Burning-glass
Encyclopedia
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
's rays onto a small area, heating up the area and thus resulting in ignition
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
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
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...
could be trapped for analysis. The burning glass was a useful contrivance in the days before electrical ignition was easily achieved.
History
The technology of the burning glass has been known since antiquity. Vases filled with water used to start fires were known in the ancient world, and metaphorical significance was drawn (by the early Church FathersChurch Fathers
The Church Fathers, Early Church Fathers, Christian Fathers, or Fathers of the Church were early and influential theologians, eminent Christian teachers and great bishops. Their scholarly works were used as a precedent for centuries to come...
, for instance) from the fact that the water remained cool even though the light passing through it would set materials on fire. Burning lenses were used to cauterise wounds and to light sacred fires in temples. Plutarch
Plutarch
Plutarch then named, on his becoming a Roman citizen, Lucius Mestrius Plutarchus , c. 46 – 120 AD, was a Greek historian, biographer, essayist, and Middle Platonist known primarily for his Parallel Lives and Moralia...
refers to a burning mirror made of joined triangular metal mirrors installed at the temple of the Vestal Virgins. Aristophanes
Aristophanes
Aristophanes , son of Philippus, of the deme Cydathenaus, was a comic playwright of ancient Athens. Eleven of his forty plays survive virtually complete...
mentions the burning lens in his play The Clouds
The Clouds
The Clouds is a comedy written by the celebrated playwright Aristophanes lampooning intellectual fashions in classical Athens. It was originally produced at the City Dionysia in 423 BC and it was not well received, coming last of the three plays competing at the festival that year. It was revised...
(424 BC). The perpetual sacred fire in the classic temples as the Olympic torch had to be pure and to come directly from the gods. For this they used the sun's rays focused with mirrors or lenses and not impure triggers.
Archimedes
Archimedes
Archimedes of Syracuse was a Greek mathematician, physicist, engineer, inventor, and astronomer. Although few details of his life are known, he is regarded as one of the leading scientists in classical antiquity. Among his advances in physics are the foundations of hydrostatics, statics and an...
, the renowned mathematician, was said to have used a burning glass (or more likely a large number of angled hexagonal mirrors) as a weapon in 212 BC, when Syracuse was besieged by Marcus Claudius Marcellus
Marcus Claudius Marcellus
Marcus Claudius Marcellus , five times elected as consul of the Roman Republic, was an important Roman military leader during the Gallic War of 225 BC and the Second Punic War...
. The Roman fleet
Roman Navy
The Roman Navy comprised the naval forces of the Ancient Roman state. Although the navy was instrumental in the Roman conquest of the Mediterranean basin, it never enjoyed the prestige of the Roman legions...
was supposedly incinerated, though eventually the city was taken and Archimedes was slain.
The legend of Archimedes gave rise to a considerable amount of research on burning glasses and lenses until the late 17th century. Successful recreations have been performed by Anthemius of Tralles
Anthemius of Tralles
Anthemius of Tralles was a Greek professor of Geometry in Constantinople and architect, who collaborated with Isidore of Miletus to build the church of Hagia Sophia by the order of Justinian I. Anthemius came from an educated family, one of five sons of Stephanus of Tralles, a physician...
(6th century AD), Proclus (6th century) (who by this means purportedly destroyed the fleet of Vitellus besieging Constantinople
Constantinople
Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...
), Ibn Sahl
Ibn Sahl
This article is about the physicist. For the physician, see Ali ibn Sahl Rabban al-Tabari. For the poet, see Ibn Sahl of Sevilla.Ibn Sahl was a Muslim Persian mathematician, physicist and optics engineer of the Islamic Golden Age associated with the Abbasid court of Baghdad...
in his On Burning Mirrors and Lenses (10th century), Alhazen in his Book of Optics
Book of Optics
The Book of Optics ; ; Latin: De Aspectibus or Opticae Thesaurus: Alhazeni Arabis; Italian: Deli Aspecti) is a seven-volume treatise on optics and other fields of study composed by the medieval Muslim scholar Alhazen .-See also:* Science in medieval Islam...
(1021), Roger Bacon
Roger Bacon
Roger Bacon, O.F.M. , also known as Doctor Mirabilis , was an English philosopher and Franciscan friar who placed considerable emphasis on the study of nature through empirical methods...
(13th century), Giambattista della Porta
Giambattista della Porta
Giambattista della Porta , also known as Giovanni Battista Della Porta and John Baptist Porta, was an Italian scholar, polymath and playwright who lived in Naples at the time of the Scientific Revolution and Reformation....
and his friends (16th century), Athanasius Kircher
Athanasius Kircher
Athanasius Kircher was a 17th century German Jesuit scholar who published around 40 works, most notably in the fields of oriental studies, geology, and medicine...
and Gaspar Schott
Gaspar Schott
Gaspar Schott was a German Jesuit and scientist, specializing in the fields of physics, mathematics and natural philosophy, and known for his piety.-Biography:...
(17th century), the Comte du Buffon in 1740 in Paris, Ioannis Sakas in the 1970s in Greece, and others. Sakas was able to ignite a wooden boat at some distance in only seconds. Buffon, using only 48 small mirrors, was able to melt a 3 kilogram (six pound) tin bottle, and ignite wood from a distance of 46 meters (150 ft). These recreations show the plausibility of Archimedes' achievement.
The pop science TV program MythBusters
MythBusters
MythBusters is a science entertainment TV program created and produced by Beyond Television Productions for the Discovery Channel. The series is screened by numerous international broadcasters, including Discovery Channel Australia, Discovery Channel Latin America, Discovery Channel Canada, Quest...
attempted to model Archimedes' feat by using mirrors to ignite a small wooden boat covered with tar, with only partial success—they found it too difficult to focus light from their hand-held mirrors onto a point small enough to ignite the boat. However, an episode of Richard Hammond's Engineering Connections
Richard Hammond's Engineering Connections
Richard Hammond's Engineering Connections is a documentary series originally broadcast on the National Geographic Channel, and later on BBC2. It is presented by Richard Hammond, and looks at how engineers and designers use historic inventions and clues from the natural world in ingenious ways to...
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, though not made of the same quality of materials as in the MythBusters effort.
Recent excavations at the Viking
Viking
The term Viking is customarily used to refer to the Norse explorers, warriors, merchants, and pirates who raided, traded, explored and settled in wide areas of Europe, Asia and the North Atlantic islands from the late 8th to the mid-11th century.These Norsemen used their famed longships to...
harbor town of Fröjel, Gotland
Gotland
Gotland is a county, province, municipality and diocese of Sweden; it is Sweden's largest island and the largest island in the Baltic Sea. At 3,140 square kilometers in area, the region makes up less than one percent of Sweden's total land area...
in Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
have revealed a small number of rock crystal lenses known as the Visby lenses
Visby lenses
The Visby lenses are a collection of lens-shaped manufactured objects made of rock crystal found in several Viking graves on the island of Gotland, Sweden, dating from the 11th or 12th century...
. These may have been made using pole-lathes. They have an imaging quality comparable to that of 1950s aspheric lens
Aspheric lens
An aspheric lens or asphere is a lens whose surface profiles are not portions of a sphere or cylinder. In photography, a lens assembly that includes an aspheric element is often called an aspherical lens....
es. The Viking lenses effectively concentrate sunlight enough to ignite fires; however it is not known whether they were used for this purpose. Similar technology may have been used in ancient Ireland (the Liath Meisicith) and quite possibly ancient Egypt .
In 1796, during the French Revolution
French Revolution
The French Revolution , sometimes distinguished as the 'Great French Revolution' , was a period of radical social and political upheaval in France and Europe. The absolute monarchy that had ruled France for centuries collapsed in three years...
and three years after the declaration of war between France and Great Britain, Étienne-Gaspard Robert
Étienne-Gaspard Robert
Étienne-Gaspard Robert , often known by the stage name of "Robertson", was a prominent Belgian stage magician and influential developer of phantasmagoria. He was described by Charles Dickens as "an honourable and well-educated showman"...
met with the French government and proposed the use of mirrors to burn the invading ships of the British Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...
. They decided not to take up his proposal.
Chapter 17 of 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." Needless to say, this is highly dangerous and will damage the eye in seconds.
Current use
Large burning lens are sometimes made as Fresnel lensFresnel lens
A Fresnel lens is a type of lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design...
es, similar to lighthouse
Lighthouse
A lighthouse is a tower, building, or other type of structure designed to emit light from a system of lamps and lenses or, in older times, from a fire, and used as an aid to navigation for maritime pilots at sea or on inland waterways....
lenses, including for use in solar furnace
Solar furnace
A solar furnace is a structure that captures sunlight to produce high temperatures, usually for industry. This is done with a curved mirror that acts as a parabolic reflector, concentrating light onto a focal point...
s. 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
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
array of mirrors (some facilities are several stories high) to focus light to a high intensity.
The Olympic torch that is carried around the host country of the Olympic games
Olympic Games
The Olympic Games is a major international event featuring summer and winter sports, in which thousands of athletes participate in a variety of competitions. The Olympic Games have come to be regarded as the world’s foremost sports competition where more than 200 nations participate...
is lit by means of a burning glass. The ceremony is organized at the site of ancient Olympia
Olympia, Greece
Olympia , a sanctuary of ancient Greece in Elis, is known for having been the site of the Olympic Games in classical times, comparable in importance to the Pythian Games held in Delphi. Both games were held every Olympiad , the Olympic Games dating back possibly further than 776 BC...
in Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
. The first use of this torch was for the 1936 Summer Olympics
1936 Summer Olympics
The 1936 Summer Olympics, officially known as the Games of the XI Olympiad, was an international multi-sport event which was held in 1936 in Berlin, Germany. Berlin won the bid to host the Games over Barcelona, Spain on April 26, 1931, at the 29th IOC Session in Barcelona...
in Berlin.