, and received the enthusiastic applause of his admiring countrymen.

[edit] Later public demonstrations

The later form based on Gray's liquid transmitter was publicly exhibited on 4 May 1877 at a lecture given by Professor Bell in the Boston Music Hall. According to a report: [3] Going to the small telephone box with its slender wire attachments, Mr. Bell coolly asked, as though addressing some one in an adjoining room, “Mr. Watson, are you ready!” Mr. Watson, five miles away in Somerville, promptly answered in the affirmative, and soon was heard a voice singing “America”. [...] Going to another instrument, connected by wire with Providence, forty-three miles distant, Mr. Bell listened a moment, and said, “Signor Brignolli, who is assisting at a concert in Providence Music Hall, will now sing for us.” In a moment the cadence of the tenor's voice rose and fell, the sound being faint, sometimes lost, and then again audible. Later, a cornet solo played in Somerville was very distinctly heard. Still later, a three-part song floated over the wire from the Somerville terminus, and Mr. Bell amused his audience exceedingly by exclaiming, “I will switch off the song from one part of the room to another, so that all can hear.” At a subsequent lecture in Salem, Massachusetts, communication was established with Boston, eighteen miles distant, and Mr. Watson at the latter place sang “Auld Lang Syne”, “The Star-Spangled Banner”, and “Hail Columbia”, while the audience at Salem joined in the chorus.

[edit] Summary of Bell's achievements

Bell adopted Gray's, and later Edison's resistive transmitters and adapted switching plug boards developed for telegraphy by Western Union. It would be inappropriate to minimize Bell's contribution to the development of telephony. Additionally, Bell succeeded where others failed to assemble a commercially viable telephone system. It can be argued that Bell invented the telephone company.

[edit] Later developments

Bell had overcome the difficulty which baffled Reis, and succeeded in making the undulations of the current fit the vibrations of the voice as a glove will fit the hand. But the articulation, though distinct, was feeble, and it remained for Edison (by inventing a transmitter that provided for independent power on the transmitting circuit) and David E. Hughes (by inventing the carbon microphone in 1878) to render the telephone the useful and widespread apparatus which we see it now.

[edit] Controversy

Until recently, Bell was widely recognized as the "inventor" of the telephone, outside of Italy, where Meucci was championed as its inventor. In the United States, there are numerous reflections of him as a North American icon for inventing the device, and the matter was for a long time fairly uncontroversial. In 2002, however, the United States House of Representatives passed a symbolic bill conferring official recognition for the invention of the telephone to Meucci, throwing the matter into heated controversy. Later that year, the Parliament of Canada countered with a symbolic bill conferring official recognition for the invention of the telephone to Bell.

Champions of Meucci, of Manzetti, and of Gray have each offered fairly precise tales of a contrivance whereby Bell actively stole the invention of the telephone from their specific inventor. It is noted that Bell worked in a laboratory in which Meucci's materials had earlier been stored, and claimed that Bell must thus have had access to those materials. Manzetti claimed that Bell visited him and examined his device in 1865. And it is alleged that Bell bribed a patent examiner, Zenas Wilber, not only into processing his application before Gray's, but allowing a look at his rival's designs before final submission. Each such claim of theft, however, remains unproven, and if Bell had stolen from any one of these men then he would have had little cause to steal the very same idea from the other two.

One of the valuable claims in Bell's 1876 patent US 174,465 was claim 4, a method of producing variable electrical current in a circuit by varying the resistance in the circuit. That feature was not shown in any of Bell's patent drawings, but was shown in Elisha Gray's drawings in his caveat filed the same day 14 February 1876. A description of the variable resistance feature, consisting of 7 sentences, was inserted into Bell's application. That it was inserted is not disputed. But when it was inserted is a controversial issue. Bell testified that he wrote the sentences containing the variable resistance feature before January 18, 1876 "almost at the last moment" before sending his draft application to his lawyers. A book by Evenson^[7] argues that the 7 sentences and claim 4 were inserted, without Bell's knowledge, just before Bell's application was hand carried to the Patent Office by one of Bell's lawyers on 14 February 1876.

Contrary to the popular story, Gray's caveat was taken to the US Patent Office a few hours before Bell's application. Gray's caveat was taken to the Patent Office in the morning of 14 February shortly after the Patent Office opened and remained near the bottom of the in-basket until that afternoon. Bell's application was filed shortly before noon on 14 February 1876 by Bell's lawyer who requested that the filing fee be entered immediately onto the cash receipts blotter and Bell's application was taken to the Examiner immediately. Late in the afternoon, Gray's caveat was entered on the cash blotter and was not taken to the Examiner until the following day. The fact that Bell's filing fee was recorded earlier than Gray's led to the myth that Bell had had arrived at the Patent Office earlier.^[8] Bell was in Boston on February 14 and did not know this was happening until later. Whether Gray filed before or after Bell no longer mattered after Gray abandoned his caveat and that opened the door to Bell being granted US patent 174,465 for the telephone on 7 March 1876.

Further information: Elisha Gray and Alexander Bell Controversy

[edit] Patents

• U.S. Patent 0,161,739  -- Transmitter and Receiver for Electric Telegraphs (tuned steel reeds) -- Alexander Graham Bell (April 6, 1875)
• U.S. Patent 0,174,465  -- Telegraphy (Bell's first telephone patent) -- Alexander Graham Bell (March 7, 1876)
• U.S. Patent 0,178,399  -- Telephonic Telegraphic Receiver (vibrating reed) -- Alexander Graham Bell (June 6, 1876)
• U.S. Patent 0,181,553  -- Generating Electric Currents (magneto) -- Alexander Graham Bell (August 29, 1876)
• U.S. Patent 0,186,787  -- Electric Telegraphy (permanent magnet receiver) -- Alexander Graham Bell
• U.S. Patent 0,201,488  -- Speaking Telephone (receiver designs) -- Alexander Graham Bell (March 19, 1878)
• U.S. Patent 0,213,090  -- Electric Speaking Telephone (frictional transmitter) -- Alexander Graham Bell (March 11, 1879)
• U.S. Patent 0,220,791  -- Telephone Circuit (twisted pairs of wire) -- Alexander Graham Bell (October 21, 1879)
• U.S. Patent 0,228,507  -- Electric Telephone Transmitter (hollow ball transmitter) -- Alexander Graham Bell (June 8, 1880)
• U.S. Patent 0,230,168  -- Circuit for Telephone -- Alexander Graham Bell (July 20, 1880)
• U.S. Patent 0,238,833  -- Electric Call-Bell -- Alexander Graham Bell (March 15, 1881)
• U.S. Patent 0,241,184  -- Telephonic Receiver (local battery circuit with coil) -- Alexander Graham Bell (May 10, 1881)
• U.S. Patent 0,244,426  -- Telephone Circuit (cable of twisted pairs) -- Alexander Graham Bell (July 19, 1881)
• U.S. Patent 0,474,230  -- Speaking Telegraph (graphite transmitter) -- Thomas Edison
• U.S. Patent 0,203,016  -- Speaking Telephone (carbon button transmitter) -- Thomas Edison
• U.S. Patent 0,222,390  -- Carbon Telephone (carbon granules transmitter) -- Thomas Edison
• U.S. Patent 0,485,311  -- Telephone (solid back carbon transmitter) -- Anthony C. White (Bell engineer)
• U.S. Patent 0,597,062  -- Calling Device for Telephone Exchange (dial) -- A. E. Keith (Jan 11, 1898)
• U.S. Patent 3,449,750  -- Duplex Radio Communication and Signalling Appartus -- G. H. Sweigert
• U.S. Patent 3,663,762  -- Cellular Mobile Communication System -- Amos Edward Joel (Bell Labs)
• U.S. Patent 3,906,166  -- Radio Telephone System (DynaTAC cell phone) -- Martin Cooper et al. (Motorola)

[edit] See also

• Telephone
• Timeline of the telephone
• Antonio Meucci
• Johann Philipp Reis
• Alexander Graham Bell
• Elisha Gray

[edit] References