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发表于 2010-3-7 10:34:42
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March 07, 1876: Alexander Graham Bell received a patent for the telephone.
Bell, Alexander Graham
Gray and Bell: the transmission of speech
The first devices
In the 1870s two American inventors, Elisha Gray and Alexander Graham Bell, both independently designed devices that could transmit speech electrically. Gray's first device made use of a harmonic telegraph, the transmitter and receiver of which consisted of a set of metallic reeds tuned to different frequencies. An electromagnetic coil was located near each of the reeds. When a reed in the transmitter was vibrated by sound waves of its resonant frequency—for example, 400 hertz—it induced an electric current of corresponding frequency in its matching coil. This coil was connected to all the coils in the receiver, but only the reed tuned to the transmitting reed's frequency would vibrate in response to the electric current. Thus, simple tones could be transmitted. In the spring of 1874 Gray realized that a receiver consisting of a single steel diaphragm in front of an electromagnet could reproduce any of the transmitted tones. Gray, however, was initially unable to conceive of a transmitter that would transmit complex speech vibrations and instead chose to demonstrate the transmission of tones via his telegraphic device in the summer of 1874.
Bell, meanwhile, also had considered the transmission of speech using the harmonic telegraph concept, and in the summer of 1874 he also conceived of a membrane receiver similar to Gray's. However, since Bell, too, had no transmitter, the membrane device was never constructed. Following some earlier experiments, Bell postulated that, if two membrane receivers were connected electrically, a sound wave that caused one membrane to vibrate would induce a voltage in the electromagnetic coil that would, in turn, cause the other membrane to vibrate. Working with a young machinist, Thomas Augustus Watson, Bell had two such instruments constructed in June 1875. The device was tested on June 3, 1875, and, although no intelligible words were transmitted, “speechlike” sounds were heard at the receiving end.
An application for a U.S. patent on Bell's work was filed on Feb. 14, 1876. Several hours later that same day, Gray filed a caveat on the concept of a telephone transmitter and receiver. A caveat was a confidential, formal declaration by an inventor to the U.S. Patent Office of an intent to file a patent on an idea yet to be perfected; it was intended to prevent the idea from being used by other inventors. (At this point neither Gray nor Bell had yet constructed a working telephone that could convey speech.) On the basis of its earlier filing time, Bell's patent application was allowed over Gray's caveat. On March 7, 1876, Bell was awarded U.S. patent 174,465. This patent is often referred to as the most valuable ever issued by the U.S. Patent Office, as it described not only the telephone instruments but also the concept of a telephone system.
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