Alexander Graham Bell : biography
In March 1875, Bell and Pollok visited the famous scientist Joseph Henry, who was then director of the Smithsonian Institution, and asked Henry’s advice on the electrical multi-reed apparatus that Bell hoped would transmit the human voice by telegraph. Henry replied that Bell had "the germ of a great invention". When Bell said that he did not have the necessary knowledge, Henry replied, "Get it!" That declaration greatly encouraged Bell to keep trying, even though he did not have the equipment needed to continue his experiments, nor the ability to create a working model of his ideas. However, a chance meeting in 1874 between Bell and Thomas A. Watson, an experienced electrical designer and mechanic at the electrical machine shop of Charles Williams, changed all that.
With financial support from Sanders and Hubbard, Bell hired Thomas Watson as his assistant, and the two of them experimented with acoustic telegraphy. On June 2, 1875, Watson accidentally plucked one of the reeds and Bell, at the receiving end of the wire, heard the overtones of the reed; overtones that would be necessary for transmitting speech. That demonstrated to Bell that only one reed or armature was necessary, not multiple reeds. This led to the "gallows" sound-powered telephone, which could transmit indistinct, voice-like sounds, but not clear speech.
The race to the patent office
In 1875, Bell developed an acoustic telegraph and drew up a patent application for it. Since he had agreed to share U.S. profits with his investors Gardiner Hubbard and Thomas Sanders, Bell requested that an associate in Ontario, George Brown, attempt to patent it in Britain, instructing his lawyers to apply for a patent in the U.S. only after they received word from Britain (Britain would issue patents only for discoveries not previously patented elsewhere).Bruce 1990, pp. 158–159.
Meanwhile, Elisha Gray was also experimenting with acoustic telegraphy and thought of a way to transmit speech using a water transmitter. On February 14, 1876, Gray filed a caveat with the U.S. Patent Office for a telephone design that used a water transmitter. That same morning, Bell’s lawyer filed Bell’s application with the patent office. There is considerable debate about who arrived first and Gray later challenged the primacy of Bell’s patent. Bell was in Boston on February 14 and did not arrive in Washington until February 26.
Bell’s patent 174,465, was issued to Bell on March 7, 1876, by the U.S. Patent Office. Bell’s patent covered "the method of, and apparatus for, transmitting vocal or other sounds telegraphically … by causing electrical undulations, similar in form to the vibrations of the air accompanying the said vocal or other sound"MacLeod 1999, pp. 12–13. Bell returned to Boston the same day and the next day resumed work, drawing in his notebook a diagram similar to that in Gray’s patent caveat.
On March 10, 1876, three days after his patent was issued, Bell succeeded in getting his telephone to work, using a liquid transmitter similar to Gray’s design. Vibration of the diaphragm caused a needle to vibrate in the water, varying the electrical resistance in the circuit. When Bell spoke the famous sentence "Mr Watson—Come here—I want to see you" into the liquid transmitter, loc.gov. Retrieved: July 28, 2010. Watson, listening at the receiving end in an adjoining room, heard the words clearly.MacLeod 1999, p. 12.
Although Bell was, and still is, accused of stealing the telephone from Gray,Shulman 2008, p. 211. Bell used Gray’s water transmitter design only after Bell’s patent was granted and only as a proof of concept scientific experimentEvenson 2000, p. 99. to prove to his own satisfaction that intelligible "articulate speech" (Bell’s words) could be electrically transmitted.Evenson 2000, p. 98. After March 1876, Bell focused on improving the electromagnetic telephone and never used Gray’s liquid transmitter in public demonstrations or commercial use.Evenson 2000, p. 100.