Taxonomy and phylogeny.

The giant anteater got its binomial name from Carl Linnaeus in 1758. Its generic name, "Myrmecophaga", and specific name, "tridactyla", are both Greek, meaning "anteater" and "three fingers", respectively. "Myrmecophaga jubata" was used as a synonym. Three subspecies have been tentatively proposed: "M. t. tridactyla" (ranging from Venezuela and the Guianas to northern Argentina), "M. t. centralis" (native to Central America, northwestern Colombia, and northern Ecuador), and "M. t. artata" (native to northeastern Colombia and northwestern Venezuela). The giant anteater is grouped with the semiarboreal northern and southern tamanduas in the family Myrmecophagidae. Together with the family Cyclopedidae, whose only extant member is the arboreal silky anteater, the two families comprise the suborder Vermilingua.  Anteaters and sloths belong to order Pilosa and share superorder Xenarthra with the Cingulata (whose only extant members are armadillos). The two orders of Xenarthra split 66 million years ago (Mya) during the Late Cretaceous epoch. Anteaters and sloths diverged around 55 Mya, between the Paleocene and Eocene epochs. The "Cyclopes" lineage emerged around 30 Mya in the Oligocene epoch, while the "Myrmecophaga" and "Tamandua" lineages split 10 Mya in the Late Miocene subepoch. During most of the Cenozoic era, anteaters were confined to South America, which was formerly an island continent. Following the formation of the Isthmus of Panama about 3 Mya, anteaters of all three extant genera invaded Central America as part of the Great American Interchange.  The fossil record for anteaters is generally sparse. Known fossils include the Pliocene genus "Palaeomyrmidon", a close relative to the silky anteater, "Protamandua", the sister taxon to the clade that includes the giant anteater and the tamanduas from the Miocene, and "Neotamandua", a sister taxon to "Myrmecophaga". "Protamandua" was larger than the silky anteater, but smaller than a tamandua, while "Neotamandua" was larger, falling somewhere between a tamandua and a giant anteater. "Protamandua" did not appear to have feet specialized for terrestrial or arboreal locomotion, but it may have had a prehensile tail. "Neotamandua", though, is unlikely to have had a prehensile tail and its feet were intermediate in form between those of the tamanduas and the giant anteater. The species "Neotamandua borealis" was suggested to be an ancestor of the latter. Another member of the genus "Myrmecophaga" has been recovered from the Montehermosan Monte Hermoso Formation in Argentina and was described by Kraglievitch in 1934 as "Nunezia caroloameghinoi". The species was reclassified as "Myrmecophaga caroloameghinoi" by S. E. Hirschfeld in 1976.  The giant anteater is the most terrestrial of the living anteater species. Its ancestors may originally have been adapted to arboreal life; the transition to life on the ground could have been aided by the expansion of open habitats such as savanna in South America and the availability there of colonial insects, such as termites, that provided a larger potential food source. Both the giant anteater and the southern tamandua are well represented in the fossil record of the late Pleistocene and early Holocene.

Description.

The giant anteater can be identified by its large size, elongated muzzle, and long bushy tail. It has a total body length of. Males weigh and females weigh, making the giant anteater the biggest extant species in its suborder. The head of the giant anteater, at long, is particularly elongated, even when compared to other anteaters. Its tubular snout, which ends in its tiny mouth opening and nostrils, takes up most of its head. Its eyes and ears are relatively small. It has poor eyesight, but its sense of smell is 40 times more sensitive than that of humans. Giant anteaters can live around 16 years in captivity.  Even for an anteater, the neck is especially thick compared to the back of the head, and a small hump is found at the back of the neck. The coat is mostly greyish, brown or black and salted with white. The forelimbs are white, with black bands around the wrists, while the hindlimbs are dark. Thick black bands with white outlines stretch from throat to shoulder, ending in triangular points. The body ends in a brown tail. The coat hairs are long, especially on the tail, which makes the tail look larger than it actually is. A stiff mane stretches along the back. The bold pattern was thought to be disruptive camouflage, but a 2009 study suggests it is warning coloration. While adult males are slightly larger and more muscular than females, with wider heads and necks, visual sex determination can be difficult. The penis and testes are located internally between the rectum and urinary bladder in males, and females have a single pair of mammary glands near the armpits.  The giant anteater has broad ribs. Despite its specific name, "tridactyla," meaning three fingers, it has five toes on each foot. Four toes on the front feet have claws, which are particularly elongated on the second and third digits. It walks on its front knuckles similar to gorillas and chimpanzees. Doing this allows the giant anteater to keep its claws out of the way while walking. The middle digits, which support most of its weight, are extended at the metacarpophalangeal joints and bent at the interphalangeal joints. Unlike the front feet, the hind feet have short claws on all five toes and walk plantigrade. As a "hook-and-pull" digger, the giant anteater's enlarged supraspinous fossa gives the teres major more leverage—increasing the front limbs' pulling power—and the triceps muscle helps power the flexion of the thickened third digit of the front feet.  The giant anteater has a low body temperature for a mammal, about, a few degrees lower than a typical mammalian temperature of. Xenarthrans in general tend to have lower metabolic rates than most other mammals, a trend thought to correlate with their dietary specializations and low mobility.

Feeding anatomy.

The giant anteater has no teeth and is capable of only very limited jaw movement. It relies on the rotation of the two halves of its lower jaw, held together by a ligament at the tip, to open and close its mouth. This is accomplished by its masticatory muscles, which are relatively underdeveloped. Jaw depression creates an oral opening large enough for the slender tongue to flick out. It is typically long and is triangular posteriorly, rounded anteriorly, and ends in a small, rounded tip. The tongue is covered in backward-curving papillae and coated in thick, sticky saliva secreted from its enlarged salivary glands, which allows the giant anteater to collect insects with it.  The tube-like rostrum and small mouth opening restrict the tongue to protrusion-retraction movements. During feeding, the animal relies on the orientation of its head for aim. The tongue can reach up to, longer than the length of the skull, and move in and out around 160 times per minute (nearly three times per second). The anteater's tongue has little to no attachments to the hyoid and this is what allows it to flick its tongue at such distances and speed. The long sternoglossus muscle, which is formed by the fusion of the sternohyoid and the hyoglossus, is directly anchored to the sternum. The hyoid apparatus is large, V-shaped and flexible and supports the tongue as it goes in and out of the mouth. The buccinators allow it to slide back in without losing attached food and tighten the mouth to prevent food from escaping as it extends. When retracted, the tongue is held in the oropharynx by the secondary palate, preventing it from blocking respiration.  Giant anteaters swallow at a much higher rate than most other mammals; when feeding, they swallow almost continuously. Before being swallowed, insects are crushed against the palate. The giant anteater's stomach, similar to a bird's gizzard, has hardened folds and uses strong contractions to grind up the insects. The digestive process is assisted by small amounts of ingested sand and soil. The giant anteater cannot produce stomach acid of its own, but uses the formic acid of its prey for digestion.

Distribution and status.

The giant anteater is native to Central and South America. Its known range stretches from Honduras to northern Argentina, and fossil remains have been found as far north as northwestern Sonora, Mexico. It is largely absent from the Andes and has been extirpated in Uruguay. It may also be extirpated in Belize, Costa Rica, and Guatemala. The species is found in a number of habitats including both tropical rainforest and xeric shrubland, provided enough prey is present to sustain it.  The species is listed as Vulnerable by the IUCN, due to the number of regional extirpations, and under Appendix II by CITES, tightly restricting trade in specimens of the animal. Between 2000 and 2010, the total population declined by 30%. In 1994, some 340 giant anteaters died due to wildfires at Emas National Park in Brazil. The animal is particularly vulnerable to fires due to its slow movement and flammable coat.  Human-induced threats include collision with vehicles, attacks by dogs, and destruction of habitat. The giant anteater is commonly hunted in Bolivia, both for sport and sustenance. The animal's thick, leathery hide is used to make equestrian equipment in the Chaco. In Venezuela, it is hunted for its claws. Giant anteaters are killed for safety reasons, due to their reputation as dangerous animals. The giant anteater remains widespread. Some populations are stable and the animal is found in various protected areas in the Amazon, Pantanal and the "Cerrado". It is officially protected in some Argentine provinces as a national heritage species.

Behavior and ecology.

The giant anteater may use multiple habitats. A 2007 study of giant anteaters in the Brazilian Pantanal found the animals generally forage in open areas and rest in forested areas, possibly because forests are warmer than grasslands on cold days and cooler on hot days. Giant anteaters can be either diurnal or nocturnal. A 2006 study in the Pantanal found those anteaters to be mostly nocturnal: they are most active during nighttime and early morning, and retire as the temperature rises. On colder days, they start and end periods of activity earlier, shifting them into daylight hours, and may become diurnal. Diurnal giant anteaters have been observed at Serra da Canastra. Nocturnality in anteaters may be a response to human disturbances.  Giant anteaters typically rest in dense brush, but may use tall grass on cooler days. They carve a shallow cavity in the ground for resting. The animal sleeps curled up with its bushy tail folded over its body. The tail serves both to conserve body heat and as camouflage. One anteater was recorded sleeping with its tail stretched out on a sunny morning with an ambient temperature of ; possibly it was positioned this way to allow its body to absorb the sun's rays for warmth.  Giant anteaters are good swimmers and are capable of moving through wide rivers. They have been observed to bathe. They are also able to climb and have been recorded ascending both termite mounds and trees while foraging. One individual was observed holding onto a branch with its feet just touching the ground.

Spacing.

Giant anteaters' home ranges vary in size depending on the location. At Serra da Canastra National Park in Brazil, female anteaters have home ranges around, while males live in home ranges of. In other parts of Brazil, anteaters may have ranges. Anteaters from Venezuela have been recorded living in home ranges as large as. Individuals mostly live alone, except for females that nurse their young and males courting females. Anteaters communicate their presence, status, and sexual condition with secretions from their anal glands. They also advertise their presence to other individuals though tree markings and urine. They appear to be able to recognize each other's saliva by scent.  Females appear to be more tolerant of females than males are of males, leading to greater overlap in female home ranges. Males are more likely to engage in agonistic behaviors, such as slowly circling each other, chasing, or actual fighting. Circling anteaters may cry a drawn-out "harrr". In combat, they slash at each other with their claws and wrestle each other to the ground. Fighting anteaters may emit roars or bellows. Males are possibly territorial.

Foraging and predation.

This animal is an insectivore, feeding mostly on ants or termites. In areas that experience seasonal flooding, like the grassy plains of the Venezuelan llanos, anteaters mainly feed on ants, because termites are less available. Conversely, anteaters at Emas National Park eat mainly termites, which occur in high density on the grasslands. At Serra da Canastra, anteaters switch between eating mainly ants during the wet season (October to March) and termites during the dry season (May to September).  Anteaters track prey by their scent. After finding a nest, the animal tears it open with its long fore claws and inserts its long, sticky tongue to collect its prey. An anteater spends one minute on average feeding at a nest, visiting up to 200 nests in one day and consuming as many as 30,000 insects. The anteater may be driven away from a nest by the chemical or biting attacks of soldiers. Some termite species rely on their fortified mounds for protection and many individuals escape while the predator digs. These modes of defense prevent the entire colony from being eaten in one anteater attack.  Other prey include the larvae of beetles and western honey bees that have located their hives in termite mounds. Anteaters may target termite mounds with bee hives. In captivity, anteaters are fed mixtures made of milk, eggs, mealworms, and ground beef. To drink, an anteater may dig for water when no surface water is available, creating waterholes for other animals. Giant anteaters are primarily prey for jaguars and pumas. They typically flee from danger by galloping, but if cornered, will rear up on their hind legs and slash at the attacker. The front claws of the giant anteater are formidable weapons, capable of killing a jaguar. The giant anteater is a host of the Acanthocephalan intestinal parasites "Gigantorhynchus echinodiscus" and "Moniliformis monoechinus".

Reproduction and parenting.

Giant anteaters can mate throughout the year. During courtship, a male consorts with an estrous female, following and sniffing her. Male and female pairs are known to feed at the same insect nest. While mating, the female lies on her side as the male crouches over her. A couple may stay together for up to three days and mate several times during that period. Gestation lasts around 190 days and ends with the birth of a single pup, which typically weighs around. Females give birth standing upright.  Pups are born with eyes closed and begin to open them after six days. The mother carries its dependent pup on its back. The pup's black and white band aligns with its mother's, camouflaging it. The young communicate with their mothers with sharp whistles and use their tongues during nursing. After three months, the pup begins to eat solid food and is fully weaned by ten months. The mother grooms her offspring during rest periods lasting up to an hour. Grooming peaks during the first three months and declines as the young reaches nine months of age, ending by ten months. The decline mirrors that of the weakening bond between mother and offspring; young anteaters usually become independent by nine or ten months. Anteaters are sexually mature in 2.5–4 years.

Interactions with humans.

Although they are shy and typically attempt to avoid humans, giant anteaters can inflict severe wounds with their front claws and have been known to seriously injure or kill humans who corner and threaten them. Between 2010 and 2012, two hunters were killed by giant anteaters in Brazil; in both cases, the hunters were agitating and wounding cornered animals and the attacks appeared to be defensive behaviors. In April 2007, an anteater at the Florencio Varela Zoo mauled and killed a zookeeper with its front claws. The animal in question, a male named Ramon, had a reputation for aggressiveness.

In culture.

In the mythology and folklore of the indigenous peoples of the Amazon Basin, the giant anteater is depicted as a trickster foil to the jaguar, as well as a humorous figure due to its long snout. In one Shipib tale, an anteater challenged a jaguar to a breath-holding contest under water, which the jaguar accepted. After the two removed their pelts and submerged, the anteater jumped out of the water and stole the jaguar's pelt, leaving the jaguar with the anteater's pelt. In a Yarabara myth, the evil ogre Ucara is transformed into one by the sun. This myth emphasizes the nearly immobile nature of the anteater's mouth, which was considered a burden. The Kayapo people wear masks of various animals and spirits, including the anteater, during naming and initiation ceremonies. They believe women who touched anteater masks or men who stumbled while wearing them would die or receive some sort of physical disorder.  During the Spanish colonization of the Americas, the giant anteater was one of many native fauna taken to Europe for display. At first, Europeans believed all anteaters were female and mated with their noses, a misconception corrected by naturalist Félix de Azara. In the 20th century, Salvador Dalí wrote imaginatively that the giant anteater "reaches sizes bigger than the horse, possesses enormous ferocity, has exceptional muscle power, is a terrifying animal." Dalí depicted an anteater in the style of "The Great Masturbator". It was used as a bookplate for André Breton, who compared the temptations a man experiences in life to what "the tongue of the anteater must offer to the ant."  The 1940 Max Fleischer cartoon "Ants in the Plants" features a colony of ants fighting off a villainous anteater. Released during the Phoney War, the film may have alluded to France's Maginot Line. An anteater is also a recurring character in the comic strip B.C.. This character was the inspiration for Peter the Anteater, the University of California, Irvine team mascot. In the Stephen King miniseries "Kingdom Hospital", the character Antubis appears in the form of an anteater-like creature with razor-sharp teeth.

The giant anteater ("Myrmecophaga tridactyla"), also known as the ant bear, is an insectivorous mammal native to Central and South America. It is one of four living species of anteaters, the only extant member of the genus Myrmecophaga, and is classified with sloths in the order Pilosa. This species is mostly terrestrial, in contrast to other living anteaters and sloths, which are arboreal or semiarboreal. The giant anteater is the biggest of its family, in length, with weights of for males and for females. It is recognizable by its elongated snout, bushy tail, long fore claws, and distinctively colored pelage.

大食蚁兽(学名:"Myrmecophaga tridactyla")是异关节总目披毛目食蚁兽的一种,为一种大型的食虫动物,和树懒为近亲。分布在中美洲与南美洲部分地区,生活在草地、落叶林和雨林地区。主要以蚂蚁和白蚁为食,一天最多可食30,000只昆虫。


伊丽莎白公主 (普法尔茨)

Life.

Elisabeth Simmern van Pallandt was born on December 26, 1618 in Heidelberg. She was the third of thirteen children and eldest daughter of Frederick V, Elector Palatine, and Elizabeth Stuart, granddaughter of James I of England and sister of Charles I.  Much of Elisabeth's early life outside of her familial relations is unknown. After a short, unsuccessful reign in Bohemia, Elisabeth's parents were forced into exile in the Netherlands in 1620. Elisabeth stayed with her grandmother Louise Juliana of Nassau in Heidelberg before moving to the Netherlands at the age of nine.  Elisabeth had a wide ranging education, studying philosophy, astronomy, mathematics, jurisprudence, history, modern and classical languages. Her siblings nicknamed her "La Grecque" ("The Greek") based on her skill with the ancient language.  Elisabeth also studied the fine arts including painting, music and dancing. She may have been tutored by Constantijn Huygens.  In 1633, Elisabeth received a proposal of marriage from Władysław IV Vasa, King of Poland. The marriage would have been beneficial to the Palatine fortunes, but the king was a Catholic, and Elisabeth refused to convert from her Protestant faith in order to facilitate the marriage.  Edward Reynolds dedicated his "Treatise on the passions and the faculties of the soule of man" (1640) to Elisabeth. Although the exact context of the dedication is unknown, the dedication suggests that Elisabeth had seen a draft of the work.  In 1642, Elisabeth read Descartes' "Meditations on First Philosophy".  In 1646, Elisabeth's brother Philip killed a man in a duel. Elisabeth was sent to stay with family in Germany where she tried to interest professors in Descartes' work.  In 1660, Elisabeth entered the Lutheran convent at Herford, and in 1667 she became abbess of the convent. While the convent was Lutheran, Elisabeth was a Calvinist. Although the previous abbess (Elisabeth's cousin) had also been a Calvinist, this difference in faith created some initial distrust.  As abbess, she presided over the convent and also governed the surrounding community of 7,000 people. While Elisabeth was abbess, the convent became a refuge from religious persecution for people and she welcomed more marginal religious sects, including the Labadists. When Robert Barclay's father David was imprisoned, Elisabeth intervened and helped to get him released.  Elisabeth died on February 12, 1680. She was buried in the Abbey Church of Herford.

Correspondence.

Throughout her adult years, Elisabeth corresponded with many renowned intellectuals of her time.  By 1639, Elisabeth was corresponding with Anna Maria van Schurman, a learned woman, called the Dutch Minerva. In an early letter van Schurman offered Elisabeth guidance on what subjects to study, arguing for the usefulness of history.  Elisabeth's correspondence with Descartes began in 1643 and continued until Descartes's death in early 1650. At her request, Descartes became her teacher in philosophy and morals, and in 1644 he dedicated to her his "Principia".  Many of Descartes's letters to Elisabeth were published in the volumes of his correspondence edited by Claude Clerselier, but Elisabeth refused the request to publish her side of the exchange. Elisabeth's side of the correspondence was first published in 1879 by Louis-Alexandre Foucher de Careil, after he was alerted to its existence by an antiquarian bookseller, Frederick Müller, who had found a packet of letters in Rosendael.  Elisabeth also corresponded with a number of prominent Quakers, including Robert Barclay and William Penn.  There are letters written both by and to her concerning political and financial matters in the English Calendar of State Papers.

Family.

Siblings

Contributions to philosophy: Descartes and other prominent figures.

Elisabeth met Descartes on one of Descartes' visits to The Hague. Descartes visited The Hague to meet some of the leading intellectual figures in Holland who might support his philosophy. The Hague was often a gathering place to meet other influential, powerful people. As Descartes talked of his ideas, Elisabeth intently listened and became very interested in Descartes' thoughts of the mind and body. After Descartes' visit, it was told to him that Elisabeth had been very interested in his work. Descartes was flattered and told others that he would like to get to know the princess better. Descartes made another visit to The Hague, and was intent on having a conversation with Elisabeth, although this conversation for some reason did not happen.Elisabeth, upon hearing of Descartes' failed attempt to converse with her, wrote to Descartes a letter. In this letter, dated May 16, 1643, Elisabeth writes, "tell me please how the soul of a human being (it being only a thinking substance) can determine the bodily spirits and so bring about voluntary actions". Elisabeth is questioning Descartes' idea of dualism and how the soul and the body could interact. Elisabeth rightly questioned how something immaterial (Descartes' idea of the mind) could move something material (the body). Descartes replied to Elisabeth's letter with the answer that this interaction should not be thought of as between two bodies and that it is the kind of union that exists between the two qualities of heaviness and bodies.  Elisabeth was not satisfied with this answer, so she wrote to Descartes again. In this letter, dated June 20, 1643, Elisabeth writes that she cannot "understand the idea through which we must judge how the soul (nonextended and immaterial) is able to move the body, that is, by that idea through which you have at another time understood heaviness... And I admit that it would be easier for me to concede matter and extension to the mind than it would be for me to concede the capacity to move a body and be moved by one to an immaterial thing." Jaegwon Kim cites this as the first causal argument for the doctrine of physicalism in philosophy of mind. In another letter from Elisabeth to Descartes dated July 1, 1643, Elisabeth agrees with Descartes that our senses are evidence that the soul does move the body and the body moves the soul, but that this interaction does not teach us anything about how this happens. In Elisabeth's correspondence with Descartes, we can see that Elisabeth assumes that Descartes does have an account of how the soul and body interact and asks for clarification on how the soul does this. In fact, Descartes did not have an exact account of how this happens, but merely assumed the soul had this capability. This particular correspondence between Descartes and Elisabeth ended with this July 1 letter.  The correspondence began again, but two years later. In this correspondence, Elisabeth and Descartes discuss an illness Elisabeth suffered from in the summer of 1645. Descartes writes to Elisabeth that he thinks her symptoms are caused by sadness. This could very well have been true, as Elisabeth's brother Philip had challenged a family suitor and then stabbed the suitor in public, resulting in social backlash. This caused Elisabeth much distress and worry. Elisabeth originally intended the letters to be private and has no extant philosophical works. This makes her place in the history of philosophy complex and the subject of debate. This specific correspondence between Elisabeth and Descartes is often ignored by many historians, as they see it as insignificant, but a few regard it as influential in that Descartes and Elisabeth seem to be talking of the "passions of the soul", as Descartes referred to them. Some historians have remarked that Elisabeth could have been a philosopher in her own right if it had not been for a lack of a systematic presentation of her philosophical position.  In addition to Descartes, Elisabeth held correspondence with many others, including various Quakers. Among them most notably were Edward Reynolds, Nicholas Malebranche, Gottfried Wilhelm Leibniz, Robert Barclay, and William Penn. While they seemed to have the aim of converting her to their faith, Elisabeth seemed to be focused on the intellectual interest of their ideals and beliefs. She also held a correspondence for a time with the "Dutch Minerva", Anna Maria van Schurman, who encouraged Elisabeth to further her studies in history, physics, and astronomy. While their correspondence was not extensive, Van Schurman was a mentor to Elisabeth and guided her in her scholarly studies. She was respected and revered by Princess Elisabeth to a great degree. Elisabeth asked for her advice on new topics and subjects of study often. Van Schurman took the initiative in giving Elisabeth her opinion on the new discoveries of their time. The area in which they seemed to diverge was in their opinion of Descartes. Elisabeth was intrigued by the new Cartesian philosophy and wanted to learn more about it. Van Schurman, however, emphatically refuted the idea when Elisabeth inquired about it, instead defending the scholastic traditional view. As much as she respected Van Schurman, this did not stop Elisabeth from pursuing her interest in Descartes and his doctrine. It has been speculated that Elisabeth's correspondence and deep connection with Descartes effectively ended her communications with Van Schurman.

Contributions to the feminist history of philosophy.

Elisabeth of Bohemia has been a key subject in the feminist history of philosophy. She has garnered attention as prominent female thinker and for her practical role in the development of 17th century female scholars. Feminist scholars study her correspondences and life to understand the limitations placed on 17th century female thinkers. Some scholars cite Elisabeth as an example of how philosophical conceptions of women as philosophers excluded them from the philosophical canon. For feminist scholars, her correspondence with Descartes presents an example of the value of including women in the canon. Some argue that Elisabeth's correspondence with Descartes helps feminist scholars re-conceptualize how women are to be included in the philosophical canon. Feminist scholars are concerned with how Elisabeth's gender informed her philosophy. Many believe that Elisabeth was keenly aware of the limitations of her sex. One scholar states that Elisabeth's health and femininity informed her interest about the immaterial soul's influence on the material body. Elisabeth's influence also extends to the development of other 17th century female thinkers. She utilized her exile court in The Hague to create a network of female scholars. Her network was a space where women could engage in philosophical inquiry through correspondence. Including Elisabeth, the network consisted of Anna Maria van Schurman, Marie de Gournay, and Lady Ranelagh.

Elisabeth of the Palatinate (26 December 1618 – 11 February 1680), also known as Elisabeth of Bohemia, Princess Elisabeth of the Palatinate, or Princess-Abbess of Herford Abbey, was the eldest daughter of Frederick V, Elector Palatine (who was briefly King of Bohemia), and Elizabeth Stuart. Elisabeth of the Palatinate was a philosopher best known for her correspondence with René Descartes. She was critical of Descartes' dualistic metaphysics and her work anticipated the metaphysical concerns of later philosophers.

普法尔茨的伊丽莎白(),或以波希米亚的伊丽莎白、普法尔茨的伊丽莎白公主、的公主兼女院长等为人所知,是普法尔茨选侯腓特烈五世与(其父为詹姆士六世及一世)最年长的女儿。


Features.

Object-oriented programming uses objects, but not all of the associated techniques and structures are supported directly in languages that claim to support OOP. The features listed below are common among languages considered to be strongly class- and object-oriented (or multi-paradigm with OOP support), with notable exceptions mentioned.

Shared with non-OOP predecessor languages.

Modular programming support provides the ability to group procedures into files and modules for organizational purposes. Modules are namespaced so identifiers in one module will not conflict with a procedure or variable sharing the same name in another file or module.

Objects and classes.

Languages that support object-oriented programming (OOP) typically use inheritance for code reuse and extensibility in the form of either classes or prototypes. Those that use classes support two main concepts:  Objects sometimes correspond to things found in the real world. For example, a graphics program may have objects such as "circle", "square", "menu". An online shopping system might have objects such as "shopping cart", "customer", and "product". Sometimes objects represent more abstract entities, like an object that represents an open file, or an object that provides the service of translating measurements from U.S. customary to metric.  Each object is said to be an instance of a particular class (for example, an object with its name field set to "Mary" might be an instance of class Employee). Procedures in object-oriented programming are known as methods; variables are also known as fields, members, attributes, or properties. This leads to the following terms:  Objects are accessed somewhat like variables with complex internal structure, and in many languages are effectively pointers, serving as actual references to a single instance of said object in memory within a heap or stack. They provide a layer of abstraction which can be used to separate internal from external code. External code can use an object by calling a specific instance method with a certain set of input parameters, read an instance variable, or write to an instance variable. Objects are created by calling a special type of method in the class known as a constructor. A program may create many instances of the same class as it runs, which operate independently. This is an easy way for the same procedures to be used on different sets of data.  Object-oriented programming that uses classes is sometimes called class-based programming, while prototype-based programming does not typically use classes. As a result, a significantly different yet analogous terminology is used to define the concepts of "object" and "instance".  In some languages classes and objects can be composed using other concepts like traits and mixins.

Class-based vs prototype-based.

In class-based languages the "classes" are defined beforehand and the "objects" are instantiated based on the classes. If two objects "apple" and "orange" are instantiated from the class "Fruit", they are inherently fruits and it is guaranteed that you may handle them in the same way; e.g. a programmer can expect the existence of the same attributes such as "color" or "sugar_content" or "is_ripe".  In prototype-based languages the "objects" are the primary entities. No "classes" even exist. The "prototype" of an object is just another object to which the object is linked. Every object has one "prototype" link (and only one). New objects can be created based on already existing objects chosen as their prototype. You may call two different objects "apple" and "orange" a fruit, if the object "fruit" exists, and both "apple" and "orange" have "fruit" as their prototype. The idea of the "fruit" class doesn't exist explicitly, but as the equivalence class of the objects sharing the same prototype. The attributes and methods of the "prototype" are delegated to all the objects of the equivalence class defined by this prototype. The attributes and methods "owned" individually by the object may not be shared by other objects of the same equivalence class; e.g. the attribute "sugar_content" may be unexpectedly not present in "apple". Only single inheritance can be implemented through the prototype.

Dynamic dispatch/message passing.

It is the responsibility of the object, not any external code, to select the procedural code to execute in response to a method call, typically by looking up the method at run time in a table associated with the object. This feature is known as dynamic dispatch, and distinguishes an object from an abstract data type (or module), which has a fixed (static) implementation of the operations for all instances. If the call variability relies on more than the single type of the object on which it is called (i.e. at least one other parameter object is involved in the method choice), one speaks of multiple dispatch.  A method call is also known as "message passing". It is conceptualized as a message (the name of the method and its input parameters) being passed to the object for dispatch.

Encapsulation.

Encapsulation is an object-oriented programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse. Data encapsulation led to the important OOP concept of data hiding.  If a class does not allow calling code to access internal object data and permits access through methods only, this is a strong form of abstraction or information hiding known as encapsulation. Some languages (Java, for example) let classes enforce access restrictions explicitly, for example denoting internal data with the codice_1 keyword and designating methods intended for use by code outside the class with the codice_2 keyword. Methods may also be designed public, private, or intermediate levels such as codice_3 (which allows access from the same class and its subclasses, but not objects of a different class). In other languages (like Python) this is enforced only by convention (for example, codice_1 methods may have names that start with an underscore). Encapsulation prevents external code from being concerned with the internal workings of an object. This facilitates code refactoring, for example allowing the author of the class to change how objects of that class represent their data internally without changing any external code (as long as "public" method calls work the same way). It also encourages programmers to put all the code that is concerned with a certain set of data in the same class, which organizes it for easy comprehension by other programmers. Encapsulation is a technique that encourages decoupling.

Composition, inheritance, and delegation.

Objects can contain other objects in their instance variables; this is known as object composition. For example, an object in the Employee class might contain (either directly or through a pointer) an object in the Address class, in addition to its own instance variables like "first_name" and "position". Object composition is used to represent "has-a" relationships: every employee has an address, so every Employee object has access to a place to store an Address object (either directly embedded within itself, or at a separate location addressed via a pointer).  Languages that support classes almost always support inheritance. This allows classes to be arranged in a hierarchy that represents "is-a-type-of" relationships. For example, class Employee might inherit from class Person. All the data and methods available to the parent class also appear in the child class with the same names. For example, class Person might define variables "first_name" and "last_name" with method "make_full_name()". These will also be available in class Employee, which might add the variables "position" and "salary". This technique allows easy re-use of the same procedures and data definitions, in addition to potentially mirroring real-world relationships in an intuitive way. Rather than utilizing database tables and programming subroutines, the developer utilizes objects the user may be more familiar with: objects from their application domain.  Subclasses can override the methods defined by superclasses. Multiple inheritance is allowed in some languages, though this can make resolving overrides complicated. Some languages have special support for mixins, though in any language with multiple inheritance, a mixin is simply a class that does not represent an is-a-type-of relationship. Mixins are typically used to add the same methods to multiple classes. For example, class UnicodeConversionMixin might provide a method unicode_to_ascii() when included in class FileReader and class WebPageScraper, which don't share a common parent.  Abstract classes cannot be instantiated into objects; they exist only for the purpose of inheritance into other "concrete" classes which can be instantiated. In Java, the codice_5 keyword can be used to prevent a class from being subclassed.  The doctrine of composition over inheritance advocates implementing has-a relationships using composition instead of inheritance. For example, instead of inheriting from class Person, class Employee could give each Employee object an internal Person object, which it then has the opportunity to hide from external code even if class Person has many public attributes or methods. Some languages, like Go do not support inheritance at all.  The "open/closed principle" advocates that classes and functions "should be open for extension, but closed for modification".  Delegation is another language feature that can be used as an alternative to inheritance.

Polymorphism.

Subtyping – a form of polymorphism – is when calling code can be agnostic as to which class in the supported hierarchy it is operating on – the parent class or one of its descendants. Meanwhile, the same operation name among objects in an inheritance hierarchy may behave differently.  For example, objects of type Circle and Square are derived from a common class called Shape. The Draw function for each type of Shape implements what is necessary to draw itself while calling code can remain indifferent to the particular type of Shape being drawn.  This is another type of abstraction which simplifies code external to the class hierarchy and enables strong separation of concerns.

Open recursion.

In languages that support open recursion, object methods can call other methods on the same object (including themselves), typically using a special variable or keyword called codice_6 or codice_7. This variable is "late-bound"; it allows a method defined in one class to invoke another method that is defined later, in some subclass thereof.

History.

Terminology invoking "objects" and "oriented" in the modern sense of object-oriented programming made its first appearance at MIT in the late 1950s and early 1960s. In the environment of the artificial intelligence group, as early as 1960, "object" could refer to identified items (LISP atoms) with properties (attributes); Alan Kay was later to cite a detailed understanding of LISP internals as a strong influence on his thinking in 1966.  Another early MIT example was Sketchpad created by Ivan Sutherland in 1960–61; in the glossary of the 1963 technical report based on his dissertation about Sketchpad, Sutherland defined notions of "object" and "instance" (with the class concept covered by "master" or "definition"), albeit specialized to graphical interaction. Also, an MIT ALGOL version, AED-0, established a direct link between data structures ("plexes", in that dialect) and procedures, prefiguring what were later termed "messages", "methods", and "member functions".  In the 1960s, object-oriented programming was put into practice with the Simula language, which introduced important concepts that are today an essential part of object-oriented programming, such as class and object, inheritance, and dynamic binding. Simula was also designed to take account of programming and data security. For programming security purposes a detection process was implemented so that through reference counts a last resort garbage collector deleted unused objects in the random-access memory (RAM). But although the idea of data objects had already been established by 1965, data encapsulation through levels of scope for variables, such as private (-) and public (+), were not implemented in Simula because it would have required the accessing procedures to be also hidden.  In 1962, Kristen Nygaard initiated a project for a simulation language at the Norwegian Computing Center, based on his previous use of the Monte Carlo simulation and his work to conceptualise real-world systems. Ole-Johan Dahl formally joined the project and the Simula programming language was designed to run on the Universal Automatic Computer (UNIVAC) 1107. In the early stages Simula was supposed to be a procedure package for the programming language ALGOL 60. Dissatisfied with the restrictions imposed by ALGOL the researchers decided to develop Simula into a fully-fledged programming language, which used the UNIVAC ALGOL 60 compiler. Simula launched in 1964, and was promoted by Dahl and Nygaard throughout 1965 and 1966, leading to increasing use of the programming language in Sweden, Germany and the Soviet Union. In 1968, the language became widely available through the Burroughs B5500 computers, and was later also implemented on the URAL-16 computer. In 1966, Dahl and Nygaard wrote a Simula compiler. They became preoccupied with putting into practice Tony Hoare's record class concept, which had been implemented in the free-form, English-like general-purpose simulation language SIMSCRIPT. They settled for a generalised process concept with record class properties, and a second layer of prefixes. Through prefixing a process could reference its predecessor and have additional properties. Simula thus introduced the class and subclass hierarchy, and the possibility of generating objects from these classes. The Simula 1 compiler and a new version of the programming language, Simula 67, was introduced to the wider world through the research paper "Class and Subclass Declarations" at a 1967 conference.  A Simula 67 compiler was launched for the System/360 and System/370 IBM mainframe computers in 1972. In the same year a Simula 67 compiler was launched free of charge for the French CII 10070 and CII Iris 80 mainframe computers. By 1974, the Association of Simula Users had members in 23 different countries. Early 1975 a Simula 67 compiler was released free of charge for the DECsystem-10 mainframe family. By August the same year the DECsystem-10 Simula 67 compiler had been installed at 28 sites, 22 of them in North America. The object-oriented Simula programming language was used mainly by researchers involved with physical modelling, such as models to study and improve the movement of ships and their content through cargo ports.  In the 1970s, the first version of the Smalltalk programming language was developed at Xerox PARC by Alan Kay, Dan Ingalls and Adele Goldberg. Smaltalk-72 included a programming environment and was dynamically typed, and at first was interpreted, not compiled. Smalltalk got noted for its application of object orientation at the language level and its graphical development environment. Smalltalk went through various versions and interest in the language grew. While Smalltalk was influenced by the ideas introduced in Simula 67 it was designed to be a fully dynamic system in which classes could be created and modified dynamically.  In the 1970s, Smalltalk influenced the Lisp community to incorporate object-based techniques that were introduced to developers via the Lisp machine. Experimentation with various extensions to Lisp (such as LOOPS and Flavors introducing multiple inheritance and mixins) eventually led to the Common Lisp Object System, which integrates functional programming and object-oriented programming and allows extension via a Meta-object protocol. In the 1980s, there were a few attempts to design processor architectures that included hardware support for objects in memory but these were not successful. Examples include the Intel iAPX 432 and the Linn Smart Rekursiv.  In 1981, Goldberg edited the August 1981 issue of Byte Magazine, introducing Smalltalk and object-oriented programming to a wider audience. In 1986, the Association for Computing Machinery organised the first "Conference on Object-Oriented Programming, Systems, Languages, and Applications" (OOPSLA), which was unexpectedly attended by 1,000 people. In the mid-1980s Objective-C was developed by Brad Cox, who had used Smalltalk at ITT Inc., and Bjarne Stroustrup, who had used Simula for his PhD thesis, eventually went to create the object-oriented C++. In 1985, Bertrand Meyer also produced the first design of the Eiffel language. Focused on software quality, Eiffel is a purely object-oriented programming language and a notation supporting the entire software lifecycle. Meyer described the Eiffel software development method, based on a small number of key ideas from software engineering and computer science, in Object-Oriented Software Construction. Essential to the quality focus of Eiffel is Meyer's reliability mechanism, Design by Contract, which is an integral part of both the method and language. In the early and mid-1990s object-oriented programming developed as the dominant programming paradigm when programming languages supporting the techniques became widely available. These included Visual FoxPro 3.0, C++, and Delphi. Its dominance was further enhanced by the rising popularity of graphical user interfaces, which rely heavily upon object-oriented programming techniques. An example of a closely related dynamic GUI library and OOP language can be found in the Cocoa frameworks on Mac OS X, written in Objective-C, an object-oriented, dynamic messaging extension to C based on Smalltalk. OOP toolkits also enhanced the popularity of event-driven programming (although this concept is not limited to OOP).  At ETH Zürich, Niklaus Wirth and his colleagues had also been investigating such topics as data abstraction and modular programming (although this had been in common use in the 1960s or earlier). Modula-2 (1978) included both, and their succeeding design, Oberon, included a distinctive approach to object orientation, classes, and such.  Object-oriented features have been added to many previously existing languages, including Ada, BASIC, Fortran, Pascal, and COBOL. Adding these features to languages that were not initially designed for them often led to problems with compatibility and maintainability of code.  More recently, a number of languages have emerged that are primarily object-oriented, but that are also compatible with procedural methodology. Two such languages are Python and Ruby. Probably the most commercially important recent object-oriented languages are Java, developed by Sun Microsystems, as well as C# and Visual Basic.NET (VB.NET), both designed for Microsoft's.NET platform. Each of these two frameworks shows, in its own way, the benefit of using OOP by creating an abstraction from implementation. VB.NET and C# support cross-language inheritance, allowing classes defined in one language to subclass classes defined in the other language.

OOP languages.

Simula (1967) is generally accepted as being the first language with the primary features of an object-oriented language. It was created for making simulation programs, in which what came to be called objects were the most important information representation. Smalltalk (1972 to 1980) is another early example, and the one with which much of the theory of OOP was developed. Concerning the degree of object orientation, the following distinctions can be made:

OOP in dynamic languages.

In recent years, object-oriented programming has become especially popular in dynamic programming languages. Python, PowerShell, Ruby and Groovy are dynamic languages built on OOP principles, while Perl and PHP have been adding object-oriented features since Perl 5 and PHP 4, and ColdFusion since version 6.  The Document Object Model of HTML, XHTML, and XML documents on the Internet has bindings to the popular JavaScript/ECMAScript language. JavaScript is perhaps the best known prototype-based programming language, which employs cloning from prototypes rather than inheriting from a class (contrast to class-based programming). Another scripting language that takes this approach is Lua.

OOP in a network protocol.

The messages that flow between computers to request services in a client-server environment can be designed as the linearizations of objects defined by class objects known to both the client and the server. For example, a simple linearized object would consist of a length field, a code point identifying the class, and a data value. A more complex example would be a command consisting of the length and code point of the command and values consisting of linearized objects representing the command's parameters. Each such command must be directed by the server to an object whose class (or superclass) recognizes the command and is able to provide the requested service. Clients and servers are best modeled as complex object-oriented structures. Distributed Data Management Architecture (DDM) took this approach and used class objects to define objects at four levels of a formal hierarchy:  The initial version of DDM defined distributed file services. It was later extended to be the foundation of Distributed Relational Database Architecture (DRDA).

Design patterns.

Challenges of object-oriented design are addressed by several approaches. Most common is known as the design patterns codified by Gamma "et al.". More broadly, the term "design patterns" can be used to refer to any general, repeatable, solution pattern to a commonly occurring problem in software design. Some of these commonly occurring problems have implications and solutions particular to object-oriented development.

Inheritance and behavioral subtyping.

It is intuitive to assume that inheritance creates a semantic "is a" relationship, and thus to infer that objects instantiated from subclasses can always be "safely" used instead of those instantiated from the superclass. This intuition is unfortunately false in most OOP languages, in particular in all those that allow mutable objects. Subtype polymorphism as enforced by the type checker in OOP languages (with mutable objects) cannot guarantee behavioral subtyping in any context. Behavioral subtyping is undecidable in general, so it cannot be implemented by a program (compiler). Class or object hierarchies must be carefully designed, considering possible incorrect uses that cannot be detected syntactically. This issue is known as the Liskov substitution principle.

Gang of Four design patterns.

"Design Patterns: Elements of Reusable Object-Oriented Software" is an influential book published in 1994 by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides, often referred to humorously as the "Gang of Four". Along with exploring the capabilities and pitfalls of object-oriented programming, it describes 23 common programming problems and patterns for solving them. As of April 2007, the book was in its 36th printing.  The book describes the following patterns:

Object-orientation and databases.

Both object-oriented programming and relational database management systems (RDBMSs) are extremely common in software. Since relational databases don't store objects directly (though some RDBMSs have object-oriented features to approximate this), there is a general need to bridge the two worlds. The problem of bridging object-oriented programming accesses and data patterns with relational databases is known as object-relational impedance mismatch. There are a number of approaches to cope with this problem, but no general solution without downsides. One of the most common approaches is object-relational mapping, as found in IDE languages such as Visual FoxPro and libraries such as Java Data Objects and Ruby on Rails' ActiveRecord.  There are also object databases that can be used to replace RDBMSs, but these have not been as technically and commercially successful as RDBMSs.

Real-world modeling and relationships.

OOP can be used to associate real-world objects and processes with digital counterparts. However, not everyone agrees that OOP facilitates direct real-world mapping (see Criticism section) or that real-world mapping is even a worthy goal; Bertrand Meyer argues in "Object-Oriented Software Construction" that a program is not a model of the world but a model of some part of the world; "Reality is a cousin twice removed". At the same time, some principal limitations of OOP have been noted. For example, the circle-ellipse problem is difficult to handle using OOP's concept of inheritance.  However, Niklaus Wirth (who popularized the adage now known as Wirth's law: "Software is getting slower more rapidly than hardware becomes faster") said of OOP in his paper, "Good Ideas through the Looking Glass", "This paradigm closely reflects the structure of systems 'in the real world', and it is therefore well suited to model complex systems with complex behaviours" (contrast KISS principle).  Steve Yegge and others noted that natural languages lack the OOP approach of strictly prioritizing "things" (objects/nouns) before "actions" (methods/verbs). This problem may cause OOP to suffer more convoluted solutions than procedural programming.

OOP and control flow.

OOP was developed to increase the reusability and maintainability of source code. Transparent representation of the control flow had no priority and was meant to be handled by a compiler. With the increasing relevance of parallel hardware and multithreaded coding, developing transparent control flow becomes more important, something hard to achieve with OOP.

Responsibility- vs. data-driven design.

Responsibility-driven design defines classes in terms of a contract, that is, a class should be defined around a responsibility and the information that it shares. This is contrasted by Wirfs-Brock and Wilkerson with data-driven design, where classes are defined around the data-structures that must be held. The authors hold that responsibility-driven design is preferable.

SOLID and GRASP guidelines.

SOLID is a mnemonic invented by Michael Feathers that stands for and advocates five programming practices:  GRASP (General Responsibility Assignment Software Patterns) is another set of guidelines advocated by Craig Larman.

Criticism.

The OOP paradigm has been criticised for a number of reasons, including not meeting its stated goals of reusability and modularity, and for overemphasizing one aspect of software design and modeling (data/objects) at the expense of other important aspects (computation/algorithms).  Luca Cardelli has claimed that OOP code is "intrinsically less efficient" than procedural code, that OOP can take longer to compile, and that OOP languages have "extremely poor modularity properties with respect to class extension and modification", and tend to be extremely complex. The latter point is reiterated by Joe Armstrong, the principal inventor of Erlang, who is quoted as saying:  A study by Potok et al. has shown no significant difference in productivity between OOP and procedural approaches.  Christopher J. Date stated that critical comparison of OOP to other technologies, relational in particular, is difficult because of lack of an agreed-upon and rigorous definition of OOP; however, Date and Darwen have proposed a theoretical foundation on OOP that uses OOP as a kind of customizable type system to support RDBMS.  In an article Lawrence Krubner claimed that compared to other languages (LISP dialects, functional languages, etc.) OOP languages have no unique strengths, and inflict a heavy burden of unneeded complexity.  Alexander Stepanov compares object orientation unfavourably to generic programming:  Paul Graham has suggested that OOP's popularity within large companies is due to "large (and frequently changing) groups of mediocre programmers". According to Graham, the discipline imposed by OOP prevents any one programmer from "doing too much damage".  Leo Brodie has suggested a connection between the standalone nature of objects and a tendency to duplicate code in violation of the don't repeat yourself principle of software development.  Steve Yegge noted that, as opposed to functional programming:  Rich Hickey, creator of Clojure, described object systems as overly simplistic models of the real world. He emphasized the inability of OOP to model time properly, which is getting increasingly problematic as software systems become more concurrent.  Eric S. Raymond, a Unix programmer and open-source software advocate, has been critical of claims that present object-oriented programming as the "One True Solution", and has written that object-oriented programming languages tend to encourage thickly layered programs that destroy transparency. Raymond compares this unfavourably to the approach taken with Unix and the C programming language.  Rob Pike, a programmer involved in the creation of UTF-8 and Go, has called object-oriented programming "the Roman numerals of computing" and has said that OOP languages frequently shift the focus from data structures and algorithms to types. Furthermore, he cites an instance of a Java professor whose "idiomatic" solution to a problem was to create six new classes, rather than to simply use a lookup table.

Formal semantics.

Objects are the run-time entities in an object-oriented system. They may represent a person, a place, a bank account, a table of data, or any item that the program has to handle.  There have been several attempts at formalizing the concepts used in object-oriented programming. The following concepts and constructs have been used as interpretations of OOP concepts:  Attempts to find a consensus definition or theory behind objects have not proven very successful (however, see Abadi & Cardelli, "A Theory of Objects" for formal definitions of many OOP concepts and constructs), and often diverge widely. For example, some definitions focus on mental activities, and some on program structuring. One of the simpler definitions is that OOP is the act of using "map" data structures or arrays that can contain functions and pointers to other maps, all with some syntactic and scoping sugar on top. Inheritance can be performed by cloning the maps (sometimes called "prototyping").

Object-oriented programming (OOP) is a programming paradigm based on the concept of "objects", which can contain data, in the form of fields (often known as "attributes" or "properties"), and code, in the form of procedures (often known as "methods"). A feature of objects is an object's procedures that can access and often modify the data fields of the object with which they are associated (objects have a notion of "this" or "self"). In OOP, computer programs are designed by making them out of objects that interact with one another. OOP languages are diverse, but the most popular ones are class-based, meaning that objects are instances of classes, which also determine their types.

面向对象程序设计(英语:Object-oriented programming,缩写:英语:OOP)是种具有物件概念的程序编程典范,同时也是一种程序开发的抽象方针。它可能包含资料、、程序码与方法。对象则指的是类的实例。它将对象作为程序的基本单元,将程序和数据封装其中,以提高软件的重用性、灵活性和扩展性,物件里的程序可以访问及经常修改物件相关连的资料。在物件导向程序编程里,计算机程序会被设计成彼此相关的物件。


Types of gliders.

Sailplanes benefit from producing the least drag for any given amount of lift, and this is best achieved with long, thin wings, a fully faired narrow cockpit and a slender fuselage. Aircraft with these features are able to soar - climb efficiently in rising air produced by thermals or hills. In still air, sailplanes can glide long distances at high speed with a minimum loss of height in between.  Sailplanes have rigid wings and either skids or undercarriage. In contrast hang gliders and paragliders use the pilot's feet for the start of the launch and for the landing. These latter types are described in separate articles, though their differences from sailplanes are covered below. Sailplanes are usually launched by winch or aerotow, though other methods, auto tow and bungee, are occasionally used.  These days almost all gliders are sailplanes, but in the past many gliders were not. These types did not soar. They were simply engine-less aircraft towed by another aircraft to a desired destination and then cast off for landing. The prime example of non-soaring gliders were military gliders (such as those used in the Second World War). They were often used just once and then usually abandoned after landing, having served their purpose.  Motor gliders are gliders with engines which can be used for extending a flight and even, in some cases, for take-off. Some high-performance motor gliders (known as "self-sustaining" gliders) may have an engine-driven retractable propeller which can be used to sustain flight. Other motor gliders have enough thrust to launch themselves before the engine is retracted and are known as "self-launching" gliders. Another type is the self-launching "touring motor glider", where the pilot can switch the engine on and off in flight without retracting the propeller.

History.

Sir George Cayley's gliders achieved brief wing-borne hops from around 1849. In the 1890s, Otto Lilienthal built gliders using weight shift for control. In the early 1900s, the Wright Brothers built gliders using movable surfaces for control. In 1903, they successfully added an engine.  After World War I gliders were first built for sporting purposes in Germany. Germany's strong links to gliding were to a large degree due to post-WWI regulations forbidding the construction and flight of motorised planes in Germany, so the country's aircraft enthusiasts often turned to gliders and were actively encouraged by the German government, particularly at flying sites suited to gliding flight like the Wasserkuppe.  The sporting use of gliders rapidly evolved in the 1930s and is now their main application. As their performance improved, gliders began to be used for cross-country flying and now regularly fly hundreds or even thousands of kilometres in a day if the weather is suitable.

Glider design.

Early gliders had no cockpit and the pilot sat on a small seat located just ahead of the wing. These were known as "primary gliders" and they were usually launched from the tops of hills, though they are also capable of short hops across the ground while being towed behind a vehicle. To enable gliders to soar more effectively than primary gliders, the designs minimized drag. Gliders now have very smooth, narrow fuselages and very long, narrow wings with a high aspect ratio and winglets.  The early gliders were made mainly of wood with metal fastenings, stays and control cables. Later fuselages made of fabric-covered steel tube were married to wood and fabric wings for lightness and strength. New materials such as carbon-fiber, fiber glass and Kevlar have since been used with computer-aided design to increase performance. The first glider to use glass-fiber extensively was the Akaflieg Stuttgart FS-24 Phönix which first flew in 1957. This material is still used because of its high strength to weight ratio and its ability to give a smooth exterior finish to reduce drag. Drag has also been minimized by more aerodynamic shapes and retractable undercarriages. Flaps are fitted to the trailing edges of the wings on some gliders to optimise lift and drag at a wide range of speeds.  With each generation of materials and with the improvements in aerodynamics, the performance of gliders has increased. One measure of performance is the glide ratio. A ratio of 30:1 means that in smooth air a glider can travel forward 30 meters while losing only 1 meter of altitude. Comparing some typical gliders that might be found in the fleet of a gliding club – the Grunau Baby from the 1930s had a glide ratio of just 17:1, the glass-fiber Libelle of the 1960s increased that to 39:1, and modern flapped 18 meter gliders such as the ASG29 have a glide ratio of over 50:1. The largest open-class glider, the eta, has a span of 30.9 meters and has a glide ratio over 70:1. Compare this to the Gimli Glider, a Boeing 767 which ran out of fuel mid-flight and was found to have a glide ratio of 12:1, or to the Space Shuttle with a glide ratio of 4.5:1.  High aerodynamic efficiency is essential to achieve a good gliding performance, and so gliders often have aerodynamic features seldom found in other aircraft. The wings of a modern racing glider are designed by computers to create a low-drag laminar flow airfoil. After the wings' surfaces have been shaped by a mould to great accuracy, they are then highly polished. Vertical winglets at the ends of the wings decrease drag and so improve wing efficiency. Special aerodynamic seals are used at the ailerons, rudder and elevator to prevent the flow of air through control surface gaps. Turbulator devices in the form of a zig-zag tape or multiple blow holes positioned in a span-wise line along the wing are used to trip laminar flow air into turbulent flow at a desired location on the wing. This flow control prevents the formation of laminar flow bubbles and ensures the absolute minimum drag. Bug-wipers may be installed to wipe the wings while in flight and remove insects that are disturbing the smooth flow of air over the wing.  Modern competition gliders carry jettisonable water ballast (in the wings and sometimes in the vertical stabilizer). The extra weight provided by the water ballast is advantageous if the lift is likely to be strong, and may also be used to adjust the glider's center of mass. Moving the center of mass toward the rear by carrying water in the vertical stabilizer reduces the required down-force from the horizontal stabilizer and the resultant drag from that down-force. Although heavier gliders have a slight disadvantage when climbing in rising air, they achieve a higher speed at any given glide angle. This is an advantage in strong conditions when the gliders spend only a small amount of time climbing in thermals. The pilot can jettison the water ballast before it becomes a disadvantage in weaker thermal conditions. Another use of water ballast is to dampen air turbulence such as might be encountered during ridge soaring. To avoid undue stress on the airframe, gliders must jettison any water ballast before landing.  Most gliders are built in Europe and are designed to EASA Certification Specification CS-22 (previously Joint Aviation Requirements-22). These define minimum standards for safety in a wide range of characteristics such as controllability and strength. For example, gliders must have design features to minimize the possibility of incorrect assembly (gliders are often stowed in disassembled configuration, with at least the wings being detached). Automatic connection of the controls during rigging is the common method of achieving this.

Launch and flight.

The two most common methods of launching sailplanes are by aerotow and by winch. When aerotowed, the sailplane is towed behind a powered aircraft using a rope about 60 meters (about 200 ft) long. The sailplane pilot releases the rope after reaching the desired altitude. However, the rope can be released by the towplane also in case of emergency. Winch launching uses a powerful stationary engine located on the ground at the far end of the launch area. The sailplane is attached to one end of 800–1200 metres (about 2,500–4,000 ft) of cable and the winch rapidly winds it in. The sailplane can gain about 900–3000 feet (about 300–900 metres) of height with a winch launch, depending on the headwind. Less often, automobiles are used to pull sailplanes into the air, either by pulling them directly or through the use of a reverse pulley in a similar manner to the winch launch. Elastic ropes (known as bungees) are occasionally used at some sites to launch gliders from slopes, if there is sufficient wind blowing up the hill. Bungee launching was the predominant method of launching early gliders. Some modern gliders can self-launch with the use of retractable engines and/or propellers, which can also be used to sustain flight once airborne (see motor glider).  Once launched, gliders try to gain height using thermals, ridge lift, lee waves or convergence zones and can remain airborne for hours. This is known as "soaring". By finding lift sufficiently often, experienced pilots fly cross-country, often on pre-declared tasks of hundreds of kilometers, usually back to the original launch site. Cross-country flying and aerobatics are the two forms of competitive gliding. For information about the forces in gliding flight, see lift-to-drag ratio.

Glide slope control.

Pilots need some form of control over the glide slope to land the glider. In powered aircraft, this is done by reducing engine thrust. In gliders, other methods are used to either reduce the lift generated by the wing, increase the drag of the entire glider, or both. Glide slope is the distance traveled for each unit of height lost. In a steady wings-level glide with no wind, glide slope is the same as the lift/drag ratio (L/D) of the glider, called "L-over-D". Reducing lift from the wings and/or increasing drag will reduce the L/D allowing the glider to descend at a steeper angle with no increase in airspeed. Simply pointing the nose downwards only converts altitude into a higher airspeed with a minimal initial reduction in total energy. Gliders, because of their long low wings, create a high ground effect which can significantly increase the glide angle and make it difficult to bring the glider to Earth in a short distance.

Landing.

Early glider designs used skids for landing, but modern types generally land on wheels. Some of the earliest gliders used a dolly with wheels for taking off and the dolly was jettisoned as the glider left the ground, leaving just the skid for landing. A glider may be designed so the center of gravity (CG) is behind the main wheel so the glider sits nose high on the ground. Other designs may have the CG forward of the main wheel so the nose rests on a nose-wheel or skid when stopped. Skids are now mainly used only on training gliders such as the Schweizer SGS 2–33. Skids are around 100mm (3 inches) wide by 900mm (3 feet) long and run from the nose to the main wheel. Skids help with braking after landing by allowing the pilot to put forward pressure on the control stick, thus creating friction between the skid and the ground. The wing tips also have small skids or wheels to protect the wing tips from ground contact.  In most high performance gliders the undercarriage can be raised to reduce drag in flight and lowered for landing. Wheel brakes are provided to allow stopping once on the ground. These may be engaged by fully extending the spoilers/air-brakes or by using a separate control. Although there is only a single main wheel, the glider's wing can be kept level by using the flight controls until it is almost stationary.  Pilots usually land back at the airfield from which they took off, but a landing is possible in any flat field about 250 metres long. Ideally, should circumstances permit, a glider would fly a standard pattern, or circuit, in preparation for landing, typically starting at a height of 300 metres (1,000 feet). Glide slope control devices are then used to adjust the height to assure landing at the desired point. The ideal landing pattern positions the glider on final approach so that a deployment of 30–60% of the spoilers/dive brakes/flaps brings it to the desired touchdown point. In this way the pilot has the option of opening or closing the spoilers/air-brakes to extend or steepen the descent to reach the touchdown point. This gives the pilot wide safety margins should unexpected events occur. If such control devices are not sufficient, the pilot may utilize manouvours such as a forward slip to further steepening the glider slope.

Instrumentation and other technical aids.

Gliders in continental Europe use metric units, like km/h for airspeed and m/s for lift and sink rate. In the USA, UK, Australia and some other countries gliders to use knots and ft/min in common with commercial aviation worldwide.  In addition to an altimeter, compass, and an airspeed indicator, gliders are often equipped with a variometer, turn and bank indicator and an airband radio (transceiver), each of which may be required in some countries. An Emergency Position-Indicating Radio Beacon (ELT) may also be fitted into the glider to reduce search and rescue time in case of an accident.  Much more than in other types of aviation, glider pilots depend on the variometer, which is a very sensitive vertical speed indicator, to measure the climb or sink rate of the plane. This enables the pilot to detect minute changes caused when the glider enters rising or sinking air masses. Both mechanical and electronic 'varios' are usually fitted to a glider. The electronic variometers produce a modulated sound of varying amplitude and frequency depending on the strength of the lift or sink, so that the pilot can concentrate on centering a thermal, watching for other traffic, on navigation, and weather conditions. Rising air is announced to the pilot as a rising tone, with increasing pitch as the lift increases. Conversely, descending air is announced with a lowering tone, which advises the pilot to escape the sink area as soon as possible. (Refer to the "variometer" article for more information).  Gliders' variometers are sometimes fitted with mechanical devices such as a "MacCready Ring" to indicate the optimal speed to fly for given conditions. These devices are based on the mathematical theory attributed to Paul MacCready though it was first described by Wolfgang Späte in 1938. MacCready theory solves the problem of how fast a pilot should cruise between thermals, given both the average lift the pilot expects in the next thermal climb, as well as the amount of lift or sink encountered in cruise mode. Electronic variometers make the same calculations automatically, after allowing for factors such as the glider's theoretical performance, water ballast, headwinds/tailwinds and insects on the leading edges of the wings.  Soaring flight computers, often used in combination with PDAs running specialized soaring software, have been designed for use in gliders. Using GPS technology in conjunction with a barometric device these tools can:  After the flight the GPS data may be replayed on computer software for analysis and to follow the trace of one or more gliders against a backdrop of a map, an aerial photograph or the airspace.  Because collision with other gliders is a risk, the anti-collision device FLARM is becoming increasingly common in Europe and Australia. In the longer term, gliders may eventually be required in some European countries to fit transponders once devices with low power requirements become available.

Markings.

So that ground-based observers may identify gliders in flight or in gliding competition, registration marks ("insignias" or "competition numbers" or "contest ID") are displayed in large characters on the underside of a single wing, and also on the fin and rudder. Registration marks are assigned by gliding associations such as the US Soaring Society of America, and are unrelated to national registrations issued by entities such as the US Federal Aviation Administration. This need for visual ID has somewhat been supplanted by GPS position recording. Insignias are useful in two ways: First, they are used in radio communications between gliders, as pilots use their competition number as their call signs. Secondly, to easily tell a glider's contest ID when flying in close proximity to one another to alert them of potential dangers. For example, during gatherings of multiple gliders within thermals (known as "gaggles"), one pilot might report "Six-Seven-Romeo I am right below you".  Fibreglass gliders are invariably painted white to minimise their skin temperature in sunlight. Fibreglass resin loses strength as its temperature rises into the range achievable in direct sun on a hot day. Color is not used except for a few small bright patches on wing tips; these patches (typically orange or red) improving a glider's visibility to pilots while in flight. Such patches are obligatory for mountain flying in France. Non-fibreglass gliders made of aluminum and wood are not so subject to deterioration at higher temperatures and are often quite brightly painted.

Comparison of sailplanes with hang gliders and paragliders.

There is sometimes confusion about gliders, hang gliders and paragliders. In particular, paragliders and hang gliders are both foot-launched. The main differences between the types are:

Competition classes of glider.

Eight competition classes of glider have been defined by the FAI. They are:

Major manufacturers of gliders.

A large proportion of gliders have been and are still made in Germany, the birthplace of the sport. In Germany there are several manufacturers but the three principal companies are: Germany also has Stemme and Lange Aviation. Elsewhere in the world, there are other manufacturers such as Jonker Sailplanes in South Africa, Sportinė Aviacija in Lithuania, Allstar PZL in Poland, HpH in the Czech Republic and AMS Flight in Slovenia.

A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding (also called soaring). This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplanes are aerodynamically streamlined and so can fly a significant distance forward for a small decrease in altitude.

滑翔机(英文:英语:Glider)是指不依靠动力装置飞行的重于空气的固定翼航空器,起飞后仅依靠空气作用于其升力面上的反作用力进行自由飞行。