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40-597: The vine is very vigorous, and good results depend on keeping it in check. In the Douro it is grown in searing heat in steep schisty vineyards that are more rock than soil. The alternative name of Mortágua pays tribute to these harsh conditions. It is usually trained under one of the Guyot systems , and needs severe pruning to keep it under control. In contrast, the vine produces just a few bunches of blue-black grapes which vary in size from 'small' to 'tiny'. Thus yields are among

80-429: A discontinuity that may have a large influence on the mechanical behavior (strength, deformation, etc.) of rock masses in, for example, tunnel , foundation , or slope construction. A hazard may exist even in undisturbed terrain. On August 17, 1959, a magnitude 7.2 earthquake destabilized a mountain slope near Hebgen Lake , Montana, composed of schist. This caused a massive landslide that killed 26 people camping in

120-704: A microscope is necessary. Fresnel lenses are used as magnifiers, for example for reading printed text. The magnifying glass icon (🔍), represented by U+1F50D in Unicode, has evolved into a universal symbol for searching and zooming functions in digital interfaces. Originating from its practical use for detailed examination and discovery, it has been adopted by modern computer software and websites to denote tools for users to find information or closely inspect content. The right-pointing version, U+1F50E (🔎), continues this theme, often used to initiate searches. The integration of these icons into user interface design reflects

160-553: A schistose metasandstone (if the protolith is known to have been a sandstone ). If all that is known is that the protolith was a sedimentary rock, the schist will be described as a paraschist , while if the protolith was an igneous rock, the schist will be described as an orthoschist . Mineral qualifiers are important when naming a schist. For example, a quartz-feldspar-biotite schist is a schist of uncertain protolith that contains biotite mica, feldspar , and quartz in order of apparent decreasing abundance. Lineated schist has

200-421: A "standard" value of 0.25 m. A magnifying glass operates as the simplest form of optical instrument. It is essentially a hand-held lens that converges light to produce an enlarged, upright image that appears to stand where light doesn't actually converge, known as a 'virtual' image. To view an item in greater detail, it is positioned between the lens and its focal point, and the optimal observation occurs when

240-541: A glass globe filled with water, used to cauterize wounds. ( Seneca wrote that it could be used to read letters "no matter how small or dim". ) A convex lens used for forming a magnified image was described in the Book of Optics by Ibn al-Haytham in 1021. After the book was translated during the Latin translations of the 12th century , Roger Bacon described the properties of a magnifying glass in 13th-century England . This

280-441: A larger distance away, and a good image can be obtained very easily; the focus is not very sensitive to the eye's exact position. The magnifying power in this case is roughly MP  = (0.25 m)Φ. A typical magnifying glass might have a focal length of 25 cm, corresponding to an optical power of 4 dioptres. Such a magnifier would be sold as a "2×" magnifier. In actual use, an observer with "typical" eyes would obtain

320-471: A lightweight and efficient solution for enlarging visuals. The cultural impact of the magnifying glass extends far into the realms of literature and pop culture, symbolizing the pursuit of truth and the uncovering of secrets. It is famously associated with the investigative work of fictional detectives, with Sherlock Holmes being the most iconic figure to wield it, cementing its status as an emblem of detective fiction . Through its various forms and functions,

360-469: A magnifying power between 1 and 2, depending on where lens is held. A magnifying glass can serve as a fire-starting tool in survival situations. Any transparent lens with significant magnifying ability, such as a standard magnifying glass or a jeweler's loupe, can concentrate sunlight to ignite tinder. The technique involves positioning the lens to focus a small, intense spot of light onto the tinder, awaiting ignition with patience. The advantage of this method

400-466: A multiple-lens magnifier, such as a Hastings triplet . High power magnifiers are sometimes mounted in a cylindrical or conical holder with no handle, often designed to be worn on the head; this is called a loupe . Such magnifiers can reach up to about 30×, and at these magnifications the aperture of the magnifier becomes very small and it must be placed very close to both the object and the eye. For more convenient use or for magnification beyond about 30×,

440-416: A preferred direction in schist, often also forming very thin parallel layers. The ease with which the rock splits along the aligned grains accounts for the schistosity. Though not a defining characteristic, schists very often contain porphyroblasts (individual crystals of unusual size) of distinctive minerals, such as garnet , staurolite , kyanite , sillimanite , or cordierite . Because schists are

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480-412: A strong linear fabric in a rock which otherwise has well-developed schistosity. Schistosity is developed at elevated temperature when the rock is more strongly compressed in one direction than in other directions ( nonhydrostatic stress ). Nonhydrostatic stress is characteristic of regional metamorphism where mountain building is taking place (an orogenic belt ). The schistosity develops perpendicular to

520-408: A very large class of metamorphic rock, geologists will formally describe a rock as a schist only when the original type of the rock prior to metamorphism (the protolith ) is unknown and its mineral content is not yet determined. Otherwise, the modifier schistose will be applied to a more precise type name, such as schistose semipelite (when the rock is known to contain moderate amounts of mica) or

560-525: Is a different quantity). The magnifying power is the ratio of the sizes of the images formed on the user's retina with and without the lens. For the "without" case, it is typically assumed that the user would bring the object as close to one eye as possible without it becoming blurry. This point, known as the near point of accommodation , varies with age. In a young child, it can be as close as 5 cm, while, in an elderly person it may be as far as one or two metres. Magnifiers are typically characterized using

600-522: Is discernible, the schist is usually given a name reflecting its protolith, such as schistose metasandstone . Otherwise, the names of the constituent minerals will be included in the rock name, such as quartz-felspar-biotite schist . Schist bedrock can pose a challenge for civil engineering because of its pronounced planes of weakness . The word schist is derived ultimately from the Greek word σχίζειν ( schízein ), meaning "to split", which refers to

640-415: Is often used for starting fires. In another innovative form, the magnifying glass can manifest as a sheet magnifier , employing numerous slender, concentric, ring-shaped lenses. These are collectively known as a Fresnel lens , which, despite being significantly thinner, operates effectively as a single lens. This particular design finds its utility in applications such as screen magnifiers for TVs, offering

680-482: Is the orientation of grains in the surrounding medium-grained rock. The composition of the rock must permit formation of abundant platy minerals. For example, the clay minerals in mudstone are metamorphosed to mica, producing a mica schist. Early stages of metamorphism convert mudstone to a very fine-grained metamorphic rock called slate , which with further metamorphism becomes fine-grained phyllite . Further recrystallization produces medium-grained mica schist. If

720-608: Is the simplicity of the lens and the minimal effort required. However, its effectiveness is contingent upon clear, strong sunlight, which may be inconsistent depending on geographic location and time of year. Beyond survival uses, magnifying glasses are invaluable tools for jewelers and hobbyists. Jewelers rely on them to scrutinize the quality and authenticity of precious gems, ensuring accurate evaluations. Hobbyists, from those engaged in sewing and needlework to stamp collectors, depend on magnifying glasses for detailed work, enhancing both precision and enjoyment. This versatility underlines

760-418: Is uncommon but can form from metamorphosis of sedimentary beds containing abundant organic carbon . This may be of algal origin. Graphite schist is known to have experienced greenschist facies metamorphism , for example in the northern Andes . Metamorphosis of felsic volcanic rock , such as tuff, can produce quartz- muscovite schist. In geotechnical engineering a schistosity plane often forms

800-400: The Douro, but it plays a major part in the blends of the best ports . Traditionally a lot of US wine was fortified, and many of the producers of such 'port' have experimented with using Portuguese grapes as a way to improve their product. 553 tons of Touriga were crushed in 2006, up 26% on the previous year. The tiny berries of Touriga Nacional have a high skin to pulp ratio which heightens

840-401: The amount of extract in the wines. The grapes can produce intense, very aromatic wines with high tannin content. Bical Tinto, Mortágua, Mortágua Preto, Preto Mortágua, Touriga, Touriga Fina, Tourigao, Tourigo Antigo, Tourigo do Dão, and Turiga. Schist Schist ( / ˈ ʃ ɪ s t / SHIST ) is a medium-grained metamorphic rock showing pronounced schistosity (named for

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880-470: The area. Hand lens A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle. Beyond its primary function of magnification, this simple yet ingenious tool serves a variety of purposes. It can be employed to focus sunlight, harnessing the Sun's rays to create a concentrated hot spot at the lens's focus , which

920-448: The device in 1609, employing the magnifying lens in an innovative manner, further extending the application of optical technologies developed through the ages. The magnification of a magnifying glass depends upon where it is placed between the user's eye and the object being viewed, and the total distance between them. The magnifying power is equivalent to angular magnification (this should not be confused with optical power , which

960-456: The direction of greatest compression, also called the shortening direction, as platy minerals are rotated or recrystallized into parallel layers. While platy or elongated minerals are most obviously reoriented, even quartz or calcite may take up preferred orientations. At the microscopic level, schistosity is divided into internal schistosity , in which inclusions within porphyroblasts take a preferred orientation, and external schistosity , which

1000-425: The ease with which schists can be split along the plane in which the platy minerals lie. Before the mid-19th century, the terms slate , shale and schist were not sharply differentiated by those involved with mining. Geologists define schist as medium-grained metamorphic rock that shows well-developed schistosity. Schistosity is a thin layering of the rock produced by metamorphism (a foliation ) that permits

1040-419: The image is at the closest distance at which the eye can focus comfortably. The lens's magnification is the ratio of the image's apparent height to the object's actual height, correlating to the proportion of the distances from the image to the lens and the object to the lens. Moving the object nearer to the lens amplifies this effect, increasing magnification. The highest magnifying power is obtained by putting

1080-408: The intuitive connection between the physical act of magnifying to see more clearly and the metaphorical act of searching for information in the digital space. Beyond its digital symbolization for search functions, the magnifying glass also holds a place in educational symbolism, often representing curiosity, exploration, and the quest for knowledge. Educational institutions and programs frequently use

1120-408: The lens very close to one eye, and moving the eye and the lens together to obtain the best focus . The object will then typically also be close to the lens. The magnifying power obtained in this condition is MP 0  = (0.25 m)Φ + 1, where Φ is the optical power in dioptres , and the factor of 0.25 m represents the assumed near point (¼ m from the eye). This value of

1160-427: The lower-power types being much more common. At higher magnifications, the image quality of a simple magnifying glass becomes poor due to optical aberrations , particularly spherical aberration . When more magnification or a better image is required, other types of hand magnifier are typically used. A Coddington magnifier provides higher magnification with improved image quality. Even better images can be obtained with

1200-524: The lowest of any commercial grape variety. In recent years, scientists have been working on cloning the Touriga Nacional to produce vines that are able to pollinate better with the goal of increasing yields by 15% and sugar content by 10%. In the late 1990s there were 2,760 hectares of Touriga Nacional in Portugal. Its poor yields mean that it represents a tiny part of the wine production in

1240-681: The magnifying glass remains a tool of both practical utility and significant symbolic value. "The evidence indicates that the use of lenses was widespread throughout the Middle East and the Mediterranean basin over several millennia". Archaeological findings from the 1980s in Crete's Idaean Cave unearthed rock crystal lenses dating back to the Archaic Greek period , showcasing exceptional optical quality. These discoveries suggest that

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1280-592: The magnifying glass's enduring utility across a spectrum of activities, from professional assessments to leisure pursuits. Advanced digital magnifiers and apps have emerged as modern alternatives to traditional magnifying glasses, offering features such as variable magnification levels, high-contrast modes, and text-to-speech for visually impaired users. These tools not only magnify text and objects but also enhance readability and accessibility, making them invaluable for daily living and educational purposes. Magnifying glasses typically have low magnifying power: 2×–6×, with

1320-424: The magnifying power is the one normally used to characterize magnifiers. It is typically denoted " m ×", where m  =  MP 0 . This is sometimes called the total power of the magnifier (again, not to be confused with optical power). However, magnifiers are not always used as described above because it is more comfortable to put the magnifier close to the object (one focal length away). The eye can then be

1360-527: The metamorphism proceeds further, the mica schist experiences dehydration reactions that convert platy minerals to granular minerals such as feldspars, decreasing schistosity and turning the rock into a gneiss. Other platy minerals found in schists include chlorite, talc, and graphite. Chlorite schist is typically formed by metamorphism of ultramafic igneous rocks, as is talc schist. Talc schist also forms from metamorphosis of talc-bearing carbonate rocks formed by hydrothermal alteration . Graphite schist

1400-510: The other two divisions being gneiss , which has poorly developed schistosity and thicker layering, and granofels , which has no discernible schistosity. Schists are defined by their texture without reference to their composition, and while most are a result of medium-grade metamorphism, they can vary greatly in mineral makeup. However, schistosity normally develops only when the rock contains abundant platy minerals, such as mica or chlorite . Grains of these minerals are strongly oriented in

1440-400: The process of mountain building ( orogeny ) and usually reflects a medium grade of metamorphism. Schist can form from many different kinds of rocks, including sedimentary rocks such as mudstones and igneous rocks such as tuffs . Schist metamorphosed from mudstone is particularly common and is often very rich in mica (a mica schist ). Where the type of the original rock (the protolith )

1480-424: The rock to easily be split into flakes or slabs less than 5 to 10 millimeters (0.2 to 0.4 in) thick. The mineral grains in a schist are typically from 0.25 to 2 millimeters (0.01 to 0.08 in) in size and so are easily seen with a 10× hand lens . Typically, over half the mineral grains in a schist show a preferred orientation. Schists make up one of the three divisions of metamorphic rock by texture , with

1520-457: The rock). This means that the rock is composed of mineral grains easily seen with a low-power hand lens , oriented in such a way that the rock is easily split into thin flakes or plates. This texture reflects a high content of platy minerals, such as mica , talc , chlorite , or graphite . These are often interleaved with more granular minerals, such as feldspar or quartz . Schist typically forms during regional metamorphism accompanying

1560-516: The use of lenses for magnification and possibly for starting fires was widespread in the Mediterranean and Middle East, indicating an advanced understanding of optics in antiquity . The earliest explicit written evidence of a magnifying device is a joke in Aristophanes 's The Clouds from 424 BC, where magnifying lenses to ignite tinder were sold in a pharmacy, and Pliny the Elder 's "lens",

1600-431: Was followed by the development of eyeglasses in 13th-century Italy . Building on this foundation, in the late 1500s, two Dutch spectacle makers Jacob Metius and Zacharias Janssen crafted the compound microscope by assembling several magnifying lenses in a tube, marking a significant advancement in optical instruments. Not long after, Hans Lipperhey introduced the telescope in 1608 and Galileo Galilei improving on

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