page_title: Invention of the telephone
section_title: Bell's success
hierarchical_section_title: Invention of the telephone / Electro-magnetic transmitters and receivers / Bell's success
caption_attribution_description: English: Telephone_Centennial_Issue_1976-13c.jpg
context_page_description: The invention of the telephone was the culmination of work done by many individuals, and led to an array of lawsuits relating to the patent claims of several individuals and numerous companies.
context_section_description: The first successful bi-directional transmission of clear speech by Bell and Watson was made on March 10, 1876, when Bell spoke into the device, "Mr. Watson, come here, I want to see you." and Watson complied with the request. Bell tested Gray's liquid transmitter design in this experiment, but only after Bell's patent was granted and only as a proof of concept scientific experiment to prove to his own satisfaction that intelligible "articulate speech" (Bell's words) could be electrically transmitted. Because a liquid transmitter was not practical for commercial products, Bell focused on improving the electromagnetic telephone after March 1876 and never used Gray's liquid transmitter in public demonstrations or commercial use.
  Bell's telephone transmitter (microphone) consisted of a double electromagnet, in front of which a membrane, stretched on a ring, carried an oblong piece of soft iron cemented to its middle. A funnel-shaped mouthpiece directed the voice sounds upon the membrane, and as it vibrated, the soft iron "armature" induced corresponding currents in the coils of the electromagnet. These currents, after traversing the wire, passed through the receiver which consisted of an electromagnet in a tubular metal can having one end partially closed by a thin circular disc of soft iron. When the undulatory current passed through the coil of this electromagnet, the disc vibrated, thereby creating sound waves in the air.
  This primitive telephone was rapidly improved. The double electromagnet was replaced by a single permanently magnetized bar magnet having a small coil or bobbin of fine wire surrounding one pole, in front of which a thin disc of iron was fixed in a circular mouthpiece. The disc served as a combined diaphragm and armature. On speaking into the mouthpiece, the iron diaphragm vibrated with the voice in the magnetic field of the bar-magnet pole, and thereby caused undulatory currents in the coil. These currents, after traveling through the wire to the distant receiver, were received in an identical apparatus. This design was patented by Bell on January 30, 1877. The sounds were weak and could only be heard when the ear was close to the earphone/mouthpiece, but they were distinct.
  In the third of his tests in Southern Ontario, on August 10, 1876, Bell made a call via the telegraph line from the family homestead in Brantford, Ontario, to his assistant located in Paris, Ontario, some 13 kilometers away. This test was claimed by many sources as the world's first long-distance call. The final test certainly proved that the telephone could work over long distances.
caption: Bell's Prototype Telephone Centennial Issue of 1976
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