Intellectual Property Law for Engineers, Scientists, and Entrepreneurs. Howard B. Rockman
His students included George Sanders, the son of a successful leather merchant, and Mabel Hubbard, the daughter of a successful lawyer. Later in life, Mr. Hubbard and Mr. Sanders were to become Bell’s chief financial backers, and Mabel Hubbard became his wife.
The early experiments of Bell that eventually led to the invention of the telephone did not even involve thinking about a telephone. Bell was trying to develop a multiple telegraph, one that could be used to convey several messages simultaneously, each at a different pitch. Telegraphy at that time involved transmission of an electrical current that was interrupted in a pattern known as the Morse Code. In the 1870s, Bell, Edison, and Elishia Gray were all seeking a telegraph device that could send upward of four messages simultaneously. Bell’s work on his multiple telegraph stemmed from Helmholtz’s device, which used a single tuning fork that continually interrupted the circuit and a resonator that kept the other tuning forks in the system in constant vibration. The Helmholtz device was used to produce vowel sounds using electromechanical means, and Bell assumed that if the vowels could be transmitted over wires, so could other sounds, including the consonants and musical tones.
Bell found it difficult to determine how to make and break the current at the precise pitch required as the pitch was conveyed along a telegraph wire. While on vacation in 1874, he constructed an “ear phonoautograph” using a hay reed and the ear bones from a dead man mounted on a wooden frame. Sounds delivered to the ear bones caused the hay reed to trace the shape of the sound waves on a smoked glass. Using his previous knowledge of electricity, speaking machines, and pitch, Bell was inspired to conclude that the smoked glass could be rolled back and forth beneath the hay reed. This also led Bell to conclude that sound could be translated into visible waves, from which he theorized that vibrations of a reed could be transformed into an undulating electrical current and reproduced as sound. The undulating current concept was crucial to his later development of the telephone.
Bell initially conceived of a device made of a plurality of reeds extending over a magnet. As the reeds responded to one’s voice, they would ultimately vibrate in the direction of and then away from the magnet, creating the undulating current. This “harp apparatus,” as Bell himself called it, did not resemble the telephone that he ultimately developed.
In 1874, Bell sketched, but never built, his “harp apparatus,” showing how undulating sound waves could be translated into electric currents of the same form. This sketched apparatus included two permanent horseshoe magnets with two steel reeds on each. Bell conceived that this would serve as a transceiver for two separate signals, the signals corresponding to each of the reeds. Bell used permanent magnets in his harp apparatus rather than the electromagnets he had previously used in his multiple telegraph experiments. He reasoned that if a magnet is moving away from a coil half of the time and moving toward the coil the other half of the time, the induced current should imitate the vibrating magnet, since the flux would be increasing half of the time when the magnet moves toward the coil, and decreasing the remaining half of the time when the magnet moves away from the coil. This periodic increasing and decreasing of the flux at discrete intervals would produce the same periodic induced current in the coil.
Bell postulated a device with a first steel reed having a specific harmonic mounted on a horseshoe‐shaped permanent magnet, and a second reed having a different harmonic on the same magnet (a transceiver). He then thought of placing a third reed having the same harmonic as the first reed, and a fourth reed having the same harmonic as the second reed on a duplicate transceiver. When the first reed was vibrated, the third reed on the transceiver would also vibrate. Likewise, when the second reed was vibrated, the fourth reed on the transceiver also vibrated.
When the first reed vibrated toward the coil, the current became more positive or negative, depending upon which pole of the magnet the first reed was on and the winding pattern of the underlying coil. When the first reed vibrated away from the coil, an opposite current was induced. The signal was sent across as a sinusoidal wave, which was precisely the same waveform produced by the phonautograph on smoked glass.
This is what Bell referred to as his “undulating current,” which became the primary feature of his first telephone patent, issued in 1876. This wave expressed in a graphical manner the vibratory movement of the air while the reeds were producing their musical tones, and the vibrations of the individual reeds attached to the permanent magnet resulted in a single undulating current waveform. Bell determined that if the waves from the two reeds could be combined to produce a more intricate wave, the proper combination of waves could be used to produce all sounds.
Bell used this mental model to develop the postulate that undulating waves traced into the smoked glass in his phonautograph could be transformed into undulating electric current, and then be reproduced as sound. This use of undulating current was different from the intermittent current used in telegraphy to produce dots and dashes. Bell also discovered that by combining undulating currents, the result would be a different sine curve produced for every combination of sounds, allowing discrimination among different messages. His future father‐in‐law, Gardiner Hubbard, who was his primary backer, urged Bell to direct his efforts toward the multiple telegraph, and forget trying to produce a “speaking” telegraph.
Bell’s initial multiple transmitter and receiver (transceiver) made and broke contact with a dish of mercury that ultimately completed an interrupted circuit. At the receiving end, electromagnets attracted the tuning fork each time the circuit was completed, thus causing the fork to vibrate. Bell had thought through a complete system for his multiple telegraphy device, and had succeeded in patenting different parts of it by the spring of 1875. A key part of his thinking was that the multiple telegraphy system would transmit an undulatory current, as opposed to the intermittent or make‐or‐break current used in single‐transmission telegraphy.
By June 2, 1875, Bell had constructed three multiple telegraph stations, each with three tuned relays. When Bell caused one of the reeds at the first station to vibrate, the corresponding reed at the second station also vibrated. His assistant, Mr. Watson, who was in another room with the third corresponding reed, advised Bell that the reed was stuck. To release the stuck reed, Watson vibrated it with his finger, and Bell noticed that the corresponding reed at Station II vibrated violently. Bell then placed his ear next to each of the other reeds at the second station in succession, and heard both the overtones and the pitch of the tuned reeds. He concluded from this incident that magneto‐electric undulating currents generated by the vibration of an armature in front of an electromagnet could produce audible effects that could be utilized for multiple telegraphy and speech transmission. Later, Mr. Watson was to comment that the speaking telephone was born as a result of this experiment.
However, extensive work did remain before a workable electric telephone was developed. As a result of the stuck reed, Bell learned that a single reed, when dampened or stuck, could also induce a current that was capable of transmitting complex vibrations or sounds over a distance, and the multiple reeds of the harp structure were not necessary. Bell then asked Mr. Watson to construct a device in which a reed relay was attached to a membrane or diaphragm having a speaking cavity. As one spoke into the cavity, the membrane vibrated, and these vibrations were translated into electric current by the dampened reed. The current thus generated was received by a similar device at the end of an electrical wire. The receiving device produced mumbling, rather than intelligible speech. However, Bell and Watson considered that they were heading in the right direction.
On January 20, 1876, Bell signed a patent application directed to his use of electrical undulations induced by the vibration of a body capable of inductive action to transmit sound. This was before speech had been transmitted electrically. Bell’s patent application was submitted to the United States Patent Office on February 14, 1876, four days after his 29th birthday, and merely a few hours before Elisha Gray submitted a caveat for a speaking telegraph. (A caveat was a document submitted by a potential inventor with the U.S. Patent Office, setting forth a broad outline of an invention they intended to make, but which was not complete. The use of caveats in the United States terminated circa 1909.)
When the Bell patent application was filed, he and Watson had still not developed a working device. On March 10, 1876, Bell removed the electromagnet from the device he and Watson had constructed that produced the mumbling transmission,