Editing Photophone (section)

==First successful wireless voice communications==
[[File:Photophone transmitter 4074931746 9f996df841 b.jpg|thumb|Illustration of a photophone transmitter, showing the path of reflected sunlight, before and after being modulated]]
[[File:Photophone receiver 4074172975 288f2808f0 o.jpg|thumb|Illustration of a photophone receiver, depicting the conversion of modulated light to sound, as well as its electrical power source (P)]]

While honeymooning in Europe with his bride [[Mabel Gardiner Hubbard|Mabel Hubbard]], Bell likely read of the newly discovered property of selenium having a variable resistance when acted upon by light, in a paper by Robert Sabine as published in ''Nature'' on 25 April 1878. In his experiments, Sabine used a meter to see the effects of light acting on selenium connected in a circuit to a battery. However Bell reasoned that by adding a telephone receiver to the same circuit he would be able to hear what Sabine could only see.<ref>Mims 1982, pp. 6–7.</ref>

As Bell's former associate, [[Thomas A. Watson|Thomas Watson]], was fully occupied as the superintendent of manufacturing for the nascent [[Bell Telephone Company]] back in Boston, Massachusetts, Bell hired [[Charles Sumner Tainter]], an instrument maker who had previously been assigned to the [[transit of Venus, 1874|U.S. 1874 Transit of Venus Commission]], for his new [[Volta Laboratory and Bureau|'L' Street laboratory in Washington]], at the rate of $15 per week.<ref>Mims 1982, p. 7.</ref>

On February 19, 1880, the pair had managed to make a functional photophone in their new laboratory by attaching a set of metallic gratings to a diaphragm, with a beam of light being interrupted by the gratings movement in response to spoken sounds. When the modulated light beam fell upon their selenium receiver Bell, on his headphones, was able to clearly hear Tainter singing ''Auld Lang Syne''.<ref>Mims 1982, p. 10.</ref>

In an April 1, 1880, [[Washington, D.C.]], experiment, Bell and Tainter communicated some {{convert|79|m|ft|}} along an alleyway to the laboratory's rear window. Then a few months later on June 21 they succeeded in communicating clearly over a distance of some 213 meters (about 700&nbsp;ft.), using plain [[sunlight]] as their light source, [[incandescent light bulb#History of the light bulb|practical electrical lighting]] having only just been introduced to the U.S. by [[Thomas Edison|Edison]]. The transmitter in their latter experiments had sunlight reflected off the surface of a very thin mirror positioned at the end of a speaking tube; as words were spoken they cause the mirror to oscillate between convex and concave, altering the amount of light reflected from its surface to the receiver. Tainter, who was on the roof of the [[Franklin School (Washington, D.C.)|Franklin School]], spoke to Bell, who was in his laboratory listening and who signaled back to Tainter by waving his hat vigorously from the window, as had been requested.<ref name="Mims 1982, p. 11"/>

The receiver was a [[parabolic reflector|parabolic mirror]] with [[selenium#Other uses|selenium cells]] at its focal point.<ref name="Groth"/> Conducted from the roof of the Franklin School to Bell's laboratory at 1325 'L' Street, this was the world's first formal wireless telephone communication (away from their laboratory), thus making the photophone the world's earliest known voice [[wireless telephone (disambiguation)|wireless telephone]] system, {{citation needed|date=February 2017}} at least 19 years ahead of the first spoken radio wave transmissions. Before Bell and Tainter had concluded their research in order to move on to the development of the [[Graphophone]], they had devised some 50 different methods of modulating and demodulating light beams for optical telephony.<ref name="Mims 1982, p. 12">Mims 1982, p. 12.</ref>