Alexander Graham Bell's telephone patent, U.S. Number 174,465, from 1876, which has been called the most valuable ever issued (source: USPTO).

The modern telephone is the culmination of work done by many individuals, all worthy of recognition for their contributions to the field. Alexander Graham Bell was the first to patent the telephone, an "apparatus for transmitting vocal or other sounds telegraphically" (patent No. 174,465), after experimenting with many primitive sound transmitters and receivers. However, the history of the invention of the telephone is a confusing collection of claims and counterclaims, made no less confusing by the many lawsuits which attempted to resolve the patent claims of several individuals.

Alexander Graham Bell of Scotland is commonly credited as the first inventor of the telephone. The classic story of his crying out "Watson, come here! I want to see you!" is a well known part of American history.

As Professor of Vocal Physiology at Boston University, Bell was engaged in training teachers in the art of instructing deaf mutes how to speak, and experimented with the Leon Scott phonautograph in recording the vibrations of speech.

Bell reasoned by analogy with the mechanical phonautograph that a skin diaphragm would reproduce sounds like the human ear when connected to a vibrating steel or iron reed or hinged armature. On 1 July 1875, he instructed Watson to build a receiver consisting of a stretched diaphragm or drum of goldbeater's skin (the outer membrane of calf's intestine) with an armature of magnetized iron attached to its middle, and free to vibrate in front of the pole of an electromagnet in circuit with the line. A second membrane-device was built for use as a transmitter. This was the "gallows" phone - because of its resemblance to the wooden construction used for execution by hanging.

A few days later they were at each end of the line, which ran from a room in the inventor's house in Boston to the cellar underneath. Bell, in the work room, held one instrument in his hands, while Watson in the cellar listened at the other. Bell spoke into his instrument, “Do you understand what I say?” and Mr. Watson answered “Yes”. However, the voice sounds were not distinct and the armature tended to stick to the electromagnet pole and tear the membrane.

On 14 February 1876, Elisha Gray filed a patent caveat* for a telephone on the very same day in 1876 as did Bell's lawyer. The water transmitter described in Gray's caveat was strikingly similar to Bell's telephone transmitter, a fact which raised questions about whether Bell (who knew of Gray's work) was inspired by Gray's design or vice versa.

What happened on this critical day at USPTO is not clear till today, however, some evidence suggests that Bell's lawyers may have obtained an unfair advantage over Gray. https://en.wikipedia.org...

As a rersult Bell was granted the first telephone patent, U.S. Number 174,465, which has been called the most valuable ever issued.

* A caveat is an official notice of intention to file a patent application at a later date. It was like a patent application with a description of an invention and drawings, but without claims. The primary objective of a caveat was to prevent the issuing of a rival patent for the same invention to a subsequent inventor. A caveat expired after one year. Caveats were discontinued in 1909.

Bell's tuning fork sounder from 1872. Bell's first experiments for improving telegraphy involved a replication and improvement upon on Helmholtz's electrical transmission of musical tones from one vibrating tuning fork to another.

Bell's drawing of the liquid transmitter that transmitted the first human speech on March 10, 1876