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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 13 in its ultimate electronic form the photophone receiver used a photoresistor based on a selenium cell at the focus of a parabolic mirror 5 the cell s electrical resistance was higher when dimly lit and lower when brightly lit thus the photoresistor modulated the current flowing through an earphone and thereby converted light into sound 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 5 14 because the device used radiant energy the french scientist 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 band 15 bell used the name for a while but it should not be confused with the later invention radiophone which used radio waves 16 first successful wireless voice communications edit illustration of a photophone transmitter showing the path of reflected sunlight before and after being modulated 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 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 17 as bell s former associate 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 u s 1874 transit of venus commission for his new l street laboratory in washington at the rate of 15 per week 18 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 19 in an april 1 1880 washington d c experiment bell and tainter communicated some 79 metres 259 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 ft using plain sunlight as their light source practical electrical lighting having only just been introduced to the u s by 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 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 6 the receiver was a parabolic mirror with selenium cells at its focal point 5 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 system citation needed 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 20 reception and adoption edit 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 21 22 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 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 bell they instead chose marian with daisy as her nickname 23 he wrote somewhat enthusiastically 4 24 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 american bell telephone company in may 1880 25 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 26 his design failed to protect its transmissions from outdoor interferences such as clouds fog rain snow and such that could easily disrupt the transmission of light 27 factors such as the weather and the lack of light inhibited the use of bell s invention 28 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 lines 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 spectral analysis of artificial light sources stars and sunspots he later also speculated on its possible future applications though he did not anticipate either the laser or fiber optic telecommunications 24 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 edit ernst ruhmer at his photo electric optical telephone system station 1905 29 although bell telephone researchers made several modest incremental improvements on bell and tainter s design marconi s radio transmissions started to far surpass the maximum range of the photophone as early as 1897 8 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 river and on lake wannsee from 1901 to 1902 he reported achieving sending distances under good conditions of 15 kilometers 9 miles 30 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 31 the german siemens halske company boosted the photophone s range by utilizing current modulated carbon arc lamps which provided a useful range of approximately 8 kilometres 5 0 mi they produced units commercially for the german navy which were further adapted to increase their range to 11 kilometres 6 8 mi using voice modulated ship searchlights 5 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 infrared radiation replaced the older selenium cells in 1917 5 the united states and german governments also worked on technical improvements to bell s system 32 by 1935 the german carl zeiss company had started producing infrared photophones for the german army s tank battalions employing tungsten lamps with infrared 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 14 kilometres 8 7 mi under optimal conditions the japanese and italian armies also attempted similar development of lightwave telecommunications before 1945 5 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 5 commemorations edit 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 marker on the franklin school commemorating the first formal trial on march 3 1947 the centenary of alexander graham bell s birth the telephone pioneers of america dedicated a historical marker on the side of one of the buildings the franklin school which bell and 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 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 in washington d c for a commemoration of the event 11 33 the photophone centenary commemoration had first been proposed by electronics researcher and writer 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 20 note 1 mims also built and provided a pair of modern hand held battery powered led transceivers connected by 100 yards 91 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 34 see also edit 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 references edit footnotes 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 citations bruce 1990 pg 336 jones newell first radio built by san diego resident partner of inventor of telephone keeps notebook of experiences with bell archived 2002 02 19 at the wayback machine san diego evening tribune july 31 1937 retrieved from the university of san diego history department website november 26 2009 bruce 1990 pg 338 1 2 carson 2007 pg 76 78 1 2 3 4 5 6 7 8 9 groth mike photophones revisted amateur radio magazine wireless institute of australia melbourne april 1987 pp 12 17 and may 1987 pp 13 17 1 2 mims 1982 p 11 phillipson donald j c and neilson laura bell alexander graham the canadian encyclopedia online retrieved 2009 08 06 1 2 mims 1982 p 14 morgan tim j the fiber optic backbone university of north texas 2011 miller stewart e lightwaves and telecommunication american scientist sigma xi the scientific research society january february 1984 vol 72 no 1 pp 66 71 issue stable url 1 2 gallardo arturo mims iii forrest m fiber optic communication began 130 years ago san antonio express news june 21 2010 accessed january 1 2013 clark j 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 bell alexander graham 28 may 1881 the production of sound by radiant energy science 2 48 242 253 doi 10 1126 science os 2 49 242 jstor 2900190 pmid 17741736 retrieved 11 oct 2022 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 grosvenor and wesson 19...
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