Tom Farley's Telephone History Series. In 1820 Danish physicist Christian Oersted discovered electromagnetism, the critical idea needed to develop electrical power and to communicate. Balky electrostatic generators produced static electricity by friction, often by spinning leather against glass. And while static electricity could make hair stand on end or throw sparks, it couldn't provide the energy to do truly useful things. Inventors and industry needed a reliable and continuous current. In 1800 Alessandro Volta produced the first battery. Chemically based, as all batteries are, the battery improved quickly and became the electrical source for further experimenting. But while batteries got more reliable, they still couldn't produce the power needed to work machinery, light cities, or provide heat. And although batteries would work telegraph and telephone systems, and still do, transmitting speech required understanding two related elements, namely, electricity and magnetism. As Alexander Graham Bell, in later years, said: "I now realize that I should never have invented the telephone if I had been an electrician. What electrician would have been so foolish as to try any such thing? The advantage I had was that sound had been the study of my life -- the study of vibrations". In a famous experiment at his University of Copenhagen classroom, Oersted pushed a compass under a live electric wire. This caused its needle to turn from pointing north, as if acted on by a larger magnet. Oersted discovered that an electric current creates a magnetic field. But could a magnetic field create electricity? If so, a new source of power beckoned. And the principle of electromagnetism, if fully understood and applied, promised a new era of communication. In 1821 Michael Faraday reversed Oersted's experiment and in so doing discovered induction. He got a weak current to flow in a wire revolving around a permanent magnet. In other words, a magnetic field caused or induced an electric current to flow in a nearby wire. In so doing, Faraday had built the world's first electric generator. In 1830 the great American scientist Professor Joseph Henry transmitted the first practical electrical signal. In a stunning demonstration in his Albany Academy classroom, Henry created the forerunner of the telegraph: an electromagnet activated by a distant battery, and a pivoted iron bar that moves ( attracted by the electromagnet ) to ring a bell. In 1837 Samuel Morse invented the first workable telegraph: a key ( a switch ) to make or break the electrical circuit, a battery to produce power, a single line joining one telegraph station to another and an electromagnetic receiver or sounder that upon being turned on and off, produced a clicking noise. The key consists of two electrical contacts, which, when pressed together, make contact, closing the circuit and permitting current to flow ( pulse ). To convey intelligence, the written word, a code was developed by Morse, consisting of three elements: a dot, where the key was held down for a very short period of time; a dash, where the key was held down for a longer period of time; and a space, where the key was left in the “up” position and no current flowed. We may define the telegraph as the first digital device in the world. In a digital signal current goes on and off. No wave thing. Reproducing speech, at the other end, practically relies on the transmitter making continuous contact with the electrical circuit. A transmitter varies the electrical current depending on how much acoustic pressure it gets ( Analog signal ). Turning the current off and on like a telegraph cannot begin to duplicate speech since speech, once flowing, is a fluctuating wave of continuous character; it is not a collection of off and on again pulses. It was not until the early 1960s that digital carrier techniques simulated an analog wave with digital pulses. Even then this simulation was only possible by sampling the wave 8,000 times a second. Producing CD quality sound means sampling an analog signal 44,000 times a second. In these days all traffic in America between telephone switches is digital, but the majority of local loops are analog, still carrying your voice to the central office by varying the current.

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