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In 1830 the great American scientist Professor Joseph Henry transmitted the first practical electrical signal. A short time before Henry had invented the first efficient electromagnet. He also concluded similar thoughts about induction before Faraday but he didn't publish them first. Henry's place in electrical history however, has always been secure, in particular for showing that electromagnetism could do more than create current or pick up heavy weights -- it could communicate.

In a stunning demonstration in his Albany Academy classroom, Henry created the forerunner of the telegraph. In the demonstration, Henry first built an electromagnet by winding an iron bar with several feet of wire. A pivot mounted steel bar sat next to the magnet. A bell, in turn, stood next to the bar. From the electromagnet Henry strung a mile of wire around the inside of the classroom. He completed the circuit by connecting the ends of the wires at a battery. Guess what happened? The steel bar swung toward the magnet, of course, striking the bell at the same time. Breaking the connection released the bar and it was free to strike again. And while Henry did not pursue electrical signaling, he did help someone who did. And that man was Samuel Finley Breese Morse.

For more information on Joseph Henry, visit the Joseph Henry Papers Project at:

http://www.si.edu/archives/ihd/jhp/papers00.htm (external link)

 

From the December, 1963 American Heritage magazine, "a sketch of Henry's primitive telegraph, a dozen years before Morse, reveals the essential components: an electromagnet activated by a distant battery, and a pivoted iron bar that moves to ring a bell."  See the two books listed to the left for more information.

In 1837 Samuel Morse invented the first workable telegraph, applied for its patent in 1838, and was finally granted it in 1848. Joseph Henry helped Morse build a telegraph relay or repeater that allowed long distance operation. The telegraph later helped unite the country and eventually the world. Not a professional inventor, Morse was nevertheless captivated by electrical experiments. In 1832 he heard of Faraday's recently published work on inductance, and was given an electromagnet at the same time to ponder over. An idea came to him and Morse quickly worked out details for his telegraph.

As depicted below, his system used 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. He completed the package by devising the Morse code system of dots and dashes. A quick key tap broke the circuit momentarily, transmitting a short pulse to a distant sounder, interpreted by an operator as a dot. A more lengthy break produced a dash.

Telegraphy became big business as it replaced messengers, the Pony Express, clipper ships and every other slow paced means of communicating. The fact that service was limited to Western Union offices or large firms seemed hardly a problem. After all, communicating over long distances instantly was otherwise impossible. Yet as the telegraph was perfected, man's thoughts turned to speech over a wire.

In 1854 Charles Bourseul wrote about transmitting speech electrically in a well circulated article. In that important paper, the Belgian-born French inventor and engineer described a flexible disk that would make and break an electrical connection to reproduce sound. Bourseul never built an instrument or pursued his ideas further.

For more information on Bourseul and early communications in general, vist this German site:

http://www.fht-esslingen.de/telehistory/1870-.html (external link)

 

I have a page on easy to do electrical experiments for kids. And adults who want to understand the basics (internal link)

In 1861 Johann Phillip Reis completed the first non-working telephone. Tantalizingly close to reproducing speech, Reis's instrument conveyed certain sounds, poorly, but no more than that. A German physicist and school teacher, Reis's ingenuity was unquestioned. His transmitter and receiver used a cork, a knitting needle, a sausage skin, and a piece of platinum to transmit bits of music and certain other sounds. But intelligible speech could not be reproduced. The problem was simple, minute, and at the same time monumental. His telephone relied on its transmitter's diaphragm making and breaking contact with the electrical circuit, just as Bourseul suggested, and just as the telegraph worked. This approach, however, was completely wrong.

Reproducing speech 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. 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. The Reis instrument, in fact, worked only when sounds were so soft that the contact connecting the transmitter to the circuit remained unbroken. Speech may have traveled first over a Reis telephone however, it would have done so accidentally and against every principle he thought would make it work. And although accidental discovery is the stuff of invention, Reis did not realize his mistake, did not understand the principle behind voice transmission, did not develop his instrument further, nor did he ever claim to have invented the telephone.

The definitive book in English on Reis is:

Thompson, Silvanus P. Phillip Reis: Inventor of The Telephone. E.&F.N. Spon. London. 1883

 

For other views and explanations of the Reis instrument, visit Adventures in Cybersound:

http://www.acmi.net.au/AIC/REIS_BIO.html (external link)

In the early 1870s the world still did not have a working telephone. Inventors focused on telegraph improvements since these had a waiting market. A good, patentable idea might make an inventor millions. Developing a telephone, on the other hand, had no immediate market, if one at all. Elisha Gray, Alexander Graham Bell, as well as many others, were instead trying to develop a multiplexing telegraph, a device to send several messages over one wire at once. Such an instrument would greatly increase traffic without the telegraph company having to build more lines. As it turned out, for both men, the desire to invent one thing turned into a race to invent something altogether different. And that is truly the story of invention.

Alan J. Rogers' excellent introduction to electromagnetic waves, frequencies, and radio transmission. All applicable to telephony. Really well done. (19 pages, 164K in .pdf)

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Resources:

Analog and digital signals compared and contrasted

Analog transmission in telephone working. At the top of the illustration we depict direct current as a flat line. D.C. is the steady and continuous current your telephone company provides. The middle line shows what talking looks like. As in all things analog, it looks like a wave. The third line shows how talking varies that direct current. Your voice varies the telephone line's electrical resistance to represent speech. Click here for another diagram that complements this illustration.

Below is a simplified view of a digital signal. Current goes on and off. No wave thing. There was no chance the Reis telephone described above could transmit intelligible speech since it could not reproduce an analog wave. You can't do that making and breaking a circuit. A pulse in this case is not a wave! (internal link) It was not until the early 1960s that digital carrier techniques (internal link) 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 (internal link), still carrying your voice to the central office by varying the current.

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