Invention of Telephone

On March 10, 1876, in Boston, Massachusetts, Alexander Graham Bell invented the telephone. 

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. 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. 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 to 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.

In 1837 Samuel Morse invented the first workable telegraph, applied for its patent in 1838, and was finally granted it in 1848. . 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.

Yet as the telegraph was perfected, man's thoughts turned to speech over a wire.

On June 2, 1875, Bell and Watson were testing the harmonic telegraph when Bell heard a sound come through the receiver. Instead of transmitting a pulse, which it had refused to do in any case, the telegraph passed on the sound of Watson plucking a tuned spring, one of many set at different pitches. How could that be? Their telegraph, like all others, turned current on and off. But in this instance, a contact screw was set too tightly, allowing current to run continuously, the essential element needed to transmit speech. Bell realized what happened and had Watson build a telephone the next day based on this discovery. 

The Watson-built telephone looked odd and acted strangely. Bellowing into the funnel caused a small disk or diaphragm at the bottom to move. This disk was, in turn, attached to a wire floating in an acid-filled metal cup. A wire attached to the cup, in turn, led to a distant receiver. As the wire moved up and down it changed the resistance within the liquid. This now varying current was then sent to the receiver, causing its membrane to vibrate and thereby produce sound. This telephone wasn't quite practical; it got speech across, but badly. This transmitter was quickly dropped in favor of voice-powered or induced models. This transmitted speech on the weak electro-magnetic force that the transmitter and receiver's permanent magnets produced.

 

Finally, on March 10, 1876, one week after his patent was allowed, Bell succeeded in transmitting speech. He was not yet 30. Bell soon improved it by using an electromagnetic transmitter, a metal diaphragm, and a permanent magnet. The telephone had been invented.