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{{short description|Communication device reflecting sunlight}}
{{about|the signalling device}}
[[File:Heliograph-2.jpg|thumb|right|Fig. 1: Signaling with a Mance heliograph, Alaska-Canada border, 1910.]]

A '''heliograph''' ({{etymology|grc|''{{wikt-lang|grc|ἥλιος}}'' ([[helios|{{grc-transl|ἥλιος}}]])|sun||''{{wikt-lang|grc|γράφειν}}'' ([[wikt:-graph|{{grc-transl|γράφειν}}]])|to write}}) is a solar telegraph<ref>{{cite book |last1=Bouchet |first1=Olivier |title=Wireless Optical Communications |date=2013 |publisher=John Wiley & Sons |isbn=9781118563274 |url=https://books.google.com/books?id=HBFSt4O64VgC&dq=heliograph&pg=PT40}}</ref> system that signals by flashes of [[sunlight]] (generally using [[Morse code]]) reflected by a [[mirror]]. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter.<ref name=Woods2008/> The heliograph was a simple but effective instrument for instantaneous [[optical communication]] over long distances during the late 19th and early 20th centuries.<ref name=Woods2008/> Its main uses were military, [[Surveying|survey]] and [[forest protection]] work. Heliographs were standard issue in the British and Australian armies until the 1960s, and were used by the Pakistani army as late as 1975.<ref name="Boer"/>

==Description==
[[Image:Heliograph (1)-2.jpg|thumb|Fig. 2: German heliograph made by R. Fuess in Berlin (on display at the Museum of Communication in Frankfurt)]]
There were many heliograph types. Most heliographs were variants of the British Army Mance Mark V version (Fig.1). It used a mirror with a small unsilvered spot in the centre. The sender aligned the heliograph to the target by looking at the reflected target in the mirror and moving their head until the target was hidden by the unsilvered spot. Keeping their head still, they then adjusted the aiming rod so its cross wires bisected the target.<ref name=Manual1922>{{cite book|title=Signal Training|volume=III. Pamphlet No. 2. Heliograph, 5-inch, Mark V. 1922.|year=1922|publisher=His Majesty's Stationery Office|location=London|pages=10–13|url=http://www.royalsignals.org.uk/signals.htm}}</ref> They then turned up the sighting vane, which covered the cross wires with a diagram of a cross, and aligned the mirror with the tangent and elevation screws so the small shadow that was the reflection of the unsilvered spot hole was on the cross target.<ref name=Manual1922 /> This indicated that the sunbeam was pointing at the target.
The flashes were produced by a keying mechanism that tilted the mirror up a few degrees at the push of a lever at the back of the instrument. If the Sun was in front of the sender, its rays were reflected directly from this mirror to the receiving station. If the Sun was behind the sender, the sighting rod was replaced by a second mirror, to capture the sunlight from the main mirror and reflect it to the receiving station.<ref name="Forestry"/><ref name="British">[http://www.smecc.org/heliograph_-_signaling_by_the_sun.htm Manual Of Instruction In Army Signaling 1886 Section III- Apparatus And Method Of Using It]. Retrieved on 1 June 2008. Diagrams and instructions for British military heliograph (note British heraldry on cover).</ref> The [[United States Army Signal Corps|U. S. Signal Corps]] heliograph mirror did not tilt. This type produced flashes by a [[Shutter (photography)|shutter]] mounted on a second tripod (Fig 4).<ref name="Forestry">W. N. Millar (1920), Canadian Forestry Service. [https://books.google.com/books?id=CI5OAAAAMAAJ Methods of Communication Adapted to Forest Protection] Google Books. Retrieved on 1 June 2008. pp. 160-181 are devoted to the heliograph, with diagrams of the British, American, and Godwin type.</ref>

The heliograph had certain advantages. It allowed long distance communication without a fixed infrastructure, though it could also be linked to make a fixed network extending for hundreds of miles, as in the fort-to-fort network used for the [[Geronimo]] campaign. It was very portable, did not require any power source, and was relatively secure since it was invisible to those not near the axis of operation, and the beam was very narrow, spreading only 50 feet per mile of range. However, anyone in the beam with the correct knowledge could intercept signals without being detected.<ref name="Boer"/><ref name="Kipling">Kipling, Rudyard [http://www.kipling.org.uk/poems_codeofmorals.htm A Code of Morals]. The Kipling Society website. Retrieved on 1 June 2008.</ref> In the [[Second Boer War|Boer War]], where both sides used heliographs, tubes were sometimes used to decrease the dispersion of the beam.<ref name="Boer">Major J. D. Harris [http://rapidttp.com/milhist/vol111jh.html WIRE AT WAR - Signals communication in the South African War 1899–1902]. Retrieved on 1 June 2008. Discussion of heliograph use in the Boer War.</ref> In some other circumstances, though, a narrow beam made it difficult to stay aligned with a moving target, as when communicating from shore to a moving ship, so the British issued a dispersing lens to broaden the heliograph beam from its natural diameter of 0.5 degrees to 15 degrees.<ref name=1905Handbook>{{cite web|last=Signals|first=Royal|title=The Heliograph|url=http://royal-signals.org.uk/Datasheets/THE_HELIOGRAPH.php|work=Signalling Handbook (1905)|access-date=15 April 2012}}</ref>

The range of a heliograph depends on the opacity of the air and the effective collecting area of the mirrors. Heliograph mirrors ranged from {{convert|1.5|in|cm|spell=in}} to {{convert|12|in|cm}} or more. Stations at higher altitudes benefit from thinner, clearer air, and are required in any event for great ranges, to clear the [[curvature of the Earth]]. A good approximation for ranges of {{convert|20|to|50|mi|km}} is that the flash of a circular mirror is visible to the naked eye at a distance of {{convert|10|mi|km}} for each inch of mirror diameter,<ref name="Jacob1849">{{cite journal |last1=Jacob |first1=W.S. |title=On the Extinction of Light in the Atmosphere |journal=Proceedings of the Royal Society of Edinburgh |date=November 1849 |volume=2 |pages=272–273 |url=https://books.google.com/books?id=OgsFAAAAQAAJ&pg=PA272 |access-date=19 May 2019}}</ref> and farther with a [[telescope]]. The world record distance was established by a detachment of U.S. signal sergeants by the inter-operation of stations on [[Mount Ellen (Utah)|Mount Ellen]], [[Utah]], and [[Uncompahgre Peak|Mount Uncompahgre]], [[Colorado]], {{convert|183|mi|km}} apart on September 17, 1894, with Signal Corps heliographs carrying mirrors only 8 inches square.<ref name="Coe">Coe, Lewis [https://books.google.com/books?id=pzkZPIXm89UC The Telegraph: A History of Morse's Invention and Its Predecessors in the United States]. Google Books. Retrieved on 1 June 2008.</ref>

==History==
[[File:Turkish heliograph at Huj2.jpg|thumb|Fig. 3 [[Ottoman Empire|Ottoman]] heliograph crew at [[Huj, Gaza|Huj]] during World War I, 1917]]
[[File:Ruinen aus der Schutztruppen-Zeit Dicker Wilhelm.jpg|thumb|Ruins of German Schutztruppe on top of [[Dikwillem]], where the Germans used to have a Heliographic Station (Bird's eye view 2017)]]
The German professor [[Carl Friedrich Gauss]] of the [[University of Göttingen]] developed and used a predecessor of the heliograph (the [[heliotrope (instrument)|heliotrope]]) in 1821.<ref name=Woods2008/><ref name=GaussTitan>{{cite book|last=Dunnington|first=G. Waldo|title=Carl Friedrich Gauss: Titan of Science|year=2004|publisher=The Mathematical Association of America|location=New York|isbn=0-88385-547-X|pages=122–127|url=https://books.google.com/books?id=_dce9Jaq7iQC&q=heliotrope&pg=PA123}}</ref> His device directed a controlled beam of sunlight to a distant station to be used as a marker for [[geodetic survey]] work, and was suggested as a means of telegraphic communications.<ref>{{cite journal|title=The Heliotrope|journal=The Manchester Iris|date=September 7, 1822|volume=1|issue=32|pages=255–256|url=https://books.google.com/books?id=PDIFAAAAQAAJ&q=heliotrope&pg=PA255|access-date=18 November 2012}}</ref> This is the first reliably documented heliographic device,<ref>{{cite book|last=Holzmann|first=Gerard|title=The early history of data networks|publisher=IEEE Computer Society Press|year=1995|isbn=0818667826|url=https://archive.org/details/earlyhistoryofda0000holz|url-access=registration|editor=Björn Pehrson|access-date=18 November 2012|page=[https://archive.org/details/earlyhistoryofda0000holz/page/10 10]}}</ref> despite much speculation about possible ancient incidents of sun-flash signalling, and the documented existence of other forms of [[Optical telegraphy#History|ancient optical telegraphy]].

For example, one author in 1919 chose to "hazard the theory"<ref name=Kingman>{{cite news|last=Kingman|first=John|title=The Isle of Capri: An Imperial Residence and Probable Wireless Station of Ancient Rome|url=https://books.google.com/books?id=MXJIAAAAYAAJ&q=hazard&pg=PA224|access-date=18 November 2012|newspaper=The National Geographic Magazine|page=224|date=September 1919}}</ref> that the mainland signals Roman emperor [[Tiberius]] watched for from [[Capri]]<ref>{{cite book|last=Suetonius|title=The Lives of the First Twelve Caesars|year=1796|publisher=G.G. and J. Robinson, Paternoster-Row|pages=296|url=https://books.google.com/books?id=Ib0_AAAAYAAJ&q=signals&pg=PA296}}</ref> were mirror flashes, but admitted "there are no references in ancient writings to the use of signaling by mirrors", and that the documented means of ancient long-range visual telecommunications was by beacon fires and beacon smoke, not mirrors.

Similarly, the story that a shield was used as a heliograph at the [[Battle of Marathon]] is a modern myth,<ref>{{cite book|last=Krentz|first=Peter|title=The Battle of Marathon|year=2010|publisher=Yale University|isbn=978-0300120851|pages=160|url=https://books.google.com/books?id=ncT8JFn-ed8C&q=modern+myth&pg=PT160}}</ref> originating in the 1800s. [[Herodotus]] never mentioned any flash.<ref>{{cite book|last=Sekunda|first=Nicholas|title=Marathon 490 BC: The First Persian Invasion Of Greece|year=2002|publisher=Osprey Publishing|isbn=1841760005|pages=73|url=https://books.google.com/books?id=pDACy7M7NHoC&q=not+flashed&pg=PA73}}</ref> What Herodotus did write was that someone was accused of having arranged to "hold up a shield as a signal".<ref>{{cite book|last=Herodotus|title=Herodotus, The Histories, with an English translation by A. D. Godley|year=1920|publisher=Harvard University Press|chapter-url=https://www.perseus.tufts.edu/hopper/text?doc=hdt.+6.115.1|chapter=6.115.1, 6.121.1, 6.123.1,6.124,2}}</ref> Suspicion grew in the 1900s that the flash theory was implausible.<ref name="http://www.jstor.org/stable/625005">{{cite journal|last=Reynolds|first=P. K. Baillie|title=The Shield Signal at the Battle of Marathon|journal=The Journal of Hellenic Studies|year=1929|volume=49|issue=Part I|pages=100–105|jstor=625005|doi=10.2307/625005|s2cid=161466426 }}</ref> The conclusion after testing the theory was "Nobody flashed a shield at the Battle of Marathon".<ref>{{cite journal|last=Hodge|first=A. Trevor|title=Reflections on the Shield at Marathon|journal=The Annual of the British School at Athens|year=2001|volume=96|pages=237–259|jstor=30073279|doi=10.1017/s0068245400005281|s2cid=128558448}}</ref>

In a letter dated 3 June 1778, [[John Norris (1721–1786)|John Norris]], High Sheriff of Buckinghamshire, England, notes: "Did this day heliograph intelligence from Dr [Benjamin] Franklin in Paris to Wycombe".<ref>Deacon, Richard (1978). The Silent War: a History of Western Naval Intelligence. David & Charles. p. 21. {{ISBN|978-0715375570}}.</ref> However, there is little evidence that "heliograph" here is other than a misspelling of "[[holograph]]". The term "heliograph" for solar telegraphy did not enter the English language until the 1870s—even the word "[[telegraphy]]" was not coined until the 1790s.

[[Henry Christopher Mance]] (1840–1926), of the British Government Persian Gulf Telegraph Department, developed the first widely accepted heliograph about 1869<ref name=Woods2008/><ref name=1872Mance>{{cite journal|last=Mance|first=Henry|title=The Heliograph or Sun Telegraph|journal=United Service Institution of India|date=10 February 1872|volume=1|issue=5|pages=123–130|hdl=2027/mdp.39015035103855?urlappend=%3Bseq=665|url=http://hdl.handle.net/2027/mdp.39015035103855?urlappend=%3Bseq=665|access-date=16 June 2013}}</ref><ref name=18750614JRUSI>{{cite journal|last=Goode|first=Samuel|title=Mance's Heliograph, or Sun-Telegraph|journal=Journal of the Royal United Service Institution|date=June 14, 1875|volume=XIX|issue=LXXXIII|pages=534–548|url=https://books.google.com/books?id=sA5KDfwzI3MC&pg=PA533|access-date=2011-06-21|doi=10.1080/03071847509415772}}</ref> while stationed at [[Karachi]], in the [[Bombay Presidency]] in [[British India]]. Mance was familiar with heliotropes by their use for the [[Great Trigonometrical Survey]] of India.<ref name="Coe"/> The Mance Heliograph was operated easily by one man, and since it weighed about seven pounds, the operator could readily carry the device and its tripod. The British Army tested the heliograph in India at a range of 35 miles with favorable results.<ref name=1872Luck>{{cite journal|last=Luck|first=George|title=Army Signalling, Heliograph|journal=United Service Institution of India|date=1872-05-24|volume=2|issue=7|pages=101–105|hdl=2027/mdp.39015035103855?urlappend=%3Bseq=801|url=http://hdl.handle.net/2027/mdp.39015035103855?urlappend=%3Bseq=801}}</ref> During the [[Jowaki_Expedition|Jowaki Afridi expedition]] sent by the British-Indian government in 1877, the heliograph was first tested in war.<ref name=18800315JRUSI>{{cite journal|last=Wynne|first=Major A.S.|title=Heliography and Army Signalling Generally|journal=Journal of the Royal United Service Institution|date=March 15, 1880|volume=XXIV|issue=CV|pages=235–258|url=https://books.google.com/books?id=nAwmAQAAIAAJ&pg=235|access-date=June 21, 2011|doi=10.1080/03071848009417153}}</ref><ref name="Burns">R. W. Burns (2004) [https://books.google.com/books?id=Fm6S-CKB630C ''Communications: An International History of the Formative Years'']. Google Books. Retrieved on 2 June 2008. pp. 192-196 discuss the heliograph.</ref>

[[Image:AmericanHelio1898Engraving.jpg|thumb|Fig. 4: [[Signal Corps (United States Army)|US Signal Service]] heliograph, 1898]]
The simple and effective instrument that Mance invented was to be an important part of military communications for more than 60 years. The usefulness of heliographs was limited to daytimes with strong sunlight, but they were the most powerful type of visual signalling device known. In pre-radio times heliography was often the only means of communication that could span ranges of as much as 100 miles with a lightweight portable instrument.<ref name="Coe"/>

In the United States military, by mid-1878, Colonel [[Nelson A. Miles]] had established a line of heliographs connecting Fort Keogh and Fort Custer, Montana, a distance of {{convert|140|mi|km}}.<ref name="Steinbach1989">{{cite book |last1=Steinbach |first1=Robert |title=The Lives of Frank and Alice Baldwin |date=1989 |publisher=University of Texas Press |location=Austin |isbn=0-292-74659-8 |page=[https://archive.org/details/lonestarslegacyo00bres/page/136 136] |edition=1 |url=https://archive.org/details/lonestarslegacyo00bres/page/136 }}</ref><ref name=188001UnS>{{cite journal|last=Reade|first=Lt. Philip|title=About Heliographs|journal=The United Service|date=January 1880|volume=2|pages=91–108|url=https://books.google.com/books?id=nLCgAAAAMAAJ&pg=PA91|access-date=June 21, 2011}}</ref><ref>{{cite journal |title=The Pacific Slope |journal=Daily Alta California |date=20 September 1884 |volume=37 |issue=12578 |page=5 |url=https://cdnc.ucr.edu/cgi-bin/cdnc?a=d&cl=search&d=DAC18840920.2.58&%2520srpos=1&e=------188-en--20--1--txt-IN-heliograph----1884}}</ref> In 1886, General Nelson A. Miles set up a network of 27 heliograph stations in Arizona and New Mexico during the hunt for [[Geronimo]].<ref name="Rolak2013">{{cite web |last1=Rolak |first1=Bruno |title=General Miles' Mirrors The Heliograph in the Geromino Campaign of 1886 |url=http://huachuca-www.army.mil/pages/history/Rolak.html |website=Fort Huachuca |access-date=19 August 2018 |archive-url=https://web.archive.org/web/20130217145032/http://huachuca-www.army.mil/pages/history/Rolak.html |url-status=dead |archive-date=17 February 2013}}</ref> In 1890, Major W. J. Volkmar of the US Army demonstrated in [[Arizona]] and [[New Mexico]] the possibility of performing communication by heliograph over a heliograph network aggregating 2,000 miles in length.<ref name=1899Ainslees>{{cite journal|last1=Greely |first1=Adolphus |title=The Evolution of the Signal Corps |journal=Ainslee's Magazine |date=August 1899 |volume=IV |issue=1 |page=17 |url=https://books.google.com/books?id=q4sXAQAAMAAJ&q=volkmar&pg=PA17 |access-date=31 March 2017 }}</ref> The network of communication begun by General Miles in 1886, and continued by Lieutenant W. A. Glassford, was perfected in 1889 at ranges of 85, 88, 95, and 125 miles over a rugged and broken country, which was the stronghold of the [[Apache]] and other hostile Indian tribes.<ref name="Coe"/>

By 1887, heliographs in use included not only the British Mance and Begbie heliographs, but also the American Grugan, Garner and Pursell heliographs. The Grugan and Pursell heliographs used shutters, and the others used movable mirrors operated by a finger key. The Mance, Grugan and Pursell heliographs used two tripods, and the others one. The signals could either be momentary flashes, or momentary obscurations.<ref name="Finley">{{citation | publisher = The American Helio-Telegraph and Signal Light Company | year = 1887 | url = https://books.google.com/books?id=Mc90ZgreC8QC | title = An Improved Method in the Art of Signalling for Military and Scientific Purposes | access-date = 1 June 2008}}.</ref> In 1888, the US Signal Service reviewed all of these devices, as well as the Finley Helio-Telegraph,<ref name="Finley"/> and finding none completely suitable, developed the US Signal Service heliograph, a two-tripod, shutter-based machine of {{convert|13+7/8|lb|kg}}. total weight, and ordered 100 for a total cost of $4,205.<ref name= "Signal">{{citation | url = https://books.google.com/books?id=88ctAAAAIAAJ | title = Annual Report of the Chief Signal Officer of the Army to the Secretary of War | year = 1889 | access-date = 3 June 2008 | pages= 43–7}}.</ref> In 1893, the number of heliographs manufactured for the US Signal Service was 133.<ref>{{cite book|title=Report of the Chief Signal Officer|year=1893|publisher=U.S. G.P.O.|pages=671|url=https://books.google.com/books?id=aypHAQAAIAAJ&pg=PA671}}</ref>

The heyday of the heliograph was probably the [[Second Boer War]] in South Africa, where it was much used by both the British and the Boers.<ref name=Woods2008/><ref name="Boer" /> The terrain and climate, as well as the nature of the campaign, made heliography a logical choice. For night communications, the British used some large [[Aldis lamp]]s, brought inland on railroad cars, and equipped with leaf-type shutters for keying a beam of light into dots and dashes. During the early stages of the war, the British garrisons were besieged in [[Kimberley, Northern Cape|Kimberley]], [[Siege of Ladysmith|Ladysmith]], and [[Siege of Mafeking|Mafeking]]. With land [[telegraph]] lines cut, the only contact with the outside world was via light-beam communication, helio by day, and Aldis lamps at night.<ref name="Coe"/>

In 1909, the use of heliography for forestry protection was introduced in the United States. By 1920 such use was widespread in the US and beginning in Canada, and the heliograph was regarded as "next to the telephone, the most useful communication device that is at present available for forest-protection services".<ref name="Forestry"/> D.P. Godwin of the US Forestry Service invented a very portable (4.5 lb) heliograph of the single-tripod, shutter plus mirror type for forestry use.<ref name="Forestry"/>

Immediately prior to the outbreak of World War I, the cavalry regiments of the Russian Imperial Army were still being trained in heliograph communications to augment the efficiency of their scouting and reporting roles.<ref>{{cite book|first=Vladimir|last=Littauer|page=123|title=Russian Hussar|isbn=978-1-59048-256-8|date=May 2007}}</ref> The [[Red Army]] during the Russian Civil War made use of a series of heliograph stations to disseminate intelligence efficiently about [[basmachi]] rebel movements in [[Turkestan]] in 1926.<ref name="Red">{{citation | url = https://books.google.com/books?id=qKnZtNHJrVAC | title = Central Asia: Aspects of Transition | first = Tom | last = Everett-Heath | access-date = 3 June 2008 | page = 20| isbn = 9780700709564 | year = 2003 }}.</ref>
[[File:1940 06 17 Heliograph Helwan Egypt.jpg|thumb|right|British troops training with a heliograph, Egypt, June 1940]]
During World War II, South African and Australian forces used the heliograph while fighting German forces in Libya and Egypt in 1941 and 1942.<ref name=Woods2008/>

The heliograph remained standard equipment for military [[signaller]]s in the Australian and [[British army|British armies]] until the 1940s, where it was considered a "low probability of intercept" type of communication. The [[Canadian Army]] was the last major army to have the heliograph as an issue item. By the time the mirror instruments were retired, they were seldom used for signalling.<ref name= "Coe" /> However, as recently as the 1980s, heliographs were used by [[Afghanistan|Afghan]] forces during the [[Soviet invasion of Afghanistan]].<ref name=Woods2008>{{cite book|last=Woods|first=Daniel|title=Military Communications: From Ancient Times to the 21st Century|year=2008|publisher=ABC-CLIO|isbn=978-1851097326|page=208|chapter-url=https://books.google.com/books?id=RBC2nY1rp5MC&q=heliograph&pg=PA211|chapter=Heliograph and Mirrors|editor=Sterling, Christopher}}</ref> Signal mirrors are still included in [[survival kit]]s for emergency signaling to [[search and rescue]] aircraft.<ref name=Woods2008/>

==Automated heliographs==

Most heliographs of the 19th and 20th century were completely manual.<ref name="Forestry"/> The steps of aligning the heliograph on the target, co-aligning the reflected sunbeam with the heliograph, maintaining the sunbeam alignment as the sun moved, transcribing the message into flashes, modulating the sunbeam into those flashes, detecting the flashes at the receiving end, and transcribing the flashes into the message, were all done manually.<ref name="Forestry"/> One notable exception – many French heliographs used clockwork heliostats to automatically steer out the sun's motion. By 1884, all active units of the "Mangin apparatus" (a dual-mode French military field optical telegraph that could use either lantern or sunlight) were equipped with clockwork heliostats.<ref name=Ternant1884>{{cite book|last1=Ternant|first1=A.-L.|title=Les télégraphes|date=1884|publisher=Hachette|pages=35–65|edition=2nd|url=https://books.google.com/books?id=6wozAQAAMAAJ&q=horlogerie&pg=PA41}}</ref> The Mangin apparatus with heliostat was still in service in 1917.<ref name=Vauzelle1912>{{cite book|last1=Charles-La Vauzelle|first1=Henri|title=Instruction Pratique Sur L'Installation des Communications Optiques dans le Service De la Telegraphie Militaire: Premiere Partie, Communications Optiques de Campagne|date=1912|pages=30–32, 42–43}}</ref><ref name=Bouchethal1916>{{cite journal|last1=BOUCHETHAL|first1=J.L.|title=LA TÉLÉGRAPHIE OPTIQUE AUX ARMÉES|journal=La Science et la Vie|date=1916|issue=28|pages=337–342|url=http://gallica.bnf.fr/ark:/12148/bpt6k65514029/f351.image.langEN}}</ref><ref>{{cite web|title=Ottoman Soldiers Mounting Signal Apparatus, 1917|url=https://www.flickr.com/photos/39206470@N08/14525840798/|website=Flickr|publisher=Ottoman Imperial Archives|access-date=7 September 2015}}</ref> Proposals to automate both the modulation of the sunbeam (by clockwork) and the detection (by electrical selenium photodetectors, or photographic means) date back to at least 1882.<ref name=Engr1882>{{cite journal|title=The Heliograph in Mauritius|journal=Engineering|date=October 13, 1882|volume=34|page=363|url=https://books.google.com/books?id=_5dDAQAAIAAJ&q=mangin+heliograph&pg=PA363}}</ref> In 1961, the US Air Force was working on a space heliograph to signal between satellites<ref name=SciMech1961>{{cite journal|last1=Pursglove |first1=S. David |title=Ancient Heliograph Goes Modern for Space Age |journal=Science and Mechanics |date=1961 |page=70 |url=http://myweb.cableone.net/kd7aoi/spacehg.htm |url-status=dead |archive-url=https://web.archive.org/web/20110525175319/http://myweb.cableone.net/kd7aoi/spacehg.htm |archive-date=May 25, 2011 }}</ref>

In May 2012, "Solar Beacon" robotic mirrors designed at UC Berkeley were mounted on the towers of the Golden Gate bridge, and a web site set up<ref name=SolarBeacon052012>{{cite web|title=Solar Beacon |url=http://solarbeacon.org/? |access-date=30 May 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120530061034/http://solarbeacon.org/ |archive-date=30 May 2012 }}</ref> where the public could schedule times for the mirrors to signal with sun-flashes, entering the time and their latitude, longitude and altitude.<ref name=LATimes2012>{{cite web|last1=Boxall|first1=Bettina|title=Golden Gate Bridge is prepared for 75th birthday celebration|url=http://latimesblogs.latimes.com/lanow/2012/05/golden-gate-bridge-prepares-for-special-75th-birthday-celebration.html|website=LA Now|publisher=Los Angeles Times}}</ref> The solar beacons were later moved to Sather Tower at UC Berkeley.<ref name=DC2013>{{cite news|last1=Tuan|first1=Lydia|title=Solar Beacon atop Campanile allows for safe observation of sunlight|url=http://www.dailycal.org/2013/09/10/solar-beacon-atop-campanile-allows-for-safe-observation-of-sunlight/|work=The Daily Californian|date=10 September 2013}}</ref><ref name=SolarBeacon2015>{{cite web|title=Solar Beacon|url=http://solarbeacon.org/|access-date=7 September 2015}}</ref> By June 2012, the public could specify a "custom show" of up to 32 "on" or "off" periods of 4 seconds each, permitting the transmission of a few characters of Morse Code.<ref name=Sbeacon2012>{{cite web|last1=Vallerga|first1=John|title=Custom Show Setting|url=http://solarbeacon.org/?page_id=156#comment-82|website=Solar Beacon|access-date=28 June 2012}}</ref> The designer described the Solar Beacon as a "heliostat", not a "heliograph".<ref name="LATimes2012" />

The first digitally controlled heliograph was designed and built in 2015.<ref name=islandpacificacademy>{{cite web|title=IPA Freshman's science fair project|url=https://islandpacificacademy.org/ipa-freshmans-science-fair-project-1-of-300-best-in-the-nation/|website=Island Pacific Academy|date=3 September 2015 |access-date=6 September 2015}}</ref><ref name=DigitalHeliograph>{{cite web|last1=Welch|first1=Natalie|title=Digital Heliograph|url=https://sites.google.com/site/digitalheliograph/home|access-date=6 September 2015}}</ref> It was a semi-finalist in the Broadcom MASTERS competition.<ref>{{Cite web|url = https://member.societyforscience.org/document.doc?id=659|title = 2015 Broadcom MASTERS Semifinalists|access-date = 5 September 2015}}</ref>

==See also==
* [[Heliography]], an early photographic process invented by Joseph Nicéphore Niépce around 1822
* [[Heliotrope (instrument)]]
* [[Operation On-Target]], a Scouting program
* [[Signal lamp]]

==References==
{{reflist}}

==Further reading==
* Lewis Coe, ''Great Days of the Heliograph'', Crown Point, 1987 {{oclc|16902284}}

==External links==
{{Commons category|Heliographs}}
*[https://web.archive.org/web/20110525171910/http://myweb.cableone.net/kd7aoi/ Heliography: Communicating with Mirrors] Photographs of British, American and Portuguese heliographs.
*[https://web.archive.org/web/20170222025302/http://www.modulatedlight.org/Modulated_Light_DX/Heliograph.html The Heliograph] A description of the British Mance, Begbie and French LeSeurre heliographs with illustrations (1899)
*[https://www.morsekey.net/eliografo.html Eliografo] Detailed color photographs of a World War 2 British Mance heliograph (Italian).
*[http://trove.nla.gov.au/picture/result?q=heliograph "Heliograph" at the National Library of Australia: Trove]; 100+ historical heliograph photographs at the Australian War Memorial and elsewhere
*[http://home.arcor.de/royal-signals/page24/page26/page26.html Royal Signals Datasheet No. 2. The Heliograph (revised April 2003)]
*[https://web.archive.org/web/20121014135758/http://home.arcor.de/royal-signals/page24/page28/page28.html CHAPTER IV THE HELIOGRAPH] (PAGE 48 OF THE 1905 SIGNALLING HANDBOOK)
*[http://www.prc68.com/I/MkVHeliograph.shtml Mance Mark V Heliograph] Detailed photos of a British Mark V Heliograph and kit, links to patents. Clicking on visible photos reveals high resolution photos.
*[http://www.discoverseaz.com/History/Heliograph.html The Heliograph in the Apache Wars]
*[http://samilitaryhistory.org/vol111jh.html Signals communication in the South African War 1899-1902]
*[http://www.douglas-self.com/MUSEUM/COMMS/heliograph/heliograph.htm Heliographs] at the Museum of RetroTechnology

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[[Category:History of telecommunications]]
[[Category:Telegraphy]]
[[Category:Optical communications]]

Heliograph - Revision history

Avdhut Kamble: basic improve intro for accuracy additionally and added references for clarity

Ajay Kumar: Created a new article