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66-509: The term speculum , Latin for " mirror ", and its plural specula , may refer to: Speculum (journal) , a journal of medieval studies published by the Medieval Academy of America Speculum (medical) , a medical tool used for examining body cavities Speculum feathers , the secondary feathers on the inner part of a duck's wing which are often brightly coloured Speculum literature ,

132-481: A circular cylinder or of a parabolic cylinder . The most common structural material for mirrors is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish. The most common mirrors consist of a plate of transparent glass, with a thin reflective layer on the back (the side opposite to the incident and reflected light) backed by a coating that protects that layer against abrasion, tarnishing, and corrosion . The glass

198-465: A looking glass , is an object that reflects an image . Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the image in an equal yet opposite angle from which the light shines upon it. This allows the viewer to see themselves or objects behind them, or even objects that are at an angle from them but out of their field of view, such as around

264-405: A prism ), so that all colors are reflected nearly with the same intensity. The vast majority of visible objects are seen primarily by diffuse reflection from their surface. Exceptions include objects with polished (specularly reflecting) surfaces, and objects that themselves emit light. Rayleigh scattering is responsible for the blue color of the sky, and Mie scattering for the white color of

330-432: A virtual image of whatever is in the opposite angle from the viewer, meaning that objects in the image appear to exist in a direct line of sight —behind the surface of the mirror—at an equal distance from their position in front of the mirror. Objects behind the observer, or between the observer and the mirror, are reflected back to the observer without any actual change in orientation; the light waves are simply reversed in

396-461: A century, Venice retained the monopoly of the tin amalgam technique. Venetian mirrors in richly decorated frames served as luxury decorations for palaces throughout Europe, and were very expensive. For example, in the late seventeenth century, the Countess de Fiesque was reported to have traded an entire wheat farm for a mirror, considering it a bargain. However, by the end of that century the secret

462-418: A concave parabolic mirror (whose surface is a part of a paraboloid of revolution) will reflect rays that are parallel to its axis into rays that pass through its focus . Conversely, a parabolic concave mirror will reflect any ray that comes from its focus towards a direction parallel to its axis. If a concave mirror surface is a part of a prolate ellipsoid , it will reflect any ray coming from one focus toward

528-432: A corner. Natural mirrors have existed since prehistoric times, such as the surface of water, but people have been manufacturing mirrors out of a variety of materials for thousands of years, like stone, metals, and glass. In modern mirrors, metals like silver or aluminium are often used due to their high reflectivity , applied as a thin coating on glass because of its naturally smooth and very hard surface. A mirror

594-426: A different image in the same mirror. Thus, the images observed in a mirror depend upon the angle of the mirror with respect to the eye. The angle between the object and the observer is always twice the angle between the eye and the normal, or the direction perpendicular to the surface. This allows animals with binocular vision to see the reflected image with depth perception and in three dimensions. The mirror forms

660-401: A direction perpendicular to the mirror. However, when viewer is facing the object and the mirror is at an angle between them, the image appears inverted 180° along the direction of the angle. Objects viewed in a (plane) mirror will appear laterally inverted (e.g., if one raises one's right hand, the image's left hand will appear to go up in the mirror), but not vertically inverted (in the image

726-515: A few percent specular reflection, except in particular cases, such as grazing angle reflection by a lake, or the total reflection of a glass prism, or when structured in certain complex configurations such as the silvery skin of many fish species or the reflective surface of a dielectric mirror . Diffuse reflection can be highly efficient, as in white materials, due to the summing up of the many subsurface reflections. Up to this point white objects have been discussed, which do not absorb light. But

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792-787: A good mirror are a surface with a very high degree of flatness (preferably but not necessarily with high reflectivity ), and a surface roughness smaller than the wavelength of the light. The earliest manufactured mirrors were pieces of polished stone such as obsidian , a naturally occurring volcanic glass . Examples of obsidian mirrors found at Çatalhöyük in Anatolia (modern-day Turkey) have been dated to around 6000 BCE. Mirrors of polished copper were crafted in Mesopotamia from 4000 BCE, and in ancient Egypt from around 3000 BCE. Polished stone mirrors from Central and South America date from around 2000 BCE onwards. By

858-415: A layer of paint applied over it. Mirrors for optical instruments often have the metal layer on the front face, so that the light does not have to cross the glass twice. In these mirrors, the metal may be protected by a thin transparent coating of a non-metallic ( dielectric ) material. The first metallic mirror to be enhanced with a dielectric coating of silicon dioxide was created by Hass in 1937. In 1939 at

924-409: A left-hand glove into a right-hand glove or vice versa). When a person raises their left hand, the actual left hand raises in the mirror, but gives the illusion of a right hand raising because the imaginary person in the mirror is literally inside-out, hand and all. If the person stands side-on to a mirror, the mirror really does reverse left and right hands, that is, objects that are physically closer to

990-461: A light source. If the diffuse surface is colored , the reflected light is also colored, resulting in similar coloration of surrounding objects. In 3D computer graphics , diffuse interreflection is an important component of global illumination . There are a number of ways to model diffuse interreflection when rendering a scene. Radiosity and photon mapping are two commonly used methods. Diffuse reflectance spectroscopy can be used to determine

1056-421: A medieval genre Speculum metal , an alloy containing copper and tin used for making all-metal mirrors "Speculum", a song by Adema from Adema (album) See also [ edit ] All pages with titles beginning with Speculum Specula (disambiguation) Spiculum , a Roman weapon Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with

1122-773: A mirror is said to bring seven years of bad luck . The terms "mirror" and "reflector" can be used for objects that reflect any other types of waves. An acoustic mirror reflects sound waves. Objects such as walls, ceilings, or natural rock-formations may produce echos , and this tendency often becomes a problem in acoustical engineering when designing houses, auditoriums, or recording studios. Acoustic mirrors may be used for applications such as parabolic microphones , atmospheric studies, sonar , and seafloor mapping . An atomic mirror reflects matter waves and can be used for atomic interferometry and atomic holography . The first mirrors used by humans were most likely pools of still water, or shiny stones. The requirements for making

1188-466: A mirror. Polishing produces some specular reflection, but the remaining light continues to be diffusely reflected. The most general mechanism by which a surface gives diffuse reflection does not involve exactly the surface: most of the light is contributed by scattering centers beneath the surface , as illustrated in Figure ;1. If one were to imagine that the figure represents snow, and that

1254-526: A mixture of specular and diffuse reflection. The visibility of objects, excluding light-emitting ones, is primarily caused by diffuse reflection of light: it is diffusely-scattered light that forms the image of the object in the observer's eye. Diffuse reflection from solids is generally not due to surface roughness. A flat surface is indeed required to give specular reflection, but it does not prevent diffuse reflection. A piece of highly polished white marble remains white; no amount of polishing will turn it into

1320-402: A person's head still appears above their body). However, a mirror does not actually "swap" left and right any more than it swaps top and bottom. A mirror swaps front and back. To be precise, it reverses the object in the direction perpendicular to the mirror surface (the normal), turning the three dimensional image inside out (the way a glove stripped off the hand can be turned inside out, turning

1386-413: A point are usually made in the shape of a paraboloid of revolution instead; they are used in telescopes (from radio waves to X-rays), in antennas to communicate with broadcast satellites , and in solar furnaces . A segmented mirror , consisting of multiple flat or curved mirrors, properly placed and oriented, may be used instead. Mirrors that are intended to concentrate sunlight onto a long pipe may be

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1452-472: A protective transparent coating is added on top of the reflecting layer, to protect it against abrasion, tarnishing, and corrosion, or to absorb certain wavelengths. Thin flexible plastic mirrors are sometimes used for safety, since they cannot shatter or produce sharp flakes. Their flatness is achieved by stretching them on a rigid frame. These usually consist of a layer of evaporated aluminium between two thin layers of transparent plastic. In common mirrors,

1518-586: A small fraction of the rays are reflected. In flying relativistic mirrors conceived for X-ray lasers , the reflecting surface is a spherical shockwave (wake wave) created in a low-density plasma by a very intense laser-pulse, and moving at an extremely high velocity. A phase-conjugating mirror uses nonlinear optics to reverse the phase difference between incident beams. Such mirrors may be used, for example, for coherent beam combination. The useful applications are self-guiding of laser beams and correction of atmospheric distortions in imaging systems. When

1584-408: A sufficiently narrow beam of light is reflected at a point of a surface, the surface's normal direction n → {\displaystyle {\vec {n}}} will be the bisector of the angle formed by the two beams at that point. That is, the direction vector u → {\displaystyle {\vec {u}}} towards the incident beams's source,

1650-456: Is a wave reflector. Light consists of waves, and when light waves reflect from the flat surface of a mirror, those waves retain the same degree of curvature and vergence , in an equal yet opposite direction, as the original waves. This allows the waves to form an image when they are focused through a lens, just as if the waves had originated from the direction of the mirror. The light can also be pictured as rays (imaginary lines radiating from

1716-511: Is a dichroic mirror that efficiently reflects the entire visible light spectrum while transmitting infrared wavelengths. A hot mirror is the opposite: it reflects infrared light while transmitting visible light. Dichroic mirrors are often used as filters to remove undesired components of the light in cameras and measuring instruments. In X-ray telescopes , the X-rays reflect off a highly precise metal surface at almost grazing angles, and only

1782-443: Is broken. Lettering or decorative designs may be printed on the front face of the glass, or formed on the reflective layer. The front surface may have an anti-reflection coating . Mirrors which are reflective on the front surface (the same side of the incident and reflected light) may be made of any rigid material. The supporting material does not necessarily need to be transparent, but telescope mirrors often use glass anyway. Often

1848-658: Is irregular on a scale comparable with light wavelength, so diffuse light is generated at each interface, rather than a single reflected ray, but the story can be told the same way. This mechanism is very general, because almost all common materials are made of "small things" held together. Mineral materials are generally polycrystalline : one can describe them as made of a 3D mosaic of small, irregularly shaped defective crystals. Organic materials are usually composed of fibers or cells, with their membranes and their complex internal structure. And each interface, inhomogeneity or imperfection can deviate, reflect or scatter light, reproducing

1914-560: Is microscopically rough, like in a frost glass (Figure 2), or, of course, if their homogeneous structure deteriorates, as in cataracts of the eye lens. A surface may also exhibit both specular and diffuse reflection, as is the case, for example, of glossy paints as used in home painting, which give also a fraction of specular reflection, while matte paints give almost exclusively diffuse reflection. Most materials can give some specular reflection, provided that their surface can be polished to eliminate irregularities comparable with

1980-403: Is no archeological evidence of glass mirrors before the third century. These early glass mirrors were made by blowing a glass bubble, and then cutting off a small circular section from 10 to 20 cm in diameter. Their surface was either concave or convex, and imperfections tended to distort the image. Lead-coated mirrors were very thin to prevent cracking by the heat of the molten metal. Due to

2046-406: Is only perceived when it is placed on a scattering material (e.g. paper). This is so because light's path through the paper fibers (and through the ink) is only a fraction of millimeter long. However, light from the bottle has crossed several centimeters of ink and has been heavily absorbed, even in its red wavelengths. And, when a colored object has both diffuse and specular reflection, usually only

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2112-408: Is usually soda-lime glass, but lead glass may be used for decorative effects, and other transparent materials may be used for specific applications. A plate of transparent plastic may be used instead of glass, for lighter weight or impact resistance. Alternatively, a flexible transparent plastic film may be bonded to the front and/or back surface of the mirror, to prevent injuries in case the mirror

2178-529: The Bronze Age most cultures were using mirrors made from polished discs of bronze , copper , silver , or other metals. The people of Kerma in Nubia were skilled in the manufacturing of mirrors. Remains of their bronze kilns have been found within the temple of Kerma. In China, bronze mirrors were manufactured from around 2000 BC, some of the earliest bronze and copper examples being produced by

2244-457: The Caliphate mathematician Ibn Sahl in the tenth century. Mirrors can be classified in many ways; including by shape, support, reflective materials, manufacturing methods, and intended application. Typical mirror shapes are planar and curved mirrors. The surface of curved mirrors is often a part of a sphere . Mirrors that are meant to precisely concentrate parallel rays of light into

2310-762: The Qijia culture . Such metal mirrors remained the norm through to Greco-Roman Antiquity and throughout the Middle Ages in Europe . During the Roman Empire silver mirrors were in wide use by servants. Speculum metal is a highly reflective alloy of copper and tin that was used for mirrors until a couple of centuries ago. Such mirrors may have originated in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were only owned by

2376-663: The Schott Glass company, Walter Geffcken invented the first dielectric mirrors to use multilayer coatings. The Greek in Classical Antiquity were familiar with the use of mirrors to concentrate light. Parabolic mirrors were described and studied by the mathematician Diocles in his work On Burning Mirrors . Ptolemy conducted a number of experiments with curved polished iron mirrors, and discussed plane, convex spherical, and concave spherical mirrors in his Optics . Parabolic mirrors were also described by

2442-506: The angle of incidence between n → {\displaystyle {\vec {n}}} and u → {\displaystyle {\vec {u}}} , but of opposite sign. This property can be explained by the physics of an electromagnetic plane wave that is incident to a flat surface that is electrically conductive or where the speed of light changes abruptly, as between two materials with different indices of refraction. More specifically,

2508-419: The 16th century, was to blow a cylinder of glass, cut off the ends, slice it along its length, and unroll it onto a flat hot plate. Venetian glassmakers also adopted lead glass for mirrors, because of its crystal-clarity and its easier workability. During the early European Renaissance , a fire-gilding technique developed to produce an even and highly reflective tin coating for glass mirrors. The back of

2574-509: The 1st century CE , with the development of soda-lime glass and glass blowing . The Roman scholar Pliny the Elder claims that artisans in Sidon (modern-day Lebanon ) were producing glass mirrors coated with lead or gold leaf in the back. The metal provided good reflectivity, and the glass provided a smooth surface and protected the metal from scratches and tarnishing. However, there

2640-462: The above mechanism. Few materials do not cause diffuse reflection: among these are metals, which do not allow light to enter; gases, liquids, glass, and transparent plastics (which have a liquid-like amorphous microscopic structure); single crystals , such as some gems or a salt crystal; and some very special materials, such as the tissues which make the cornea and the lens of an eye. These materials can reflect diffusely, however, if their surface

2706-457: The above scheme continues to be valid in the case that the material is absorbent. In this case, diffused rays will lose some wavelengths during their walk in the material, and will emerge colored. Diffusion affects the color of objects in a substantial manner because it determines the average path of light in the material, and hence to which extent the various wavelengths are absorbed. Red ink looks black when it stays in its bottle. Its vivid color

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2772-412: The bulb's walls. This phenomenon was developed into the method of evaporation coating by Pohl and Pringsheim in 1912. John D. Strong used evaporation coating to make the first aluminium -coated telescope mirrors in the 1930s. The first dielectric mirror was created in 1937 by Auwarter using evaporated rhodium . The metal coating of glass mirrors is usually protected from abrasion and corrosion by

2838-428: The diffuse component is colored. A cherry reflects diffusely red light, absorbs all other colors and has a specular reflection which is essentially white (if the incident light is white light). This is quite general, because, except for metals, the reflectivity of most materials depends on their refractive index , which varies little with the wavelength (though it is this variation that causes the chromatic dispersion in

2904-407: The glass was coated with a tin-mercury amalgam, and the mercury was then evaporated by heating the piece. This process caused less thermal shock to the glass than the older molten-lead method. The date and location of the discovery is unknown, but by the 16th century Venice was a center of mirror production using this technique. These Venetian mirrors were up to 40 inches (100 cm) square. For

2970-423: The greater availability of affordable mirrors. Mirrors are often produced by the wet deposition of silver, or sometimes nickel or chromium (the latter used most often in automotive mirrors) via electroplating directly onto the glass substrate. Glass mirrors for optical instruments are usually produced by vacuum deposition methods. These techniques can be traced to observations in the 1920s and 1930s that metal

3036-440: The incident rays are parallel among themselves but not parallel to the mirror's axis, or are divergent from a point that is not the focus – as when trying to form an image of an object that is near the mirror or spans a wide angle as seen from it. However, this aberration can be sufficiently small if the object image is sufficiently far from the mirror and spans a sufficiently small angle around its axis. Mirrors reflect an image to

3102-402: The light source, that are always perpendicular to the waves). These rays are reflected at an equal yet opposite angle from which they strike the mirror (incident light). This property, called specular reflection , distinguishes a mirror from objects that diffuse light, breaking up the wave and scattering it in many directions (such as flat-white paint). Thus, a mirror can be any surface in which

3168-586: The light wavelength (a fraction of a micrometer). Depending on the material and surface roughness, reflection may be mostly specular, mostly diffuse, or anywhere in between. A few materials, like liquids and glasses, lack the internal subdivisions which produce the subsurface scattering mechanism described above, and so give only specular reflection. Among common materials, only polished metals can reflect light specularly with high efficiency, as in aluminum or silver usually used in mirrors. All other common materials, even when perfectly polished, usually give not more than

3234-414: The mirror always appear closer in the virtual image, and objects farther from the surface always appear symmetrically farther away regardless of angle. Diffuse reflection A surface built from a non-absorbing powder such as plaster , or from fibers such as paper, or from a polycrystalline material such as white marble , reflects light diffusely with great efficiency. Many common materials exhibit

3300-444: The normal vector n → {\displaystyle {\vec {n}}} , and direction vector v → {\displaystyle {\vec {v}}} of the reflected beam will be coplanar , and the angle between n → {\displaystyle {\vec {n}}} and v → {\displaystyle {\vec {v}}} will be equal to

3366-447: The observer. However, unlike a projected image on a screen, an image does not actually exist on the surface of the mirror. For example, when two people look at each other in a mirror, both see different images on the same surface. When the light waves converge through the lens of the eye they interfere with each other to form the image on the surface of the retina , and since both viewers see waves coming from different directions, each sees

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3432-457: The other focus. A convex parabolic mirror, on the other hand, will reflect rays that are parallel to its axis into rays that seem to emanate from the focus of the surface, behind the mirror. Conversely, it will reflect incoming rays that converge toward that point into rays that are parallel to the axis. A convex mirror that is part of a prolate ellipsoid will reflect rays that converge towards one focus into divergent rays that seem to emanate from

3498-531: The other focus. Spherical mirrors do not reflect parallel rays to rays that converge to or diverge from a single point, or vice versa, due to spherical aberration . However, a spherical mirror whose diameter is sufficiently small compared to the sphere's radius will behave very similarly to a parabolic mirror whose axis goes through the mirror's center and the center of that sphere; so that spherical mirrors can substitute for parabolic ones in many applications. A similar aberration occurs with parabolic mirrors when

3564-499: The polygons are its (transparent) ice crystallites, an impinging ray is partially reflected (a few percent) by the first particle, enters in it, is again reflected by the interface with the second particle, enters in it, impinges on the third, and so on, generating a series of "primary" scattered rays in random directions, which, in turn, through the same mechanism, generate a large number of "secondary" scattered rays, which generate "tertiary" rays, and so forth. All these rays walk through

3630-807: The poor quality, high cost, and small size of glass mirrors, solid-metal mirrors (primarily of steel) remained in common use until the late nineteenth century. Silver-coated metal mirrors were developed in China as early as 500 CE. The bare metal was coated with an amalgam , then heated until the mercury boiled away. The evolution of glass mirrors in the Middle Ages followed improvements in glassmaking technology. Glassmakers in France made flat glass plates by blowing glass bubbles, spinning them rapidly to flatten them, and cutting rectangles out of them. A better method, developed in Germany and perfected in Venice by

3696-407: The reflective layer is usually some metal like silver, tin, nickel , or chromium , deposited by a wet process; or aluminium, deposited by sputtering or evaporation in vacuum. The reflective layer may also be made of one or more layers of transparent materials with suitable indices of refraction . The structural material may be a metal, in which case the reflecting layer may be just the surface of

3762-588: The same. Metal concave dishes are often used to reflect infrared light (such as in space heaters ) or microwaves (as in satellite TV antennas). Liquid metal telescopes use a surface of liquid metal such as mercury. Mirrors that reflect only part of the light, while transmitting some of the rest, can be made with very thin metal layers or suitable combinations of dielectric layers. They are typically used as beamsplitters . A dichroic mirror , in particular, has surface that reflects certain wavelengths of light, while letting other wavelengths pass through. A cold mirror

3828-417: The snow crystallites, which do not absorb light, until they arrive at the surface and exit in random directions. The result is that the light that was sent out is returned in all directions, so that snow is white despite being made of transparent material (ice crystals). For simplicity, "reflections" are spoken of here, but more generally the interface between the small particles that constitute many materials

3894-930: The surface is not flat, a mirror may behave like a reflecting lens . A plane mirror yields a real-looking undistorted image, while a curved mirror may distort, magnify, or reduce the image in various ways, while keeping the lines, contrast , sharpness , colors, and other image properties intact. A mirror is commonly used for inspecting oneself, such as during personal grooming ; hence the old-fashioned name "looking glass". This use, which dates from prehistory, overlaps with uses in decoration and architecture . Mirrors are also used to view other items that are not directly visible because of obstructions; examples include rear-view mirrors in vehicles, security mirrors in or around buildings, and dentist's mirrors . Mirrors are also used in optical and scientific apparatus such as telescopes , lasers , cameras , periscopes , and industrial machinery. According to superstitions breaking

3960-409: The texture or roughness of the surface is smaller (smoother) than the wavelength of the waves. When looking at a mirror, one will see a mirror image or reflected image of objects in the environment, formed by light emitted or scattered by them and reflected by the mirror towards one's eyes. This effect gives the illusion that those objects are behind the mirror, or (sometimes) in front of it . When

4026-467: The title Speculum . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Speculum&oldid=1133044105 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Mirror A mirror , also known as

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4092-450: The water droplets in clouds. Diffuse interreflection is a process whereby light reflected from an object strikes other objects in the surrounding area, illuminating them. Diffuse interreflection specifically describes light reflected from objects which are not shiny or specular . In real life terms what this means is that light is reflected off non-shiny surfaces such as the ground, walls, or fabric, to reach areas not directly in view of

4158-661: The wealthy. Common metal mirrors tarnished and required frequent polishing. Bronze mirrors had low reflectivity and poor color rendering , and stone mirrors were much worse in this regard. These defects explain the New Testament reference in 1 Corinthians 13 to seeing "as in a mirror, darkly." The Greek philosopher Socrates urged young people to look at themselves in mirrors so that, if they were beautiful, they would become worthy of their beauty, and if they were ugly, they would know how to hide their disgrace through learning. Glass began to be used for mirrors in

4224-432: Was an important manufacturer, and Bohemian and German glass, often rather cheaper, was also important. The invention of the silvered-glass mirror is credited to German chemist Justus von Liebig in 1835. His wet deposition process involved the deposition of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate . This silvering process was adapted for mass manufacturing and led to

4290-425: Was being ejected from electrodes in gas discharge lamps and condensed on the glass walls forming a mirror-like coating. The phenomenon, called sputtering , was developed into an industrial metal-coating method with the development of semiconductor technology in the 1970s. A similar phenomenon had been observed with incandescent light bulbs : the metal in the hot filament would slowly sublimate and condense on

4356-464: Was leaked through industrial espionage. French workshops succeeded in large-scale industrialization of the process, eventually making mirrors affordable to the masses, in spite of the toxicity of mercury's vapor. The invention of the ribbon machine in the late Industrial Revolution allowed modern glass panes to be produced in bulk. The Saint-Gobain factory, founded by royal initiative in France,

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