The string or "lover's" telephone has also been known for centuries. Comprising two diaphragms connected by a taut string or wire, sound waves are carried as vibrations along the string or wire from one diaphragm to the other. The classic example is the tin can telephone, a children's toy made by connecting the two ends of a string to the bottoms of two metal cans, paper cups or similar items.
The first American demonstration of Meucci's invention took place in Staten Island, New York 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.)
Western Union laboratory reportedly lost Meucci's working models, and Meucci, who at this point was living on public assistance, was unable to renew the patent after 1874;
In March 1876 Alexander Graham Bell, who conducted experiments in the same laboratory where Meucci's materials had been stored, was granted a patent and was thereafter credited with inventing the telephone.
Meucci was recognized as the first inventor of the telephone by the United States House of Representatives in House Resolution 269 dated 11 June 2002. The resolution states that "if Meucci had been able to pay the $10 fee to maintain the caveat after 1874, no patent could have been issued to Bell." However, this declaration is non-binding and has no legal effect.
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.
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.
All this information has been published on the Scientific American Supplement No. 520, [[December 19], 1885] .
In 1854 in the magazine L'Illustration (Paris) Charles Bourseul, a French telegraphist, published a plan for conveying sounds and even speech by electricity. Bourseul's ideas were also published in Didaskalia (Frankfurt am Main) on September 28 1854. "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.”
Interestingly, Gray filed his preliminary patent petition (caveat) for a telephone on the very same day in 1876 as did Bell, and the devices described were strikingly similar, a fact which has been said to imply that Bell (who knew Gray) was inspired by Gray's design or vice versa.
Alexander Graham Bell of Scotland 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. But Alexander Graham Bell was also an astute and articulate business man with influential and wealthy friends.
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, Gray, and Antonio Meucci. 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 build a receiver consisting of a stretched diaphragm or drum of goldbeater's skin with an armature of magnetized 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.
Gray's harmonic telegraph apparatus followed in the track of Reis and Bourseul — that is to say, the interruption of the current by a vibrating contact. But 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 more closely model the movements of the diaphragm, rather than simply opening and closing the circuit, greater fidelity might be achieved. Gray filed a patent caveat with the US patent office on February 14 1876 for a liquid microphone. The device used a metal needle or rod that was placed — just barely — in a liquid conductor, such as a water/acid mixture. In response to the diaphragm's vibrations, the needle dipped more or less into the liquid, varying the electrical resistance and thus the current passing through the device and on 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.
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. Bell used Gray's liquid transmitter design in his famous 10 March 1876 experiment, but avoided describing the liquid transmitter in his public demonstrations. The liquid transmitter had the problem that waves formed on the surface of the liquid, resulting in interference.
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 fine 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.
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: 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.
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.
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 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 arrived at the Patent Office earlier. 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.