About ten years ago I wrote a book titled Introduction to Telecommunications Networks. About half the book described how the now rapidly disappearing public switched telephone network (PSTN) worked. I haven't picked up the book in a while but a recent flip through has certainly brought back some memories. I thought it would be interesting to take a look at some of the history. Here's how it all started.
Alexander Graham Bell and Elisha Gray, another inventor competing with Bell, are both scrambling to get their voice transmission inventions patented.
February 14, 1876
On this day Alexander Graham Bell’s father in law, attorney Gardiner Hubbard, delivered a patent application from Bell to the U.S. Patent for a device that transmits voice frequencies across wires.
Approximately three hours later on the same day Elisha Gray filed a caveat (a formal notice of an invention Gray hoped to patent) with the U.S. Patent Office describing a device that also transmitted voice frequencies across wires.
March 10, 1876
Alexander Graham Bell and Thomas A. Watson demonstrate a working telephone system but not without controversy. When Bell’s original patent and Gray’s caveat, both filed on February 14, were reviewed it was determined the device Bell described would not have worked while Gray’s would have. It was speculated that Bell had copied parts of Gray’s design. In Gray’s caveat he had detailed the use of a variable resistance transmitter which was used to produce a transmitter signal robust enough for the receiver to hear. Bell had been struggling to solve this same problem. In Bell’s patent application he made what appeared to be a last minute handwritten notation about the use of a variable resistance transmitter. People speculated that Bell had found out about Gray’s caveat and learned of Gray’s use of a variable resistance transmitter and, at the last minute before filing, Bell made a note on the patent application about using the new transmitter.
The variable resistance transmitter demonstrated by Bell on March 10, 1876 used a voice cone attached to a diaphragm. Also attached to the diaphragm was a wire that was emersed in a metal container of acidic solution.
The user talked into the voice cone, voice sound waves caused the diaphragm to vibrate and the wire moved up and down in the acidic solution. As the wire moved up and down in the solution the resistance between the wire and the metal container changed causing the DC current to vary in proportion to the variation in sound waves.
The controversy between Bell and Gray lead to years of litigation to the level of the United States Supreme Court where a split decision gave Bell the patent for the telephone entitled Improvements in Telegraphy.It took a little over a year for Bell to acquire and convince his wealthy father-in-law, Gardinar Hubbard, to finance the Bell Telephone Company and fund the building of the voice network infrastructure.
It's interesting to look back at the legal back and forth between Bell and Gray. It reminds me a lot of what we're seeing between Mark Zuckerberg and Facebook, the Winklevoss Twins, Wayne Chang, Paul Ceglia.... and others.