Editing Burning glass

{{Short description|Convex lens for fire making}}
{{Use dmy dates|date=January 2025}}
[[Image:Priestley Burning Lens Replica.jpg|thumb|A replica (on a smaller scale) of the burning lens owned by [[Joseph Priestley]], in his laboratory]]
A '''burning glass''' or '''burning lens''' is a large [[Biconvex lens|convex lens]] that can concentrate the Sun's rays onto a small area, heating up the area and thus resulting in [[Combustion|ignition]] of the exposed surface. '''Burning mirrors''' achieve a similar effect by using reflecting surfaces to focus the light. They were used in 18th-century chemical studies for burning materials in closed glass vessels where the products of combustion could be trapped for analysis. The burning glass was a useful contrivance in the days before electrical ignition was easily achieved.

==History==
[[File:OrbisPictus b 162.jpg|thumb|1658 illustration depicting the sun's rays being focused to start a fire]]
Burning glass technology has been known since antiquity, as described by Greek and Roman writers who recorded the use of lenses to start fires for various purposes.<ref>{{Cite book |title= Greek and Roman Technology: A Sourcebook of Translated Greek and Roman Texts |last1= Sherwood |first1= Andrew N. |last2= Nikolic |first2= Milorad |last3= Humphrey |first3= John W.|last4= Oleson |first4= John P. |year= 2019 |publisher= [[Routledge]] |page=25 |isbn= 978-1138927896}}</ref> [[Pliny the Elder]] noted the use of glass vases filled with water to concentrate sunlight heat intensely enough to ignite clothing, as well as convex lenses that were used to [[cauterize]] wounds.<ref>{{cite journal |last1= Plantzos |first1= Dimitris |date= 1997 |title= Crystals and Lenses in the Graeco-Roman World |journal= American Journal of Archaeology |volume=101 |issue=3 |pages=451–464 |doi=10.2307/507106|jstor= 507106 |s2cid= 193082510 }}</ref> [[Plutarch]] refers to a burning mirror made of joined triangular metal mirrors installed at the temple of the [[Vestal Virgins]]. [[Aristophanes]] mentions the burning lens in his play ''[[The Clouds]]'' (424 BC).<ref>{{cite web |url=http://classics.mit.edu/Aristophanes/clouds.html |title=The Clouds |author=Aristophanes |website=The Internet Classics Archive |publisher=Daniel C. Stevenson, Web Atomics |access-date=21 February 2018}}</ref>

{{Blockquote|Strepsiades. Have you ever seen a beautiful, transparent stone at the druggists', with which you may kindle fire?}}

The [[Hellenistic Greek]] mathematician [[Archimedes]] was said to have used a burning glass as a weapon in 212 BC, when [[Syracuse, Sicily|Syracuse]] was besieged by [[Marcus Claudius Marcellus]] of the [[Roman Republic]]. The [[Roman Navy|Roman fleet]] was supposedly incinerated, though eventually the city was taken and Archimedes was slain.<ref>Meijer, Fik (1986), A History of Seafaring in the Classical World, Routledge, {{ISBN|978-0-7099-3565-0}}</ref>
[[File:Lentilles ardentes Lavoisier.png|360px|thumb|{{center|Lavoisier with French Academy of Sciences' ''lentilles ardentes''}}]]

The legend of Archimedes gave rise to a considerable amount of research on burning glasses and lenses until the late 17th century. Various researchers from medieval [[Christendom]] to the [[Islamic world]] worked with burning glasses, including [[Anthemius of Tralles]] (6th century AD), Proclus (6th century;<ref>{{Cite book|title=The table book: or, Daily recreation and information concerning remarkable men, manners, times, seasons, solemnities, mrry-makings, antiquities and novelties, forming a complete history of the year|last=Hone|first=William|publisher=William Tegg and Co|year=1857|location=London|pages=813}}</ref> who by this means purportedly destroyed the fleet of [[Vitalian (general)|Vitalian]] besieging [[Constantinople]]), [[Ibn Sahl (mathematician)|Ibn Sahl]] in his ''On Burning Mirrors and Lenses'' (10th century), [[Ibn al-Haytham|Alhazen]] in his ''[[Book of Optics]]'' (1021),<ref>Roshdi Rashed (1990), "A Pioneer in Anaclastics: Ibn Sahl on Burning Mirrors and Lenses", ''[[Isis (journal)|Isis]]'' '''81''' (3), pp. 464–491 [464–468].</ref> [[Roger Bacon]] (13th century), [[Giambattista della Porta]] and his friends (16th century), [[Athanasius Kircher]] and [[Gaspar Schott]] (17th century), and the [[Georges-Louis Leclerc, Comte de Buffon|Comte de Buffon]] in 1740 in Paris.

While the effects of [[camera obscura]] were mentioned by Greek philosopher [[Aristotle]] in the 4th century BC, contemporary Chinese [[Mohist]]s of China's [[Warring States Period]] who compiled the ''[[Mozi (book)|Mozi]]'' described their experiments with burning mirrors and the [[pinhole camera]].<ref name="needham4 98">{{cite book|last=Needham|first=Joseph|title=Science and Civilization in China, vol. IV, part 1: Physics and Physical Technology|url=https://monoskop.org/images/7/70/Needham_Joseph_Science_and_Civilisation_in_China_Vol_4-1_Physics_and_Physical_Technology_Physics.pdf|access-date=5 September 2016|archive-url=https://web.archive.org/web/20170703010030/https://monoskop.org/images/7/70/Needham_Joseph_Science_and_Civilisation_in_China_Vol_4-1_Physics_and_Physical_Technology_Physics.pdf|archive-date=3 July 2017|page=98|url-status=dead}}</ref> A few decades after Alhazen described camera obscura in Iraq, the [[Song dynasty]] Chinese statesman [[Shen Kuo]] was nevertheless the first to clearly describe the relationship of the [[Focus (optics)|focal point]] of a [[concave mirror]], the burning point and the pinhole camera as separate radiation phenomena in his ''[[Dream Pool Essays]]'' (1088).<ref>{{cite book|last=Needham|first=Joseph|title=Science and Civilization in China, vol. IV, part 1: Physics and Physical Technology|url=https://monoskop.org/images/7/70/Needham_Joseph_Science_and_Civilisation_in_China_Vol_4-1_Physics_and_Physical_Technology_Physics.pdf|access-date=5 September 2016|archive-url=https://web.archive.org/web/20170703010030/https://monoskop.org/images/7/70/Needham_Joseph_Science_and_Civilisation_in_China_Vol_4-1_Physics_and_Physical_Technology_Physics.pdf|archive-date=3 July 2017|pages=97–99|url-status=dead}}</ref> By the late 15th century [[Leonardo da Vinci]] would be the first in Europe to make similar observations about the focal point and pinhole.<ref>{{cite book|last=Needham|first=Joseph|title=Science and Civilization in China, vol. IV, part 1: Physics and Physical Technology|url=https://monoskop.org/images/7/70/Needham_Joseph_Science_and_Civilisation_in_China_Vol_4-1_Physics_and_Physical_Technology_Physics.pdf|access-date=5 September 2016|archive-url=https://web.archive.org/web/20170703010030/https://monoskop.org/images/7/70/Needham_Joseph_Science_and_Civilisation_in_China_Vol_4-1_Physics_and_Physical_Technology_Physics.pdf|archive-date=3 July 2017|page=99|url-status=dead}}</ref>

Burning lenses were used in the 18th century by both [[Joseph Priestley]] and [[Antoine Lavoisier]] in their experiments to obtain oxides contained in closed vessels under high temperatures. These included carbon dioxide by burning diamond, and [[Mercury(II) oxide|mercuric oxide]] by heating [[Mercury (element)|mercury]]. This type of experiment contributed to the discovery of "[[Phlogiston theory|dephlogisticated air]]" by Priestley, which became better known as oxygen, following Lavoisier's investigations.<ref>Joseph Priestley, ''Experiments and Observations on Different Kinds of Air'' [https://books.google.com/books?id=rk4TaRQTY7cC Vol.2] (1776)</ref>

Chapter 17 of [[William Bates (physician)|William Bates]]' 1920 book ''Perfect Sight Without Glasses'', in which the author argues that observation of the sun is beneficial to those with poor vision, includes a figure of somebody "Focussing the Rays of the Sun Upon the Eye of a Patient by Means of a Burning Glass."<ref name="BatesChap17">{{cite book | last=Bates | first=William H. | title=Perfect Sight Without Glasses | year=1920 | chapter = Chapter 17: Vision Under Adverse Conditions a Benefit to the Eye | pages=183–197 | publisher=New York: Central Fixation Publish Co. | chapter-url=https://books.google.com/books?id=Vl3SiyXmZVMC&pg=PA183 | isbn=88-900756-3-5 }}</ref>

The burning lens of the Grand Duke of Tuscany was used by Sir [[Humphry Davy]] and [[Michael Faraday]] to burn a diamond in oxygen on 27 March 1814.

==Use==
=== War: since the legend of Archimedes ===
The first story akin to that of burning glass is by Archimedes, for the purpose of war, in 212 BC. When Syracuse was besieged by Marcus Claudius Marcellus, the Roman fleet was supposedly incinerated by the use of not glass per se, but a concave mirror made of brass focusing sunlight. Whether or not that actually happened, eventually the city was taken and Archimedes was slain.<ref>Meijer, Fik (1986), A History of Seafaring in the Classical World, Routledge, {{ISBN|978-0-7099-3565-0}}</ref>

In 1796, during the [[French Revolution]] and three years after the declaration of war between France and Great Britain, physicist [[Étienne-Gaspard Robert]] met with the French government and proposed the use of mirrors to burn the invading ships of the British [[Royal Navy]].  They decided not to take up his proposal.<ref name="PreCinema">Burns, Paul.  "[http://www.precinemahistory.net/1750.htm The History of The Discovery of Cinematography: Chapter Six, 1750–1799]".  Accessed 29 July 2007.</ref>

=== Domestic use: primitive fire making ===
[[File:Flat_flexible_plastic_sheet_lens.JPG|thumb|240x240px|Close-up view of a flat [[Fresnel lens]]. This thin, lightweight, non-fragile and low-cost lens can be used as burning-glass in emergency situations.]]
[[File:Leaf being burned with telescope.jpg|thumb|222x222px|A makeshift burning glass, using the eyepiece of a [[telescope]], being used to burn a leaf.]]
Burning glasses (often called '''fire lenses''') are still used to light fires in outdoor and primitive settings.<ref>{{cite web|url=http://www.primitivefire.com/Fire-Glass_c_1.html |title=Fire Glass |publisher=Primitivefire.com |access-date=2012-12-18}}</ref> Large burning lenses sometimes take the form of [[Fresnel lens]]es, similar to [[lighthouse]] lenses,<ref>
{{cite journal
 | journal = Proceedings of the Engineers' Society of Western Pennsylvania
 | title = Light House Lenses
 | author = George A. Macbeth
 | year = 1914
 | page = 245
 | volume = 30
 | url = https://books.google.com/books?id=rFTOAAAAMAAJ&q=fresnel%20%22burning%20glass%22&pg=RA1-PA245
 }}</ref> including those for use in [[solar furnace]]s.<ref>
{{cite book
 | title = Solar Energy: Fundamentals and Applications
 | author = H. P. Garg, J. Prakash
 | publisher = Tata McGraw-Hill Education
 | year = 2000
 | isbn = 9780074636312
 | page = 305
 | url = https://books.google.com/books?id=-v_LfcIdJxIC&q=lens+solar+furnace&pg=PA305
 }}</ref> Solar furnaces are used in industry to produce extremely high temperatures without the need for fuel or large supplies of electricity. They sometimes employ a large [[Parabolic reflector|parabolic]] array of mirrors (some facilities are several stories high) to focus light to a high intensity.

=== Religion: sacred fire ===
In various religions settings, a burning glass is used to set off some sort of [[Fire worship|sacred fire]].

From the 7th to the 16th centuries, a burning glass was used by Christians to set off the [[Easter Fire]] during the [[Easter vigil]]. Thus, [[Saint Boniface]] explained to [[Pope Zachary]] that he produced the new fire of Holy Saturday by means of a crystal lens concentrating the rays of the sun. This process was also mentioned in liturgical books until the [[Roman Pontifical]] of 1561.<ref>{{Cite web|last=de Villiers|first=Henri|date=30 March 2021|title=La réforme de la Semaine Sainte de 1955 – 7ème partie – La Vigile pascale|url=https://schola-sainte-cecile.com/2021/03/31/la-reforme-de-la-semaine-sainte-de-1955-7eme-partie-la-vigile-pascale/|access-date=2021-04-26|website=Schola Sainte-Cécile Official website|language=fr-FR}}</ref>

In [[Cambodia]], a burning glass has also been used since ancient times for the [[cremation]] of kings and most recently for the funeral of [[King Sihanouk]]. The crematorium of the king is traditionally prepared by the [[Baku (brahmin)|Bakus brahmin]] from the [[Royal Palace of Cambodia|Royal Palace]] on the last day of the week-long funeral. Small pieces of fragrant [[agarwood]] are placed beneath the magnifying glass until it ignites. The incandescent wood is used to light candles and pass on the fire to the attendees, who usually take their lit candles home.<ref>{{Cite web|title=The King and Queen Mother offer fire to His Majesty the King|url=https://www.rfa.org/khmer/indepth/late-ex-king-cremation-02042013072246.html|url-status=live|access-date=2021-04-26|website=Radio Free Asia|language=en|archive-url=https://web.archive.org/web/20210426143845/https://www.rfa.org/khmer/indepth/late-ex-king-cremation-02042013072246.html |archive-date=2021-04-26 }}</ref>

=== Sports: lighting the Olympic torch ===
The [[Olympic torch]] that is carried around the host country of the [[Olympic Games]] is lit by a burning glass, at the site of ancient [[Olympia, Greece|Olympia]] in Greece.<ref>{{cite web |url=http://www.london2012.com/torch-relay/history/ |publisher=London 2012 Olympic Games |title=Olympic Torch Relay history |access-date=27 November 2012 |archive-date=19 July 2012 |archive-url=https://web.archive.org/web/20120719144531/http://www.london2012.com/torch-relay/history/ |url-status=dead }}</ref>

=== Popular culture: verification attempts ===
There have been several real-world tests to evaluate the validity of the legend of Archimedes described above {{crossreference|(see {{slink||War: since the legend of Archimedes}})}} over the centuries, including a test by [[Georges-Louis Leclerc, Comte de Buffon|Comte de Buffon]] (circa 1747), documented in the paper titled "Invention De Miroirs Ardens, Pour Brusler a Une Grande Distance", and an experiment by John Scott, which was documented in an 1867 paper.<ref>{{Cite web |last=Gbur |first=Gregory |author-link=Greg Gbur |date=7 February 2010 |title=Mythbusters were scooped — by 130 years! (Archimedes death ray) |url=https://skullsinthestars.com/2010/02/07/mythbusters-were-scooped-by-130-years-archimedes-death-ray/ |access-date=2022-12-07 |website=Skulls in the Stars |language=en}}</ref>
In 1973, Greek scientist Dr. Ioannis Sakkas, curious about whether Archimedes could really have used a "burning glass" to destroy the Roman fleet in 212 BC, lined up nearly 60 Greek sailors, each holding an oblong mirror tipped to catch the sun's rays and direct them at a wooden ship 160 feet away. The ship caught fire at once. Sakkas said after the experiment there was no doubt in his mind the great inventor could have used bronze mirrors to scuttle the Romans.<ref>{{Cite web |title=Archimedes and his Burning Mirrors, Reality or Fantasy? |url=http://www.mlahanas.de/Greeks/Mirrors.htm |access-date=2022-12-07 |website=www.mlahanas.de}}</ref>

However, accounting for battle conditions makes such a weapon impractical, with modern tests refuting such claims. An experiment was carried out by a group at the [[Massachusetts Institute of Technology]] in 2005. It concluded that although the theory was sound for stationary objects, the mirrors would not likely have been able to concentrate sufficient [[solar energy]] to set a ship on fire under battle conditions.<ref>{{Cite web |title=2.009 Product Engineering Processes: Archimedes<!-- Bot generated title --> |url=http://web.mit.edu/2.009/www//experiments/deathray/10_ArchimedesResult.html |url-status=dead |archive-url=https://web.archive.org/web/20171212185131/http://web.mit.edu/2.009/www/experiments/deathray/10_ArchimedesResult.html |archive-date=2017-12-12 |access-date=2009-12-05}}</ref> Similar experiments were conducted on the popular science-based TV show ''[[MythBusters]]'' in 2004, [[MythBusters (2006 season)#Episode 46 – "Archimedes' Death Ray"|2006]], and [[MythBusters (2010 season)#Episode 157 .E2.80.93 .22President.27s Challenge.22|2010]], arriving at similar results based on the premise of the controversial myth.

However, an episode of ''[[Richard Hammond's Engineering Connections]]'' relating to the [[Keck Observatory]] (whose reflector glass is based on the Archimedes' Mirror) did successfully use a much smaller curved mirror to burn a wooden model, although the scaled-down model was not made of the same quality of materials as in the ''MythBusters'' effort.<ref>{{Citation |title=Richard Hammond Engineering Connections S01E03 – Deep Space Observatory – Keck, Hawaii |url=https://www.youtube.com/watch?v=ix_tsqKzkrQ |language=en |access-date=2022-12-07}}</ref><ref>{{Citation |last=Metcalfe |first=Nick |title=Deep Space Observer |date=23 December 2010 |url=https://www.imdb.com/title/tt1297757/ |series=Engineering Connections |access-date=2022-12-07}}</ref>

==See also==
* [[Diocles (mathematician)]]
* [[Nimrud lens]]
* [[Pyreliophorus]]
* [[Visby lenses]]
* [[Solar furnace]]

==References==
{{Reflist}}

==Further reading==
*Temple, Robert. ''The Crystal Sun'', {{ISBN|0-7126-7888-3}}.

==External links==
*{{Commons category-inline}}
{{Firelighting}}

{{DEFAULTSORT:Burning Glass}}
[[Category:Magnifiers]]
[[Category:Lenses]]
[[Category:Ancient weapons]]