Editing Photophone

{{Short description|Device that uses light to transmit speech}} {{distinguish|Videotelephony}}
{{About|Alexander Graham Bell and Sumner Tainter's optical phone|the sound-on-film technology|RCA Photophone}}
[[File:Photophone plaque (no copyright applies).jpg|thumb|alt=An image of darkened brass historical plaque with a streak of green corrosion running down it, mounted on the exterior side of a brick building. |A historical plaque on the side of the Franklin School in Washington, D.C. which marks one of the points from which the photophone was demonstrated]]
[[File:Bells Photophon Schema.jpg|thumb|A diagram from one of Bell's 1880 papers]]

The '''photophone''' is a [[telecommunications]] device that allows [[transmission (telecommunications)|transmission]] of speech on a beam of [[light]]. It was invented jointly by [[Alexander Graham Bell]] and his assistant [[Charles Sumner Tainter]] on February 19, 1880, at Bell's laboratory at 1325 L Street in Washington, D.C.<ref>Bruce 1990, pg. 336</ref><ref name="SDU"/> Both were later to become full associates in the [[Volta Laboratory and Bureau#Laboratory projects|Volta Laboratory Association]], created and financed by Bell.

On June 3, 1880, Bell's assistant transmitted a wireless voice telephone message from the roof of the [[Franklin School (Washington, D.C.)|Franklin School]] to the window of Bell's laboratory, some 213 meters (about 700&nbsp;ft.) away.<ref>Bruce 1990, pg. 338</ref><ref name="Carson 2007, pg. 76–78">Carson 2007, pg. 76–78</ref><ref name="Groth"/><ref name="Mims 1982, p. 11">Mims 1982, p. 11.</ref>

Bell believed the photophone was his most important [[invention]]. Of the 18 [[patent]]s granted in Bell's name alone, and the 12 he shared with his collaborators, four were for the photophone, which Bell referred to as his "greatest achievement", telling a reporter shortly before his death that the photophone was "the greatest invention [I have] ever made, greater than the telephone".<ref name="Phillipson+Neilson"/><ref name="Mims 1982, p. 14">Mims 1982, p. 14.</ref>

The photophone was a precursor to the [[fiber-optic communication]] systems that achieved worldwide popular usage starting in the 1980s.<ref name="Morgan"/><ref name="AmericanScientist-1984.V72.No1"/><ref name="Gallardo+Mims"/> The master patent for the photophone ({{US patent|235199}} ''Apparatus for Signalling and Communicating, called Photophone'') was issued in December 1880,<ref name="Groth"/> many decades before its principles came to have practical applications.

==Design==
[[File:Photophony1.jpg|thumb|A photophone receiver and headset, one half of Bell and Tainter's optical telecommunication system of 1880]]

The photophone was similar to a contemporary telephone, except that it used [[free-space optical communication#Visible light communication|modulated light]] as a means of wireless transmission while the telephone relied on [[modulation|modulated]] [[electricity]] carried over a conductive [[two-wire circuit|wire circuit]].

Bell's own description of the light modulator:<ref name="Clark"/>

{{Blockquote
| We have found that the simplest form of apparatus for producing the effect consists of a plane mirror of flexible material against the back of which the speaker's voice is directed. Under the action of the voice the mirror becomes alternately convex and concave and thus alternately scatters and condenses the light.}}

The brightness of a reflected beam of light, as observed from the location of the receiver, therefore varied in accordance with the audio-frequency variations in air pressure—the sound waves—which acted upon the mirror.

In its initial form, the photophone receiver was also non-electronic, using the [[photoacoustic effect]]. Bell found that many substances could be used as direct light-to-sound transducers. [[Lampblack]] proved to be outstanding. Using a fully modulated beam of sunlight as a test signal, one experimental receiver design, employing only a deposit of lampblack, produced a tone that Bell described as "painfully loud" to an ear pressed close to the device.<ref>{{cite journal |last1=Bell |first1=Alexander Graham |title=The Production of Sound by Radiant Energy |journal=Science |date=28 May 1881 |volume=2 |issue=48 |pages=242–253 |doi=10.1126/science.os-2.49.242 |jstor=2900190 |pmid=17741736 |url=https://www.jstor.org/stable/2900190 |access-date=11 Oct 2022}}</ref>

In its ultimate electronic form, the photophone receiver used a simple [[selenium#Other uses|selenium cell]] [[photodetector]] at the [[focus (optics)|focus]] of a parabolic mirror.<ref name="Groth"/> The cell's [[electrical resistance]] (between about 100 and 300 [[ohm]]s) varied inversely with the light falling upon it, i.e., its resistance was higher when dimly lit, lower when brightly lit. The selenium cell took the place of a carbon microphone—also a variable-resistance device—in the circuit of what was otherwise essentially an ordinary telephone, consisting of a battery, an electromagnetic earphone, and the variable resistance, all connected in series. The selenium modulated the current flowing through the circuit, and the current was converted back into variations of air pressure—sound—by the earphone.

In his speech to the American Association for the Advancement of Science in August 1880, Bell gave credit for the first demonstration of speech transmission by light to Mr. A.C. Brown of London in the Fall of 1878.<ref name="Groth"/><ref name="Bell"/>

{{anchor|Radiophone}}Because the device used [[radiant energy]], the French scientist [[:fr:Ernest Mercadier|Ernest Mercadier]] suggested that the invention should not be named 'photophone', but 'radiophone', as its mirrors reflected the Sun's radiant energy in multiple bands including the invisible [[infrared|infrared band]].<ref name="Grosvenor & Wesson">Grosvenor and Wesson 1997, p. 104.</ref> Bell used the name for a while but it should not be confused with the later invention "[[radiophone]]" which used [[radio wave]]s.<ref>Ernest Victor Heyn, Fire of genius: inventors of the past century: based on the files of Popular Science Monthly since its founding in 1872, Anchor Press/Doubleday – 1976, page 74</ref>

==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>

==Reception and adoption==
The telephone itself was still something of a novelty, and [[radio]] was decades away from commercialization. The social resistance to the photophone's futuristic form of communications could be seen in an August 1880 ''[[New York Times]]'' commentary:<ref name="NYT-18800830"/><ref>International Fiber Optics & Communication, June 1986, p. 29</ref>

{{Blockquote
|The ordinary man ... will find a little difficulty in comprehending how sunbeams are to be used. Does Prof. Bell intend to connect Boston and Cambridge ... with a line of sunbeams hung on [[utility pole|telegraph posts]], and, if so, what diameter are the sunbeams to be ....[and] will it be necessary to insulate them against the weather ... until (the public) sees a man going through the streets with a coil of No. 12 sunbeams on his shoulder, and suspending them from pole to pole, there will be a general feeling that there is something about Professor Bell's photophone which places a tremendous strain on human credulity.}}

However at the time of their February 1880 breakthrough, Bell was immensely proud of the achievement, to the point that he wanted to name his new second daughter "Photophone", which was subtly discouraged by his wife [[Mabel Gardiner Hubbard|Mabel Bell]] (they instead chose "Marian", with "Daisy" as her [[nickname]]).<ref>Carson 2007, pg.77</ref> He wrote somewhat enthusiastically:<ref name="Carson 2007, pg. 76–78"/><ref name="Bruce 1990, pg.337">Bruce 1990, pg. 337</ref>

{{Blockquote
|I have heard articulate speech by sunlight! I have heard a ray of the sun laugh and cough and sing! ...I have been able to hear a shadow and I have even perceived by ear the passage of a cloud across the sun's disk. You are the grandfather of the Photophone and I want to share my delight at my success.|[[Alexander Graham Bell]]|in a letter to his father [[Alexander Melville Bell]], dated February 26, 1880}}

Bell transferred the photophone's [[intellectual property]] rights to the [[Bell Telephone Company|American Bell Telephone Company]] in May 1880.<ref>Bruce 1990, pg. 339</ref> While Bell had hoped his new photophone could be used by ships at sea and to also displace the plethora of telephone lines that were blooming along busy city boulevards,<ref name="NS-1984.01.12"/> his design failed to protect its transmissions from [[precipitation (meteorology)|outdoor interferences]] such as clouds, fog, rain, snow and such, that could easily disrupt the transmission of light.<ref>Carson 2007, pp. 77–78</ref> Factors such as the weather and the lack of light inhibited the use of Bell's invention.<ref>Carson 2007, pg.78</ref> Not long after its invention laboratories within the [[Bell System]] continued to improve the photophone in the hope that it could supplement or replace expensive conventional [[telephone line]]s. Its earliest non-experimental use came with military communication systems during World War I and II, its key advantage being that its light-based transmissions could not be intercepted by the enemy.

Bell pondered the photophone's possible scientific use in the [[spectroscopy|spectral analysis]] of artificial light sources, [[star]]s and [[sunspot]]s. He later also speculated on its possible future applications, though he did not anticipate either the [[laser]] or [[fiber-optic communication|fiber-optic telecommunications]]:<ref name="Bruce 1990, pg.337"/>

{{Blockquote
|Can Imagination picture what the future of this invention is to be!.... We may talk by light to any visible distance without any conduction wire.... In general science, discoveries will be make by the Photophone that are undreamed of just now.}}

==Further development==
[[File:Ernst Ruhmer, Technical World cover (1905).jpg|thumb|200px|right|Ernst Ruhmer at his "photo-electric" optical telephone system station. (1905)<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015057148481;view=1up;seq=13 Cover page] ''Technical World'', March 1905.</ref>]]
Although Bell Telephone researchers made several modest incremental improvements on Bell and Tainter's design, [[Guglielmo Marconi#Radio work|Marconi's radio transmissions]] started to far surpass the maximum range of the photophone as early as 1897<ref name="Mims 1982, p. 14"/> and further development of the photophone was largely arrested until German-Austrian experiments began at the turn of the 20th century.

The German physicist [[Ernst Ruhmer]] believed that the increased sensitivity of his improved selenium cells, combined with the superior receiving capabilities of professor H. T. Simon's "speaking arc", would make the photophone practical over longer signalling distances. Ruhmer carried out a series of experimental transmissions along the [[Havel|Havel river]] and on Lake Wannsee from 1901 to 1902. He reported achieving sending distances under good conditions of 15 kilometers (9 miles),<ref>[https://babel.hathitrust.org/cgi/pt?id=nyp.33433090837562;view=1up;seq=133 "Correspondence: Wireless Telephony"] (October 30, 1902 letter from Ernst Ruhmer), ''The Electrician'', November 7, 1902, page 111.</ref> with equal success during the day and at night. He continued his experiments around Berlin through 1904, in conjunction with the German Navy, which supplied high-powered searchlights for use in the transmissions.<ref>[https://babel.hathitrust.org/cgi/pt?id=uc1.$b33006;view=1up;seq=73 ''Wireless Telephony In Theory and Practice''] by Ernst Ruhmer, 1908, pages 55–59.</ref>

The German [[Siemens & Halske|Siemens & Halske Company]] boosted the photophone's range by utilizing current-modulated carbon arc lamps which provided a useful range of approximately {{convert|8|km|mi}}. They produced units commercially for the [[German Navy]], which were further adapted to increase their range to {{convert|11|km|mi}} using voice-modulated ship [[searchlight]]s.<ref name="Groth"/>

[[British Admiralty]] research during WWI resulted in the development of a vibrating mirror modulator in 1916. More sensitive [[molybdenite]] receiver cells, which also had greater sensitivity to infra-red radiation, replaced the older selenium cells in 1917.<ref name="Groth"/> The United States and German governments also worked on technical improvements to Bell's system.<ref>Mims 1982, pp. 14–17.</ref>

By 1935 the German [[Carl Zeiss AG|Carl Zeiss Company]] had started producing infra-red photophones for the [[German Army (Wehrmacht)|German Army]]'s tank battalions, employing tungsten lamps with infra-red filters which were modulated by vibrating mirrors or prisms. These also used receivers which employed [[lead sulfide]] detector cells and amplifiers, boosting their range to {{convert|14|km|mi}} under optimal conditions. The Japanese and Italian armies also attempted similar development of lightwave telecommunications before 1945.<ref name="Groth"/>

Several military laboratories, including those in the United States, continued R&D efforts on the photophone into the 1950s, experimenting with high-pressure vapour and mercury arc lamps of between 500 and 2,000 watts power.<ref name="Groth"/>

==Commemorations==
{{ quote box
| align = right
| halign = center
| quote = <poem>
FROM THE TOP FLOOR OF THIS BUILDING
WAS SENT ON JUNE 3, 1880
OVER A BEAM OF LIGHT TO 1325 'L' STREET
THE FIRST WIRELESS TELEPHONE MESSAGE
IN THE HISTORY OF THE WORLD.
THE APPARATUS USED IN SENDING THE MESSAGE
WAS THE PHOTOPHONE INVENTED BY
ALEXANDER GRAHAM BELL
INVENTOR OF THE TELEPHONE
THIS PLAQUE WAS PLACED HERE BY
ALEXANDER GRAHAM BELL CHAPTER
TELEPHONE PIONEERS OF AMERICA
MARCH 3, 1947
THE CENTENNIAL OF DR. BELL'S BIRTH
</poem>
| source = Marker on the Franklin School commemorating the first formal trial
}}

On March 3, 1947, the centenary of [[Alexander Graham Bell]]'s birth, the [[Pioneers, a Volunteer Network|Telephone Pioneers of America]] dedicated a historical marker on the side of one of the buildings, the [[Franklin School (Washington, D.C.)|Franklin School]], which Bell and [[Charles Sumner Tainter|Sumner Tainter]] used for their first formal trial involving a considerable distance. Tainter had originally stood on the roof of the school building and transmitted to Bell at the window of his laboratory. The marker did not acknowledge Tainter's scientific and engineering contributions.{{original research inline|date=September 2017}}

On February 19, 1980, exactly 100 years to the day after Bell and Tainter's first photophone transmission in their laboratory, staff from the [[Smithsonian Institution]], the [[National Geographic Society]] and AT&T's [[Bell Labs]] gathered at the location of Bell's former 1325 'L' Street [[Volta Laboratory and Bureau|Volta Laboratory]] in Washington, D.C. for a commemoration of the event.<ref name="Gallardo+Mims"/><ref name="NS-1986.02.27"/>

The Photophone Centenary commemoration had first been proposed by electronics researcher and writer [[Forrest Mims|Forrest M. Mims]], who suggested it to Dr. [[Melville Bell Grosvenor]], the inventor's grandson, during a visit to his office at the National Geographic Society. The historic grouping later observed the centennial of the photophone's first successful laboratory transmission by using Mims hand-made demonstration photophone, which functioned similar to Bell and Tainter's model.<ref name="Mims 1982, p. 12"/>{{#tag:ref|

The demonstration model was a replica in principle but not identical to Bell and Tainter's model. The commemorative model transmitter was a thin mirror cemented to a short aluminum speaking tube, and its receiver was a silicon solar cell and audio amplifier, both installed in a lantern light housing.

|group="Note"}}

Mims also built and provided a pair of modern hand-held battery-powered [[fiber-optic communication#Transmitters|LED transceivers]] connected by {{convert|100|yd|m}} of [[optical fiber]]. The Bell Labs' Richard Gundlach and the Smithsonian's Elliot Sivowitch used the device at the commemoration to demonstrate one of the photophone's modern-day descendants. The National Geographic Society also mounted a special educational exhibit in its Explorer's Hall, highlighting the photophone's invention with original items borrowed from the Smithsonian Institution.<ref>Mims 1982, pp. 6 & 12.</ref>

==See also==
{{Div col|colwidth=30em}}
* [[Atomic line filter]]
* [[Free-space optical communication]]
* [[History of telecommunication]]
* [[Laser microphone]]
* [[Mie scattering]]
* [[Modulating retro-reflector]]
* [[Optical sound]]
* [[Optical window]]
* [[Photoacoustic effect]]
* [[Radio window]]
* [[Rayleigh scattering]]
* [[Semaphore line]]
* [[Visible light communication]]
* [[Volta Laboratory and Bureau]]
{{Div col end}}

==References==
''' Footnotes '''
{{Reflist|group="Note"}}

''' Citations '''
{{Reflist|30em|refs=
* <ref name="SDU">Jones, Newell. [http://history.sandiego.edu/gen/recording/ar304.html First 'Radio' Built by San Diego Resident Partner of Inventor of Telephone: Keeps Notebook of Experiences With Bell] {{webarchive|url=https://web.archive.org/web/20020219111153/http://history.sandiego.edu/gen/recording/ar304.html |date=2002-02-19}}, San Diego Evening Tribune, July 31, 1937. Retrieved from the University of San Diego History Department website, November 26, 2009.</ref>
* <ref name="Groth">Groth, Mike. [https://web.archive.org/web/20211022155909/http://www.bluehaze.com.au/modlight/GrothArticle1.htm Photophones Revisted], 'Amateur Radio' magazine, [[Wireless Institute of Australia]], Melbourne, April 1987 pp. 12–17 and May 1987 pp. 13–17.</ref>
* <ref name="Phillipson+Neilson">Phillipson, Donald J.C., and Neilson, Laura [https://www.thecanadianencyclopedia.ca/en/article/alexander-graham-bell-aviation-pioneer Bell, Alexander Graham], The Canadian Encyclopedia online. Retrieved 2009-08-06</ref>
* <ref name="AmericanScientist-1984.V72.No1">Miller, Stewart E. "Lightwaves and Telecommunication", ''[[American Scientist]]'', Sigma Xi, The Scientific Research Society, January–February 1984, Vol. 72, No. 1, pp. 66–71, [https://www.jstor.org/stable/i27852430 Issue Stable URL].</ref>
* <ref name="NYT-18800830">Editorial, ''[[The New York Times]]'', August 30, 1880</ref>
* <ref name="Gallardo+Mims">Gallardo, Arturo; [[Forrest Mims|Mims III, Forrest M.]] [http://www.mysanantonio.com/default/article/Fiber-optic-communication-began-130-years-ago-783469.php Fiber-optic Communication Began 130 Years Ago], ''[[San Antonio Express-News]]'', June 21, 2010. Accessed January 1, 2013.</ref>
* <ref name="Morgan">Morgan, Tim J. "The Fiber Optic Backbone", [[University of North Texas]], 2011.</ref>
* <ref name="Bell">[[Alexander Graham Bell|Bell, Alexander Graham]]. "On the Production and Reproduction of Speech by Light", ''[[American Journal of Science]]'', October 1880, Vol. 20, No. 118, pp. 305–324.</ref>
* <ref name="Clark">Clark, J. [https://ieeexplore.ieee.org/Xplore/home.jsp;jsessionid=6C6A7AE68101019670FA3A03F201C9FE An Introduction to Communications with Optical Carriers], IEEE Students' Quarterly Journal, June 1966, Vol.36, Iss.144, pp. 218–222, {{ISSN|0039-2871}}, {{doi|10.1049/sqj.1966.0040}}. Retrieved from IEEExplore website August 19, 2011.</ref>
* <ref name="NS-1986.02.27">Hecht, Jeff. [https://books.google.com/books?id=Q9YLS_wzgfwC&pg=PA51 "Yarns From The Technological Jungle: Siliconnections: Coming Of Age In The Electronic Era"], ''[[New Scientist]]'', February 27, 1986, pp. 50–51.</ref>
* <ref name="NS-1984.01.12">Hecht, Jeff. [https://books.google.com/books?id=CHvVTAcy-tkC&pg=PA12 Fiber Optics Calls Up The Past], ''[[New Scientist]]'', January 12, 1984, pp. 12–13.</ref>
}}

''' Bibliography '''
{{Refbegin|colwidth=30em}}
* {{cite book | last = Carson | first = Mary Kay | title = Alexander Graham Bell: Giving Voice To The World | publisher = Sterling Publishing Co., Inc. | location = New York| year = 2007 | series = Sterling Biographies | pages = [https://archive.org/details/alexandergrahamb0000cars/page/76 76–78] | chapter = chapter 8 | isbn = 978-1-4027-3230-0 | oclc = 182527281 | chapter-url = https://books.google.com/books?id=a46ivzJ1yboC | url = https://archive.org/details/alexandergrahamb0000cars/page/76 }}
* [[Alexander Graham Bell|Bell, A. G]]: "On the Production and Reproduction of Sound by Light", ''[[American Journal of Science]]'', Third Series, Vol. XX, #118, October 1880, pp.&nbsp;305–324; also published as "Selenium and the Photophone" in ''[[Nature (journal)|Nature]]'', September 1880.
* [[List of Boston University people#Guggenheim Fellows|Bruce, Robert V]] ''Bell: Alexander Bell and the Conquest of Solitude'', Ithaca, New York: [[Cornell University|Cornell University Press]], 1990. {{ISBN|0-8014-9691-8}}.
* [[Forrest Mims|Mims III, Forest M]]. [https://books.google.com/books?id=zoaSp1BJu50C&pg=PA1 The First Century of Lightwave Communications], ''Fiber Optics Weekly Update'', Information Gatekeepers, February 10–26, 1982, pp.&nbsp;6–23.
* Grosvenor, Edwin S. and Morgan Wesson. ''Alexander Graham Bell: The Life and Times of the Man Who Invented the Telephone''. New York: Harry N. Abrahms, Inc., 1997. {{ISBN|0-8109-4005-1}}.
{{Refend}}

==Further reading==
* [http://www.bluehaze.com.au/modlight/ModLightBiblio.htm Chris Long and Mike Groth's optical audio telecommunications webpage]
* Ackroyd, William. "The Photophone" in "Science for All", Vol. 2 (R. Brown, ed.), Cassell & Co., London, circa 1884, pp.&nbsp;307–312. A popular account, profusely illustrated with steel engravings.
* Armengaud, J. " Le photophone de M.Graham Bell". Soc. Ing. civ. Mem., year 1880, Vol 2. pp.&nbsp;513–522.
* AT&T Company. "The Radiophone", pamphlet distributed at Louisiana Purchase Exhibition, St Louis, Missouri, 1904. Describes the photophone work of Hammond V Hayes at the Bell Labs (patented 1897) and the German engineer H T Simon in the same year.
* [[Alexander Graham Bell|Bell, Alexander Graham]]. "On the Production and Reproduction of Sound by Light: the Photophone". Am. Ass. for the Advancement of Sci., Proc., Vol 29., October 1880, pp.&nbsp;115–136. Also in ''American Journal of Science'', Series 3. No. 20, 1880, pp.&nbsp;305–324; Eng. L., 30. 1880, pp.&nbsp;240–242; Electrician, Vol 5. 1880, pp.&nbsp;214–215, 220–221, 237; ''Journal of the Society of Telegraph Engineers'', No. 9, 1880, pp.&nbsp;404–426; Nat. L., Vol 22. 1880, pp.&nbsp;500–503; Ann. Chim. Phys., Serie 5. Vol 21. 1880, pp.&nbsp;399–430; E.T.Z., Vol. 1. 1880, pp.&nbsp;391–396. Discussed at length in Eng. L., Vol 30. 1880, pp.&nbsp;253–254, 407–409. In these papers, Bell accords the credit for the first demonstrations of the transmission of speech by light to a Mr A C Brown of London "in September or October 1878".
* [[Alexander Graham Bell|Bell, Alexander Graham]]. "Sur l'application du photophone a l'etude des bruits qui ont lieu a la surface solaire". C. R., Vol. 91. 1880, pp.&nbsp;726–727.
* [[Alexander Graham Bell|Bell, Alexander Graham]]. "Professor A G Bell on Selenium and the Photophone". Pharm. J. and Trans., Series 3. Vol. 11., 1880–1881, pp.&nbsp;272–276; The Electrician No 5, 18 September 1880, pp 220–221 and 2 October 1880 pp 237; Nature (London) Vol 22, 23 September 1880, pp.&nbsp;500–503; Engineering Vol 30, pp 240–242, 253, 254, 407–409; and Journal of the Society of Telegraph Engineers Vol 9, pp 375–387.
* [[Alexander Graham Bell|Bell, Alexander Graham]]. "Other papers on the photophone" E.T.Z. No. 1, 1880, pp 391–396; ''Journal of the Society for the Arts'' 1880, No. 28, pp 847–848 & No. 29 pp 60–62; C.R. No. 91, 1880–1881, pp 595–598, 726, 727, 929–931, 982, 1882 pp 409–412, 450, 451, 1224–1227.
* [[Alexander Graham Bell|Bell, Alexander Graham]]. "Le Photophone De La Production Et De La Lumiere". Gauthier-Villars, Imprimeur-Libraire, Paris. 1880. <small>(Note: this is item #26, Folder #4, as noted in "Finding Aid for the Alexander Graham Bell Collection, 1880–1925", Collection number: 308, [[UCLA]] Library, Department of Special Collections Manuscripts Division, as viewable at the [http://oac.cdlib.org/findaid/ark:/13030/kt8c6008r5 Online Archive of California])</small>
* "Bell's Photophone". Nature Vol 24, 4 November 1880; The Electrician, Vol. 6, 1881, pp.&nbsp;136–138.
* Appleton's Journal. "The Photophone". Appleton's Journal, Vol. 10 No. 56, New York, February 1881, pp.&nbsp;181–182.
* Bidwell, Shelford. "The Photophone". Nature., 23. 1881, pp.&nbsp;58–59.
* Bidwell, Shelford. "Selenium and Its Applications to the Photophone and Telephotography". Proceedings of the Royal Institution (G.B.), Vol 9. 1881, pp.&nbsp;524–535; The English Mechanic and World Of Science, Vol. 33, 22 April 1881, pp.&nbsp;158–159 and 29 April 1881 pp.&nbsp;180–181. Also in Chem. News, Vol. 44, 1881, pp.&nbsp;1–3, 18–21. (From a lecture at the Royal Institution on 11 March 1881).
* Breguet, A. "Les recepteurs photophoniques de selenium". Ann. Chim. Phys., Series 5. Vol 21. 1880, pp.&nbsp;560–563.
* Breguet, A. "Sur les experiences photophonique du Professeur Alexander Graham Bell et de M. Sumner Tainter": C.R.; Vol 91., 1880, pp 595–598.
* Electrician. "Bell's Photophone", Electrician, Vol. 6, February 5, 1881, pp.&nbsp;136–138,183.
* Jamieson, Andrew. Nat. L., Vol. 10, 1881, p.&nbsp;11. This Glasgow scientist seems to have been the first to suggest the usage of a manometric gas flame for optical transmission, demonstrated at a meeting of the Glasgow Philosophical Society; "The History of selenium and its action in the Bell Photophone, with description of recently designed form", Proceedings of the Philosophical Society of Glasgow No. 13, 1881, ***Moser, J. "The Microphonic Action of Selenium Cells". Phys. Soc., Proc., Vol. 4, 1881, pp.&nbsp;348–360. Also in Phil. Mag., Series 5, Vol.12, 1881, pp.&nbsp;212–223.
* Kalischer, S. "Photophon Ohne Batterie". Rep. f. Phys., Vol. 17., 1881, pp.&nbsp;563–570.
* [[Catherine MacKenzie|MacKenzie, Catherine]] "Alexander Graham Bell", Houghton Mifflin Company, Boston, p.&nbsp;226, 1928.
* Mercadier, E. "La radiophonie indirecte". Lumiere Electrique, Vol. 4, 1881, pp.&nbsp;295–299.
* Mercadier, E. "Sur la radiophonie produite a l'aide du selenium". C. R., Vol. 92,1881, pp.&nbsp;705–707.
* Mercadier, E. "Sur la construction de recepteurs photophoniques a selenium". C. R., Vol. 92, 1881, pp.&nbsp;789–790.
* Mercadier, E. "Sur l'influence de la temperature sur les recepteurs radiophoniques a selenium". C. R., Vol. 92, 1881, pp.&nbsp;1407–1408.
* Molera & Cebrian. "The Photophone". Eng. L., Vol. 31, 1881, p.&nbsp;358.
* Preece, Sir William H. "Radiophony", Engineering Vol. 32, 8 July 1881, pp.&nbsp;29–33; ''Journal of the Society of Telegraph Engineers'', Vol 10, 1881, pp.&nbsp;212–228. On the photophone.
* Rankine, A.O. "Talking over a Sunbeam". El. Exp. (N. Y.), Vol. 7, 1920, pp.&nbsp;1265–1316.
* Sternberg, J.M. [https://memory.loc.gov/cgi-bin/query/P?magbell:1:./temp/~ammem_3ShO::@@@mdb=mcc,gottscho,detr,nfor,wpa,aap,cwar,bbpix,cowellbib,calbkbib,consrvbib,bdsbib,dag,fsaall,gmd,pan,vv,presp,varstg,suffrg,nawbib,horyd,wtc,toddbib,mgw,ncr,ngp,musdibib,hlaw,papr,lhbumbib,rbpebib,lbcoll,alad,hh,aaodyssey,magbell,bbc,dcm,raelbib,runyon,dukesm,lomaxbib,mtj,gottlieb,aep,qlt,coolbib,fpnas,aasm,denn,relpet,amss,aaeo,mff,afc911bib,mjm,mnwp,rbcmillerbib,molden,ww2map,mfdipbib,afcnyebib,klpmap,hawp,omhbib,rbaapcbib,mal,ncpsbib,ncpm,lhbprbib,ftvbib,afcreed,aipn,cwband,flwpabib,wpapos,cmns,psbib,pin,coplandbib,cola,tccc,curt,mharendt,lhbcbbib,eaa,haybib,mesnbib,fine,cwnyhs,svybib,mmorse,afcwwgbib,mymhiwebib,uncall,afcwip,mtaft,manz,llstbib,fawbib,berl,fmuever,cdn,upboverbib,mussm,cic,afcpearl,awh,awhbib,sgp,wright,lhbtnbib,afcesnbib,hurstonbib,mreynoldsbib,spaldingbib,sgproto,scsmbib,afccalbib,mamcol The Volta Prize of the French Academy Awarded to Prof. Alexander Graham Bell: A Talk With Dr. J.M. Sternberg], The Evening Traveler, September 1, 1880, The Alexander Graham Bell Papers at the [[Library of Congress]]
* Thompson, Silvanus P. "Notes on the Construction of the Photophone". Phys. Soc.Proc., Vol. 4, 1881, pp.&nbsp;184–190. Also in Phil. Mag., Vol. 11, 1881, pp.&nbsp;286–291. Abstracted in Chem. News, Vol. 43, 1881, p.&nbsp;43; Eng. L., Vol. 31, 1881, p.&nbsp;96.
* Tomlinson, H. "The Photophone". Nat. L., Vol. 23, 1881, pp.&nbsp;457–458.
* U.S. Radio and Television Corp. "Ultra-violet rays used in Television", New York Times, 29 May 1929, p.&nbsp;5: Demonstration of transmission of a low definition (mechanically scanned) video signal over a modulated light beam. Terminal stations 50 feet apart. Public demonstration at Bamberger and Company's Store, Newark, New Jersey. Earliest known usage of modulated light comms for conveying video signals. See also report "Invisible Ray Transmits Pictures" in Science and Invention, November 1929, Vol. 17, p.&nbsp;629.
* White, R.H. "Photophone". Harmsworth's Wireless Encyclopaedia, Vol. 3, pp.&nbsp;1541–1544.
* Weinhold, A. "Herstellung von Selenwiderstanden fur Photophonzwecke". E.T.Z., Vol. 1, 1880, p.&nbsp;423.

==External links==
{{Wiktionary}}
* [https://www.histv.net/bell-production-of-sound-by-light Bell's speech] before the [[American Association for the Advancement of Science]] in [[Boston]] on August 27, 1880, in which he presented his paper'' "On the Production and Reproduction of Sound by Light: the Photophone"''.
* [https://www.modulatedlight.org/Modulated_Light_DX/ModLightBiblio.html Long-distance Atmospheric Optical Communications, by Chris Long and Mike Groth (VK7MJ)]
* [https://www.histv.net/graham-bell-contribution-indirecte Téléphone et photophone: les contributions indirectes de Graham Bell à l'idée de la vision à distance par l'électricité (1880–1895] {{in lang|fr}}

{{Alexander Graham Bell}}
{{Optical telecommunication}}
{{Telephony}}
{{Telecommunications}}

[[Category:Alexander Graham Bell]]
[[Category:History of telecommunications]]
[[Category:History of the telephone]]
[[Category:Optical communications]]
[[Category:Photonics]]