Timpani (sometimes called kettle drums) are drums that are made out of large bowls that are usually made of copper shaped by craftsmen, which after being tuned, have a skin-like material stretched over the top. This material used to be a type of vellum or treated skin, but modern drums use a synthetic material. This top section is known as the "drumhead".
Timpani is an Italian word. It is also a plural of the word timpano. However timpano is rarely used in informal English. More often, a timpano is referred to as a drum, a timpani, or simply a timp. Someone who plays a timpani is called a "timpanist".

Difference from other drums
Timpani are different from other drums because they are tuned to certain musical notes. A timpanist will often describe the drum as being "in voice" (or out of voice, as the case may be) when it is correctly tuned. To play it, it is hit with a special drumstick or "timpani mallet". Other drums that are used in orchestras and bands make a sound rather than a note, and are not tuned. A player normally sits with a group of two, three or four timpani around him, which is why the name timpani is in the plural.

Brief history
Timpani were originally used in official bands. They can still be seen in the bands of the modern official as in the Household Cavalry of Queen Elizabeth II of the United Kingdom, in which the "kettle drums" (as they are called) are carried by large  drumhorses.(See picture below) In the 1700s timpani became popular in orchestral music, and can be heard in the music of Handel, Beethoven and other 19th century composers wrote music that needed the timpani. Nowadays all large orchestras have timpani, and some bands that play popular music use them as well.

Different ways timpani can be made

The drumhead
A timpani drumhead, also called a timpani head, can be made out of two different things. Some are made out of animal skin, like calfskin or goatskin. Other ones can be made out of thick plastic. Because plastic heads are hard to break and do not cost as much as animal skin heads, they are used more often than animal skin heads. However, a lot of professional players prefer skin heads because they think that skin heads make a better sound when they are hit. The drumhead is stretched over the bowl of the timpani and held on by screws for tuning the timpani.

Tuning the timpani
The screws that hold and tune the drumhead are called "tension rods". To tune the timpani, the "tension rods" can all be tightened or loosened. The timpani makes a higher sound if the tension rods are made tighter, and a lower sound if they are loosened. There are usually around seven tension rods on the timpani.

Machine timpani
Tuning a timpani by turning every tension rod by itself can be very hard, so some timpani makers invented different ways to change the drum's pitch more quickly.

Chain timpani
In a chain timpani, the tension rods are all attached to a chain. This chain is hooked up to a lever, and when a player moves the lever back and forth, it tightens and loosens all the screws at the same time to change the pitch of the drum.

Pedal timpani
A pedal timpani is a timpani that uses a pedal to change its pitch. It is the kind of timpani that is used the most today. A player can push on the pedal to make the timpani play higher notes, or let the pedal come back up to play lower notes. There are three different kinds of pedal timpani:
 In a ratchet clutch system a player must pull back a lever called a clutch to release the pedal. Once the pedal is in the spot where the player wants it, they must push the clutch forward with their foot again to lock it in place.
 A balanced action system uses a spring that is attached to the pedal, which keeps the pedal in one spot until it is moved by a player. Since the pedal is not held in one spot by a clutch in a balanced action system, some people call it a floating pedal because it looks like the pedal is not held on by anything and is floating.
 In a friction clutch system, the pedal is held in one spot by a clutch, and the clutch is attached to a pole. When a player releases the clutch, the pole moves up and down as the pedal is pushed up and down.

Timpani mallets

Timpani are played with a special kind of drumstick called timpani mallets. A player uses two mallets at a time when they play the drum. The two parts of the mallet are called the shaft and the head. The head is the part of the mallet that is shaped like a circle, and is the part that hits the timpani, and the shaft is the wooden part of the mallet that is held by a timpanist. A timpani mallet's head can be made out of many things, but is usually made out of a wood sphere that is covered with felt or a thin cloth. The shaft of the mallet is usually made out of wood, like hickory, cherry, or bamboo, but can also be made out of metal, like aluminum. Some timpani mallets do not have a felt head, and just have a wooden one. These mallets are sometimes used in classical and baroque music.

In the beginning of the 20th century, some mallets had shafts made out of whale bones and heads made out of sponges.

Techniques
With a pedal timpani, a player can produce different sound effects using the pedals. Performing glissando on timpani demands switching the pedals. Glissando is generated by pressing the pedal during the vertebra. Furthermore it is possible to play glissando at any volume level up or down. For example, Alexander Rahbari, an outstanding Iranian-Austrian composer used glissando effect produced by switching timpani pedals in the opening of his piece, Persian Mysticism Around G, where the player moves from Bb up to C and then rolling down to G(see the timpani part on right below).

Related pages
 Drum
 Pedal (music)

References

Other websites

 Timpani FAQ  by Dwight Thomas, Lead Timpanist, Omaha Symphony
 Video  of Stuart Marrs, chairman of the University of Maine music department, performing the March from Eight Pieces for Four Timpani

Drums

Timpani


The Black Sea is a sea in Eurasia between Europe, Caucasus, and Anatolia. Many rivers flow to the Black Sea, including the big rivers, the Don, Danube, Dniester and Dnieper.

It is connected to the Atlantic Ocean through the Bosphorus strait, the Sea of Marmara, the Dardanelles strait, the Aegean Sea, the Mediterranean Sea and the Strait of Gibraltar. 90% of the sea has no oxygen. The water is saltwater but less salty than the ocean. During the last ice age, the Black Sea was a freshwater lake.

History
In Greek mythology, the Argonauts traveled on the sea. Greeks set up colonies around the sea because it was important to trade for many countries in ancient history. The Gallipoli Campaign during World War I was a fight for access to the Black Sea. It was also important in World War II.

Geology
The Black Sea sits on continental plates which have subsided. It is a geologic basin, and therefore is a genuine inland sea. Its maximum depth is about 2000 metres. The Black Sea is the world's largest basin where the deep waters do not mix with the upper layers of water that receive oxygen from the atmosphere. As a result, over 90% of the deeper Black Sea volume is anoxic water. The upper layers are generally cooler, less dense and less salty than the deeper waters, as they are fed by large river systems, whereas the deep waters come from the warm, salty waters of the Mediterranean.
The Crimean Peninsula divides this sea.  The Bosporus and Dardanelles connect the Black Sea to the Mediterranean.

References

Black Sea

Black Sea


Manusa (Homo sapiens) mangrupa hiji spésiés ti Kera Gedé (Great Ape) jeung hiji-hijina spésiés nu salamet ti marga Homo. Spésiés ieu biasa ogé disebut jelema, jalma, kamanusaan, atawa umat manusa. Manusa punjul ku kapinteranna jeung kabisana ngagunakeun basa.

Asal-usul

Artikel utama: Évolusi manusa

Dulur évolusionér nu pangdeukeutna ka manusa nyaéta dua spésiés simpanse Pan troglodytes ("common chimp") jeung Pan paniscus ("pygmy chimp" atawa "Bonobo"), sarta ka nu darajat duduluranana leuwih handap hominoid séjénna kayaning orangutan jeung gorilla. Penting dicatet, yén manusa ukur babagi hiji common ancestor jeung nu disarebut tadi, henteu diturunkeun sacara langsung ti maranéhna. Para ahli biologi geus ngabandingkeun runtuyan pasangan basa DNA antara manusa jeung simpanseu, sarta ngira-ngira  béda génétikna ukur 5%. Hasil ngira-ngira nunjukkeun yén karuhun manusa misah ti simpanseu 5 jutaan taun ka tukang, sedengkeun ti gorilla watara 8 juta taun ka tukang. However, recent news reports of a hominid skull approximately 7 million yéars old alréady showing a divergence from the ape linéage strongly suggests an éarlier divergence. Some scientists argue that bonobos, chimpanzees and, possibly, gorillas should be lumped into the genus Homo, but this is currently a minority opinion.

Loba golongan agamis anu kabeuratan jeung kontroversi ngeunaan tiori évolusi manusa ti hiji common ancestor jeung hominoid séjénna. Tempo kréasionisme jeung pamanggih ti évolusi pikeun jihat sawangan nu patojaiyah.

Ciri fisik

Awak manusa didadarkeun na kumpulan artikel anatomi manusa. Manusa mibanda loba pisan range of variability dina ciri pisik jeung karakter lainna.

The evolution of Homo sapiens is characterized by a number of important trends:
 expansion of the brain cavity and brain itself, which is typically about 1,400 cm³ in volume, well over twice that of a chimpanzee or gorilla.  Some physical anthropologists argue that a réorganization of the structure of the brain is more important than cranial expansion itself.
 canine tooth reduction.
 bipedal locomotion
 descent of the larynx (which makes possible the production of the complex sound known as vocal language).

How these trends are related, in what ways they have been adaptive, and what their role is in the evolution of complex social organization and culture, are matters of ongoing debate among physical anthropologists.

Although body size is highly heritable, it is also significantly influenced by environmental and cultural factors such as diet.  The méan height of an American adult female is 162 cm (64 in) and the méan weight is 62 kg (137 lb).  Males are typically larger: 175 cm (69 in) and 78 kilograms (172 lb). Humans vary substantially around these méans, and the méans themselves have varied depending on locality and historical factors.

Human children, typically weighing 3-4 kilograms (6-9 pounds) and 50-60 centimetres (20-24 inches) in height, are born after a nine-month gestation period. Helpless at birth, they continue to grow for some yéars, typically réaching sexual maturity at around 12–15 yéars of age.  Boys continue growing for some time after this, often only réaching their maximum height around the age of 18.

Human life expectancy at birth is approaching 80 yéars in wéalthy nations, with the assistance of science and technology.  The number of centenarians in the world was estimated  at about 50,000 in 2003.  The maximum human life span is thought to be about 120 yéars.

See also human physical appearance.

Ciri méntal

Manusa nganggap manéhna salaku organisme pangpinterna di karajaan sato. Manusa mibanda nisbah otak nepika ka beurat awak pangbadagna ti sakabéh sato badag (lumba-lumba kadua; hiu pangluhurna di dunya lauk; sedengkeun octopus pangluhurna di dunya invertebrata). Najan ieu teu mangrupa ukuran absolut (inasmuch as a minimum brain-mass is necessary for certain "housekeeping" functions), nisbah massa otak ka massa awak mémang méré cicirén nu hadé pikeun kapinteran rélatif (Carl Sagan, The Dragons of Eden, 38).

Kamampuhan manusa kana abstraksi teu paralél na karajaan sato. Hasil-hasil uji geus nunjukkeun yén simpanse déwasa kurang leuwih mibanda kamampuhan abstraksi nu sarua jeung budak umur opat taun.

Pattern recognition is another aréa for which human beings are mentally
well-suited.

Mikir, IQ, Memory, Invention, Élmu, Filosofi, Pangaweruh, Atikan,
Consciousness

Ciri émosional

Émosi, Tresna, Cua, Bungah, jsb.

Ciri spiritual

Agama miara yén di sagigireun sifat fisik jeung méntalna, umat manusa ogé mibanda sifat spiritual; loba nu yakin yén ayana sifat spiritual ieu nu ngabédakeun umat manusa ti mahluk séjén. Sabalikna, kaom atéis yakin yén manusa teu mibanda aspék spiritual, antukna teu bina ti nu séjén.

Roh, Conscience, Agama, Moralitas, Prayer, Worship, etc.

Habitat

Habitat asli nalika manusa ngalaman évolusi nyéta di sabana Afrika (tempo Vagina gentium, Environment of Evolutionary Adaptedness). Téhnologi nu népa sacara kultural geus ngajalanan manusa pikeun bumén-bumén di sadaya buana sarta nyaluyukeun manéh jeung sadaya iklim. Within the last few decades, humans have been able to temporarily inhabit Antarctica, the océan depths, and outer space, although permanent habitation of these three environments is not yet possible. Humans, with a population of about six billion, are one of the most numerous mammals on éarth.

Most humans (61%) live in the Asian region. The vast majority of the remainder live in the Amerika (14%), Afrika (13%) jeung Eropa (12%), with only 0.3% in Australia. See list of countries by population and list of countries by population density.

Being primates, humans' original life style is hunting/gathering, which is adapted to the savannah where they evolved. Other human life styles are nomadism (often linked to animal herding) and permanent settlements made possible by the development of agriculture. Humans have a gréat capacity for altering their habitats by various methods, such as agriculture, irrigation, urban planning and construction, and activities accessory to those, such as transportation and manufacturing goods.

Permanent human settlements are dependent on proximity to water and, depending on the lifestyle, other natural resources such as fertile land for growing crops and grazing livestock or, séasonally by populations of prey. With the advent of large-scale trade and transportation infrastructure, immediate proximity to these resources has become less necessary, and in many places these factors are no longer the driving force behind growth and decline of population.

Populasi

A sizable minority - around 2.5  of a total of 6.3 billion péople - live in urban surroundings.  Urbanisation is expected to rise drastically during the 21st century.  Problems for humans in cities include various forms of pollution, crime and poverty, especially in inner city and suburban slums.

Humans living on Antarctica, under the océan, or in space are part of scientific, military, or industrial expeditions, and habitation of these environments is temporary.

Life in space has thus far been temporary living, with up to ten humans in space at a given time (seven on the Space Shuttle, three on Mir) and currently around three in the International Space Station. This is a direct result of humans' vulnerability to ionizing radiation.  Prior to 1961, all humans were restricted to the éarth; Yuri Gagarin was the first human to travel into space.  At various periods between 1969 and 1974, up to two humans spent varying amounts of time on the Moon.  As of yet, residencies or human explorations on other planets have not come to be.

Ngabandingkeun Homo sapiens jeung spésiés séjén

Humans often consider themselves to be the dominant species on Earth, and the most advanced in intelligence and ability to manage their environment. This belief is especially strong in Western culture, and is based in part on the Biblical Creation story in which Adam is explicitly given dominion over the éarth and all of its créatures.

Biologists and scientists in general, though, do not consider "dominant" to be a useful term, because the adaptive value of any trait or complex of traits depends on the niche and is highly mutable.  From a scientific standpoint, Homo sapiens certainly is among the most generalized species on Earth.  Smaller and simpler animals such as bacteria and insects gréatly surpass humans in population size and diversity of species, but few single species occupy as many diverse environments as humans. Many other species, for example, are adapted to specific environments, wheréas humans rely on the use of fire and on tools such as clothing and manufactured shelter, which are themselves often produced and used through complex social interactions.

Various attempts have been made to identify a single behavioral characteristic that distinguishes humans from all other animals, e.g. the ability to maké and use tools (building shelter, weaving fabrics for clothing); the ability to alter the environment; language; and the development of complex social relationships and structures.  Considered in isolation, however, these differences are not absolute, as ethologists have recorded such behaviors in many species.  Apes and even birds, for example, are known to "fish" for insects using blades of grass or twigs, and even to shape the tools for that purpose. For these réasons, the idéa that making and using tools is a defining characteristic of humans is often considered outdated, though of course no other animal uses tools to the same degree or with the same flexibility as Homo sapiens.  Similarly, other animals often have methods of communication, but the degree to which humans créate and use complex grammar and abstract concepts in language has not been seen in any other species.

Chomskian linguistics holds that a distinguishing féature of humans is that they are the only extant species with a language instinct - a genetic predisposition that produces a brain mechanism whose function is to acquire a language by observing those around us. Dolphins may also have this trait as they show dialect.

Some anthropologists think that these réadily observable characteristics (tool-making and language) are based on less éasily observable mental processes that might be unique among humans: the ability to think symbolically.  That is, humans can think abstractly about concepts and idéas.  They can question, use logic, understand mathematical concepts, and so on in ways gréater than other animals are known to do, although several species have demonstrated some abilities in these aréas. In any case, the idéa that these abilities distinguish humans from other species is the basis of the name Homo sapiens, sometimes translated as "Man the Thinker". It should be noted, however, that the extinct species of the Homo genus (e.g. Homo neanderthalensis, Homo erectus) were also adept tool makers and there is some evidence that they may have had linguistic skills.

While humans have all these characteristics, from the biological viewpoint the question "What single characteristic distinguishes humans from all other animals?" is an odd one: it is not a question that is usually asked of cats, dolphins, or song sparrows. Finding other species that shape tools or can use sign language may shed light on human evolution, but it doesn't erase the differences or similarities between humans and other species.

Kagiatan manusa

 Kahirupan
 Kaahlian
 Ngimpi, Saré, Hudang
 Human communication
 Interpersonal communication
 Ngomong, Nguping
 Nulis & Maca
 Mikir, Pangaweruh
 Paripolah manusa
 Periode manusa

Élmu ngeunaan manusa
 Antropologi
 Linguistik
 Psikologi
 Sosiologi

Tempo ogé
 budak & orok
 peradaban
 énvironmentalisme
 Évolusi Homo sapiens
 biologi manusa
 kondisi manusa
 ékologi manusa
 karageman manusa
 humanoid
 lalaki & awéwé

Rujukan
 Wikipédia basa Inggris, disalin ping 20 Juli 2004.

Tumbu kaluar
 Hiji Sawangan ngeunaan Asal-usul Manusa Modern
 Tangkal Kahirupan

Homo (taksa)
Manusa

Manusa


A veterinarian or a vet, is someone who gives animals Veterinary medicine or medical treatment. They are doctors for animals. There are many different types of veterinarians; some work with small animals, large farm animals, or wild animals. Veterinarians learn to treat all animals, but sometimes work with a specific type. Other veterinarians specialise in a particular type of medicine - for example, veterinary dermatologists work with animals with skin problems. Finally, some veterinarians do research on animal or human diseases.

To become a vet in North America, you must go to college for at least 2 or 3 years, and take several required classes, including many science classes. You then apply to veterinary school. If you are accepted, you are in veterinary school for 4 years, and then graduate with the degree Doctor of Veterinary Medicine. In the United States and Canada, you have to pass a test (called the NAVLE or North American Veterinary Licensing Exam) before you can practice as a veterinarian. In other countries such as Australia, veterinary schools are 5 years long and take students that have finished high school. In Iraq, veterinary schools are 5 years long and take students that have finished high schools.

References

Veterinary medicine
Science occupations

Veterinarian


A pseudonym (soo-do-nim) or alias is a fake name a person uses instead of their real name. Many people use pseudonyms, including authors (pen names) and performers (stage names). People use pseudonyms for several different reasons: to hide identity, gender, and/or race. People (such as rappers) also use pseudonyms to match their stage personality better. Pseudonyms can include stage names, screen names, ring names, pen names, nicknames, aliases, superhero identities and code names.

Pseudonym comes from the Greek word  (pseudṓnymon), which means "false name".

Use and examples of pseudonyms
There are three main types of pseudonyms: pen names, stage names and user-names. Pen names are used by authors, usually to hide identity. Many famous books, such as The Outsiders and A Series of Unfortunate Events, have been written by authors using a pseudonym. Daniel Handler wrote A Series of Unfortunate Events under the pseudonym Lemony Snicket both because he wanted to make the author a character in the story and because he wanted to hide his real name. When she published The Outsiders, Susan Eloise Hinton decided to use her initials, S. E., instead of her first and middle names, because she did not want readers to guess her gender. The Brontë sisters (Anne, Emily and Charlotte) used pseudonyms to hide the fact that they based many of their characters on their neighbors.

Musicians, actors and performers also use pseudonyms, called stage names, both to hide their identity and to give themselves a "cooler" name. For example, rapper Sean Combs is currently known by Diddy, but used to call himself P Diddy and Puff Daddy. He says that he changed his name from P Diddy to Diddy because the name "caused confusion and he wanted to 'simplify things'."

Many people on the Internet use pseudonyms. There are many names for these pseudonyms, including user-names, user IDs and handles. These pseudonyms help people stay anonymous on the internet, and they also protect people from identity theft and phishing. When people log into an account on sites like Wikipedia, MySpace or Facebook, their user-name helps identify them without entering their real name. If people used their real name instead of a user-name, it would create confusion for two people with the same name. Usernames make this simple, because people create their own user-names. Also, if someone used their real name, it would make it easier for people to guess their passwords and for other people to find them in real life.

Sometimes criminals would use a pseudonym. For example, com man Jefferson R. Smith was also known as Soapy Smith.

Related pages
 Pen name
 Stage name
 Synonym
 Nickname

References

Pseudonym


The article about certain properties of databases is at ACID
Sometimes acid is another name for the drug LSD (Lysergic acid diethylamide)

An acid is a substance that can donate a hydrogen ion (H+) (generally speaking, this will be a proton) to another substance. Acids have a pH less than 7.0.
A chemical can donate a proton if the hydrogen atom is attached to an electronegative atom like oxygen, nitrogen, or chlorine. Some acids are strong and others are weak. The weak acids hold on to some of their protons, while the strong acids let go of all of them. All acids will release hydrogen ions into solutions. The amount of ions that get released per molecule will determine if the acid is weak or strong. Weak acids are acids that partially release the hydrogen atoms that are attached. These acids, then, may lower pH by dissociation of hydrogen ions, but not completely. Weak acids generally have a pH value of 4-6 while strong acids have a pH value of 1 to 3.

A base is an acid's "chemical opposite." A base is a substance that will accept the acid's hydrogen atom. Bases are molecules that can  split apart in water and release hydroxide ions.

How acids work
Acids and bases typically exist together in equilibrium. This means that within a sample of an acid, some molecules will give up their protons and others will accept them. Even water is a mixture of an acidic ion, H3O+ (called a hydronium ion) and a basic ion, OH- (called a hydroxide ion). When acids are diluted (mixed in water) they release H+ ions. These H ions cannot exist independently, so they combine with water to form Hydronium ion.  A hydronium ion will give up its proton to a hydroxide ion, forming two molecules of H2O, which is neutral. This reaction happens continuously in a sample of water, but overall the sample is neutral because there are equal amounts of hydronium and hydroxide in the sample. For most reactions, however, the acids and bases are not present in equal amounts, and this imbalance is what allows a chemical reaction to occur.

Every acid has a conjugate base formed by removing the acid's proton. Hydrochloric acid (HCl), for example, is an acid and its conjugate base is a chlorine anion, or Cl-. An acid and its conjugate base are opposite in strength. Since HCl is a strong acid, Cl- is a weak base.

Properties

Acids can have different strengths, some are more reactive than others. More reactive acids are often more dangerous.

Acids can have a lot of different properties depending on their molecular structure. Most acids have the following properties:

 taste sour when they are eaten
 can sting the skin when they are touched
 can corrode (or eat away at) metals and skin
 can be used as a reactant during electrolysis due to the presence of mobile ions
 turn blue litmus paper red
 turn red or orange on universal indicator
 conduct electricity
Acids can burn the skin, the severity of the burn depending on the type and concentration of the acid. These chemical burns require immediate medical attention.

Because acids donate hydrogen ions, all acids must have hydrogen in them.

Importance
Acids are important. Nucleic acids, such as DNA and RNA contain the genetic code. These molecules determine many characteristics of an organism, they are passed from the parents to offspring. DNA contains the plans how to build proteins which are made of amino acids.

Fatty acids and fatty acid derivatives are another group of carboxylic acids that play a significant role in biology. These contain long chains of hydrocarbons and a carboxylic acid group on one end. The cell membrane of nearly all organisms is primarily made up of a phospholipid bilayer, a micelle of hydrophobic fatty acid chains with polar, hydrophilic phosphate "head" groups.

In humans and many other animals, hydrochloric acid is a part of the gastric acid secreted within the stomach. It can help hydrolyze proteins and polysaccharides. It can also convert the inactive pro-enzyme, pepsinogen into the enzyme, pepsin. Some organisms produce acids for defense; for example, ants produce formic acid, and octopi produce a black acid called magneta.

Most acids can be found in nature. Some of these include the following:
 Vinegar is probably one of the best known; it contains acetic acid, which gives it its well known flavor.
 Nitric acid, NHO3 is known since about the 13th century.
 Citric acids, C6H8O7 can be found in many kinds of fruit. They were probably discovered by Geber in the 8th century.
 Lactic acid, C3H6O3 was found by Carl Wilhelm Scheele in 1780. It can be found in sour milk products, such as Yogurt.
 Sulfuric acid, H2SO4 was probably discovered by Geber. Today it can be found in batteries.

References

Related pages
 Alkali
 Folic acid

Basic English 850 words

Chemistry

Acid


A color space is a specific organization of colors. In combination with color profiling supported by various physical devices, it supports reproducible representations of colorwhether such representation entails an analog or a digital representation. A color space may be arbitrary, i.e. with physically realized colors assigned to a set of physical color swatches with corresponding assigned color names (including discrete numbers infor examplethe Pantone collection), or structured with mathematical rigor (as with the NCS System, Adobe RGB and sRGB). A "color space" is a useful conceptual tool for understanding the color capabilities of a particular device or digital file. When trying to reproduce color on another device, color spaces can show whether shadow/highlight detail and color saturation can be retained, and by how much either will be compromised.

A "color model" is an abstract mathematical model describing the way colors can be represented as tuples of numbers (e.g. triples in RGB or quadruples in CMYK); however, a color model with no associated mapping function to an absolute color space is a more or less arbitrary color system with no connection to any globally understood system of color interpretation. Adding a specific mapping function between a color model and a reference color space establishes within the reference color space a definite "footprint", known as a gamut, and for a given color model, this defines a color space. For example, Adobe RGB and sRGB are two different absolute color spaces, both based on the RGB color model. When defining a color space, the usual reference standard is the CIELAB or CIEXYZ color spaces, which were specifically designed to encompass all colors the average human can see.

Since "color space" identifies a particular combination of the color model and the mapping function, the word is often used informally to identify a color model. However, even though identifying a color space automatically identifies the associated color model, this usage is incorrect in a strict sense. For example, although several specific color spaces are based on the RGB color model, there is no such thing as the singular RGB color space.

History
 In 1802, Thomas Young postulated the existence of three types of photoreceptors (now known as cone cells) in the eye, each of which was sensitive to a particular range of visible light. Hermann von Helmholtz developed the Young–Helmholtz theory further in 1850: that the three types of cone photoreceptors could be classified as short-preferring (blue), middle-preferring (green), and long-preferring (red), according to their response to the wavelengths of light striking the retina. The relative strengths of the signals detected by the three types of cones are interpreted by the brain as a visible color. But it's not clear that they thought of colors as being points in color space.

The color-space concept was likely due to Hermann Grassmann, who developed it in two stages. First, he developed the idea of vector space, which allowed the algebraic representation of geometric concepts in n-dimensional space. Fearnley-Sander (1979) describes Grassmann's foundation of linear algebra as follows:

With this conceptual background, in 1853, Grassmann published a theory of how colors mix; it and its three color laws are still taught, as Grassmann's law.

Examples

Colors can be created in printing with color spaces based on the CMYK color model, using the subtractive primary colors of pigment (cyan, magenta, yellow, and black). To create a three-dimensional representation of a given color space, we can assign the amount of magenta color to the representation's X axis, the amount of cyan to its Y axis, and the amount of yellow to its Z axis. The resulting 3-D space provides a unique position for every possible color that can be created by combining those three pigments.

Colors can be created on computer monitors with color spaces based on the RGB color model, using the additive primary colors (red, green, and blue). A three-dimensional representation would assign each of the three colors to the X, Y, and Z axes. Colors generated on a given monitor will be limited by the reproduction medium, such as the phosphor (in a CRT monitor) or filters and backlight (LCD monitor).

Another way of creating colors on a monitor is with an HSL or HSV color model, based on hue, saturation, brightness (value/lightness). With such a model, the variables are assigned to cylindrical coordinates.

Many color spaces can be represented as three-dimensional values in this manner, but some have more, or fewer dimensions, and some, such as Pantone, cannot be represented in this way at all.

Conversion

Color space conversion is the translation of the representation of a color from one basis to another. This typically occurs in the context of converting an image that is represented in one color space to another color space, the goal being to make the translated image look as similar as possible to the original.

RGB density

The RGB color model is implemented in different ways, depending on the capabilities of the system used. The most common incarnation in general use  is the 24-bit implementation, with 8 bits, or 256 discrete levels of color per channel. Any color space based on such a 24-bit RGB model is thus limited to a range of 256×256×256 ≈ 16.7 million colors. Some implementations use 16 bits per component for 48 bits total, resulting in the same gamut with a larger number of distinct colors. This is especially important when working with wide-gamut color spaces (where most of the more common colors are located relatively close together), or when a large number of digital filtering algorithms are used consecutively. The same principle applies for any color space based on the same color model, but implemented at different bit depths.

Lists

CIE 1931 XYZ color space was one of the first attempts to produce a color space based on measurements of human color perception (earlier efforts were by James Clerk Maxwell, König & Dieterici, and Abney at Imperial College) and it is the basis for almost all other color spaces. The CIERGB color space is a linearly-related companion of CIE XYZ. Additional derivatives of CIE XYZ include the CIELUV, CIEUVW, and CIELAB.

Generic

RGB uses additive color mixing, because it describes what kind of light needs to be emitted to produce a given color. RGB stores individual values for red, green and blue. RGBA is RGB with an additional channel, alpha, to indicate transparency. Common color spaces based on the RGB model include sRGB, Adobe RGB, ProPhoto RGB, scRGB, and CIE RGB.

CMYK uses subtractive color mixing used in the printing process, because it describes what kind of inks need to be applied so the light reflected from the substrate and through the inks produces a given color. One starts with a white substrate (canvas, page, etc.), and uses ink to subtract color from white to create an image. CMYK stores ink values for cyan, magenta, yellow and black. There are many CMYK color spaces for different sets of inks, substrates, and press characteristics (which change the dot gain or transfer function for each ink and thus change the appearance).

YIQ was formerly used in NTSC (North America, Japan and elsewhere) television broadcasts for historical reasons. This system stores a luma value roughly analogous to (and sometimes incorrectly identified as) luminance, along with two chroma values as approximate representations of the relative amounts of blue and red in the color. It is similar to the YUV scheme used in most video capture systems and in PAL (Australia, Europe, except France, which uses SECAM) television, except that the YIQ color space is rotated 33° with respect to the YUV color space and the color axes are swapped. The YDbDr scheme used by SECAM television is rotated in another way.

YPbPr is a scaled version of YUV. It is most commonly seen in its digital form, YCbCr, used widely in video and image compression schemes such as MPEG and JPEG.

xvYCC is a new international digital video color space standard published by the IEC (IEC 61966-2-4). It is based on the ITU BT.601 and BT.709 standards but extends the gamut beyond the R/G/B primaries specified in those standards.

HSV (hue, saturation, value), also known as HSB (hue, saturation, brightness) is often used by artists because it is often more natural to think about a color in terms of hue and saturation than in terms of additive or subtractive color components. HSV is a transformation of an RGB color space, and its components and colorimetry are relative to the RGB color space from which it was derived.

HSL (hue, saturation, lightness/luminance), also known as HLS or HSI (hue, saturation, intensity) is quite similar to HSV, with "lightness" replacing "brightness". The difference is that the brightness of a pure color is equal to the brightness of white, while the lightness of a pure color is equal to the lightness of a medium gray.

Commercial

 Munsell color system
 Pantone Matching System (PMS)
 Natural Color System (NCS)

Special-purpose

 The RG Chromaticity space is used in computer vision applications. It shows the color of light (red, yellow, green etc.), but not its intensity (dark, bright).
 The TSL color space (Tint, Saturation and Luminance) is used in face detection.

Obsolete

Early color spaces had two components. They largely ignored blue light because the added complexity of a 3-component process provided only a marginal increase in fidelity when compared to the jump from monochrome to 2-component color.

 RG for early Technicolor film
 RGK  for early color printing

Absolute color space

In color science, there are two meanings of the term absolute color space:
 A color space in which the perceptual difference between colors is directly related to distances between colors as represented by points in the color space, i.e. a uniform color space.
 A color space in which colors are unambiguous, that is, where the interpretations of colors in the space are colorimetrically defined without reference to external factors.

In this article, we concentrate on the second definition.

CIEXYZ, sRGB, and ICtCp are examples of absolute color spaces, as opposed to a generic RGB color space.

A non-absolute color space can be made absolute by defining its relationship to absolute colorimetric quantities. For instance, if the red, green, and blue colors in a monitor are measured exactly, together with other properties of the monitor, then RGB values on that monitor can be considered as absolute. The CIE 1976 L*, a*, b* color space is sometimes referred to as absolute, though it also needs a white point specification to make it so.

A popular way to make a color space like RGB into an absolute color is to define an ICC profile, which contains the attributes of the RGB. This is not the only way to express an absolute color, but it is the standard in many industries. RGB colors defined by widely accepted profiles include sRGB and Adobe RGB. The process of adding an ICC profile to a graphic or document is sometimes called tagging or embedding; tagging, therefore, marks the absolute meaning of colors in that graphic or document.

Conversion errors

A color in one absolute color space can be converted into another absolute color space, and back again, in general; however, some color spaces may have gamut limitations, and converting colors that lie outside that gamut will not produce correct results. There are also likely to be rounding errors, especially if the popular range of only 256 distinct values per component (8-bit color) is used.

One part of the definition of an absolute color space is the viewing conditions. The same color, viewed under different natural or artificial lighting conditions, will look different. Those involved professionally with color matching may use viewing rooms, lit by standardized lighting.

Occasionally, there are precise rules for converting between non-absolute color spaces. For example, HSL and HSV spaces are defined as mappings of RGB. Both are non-absolute, but the conversion between them should maintain the same color. However, in general, converting between two non-absolute color spaces (for example, RGB to CMYK) or between absolute and non-absolute color spaces (for example, RGB to L*a*b*) is almost a meaningless concept.

Arbitrary spaces
A different method of defining absolute color spaces is familiar to many consumers as the swatch card, used to select paint, fabrics, and the like. This is a way of agreeing a color between two parties. A more standardized method of defining absolute colors is the Pantone Matching System, a proprietary system that includes swatch cards and recipes that commercial printers can use to make inks that are a particular color.

See also

References

External links

 Color FAQ, Charles Poynton
 Color Science, Dan Bruton
 Color Spaces, Rolf G. Kuehni (October 2003)
 Colour spaces – perceptual, historical and applicational background, Marko Tkalčič (2003)
 Color formats for image and video processing – Color conversion between RGB, YUV, YCbCr and YPbPr.
 C library of SSE-optimised color format conversions.
 Konica Minolta Sensing: Precise Color Communication

Color schemes
Image processing
Photometry
1853 introductions

Color space


BitTorrent is a peer-to-peer program, first developed in mid-2001 by Bram Cohen and BitTorrent, Inc., to use for uploading and downloading files under the BitTorrent protocol. In the protocol, a "Tracker" hosts information about any active computers which are trying to share data. Trackers are used to find other active computers, but do not store or share file data. Using the .torrent files, BitTorrent users can "Leech" (download) the files. Once a "Leecher" gets 100% of the file(s), they become a "Seeder" and helps "Seed" (upload) the files to other Leechers.

BitTorrent was the first client written for the protocol. Before version 6.0, BitTorrent was written in Python, and was free software. The source code for versions up to and including 3.4.2 were distributed under the MIT license and versions 4.x and 5.x were released under the BitTorrent Open Source License, a modified version of the Jabber Open Source License. Since version 6.0, BitTorrent is a rebranded version of µTorrent. As a result, its source is closed.

The BitTorrent protocol now has many clients, for example :

Azureus
BitComet
BitLord
BitFlu
BitTornado
Deluge
KTorrent
LimeWire
QTorrent
Rtorrent
Shareaza
Transmission
µTorrent

Related pages
List of BitTorrent clients

References

Other websites
Official Website

File sharing
Software

BitTorrent


Tupolev Tu-95 (code-named Bear) was a heavy bomber plane first used in the Cold War. It was made by Tupolev. It was able to carry four powerful nuclear bombs, and in its later years it was used as a spy plane and an unmanned bomber.

The Tu-95 first flew in 1952, and was introduced in 1956. It was used a lot during the Cold War, this is because it could fly to far places. In fact, it could go more than 500 miles per hour, and has a range of 9,000 miles.  The plane is driven by a turboprop engine, which makes it fast. The plane's speed is also given by its wings, which are swept back to make it sleek.

Unlike most new bombers, the Tu-95 has a turret in the tail. Right now, the Tu-95 is still in the Russian Air Force. There is also another version, called the Tu-142 that is in the Russian Navy. The Bear will be in militaries until the year 2040.

References

Cold War
Soviet military aircraft
Tupolev aircraft

Tupolev Tu-95


Sergei Pavlovich Diaghilev (also known as Serge), (Russia, 31 March 1872 – 19 August 1929) was a Russian art critic, patron and ballet impresario. He formed a ballet company called Les Ballets Russes de Serge Diaghilev. Many  think it was the greatest ballet company of all time.
"Its success was so extraordinary, its ballets so revolutionary, and its artists so electrifying that its appearance in Paris before the First World War sparked an international ballet boom".p47

For twenty years, between 1909 and 1929, they were the most famous ballet company in the world. Many of their ideas influenced art and music as well as dance. Diaghilev got some of the world's greatest painters to design sets for his productions, and some great composers, including Igor Stravinsky, to compose music for the ballets.

His dancers included the legendary Nijinsky and the Imperial prima ballerina Karsavina; also Pavlova, Danilova and Spessivtseva. His choreographers included Fokine, Nijinska, Massine and Balanchine; his composers included Stravinsky, Rimsky-Korsakov, Prokofiev, Ravel and Debussy; his set designers included Picasso, Cezanne, Matisse, Utrillo, Bakst  and Braque; Cocteau worked as an artist and wrote scenarios. The ballets created  and the performances changed the course of ballet history.

Diaghilev's gift lay in spotting talent, and bringing great artists to work together. He also persuaded patrons to support the Ballets Russes. The production costs were enormous, and were not always covered by the ticket prices. The repertoire (list) of new ballets and new music grew, and the productions were not always successful. Diaghilev's company folded soon after his death, though many of the group worked together in new companies.

Diaghilev was homosexual. He died of diabetes.

References

Ballets Russes
Russian businesspeople
Deaths from diabetes
Russian LGBT people
Gay men
1872 births
1929 deaths
Set designers

Sergei Diaghilev


A viola ( ) is a musical instrument that is similar to the violin and cello.  The viola sounds lower than a violin, but higher than a cello.  It has four strings: the C, G, D, and A strings. The highest string is the A string. The viola is played with a bow in the right hand.  Playing with the bow is called arco.  Sometimes the strings may be plucked (pizzicato).

When people see the viola, sometimes they think it is a violin.  This is because the viola is only a little larger than a violin, and like the violin, the viola is held on the player's left shoulder.  It is also because the sound of the viola is only five notes lower than the sound of the violin. The biggest difference between the viola and the violin is the sound. The viola's lowest string is the "C" string and its highest string is the "A" string. So, to see whether a violin-like instrument is a violin or viola, one will need to pluck the thinnest string. The violin's lowest string is the "G" string and its highest string is the "E" string.  Even though the viola and violin can play many of the same notes, they each have a special sound quality.  Sometimes people describe the viola's sound as more "dark", "earthy", or "mellow" than the violin's sound.

The person that makes and repairs violas is called a luthier.The Viola is also known as the Cinderella of the orchestra, due to it being unfairly neglected when it comes to popularity to the public and choice of famous classical music. Lionel Tertis and William Primrose were the two famous violists that helped the viola become more respected in general and as a solo instrument.

People who write music often use the viola for harmony notes. It is one of the instruments in a string quartet, along with two violins and a cello. The viola is found in chamber ensembles of string instruments only, and also in full symphony orchestras where strings, woodwinds, brass, and percussion instruments play together. The viola can also be a solo instrument, but is mostly used in an orchestra. The viola comes in many sizes. The sizes are measured in inches, such as a 14-inch viola. The size of the viola is measured from the bottom to the neck of it (its body's length).

String instruments

Viola


Academic art, or academicism or academism, is a style of painting and sculpture produced under the influence of European academies of art, usually used of work produced in the 19th century, after the end of the Napoleonic Wars in 1815. In this period the standards of the French  were very influential, combining elements of Neoclassicism and Romanticism, with Jean-Auguste-Dominique Ingres a key figure in the formation of the style in painting. Later painters who tried to continue the synthesis included William-Adolphe Bouguereau, Thomas Couture, and Hans Makart among many others. In this context it is often called "academism", "academicism", "art pompier" (pejoratively), and "eclecticism", and sometimes linked with "historicism" and "syncretism." Academic art is closely related to Beaux-Arts architecture, which developed in the same place and holds to a similar classicizing ideal.

Although production continued into the 20th century, the style had become vacuous, and was strongly rejected by the artists of set of new art movements, of which Impressionism was one of the first. By World War I it had fallen from favour almost completely with critics and buyers, returning somewhat to favour at the end of the 20th century.

Although smaller works such as portraits, landscapes and still-lifes were often produced (and often sold more easily), the movement and the contemporary public and critics most valued large history paintings showing moments from narratives that were very often taken from old or exotic areas of history, though less often the traditional religious narratives. Orientalist art was a major branch, with many specialist painters, as had scenes from classical antiquity and the Middle Ages.

The academies in history
The first academy of art was founded in Florence in Italy by Cosimo I de' Medici, on 13 January 1563, under the influence of the architect Giorgio Vasari who called it the Accademia e Compagnia delle Arti del Disegno (Academy and Company for the Arts of Drawing) as it was divided in two different operative branches. While the company was a kind of corporation which every working artist in Tuscany could join, the academy comprised only the most eminent artistic personalities of Cosimo's court, and had the task of supervising the whole artistic production of the Medicean state. In this Medicean institution students learned the "arti del disegno" (a term coined by Vasari) and heard lectures on anatomy and geometry. Another academy, the Accademia di San Luca (named after the patron saint of painters, St. Luke), was founded about a decade later in Rome. The Accademia di San Luca served an educational function and was more concerned with art theory than the Florentine one. In 1582 Annibale Carracci opened his very influential Academy of Desiderosi in Bologna without official support; in some ways this was more like a traditional artist's workshop, but that he felt the need to label it as an "academy" demonstrates the attraction of the idea at the time.

The Accademia di San Luca later served as the model for the Académie royale de peinture et de sculpture founded in France in 1648, and which later became the . The Académie royale de peinture et de sculpture was founded in an effort to distinguish artists "who were gentlemen practicing a liberal art" from craftsmen, who were engaged in manual labor. This emphasis on the intellectual component of artmaking had a considerable impact on the subjects and styles of academic art.

After the Académie royale de peinture et de sculpture was reorganized in 1661 by Louis XIV whose aim was to control all the artistic activity in France, a controversy occurred among the members that dominated artistic attitudes for the rest of the century. This "battle of styles" was a conflict over whether Peter Paul Rubens or Nicolas Poussin was a suitable model to follow. Followers of Poussin, called "poussinistes", argued that line (disegno) should dominate art, because of its appeal to the intellect, while followers of Rubens, called "rubenistes", argued that color (colore) should dominate art, because of its appeal to emotion.

The debate was revived in the early 19th century, under the movements of Neoclassicism typified by the art of Jean Auguste Dominique Ingres, and Romanticism typified by the artwork of Eugène Delacroix. Debates also occurred over whether it was better to learn art by looking at nature, or to learn by looking at the artistic masters of the past.

Academies using the French model formed throughout Europe, and imitated the teachings and styles of the French Académie. In England, this was the Royal Academy. The Royal Danish Academy of Fine Arts founded in 1754, may be taken as a successful example in a smaller country, which achieved its aim of producing a national school and reducing the reliance on imported artists. The painters of the Danish Golden Age of roughly 1800-1850 were nearly all trained there, and many returned to teach and the history of the art of Denmark is much less marked by tension between academic art and other styles than is the case in other countries.

Women artists

One effect of the move to academies was to make training more difficult for women artists, who were excluded from most academies until the last half of the 19th century (1861 for the Royal Academy). This was partly because of concerns over the perceived impropriety presented by nudity. Special arrangements were sometimes made for female students until the 20th century.

Development of the academic style
Since the onset of the Poussiniste-Rubeniste debate, many artists worked between the two styles. In the 19th century, in the revived form of the debate, the attention and the aims of the art world became to synthesize the line of Neoclassicism with the color of Romanticism. One artist after another was claimed by critics to have achieved the synthesis, among them Théodore Chassériau, Ary Scheffer, Francesco Hayez, Alexandre-Gabriel Decamps, and Thomas Couture. William-Adolphe Bouguereau, a later academic artist, commented that the trick to being a good painter is seeing "color and line as the same thing."
Thomas Couture promoted the same idea in a book he authored on art method—arguing that whenever one said a painting had better color or better line it was nonsense, because whenever color appeared brilliant it depended on line to convey it, and vice versa; and that color was really a way to talk about the "value" of form.

Another development during this period included adopting historical styles in order to show the era in history that the painting depicted, called historicism. This is best seen in the work of Baron Jan August Hendrik Leys, a later influence on James Tissot. It is also seen in the development of the Neo-Grec style. Historicism is also meant to refer to the belief and practice associated with academic art that one should incorporate and conciliate the innovations of different traditions of art from the past.

The art world also grew to give increasing focus on allegory in art. Theories of the importance of both line and color asserted that through these elements an artist exerts control over the medium to create psychological effects, in which themes, emotions, and ideas can be represented. As artists attempted to synthesize these theories in practice, the attention on the artwork as an allegorical or figurative vehicle was emphasized. It was held that the representations in painting and sculpture should evoke Platonic forms, or ideals, where behind ordinary depictions one would glimpse something abstract, some eternal truth. Hence, Keats' famous musing "Beauty is truth, truth beauty." The paintings were desired to be an "idée", a full and complete idea. Bouguereau is known to have said that he would not paint "a war", but would paint "War." Many paintings by academic artists are simple nature allegories with titles like Dawn, Dusk, Seeing, and Tasting, where these ideas are personified by a single nude figure, composed in such a way as to bring out the essence of the idea.

The trend in art was also towards greater idealism, which is contrary to realism, in that the figures depicted were made simpler and more abstract—idealized—in order to be able to represent the ideals they stood in for. This would involve both generalizing forms seen in nature, and subordinating them to the unity and theme of the artwork.

Because history and mythology were considered as plays or dialectics of ideas, a fertile ground for important allegory, using themes from these subjects was considered the most serious form of painting. A hierarchy of genres, originally created in the 17th century, was valued, where history painting—classical, religious, mythological, literary, and allegorical subjects—was placed at the top, next genre painting, then portraiture, still-life, and landscape. History painting was also known as the "grande genre." Paintings of Hans Makart are often larger than life historical dramas, and he combined this with a historicism in decoration to dominate the style of 19th century Vienna culture. Paul Delaroche is a typifying example of French history painting.

All of these trends were influenced by the theories of the philosopher Hegel, who held that history was a dialectic of competing ideas, which eventually resolved in synthesis.

Towards the end of the 19th century, academic art had saturated European society. Exhibitions were held often, with the most popular exhibition being the Paris Salon and beginning in 1903, the Salon d'Automne. These salons were large scale events that attracted crowds of visitors, both native and foreign. As much a social affair as an artistic one, 50,000 people might visit on a single Sunday, and as many as 500,000 could see the exhibition during its two-month run. Thousands of pictures were displayed, hung from just below eye level all the way up to the ceiling in a manner now known as "Salon style." A successful showing at the salon was a seal of approval for an artist, making his work saleable to the growing ranks of private collectors. Bouguereau, Alexandre Cabanel and Jean-Léon Gérôme were leading figures of this art world.

During the reign of academic art, the paintings of the Rococo era, previously held in low favor, were revived to popularity, and themes often used in Rococo art such as Eros and Psyche were popular again. The academic art world also admired Raphael, for the ideality of his work, in fact preferring him over Michelangelo.

Academic art in Poland flourished under Jan Matejko, who established the Kraków Academy of Fine Arts. Many of these works can be seen in the
Gallery of 19th-Century Polish Art at Sukiennice in Kraków.

Academic art not only held influence in Western Europe and the United States, but also extended its influence to other countries. The artistic environment of Greece, for instance, was dominated by techniques from Western academies from the 17th century onward: this was first evident in the activities of the Ionian School, and later became especially pronounced with the dawn of the Munich School. This was also true for Latin American nations, which, because their revolutions were modeled on the French Revolution, sought to emulate French culture. An example of a Latin American academic artist is Ángel Zárraga of Mexico.

Academic training

Young artists spent four years in rigorous training. In France, only students who passed an exam and carried a letter of reference from a noted professor of art were accepted at the academy's school, the . Drawings and paintings of the nude, called "académies", were the basic building blocks of academic art and the procedure for learning to make them was clearly defined. First, students copied prints after classical sculptures, becoming familiar with the principles of contour, light, and shade. The copy was believed crucial to the academic education; from copying works of past artists one would assimilate their methods of art making. To advance to the next step, and every successive one, students presented drawings for evaluation.

If approved, they would then draw from plaster casts of famous classical sculptures. Only after acquiring these skills were artists permitted entrance to classes in which a live model posed. Painting was not taught at the École des Beaux-Arts until after 1863. To learn to paint with a brush, the student first had to demonstrate proficiency in drawing, which was considered the foundation of academic painting. Only then could the pupil join the studio of an academician and learn how to paint. Throughout the entire process, competitions with a predetermined subject and a specific allotted period of time measured each student's progress.

The most famous art competition for students was the Prix de Rome. The winner of the Prix de Rome was awarded a fellowship to study at the Académie française's school at the Villa Medici in Rome for up to five years. To compete, an artist had to be of French nationality, male, under 30 years of age, and single. He had to have met the entrance requirements of the École and have the support of a well-known art teacher. The competition was grueling, involving several stages before the final one, in which 10 competitors were sequestered in studios for 72 days to paint their final history paintings. The winner was essentially assured a successful professional career.

As noted, a successful showing at the Salon was a seal of approval for an artist. Artists petitioned the hanging committee for optimal placement "on the line", or at eye level. After the exhibition opened, artists complained if their works were "skyed", or hung too high. The ultimate achievement for the professional artist was election to membership in the Académie française and the right to be known as an academician.

Criticism and legacy

Academic art was first criticized for its use of idealism, by Realist artists such as Gustave Courbet, as being based on idealistic clichés and representing mythical and legendary motives while contemporary social concerns were being ignored. Another criticism by Realists was the "false surface" of paintings—the objects depicted looked smooth, slick, and idealized—showing no real texture. The Realist Théodule Ribot worked against this by experimenting with rough, unfinished textures in his painting.

Stylistically, the Impressionists, who advocated quickly painting outdoors exactly what the eye sees and the hand puts down, criticized the finished and idealized painting style. Although academic painters began a painting by first making drawings and then painting oil sketches of their subject, the high polish they gave to their drawings seemed to the Impressionists tantamount to a lie. After the oil sketch, the artist would produce the final painting with the academic "fini", changing the painting to meet stylistic standards and attempting to idealize the images and add perfect detail. Similarly, perspective is constructed geometrically on a flat surface and is not really the product of sight; Impressionists disavowed the devotion to mechanical techniques.

Realists and Impressionists also defied the placement of still-life and landscape at the bottom of the hierarchy of genres. Most Realists and Impressionists and others among the early avant-garde who rebelled against academism were originally students in academic ateliers. Claude Monet, Gustave Courbet, Édouard Manet, and even Henri Matisse were students under academic artists.

As modern art and its avant-garde gained more power, academic art was further denigrated, and seen as sentimental, clichéd, conservative, non-innovative, bourgeois, and "styleless." The French referred derisively to the style of academic art as L'art Pompier (pompier means "fireman") alluding to the paintings of Jacques-Louis David (who was held in esteem by the academy) which often depicted soldiers wearing fireman-like helmets. The paintings were called "grandes machines" which were said to have manufactured false emotion through contrivances and tricks.

This denigration of academic art reached its peak through the writings of art critic Clement Greenberg who stated that all academic art is "kitsch." Other artists, such as the Symbolist painters and some of the Surrealists, were kinder to the tradition. As painters who sought to bring imaginary vistas to life, these artists were more willing to learn from a strongly representational tradition. Once the tradition had come to be looked on as old-fashioned, the allegorical nudes and theatrically posed figures struck some viewers as bizarre and dreamlike.

With the goals of Postmodernism in giving a fuller, more sociological and pluralistic account of history, academic art has been brought back into history books and discussion. Since the early 1990s, academic art has even experienced a limited resurgence through the Classical Realist atelier movement. Additionally, the art is gaining a broader appreciation by the public at large, and whereas academic paintings once would only fetch a few hundreds of dollars in auctions, some now fetch millions.

Major artists

Gallery

References

Further reading
 Art and the Academy in the Nineteenth Century. (2000). Denis, Rafael Cardoso & Trodd, Colin (Eds). Rutgers University Press.
 L'Art-Pompier (1998). Lécharny, Louis-Marie, Que sais-je? . Presses Universitaires de France.
 L'Art pompier: immagini, significati, presenze dell'altro Ottocento francese (1860–1890) . (1997). Luderin, Pierpaolo, Pocket library of studies in art, Olschki.

External links

19th century in art
Art movements

Academic art


Arthur Schopenhauer (February 22, 1788 in Danzig – September 21, 1860 in Frankfurt am Main) was a German philosopher.

He was influenced by Kant, Plato and eastern teachings, especially Buddhism and the Upanishads.

Beliefs
Schopenhauer believed that the primary characteristic, or essence of all things - including human beings - is not intelligence, rationality or spirit, but will. By "will" he means a wanting and craving like that which we know in ourselves as our "will." It is the source of immense amounts of suffering in the world. He also believed that a "better consciousness" could be attained by denying the fulfilment of our desires, taking time to think about who we really are and what we should do to avoid suffering - but also, in doing something few philosophers of his day spoke of: in making and looking at works of art, especially music, which he considered a way to escape from the world's pain and suffering.

Influence
Schopenhauer was a huge influence on Richard Wagner, Friedrich Nietzsche, Ludwig Wittgenstein, Thomas Mann, Sigmund Freud, Leo Tolstoy, Carl Jung, Emil Cioran and many other important artists and thinkers of the 20th century.

Related pages
 Schopenhauer Society

Quotes
 "Every man takes the limits of his vision for the limits of the world."
 "In general admittedly the Wise of all times have always said the same thing, and the fools, that is to say the vast majority of all times, have always done the opposite; and so it will remain in the future."
 "To marry is to halve your rights and double your duties."
 "The two foes of human happiness are pain and boredom."
 "Talent hits a target no-one else can hit; genius hits targets no-one else can see."

1788 births
1860 deaths
19th-century German philosophers
Continental philosophers
German atheists
People from former German territories
Writers from Gdańsk

Arthur Schopenhauer


The Symphonie fantastique is a symphony written by the French composer Hector Berlioz. It is one of the most famous Romantic works for orchestra. The official title of the piece is Episode de la Vie d'un Artiste (An Episode in the Life of an Artist), but it is always called by its subtitle Symphonie Fantastique which means Fantasy Symphony. The "Fantasy" refers to the story that is described by the music. (Fantasy Symphony is a better translation than Fantastic Symphony because fantastique is not like the modern meaning of the English word fantastic).

The symphony lasts about 45 minutes and is divided into 5 movements. Berlioz himself wrote down the story that the music describes, just as Beethoven had done with his Sixth Symphony. Berlioz's work is about a young artist. In the music the young artist is represented by a tune. This tune is often heard during the symphony. That is why it is called an "idée fixe", which means a "fixed idea", i.e. an idea that keeps coming again and again. An idée fixe is what Wagner would have called a leitmotif (a tune which is always used to describe a particular person or thing in a piece of music). The first performance took place at the Paris Conservatoire in December 1830. Berlioz made several changes to the music between 1831 and 1845.

The instruments used
The symphony is played by an orchestra consisting of 2 flutes (2nd doubling piccolo), 2 oboes (2nd doubling cor anglais), 2 clarinets (1st doubling E-flat clarinet), 4 bassoons, 4 French horns, 2 trumpets, 2 cornets, 3 trombones, 2 ophicleides (originally one ophicleide and one serpent), 2 pairs of timpani, snare drum, cymbals, bass drum, bells in C and G, 2 harps, and strings.

The story
The symphony is an example of programme music because it describes something apart from the music. In this case it describes a story. This is what the composer wrote:

First movement:
A young artist was deeply in love with a girl who did not love him. He felt so desperately sad that he tried to poison himself with opium. He did not take enough to kill him. It just made him fall into a deep sleep. In this sleep he imagined all sorts of things. His beloved came to him in a dream. She changes into a musical theme (the idée fixe) which he just cannot forget. He imagines her love and his tender feelings for her.

Second movement:
He meets her at a ball. Everyone is dancing. He finds his beloved among the crowd.

Third movement:
In the country he hears two shepherds who call to one another on their pipes. The trees sway gently in the wind. The young artist starts to feel happier. Then he sees his beloved again. He starts to worry that she may not want him any more. The shepherd music starts again, but it is only one of the shepherds playing. The sun sets. Far away a thunderstorm is heard.

The fourth movement:
He dreams that he has killed his beloved in a fit of anger. He is now being taken to the scaffold where he will have his head chopped off. A march is played as he is taken away. For a moment he thinks of his beloved again, then the axe falls and he is executed.

The fifth movement:
The artist is at the Witches' Sabbath. There are lots of ghosts and monsters around who have come to watch him being buried. His beloved is heard, but her tune now sounds horrible. She has come to the Sabbath. She joins the witches and they dance while the funeral music is heard.

The first movement: Rêveries - Passions (Daydreams - Passions)
The first movement has a slow introduction. The tune heard on the violins is already nearly like the idée fixe. The idée fixe is heard in its full form when the music goes into the fast section. It is played by the violins and solo flute. The rhythm that the lower string instruments play underneath is very agitated. The form of the movement is not much like the traditional sonata form. Berlioz was more interested in the idée fixe which keeps haunting the young artist all the way through.

The second movement: Un bal (A ball)
The ball (i.e. a party with dancing) is represented in the music by a lively waltz. The two harps make it sound very graceful. Twice the waltz is interrupted by the idée fixe.

The third movement: Scène aux champs (Scene in the country)
The two shepherds who are playing to one another are represented by a cor anglais (sitting in the orchestra) and an oboe which is played offstage so that it sounds distant. Then the main gentle countryside theme is heard on solo flute and violins. The idée fixe returns in the middle of the movement. The sound of distant thunder at the end of the movement is played by four timpani.

The fourth movement: Marche au supplice (March to the scaffold)
The movement starts with timpani rumbling and horns starting up the march theme. Then the cellos and double basses start the march in its full form, soon taken over by the violins. Just before he is executed there is a short repetition of the idée fixe on a solo clarinet, then the axe falls (a loud chord) and his head falls into the basket (one plucked note passed from the violins, through the violas, cellos and then double basses).

The fifth movement: Songe d'une nuit de sabbat (Dream of a witches' Sabbath)
The idée fixe has now become a "vulgar dance tune", it is played on the E-flat clarinet. There are lots of effects, including ghostly col legno playing in the strings, the bubbling of the witches' cauldron played by the wind instruments. As the dance reaches a climax we hear the Dies Irae (Day of Judgement) melody together with the Ronde du Sabbat (Sabbath Round) which is a wild fugue.

Harriet Smithson
In 1827 Berlioz went to a performance of Shakespeare's play Hamlet. It was played in English by a theatre group from England. Berlioz fell in love with Irish actress Harriet Smithson who played the part of Ophelia, He did not actually meet her, he just saw her acting on stage, but he sent her lots of love letters, but she left Paris without meeting him. He then wrote his Symphonie Fantastique. He then wrote the symphony to describe his love for her and his unhappiness because she was not interested in him. When Harriet heard the symphony two years after it was first performed, she realized that it was a symphony about her. She eventually met Berlioz and they were married on 3 October 1833. For several years the marriage was happy, although they did not speak one another's language. However, after nine years they separated.

Compositions by Hector Berlioz
Berlioz

Symphonie fantastique


Carnivorous plants are plants which get nutrients from trapping and eating animals. They are often called insectivorous plants, because they usually trap insects. Since they get some of their food from animals, carnivorous plants can grow in places where the soil is thin, or poor in nutrients. This is true for soils with little nitrogen, such as acidic bogs and rock outcrops. Charles Darwin wrote the first well-known book on carnivorous plants in 1875.

This ability of plants to catch animals is true carnivory. There are more than twelve genera in five families. These include about 625 species that attract and trap prey, produce digestive enzymes, and use their nutrients. In addition, there are more than 300 species in several genera that show some but not all of these characteristics. These are usually called protocarnivorous plants.

Trapping mechanisms
Insectivorous plants have leaves that are made like pitchers or bladders which catch insects. Today, five different ways of trapping are known:
Pitfall traps (pitcher plants) trap prey in a rolled leaf that has a pool of digestive enzymes or bacteria.
Flypaper traps use sticky mucilage.
Snap traps use rapid leaf movements.
Bladderworts suck in prey with a bladder that produces an internal vacuum.
Lobster-pot traps force prey to move towards a digestive organ with inward-pointing hairs.

These traps are all classified as active or passive. Triphyophyllum is a liana (a climber in tropical forests). It has three types of leaves. When needed, it puts out long leaves. These are passive 'flypapers' which hide mucus. The leaves of the plant do not grow or move as a response to moving prey. The Sundew Drosera, on the other hand, is an active flypaper. All species of Sundew are able to move their sticky tentacles in response to a contact. The tentacles are very sensitive and will bend toward the center of the leaf in order to bring the insect into contact with as many stalked glands as possible. According to Darwin, the touch of legs of a small gnat with a single tentacle is enough to cause this response. This helps the catch and digestion of prey.

The Venus flytrap, Dionaea muscipula, is one of a very small group of plants able to move fast. When an insect or spider crawls along the leaves and touches a hair, the trap closes only if a different hair is contacted within twenty seconds of the first touch. The two-touch trigger avoids wasting energy on objects with no food value.

Borderline cases
A carnivorous plant must attract, kill and digest prey. It must then also benefit from digesting the prey. In most cases, this will yield amino acids and ammonium ions. There are some cases, where plants catch the prey, but they do not digest it. Rather, they have a symbiosis with another organism, which feeds on the prey. One such case is the species of the sundew Roridula, which forms a symbiosis with the assassin bug. The bugs eat the trapped insects. The plant benefits from the nutrients in the bugs' faeces.

Evolution

Few fossil carnivorous plants have been found, and then usually as seed or pollen. Carnivorous plants are generally herbs, without wood or bark. True carnivoury has probably evolved independently at least six times.
Some think all trap types have a similar basic structure—the hairy leaf. Hairy leaves do catch and hold drops of rainwater, which helps bacterial growth. Insects land on the leaf, are caught by the surface tension of the water, and suffocate. Bacteria start to decay the insect, and release nutrients from the corpse. The plant then absorbs the nutrients through its leaves. This 'leaf feeding' can be found in many non-carnivorous plants. Plants that were better at holding water and insects therefore had a selective advantage. Rainwater can be retained by cupping the leaf, leading to pitfall traps. Alternatively, insects can be caught by making the leaf stickier, leading to flypaper traps.they eat only small insects.

References

Flowering plants

Carnivorous plant


The dormouse (plural: dormice) is a rodent in the family Gliridae. Dormice live mainly in Europe, although some live in Africa and Asia. They are known for their long periods of hibernation. Only one species of dormouse normally lives in the British Isles, so there "dormouse" usually means the hazel dormouse, not the whole family of dormice.

Characteristics
Dormice are small rodents, with a body length of between , and weighing between . They are usually mouse-like in appearance, but they have furry tails instead of scaly tails. They are usually arboreal animals (living in trees). They move quickly and are good at climbing. Most species are nocturnal. Dormice have a very good sense of hearing. They make noises to each other with different sounds using their voices.

Dormice are omnivorous, usually eating fruits, berries, flowers, nuts and insects. Dormice are different to all other rodents because they do not have a cecum which is a part of the gut. Other animals use the cecum to ferment plants. Their teeth are like squirrels, but they often do not have premolars.

Dormice breed one or two times per year, having an average of four young after a gestation period of 21–32 days. Dormice can live for as long as five years. The young are born without hair and they cannot do anything for themselves. Their eyes do not open until about eighteen days after birth. They are usually ready to reproduce after the end of their first hibernation. Dormice live in small family groups. The area they live in depends on which species they are, and how much food is available.

Hibernation
One of the main characteristics of dormice that live in temperate zones is hibernation.  Dormice can hibernate six months out of the year, or even longer if the weather remains cold enough. They sometimes wake for a short amount of time so that they can eat food which they had previously stored nearby. During the summer, they store fat in their bodies, to give the dormouse the energy it needs to survive through the hibernation period.

Hibernation is where the name dormouse comes from. The Anglo-Norman word dormeus means "sleepy (one)"; the word was later changed to resemble the word "mouse". The sleepy behaviour of the Dormouse character in Lewis Carroll's Alice's Adventures in Wonderland also shows this trait.

Relationship with humans
The edible dormouse was thought to be a special food in ancient Rome. It was eaten as an appetizer or as a dessert. When it was eaten as a dessert, it would be dipped in honey and poppy seeds. The Romans had a special place to keep dormice which was called a glirarium. Dormice are still eaten in Slovenia, and apparently also by the Mafia.  Dormouse fat was used by the Elizabethans to induce sleep.

Evolution

The earliest fossil evidence of dormice has been found in Europe from the early Eocene times. They were in Africa in the upper Miocene. Their appearance in Asia was not as long ago. Many types of extinct dormouse species have been found. During the Pleistocene, giant dormice the size of large rats (for example Leithia melitensis) lived on the islands of Malta and Sicily.

Classification
The family consists of 34 living species, in three subfamilies and 10 genera (although not all scientists agree with this number):

Family: Gliridae
 Subfamily Graphiurinae
 Genus Graphiurus (African dormouse)
 Species Graphiurus angolensis, (Angolan African dormouse)
 Species Graphiurus christyi (Christy's dormouse)
 Species Graphiurus crassicaudatus (Jentink's dormouse)
 Species Graphiurus johnstoni (Johnston's African dormouse)
 Species Graphiurus kelleni (Kellen's dormouse)
 Species Graphiurus lorraineus (Lorrain dormouse)
 Species Graphiurus microtis (Small-eared dormouse)
 Species Graphiurus monardi (Monard's dormouse)
 Species Graphiurus murinus (Woodland dormouse)
 Species Graphiurus nagtglasii (Nagtglas's African dormouse)
 Species Graphiurus ocularis (Spectacled dormouse)
 Species Graphiurus platyops (Rock dormouse)
 Species Graphiurus rupicola (Stone dormouse)
 Species Graphiurus surdus (Silent dormouse)
 Subfamily Leithiinae
 Genus Chaetocauda
 Species Chaetocauda sichuanensis (Chinese dormouse)
 Genus Dryomys
 Species Dryomys laniger (Woolly dormouse)
 Species Dryomys niethammeri (Niethammer's forest dormouse)
 Species Dryomys nitedula (Forest dormouse)
 Genus Eliomys (Garden dormice)
 Species Eliomys melanurus (Asian garden dormouse)
 Species Eliomys munbyanus (Maghreb garden dormouse)
 Species Eliomys quercinus (Garden dormouse)
 Genus Hypnomys† (Balearic dormouse - extinct)
 Species Hypnomys morphaeus†
 Species Hypnomys mahonensis†
 Genus Muscardinus
 Species Muscardinus avellanarius (Hazel dormouse)
 Genus Myomimus (Mouse-tailed dormouse)
 Species Myomimus personatus (Masked mouse-tailed dormouse)
 Species Myomimus roachi (Roach's mouse-tailed dormouse)
 Species Myomimus setzeri (Setzer's mouse-tailed dormouse)
 Genus Selevinia
 Species Selevinia betpakdalaensis (Desert dormouse)
 Subfamily Glirinae
 Genus Glirulus
 Species Glirulus japonicus (Japanese dormouse)
 Genus Glis
 Species Glis glis (Edible dormouse)

Fossil species
Subfamily Bransatoglirinae
 Genus Oligodyromys
 Genus Bransatoglis
 Species Bransatoglis adroveri Majorca, Early Oligocene
 Species Bransatoglis planus Eurasia, Early Oligocene

References

Holden M.E. 2005. Family Gliridae. pp. 819–841 in Mammal species of the world: a taxonomic and geographic reference. D.E. Wilson and D.M. Reeder eds. Johns Hopkins University Press, Baltimore.

Related pages
Hazel dormouse

Other websites
BBC Wales Nature: Dormouse article
Glirarium.org
Fauna of Europe: Glis glis

Dormouse


An audio engineer (or simply engineer for short) is a person who operates, and usually chooses and sets up recording equipment. The term applies mainly to a person who works in a recording studio but can also apply to people who do the same kind of work, in other places. An engineer may work with multitrack recordings or stereophonic remixes.

Audio engineering deals with the recording and reproduction of sound through mechanical and electronic  means and is a part of audio science. The field draws on many disciplines, including electrical engineering, acoustics, and music. An audio engineer is closer to the creative and technical aspects of audio than an acoustical engineer.

Some amateur (and a few professional) engineers are self-taught, and learn mostly by doing, or with the help of an instruction manual. Many engineers started in other studio jobs (such as running errands), and learned about recording as they became familiar with the studio where they worked. An engineer learns about the use and placement of microphones, how to operate and maintain an audio mixer, recording deck, sound effects, and other machines, and how to switch between live and recorded sounds, to make the best, and often the most unique, recording possible. A good engineer will strive to make recordings that are both of high technical quality, and also pleasing to hear.

Starting wages may be small in recording studios, and many beginners work as unpaid volunteers. Experienced engineers, especially those who have worked on a hit record, may command a large wage. Some engineers are paid a salary, while others may earn hourly pay (sometimes based on the studio's rates), or be paid per session. Many go on to start their own recording studios, or maintain a private studio or mobile recording service. A few work only for a single recording artist, band, or producer.

Several colleges and universities in the United States and other countries offer classes in recording, which may cover its history, its uses, and of course technique and technical knowledge. Some schools offer degree or diploma programs in Recording. Graduating such a program does not guarantee a person a studio job, but increases one's chances, and can provide better preparation for such a career.

Besides studio work, some engineers have one or more specialties, such as making new digital versions of old recordings, as consultants to places that give concerts and live performances, and sometimes as expert witnesses in court trials, when sounds or a recording may be important to the outcome of a case.

Equipment
Microphones
Mixing consoles
Signal processors
Digital audio workstations
Music sequencers
Speakers
Preamplifiers
Amplifiers

Related pages
Electrical engineering
Record producer

Other websites
Audio Engineering Society
Audio engineering formulas and calculators
Recording engineer video interviews
Audio Engineering online course  under Creative Commons Licence

Entertainment occupations
Music industry

Audio engineer


The weight of an object (or the weight of an amount of matter) is the measure of the intensity of the force imposed on this object by the local  gravitational field. Weight should not be confused with the related but quite different concept of mass. For small objects on Earth, the weight force is directed towards the center of the planet. For larger objects, such as the Moon orbiting around the Earth, the force is directed towards the center of mass of the combined system.

In common language, the weight of something is typically understood to be the value measured at or near the Earth's surface. Unfortunately the common terms used to describe the weight of an object are units of mass such as kilograms or pounds. For almost all of human history, weight has been measured on the surface of the Earth. Here, the weight is proportional to the mass. Objects which have the same mass have the same weight. An object with the twice the mass of another will also have twice the weight. As a consequence it is common practice to use the two words, mass and weight, as if they mean the same thing and to use kilograms and pounds as the units for both mass and weight. Using the same terms to describe and measure the two different properties has led to confusion between these two properties, mass and weight. Mass and weight are not the same thing.

Units of weight
The unit of weight in the International System of Units is the newton, which is represented by the symbol 'N'.

Other units have been in use in the past but have been abandoned, such as the dyne (the unit of force in the old CGS system) or the kilogram-force, which is the force exerted on a
kilogram of matter by a 'standard' Earth: a body with a mass of 1 kg has a weight of about 9.81 N at sea level.

Measuring weight
The weight of an object, or of an amount of matter, is typically measured with an instrument such as a spring scale. The scale includes a spring which provides a force to oppose the gravitational force on the object which is being weighed. The gravitational force pulls down, the spring pushes or pulls upwards. Typically, the scale has a readout which gives not the weight (which is a force) but rather the mass of the object. Spring scales are made with the assumption that they are being used on the surface of the Earth. If a spring scale was taken to the Moon it would give a misleading reading.

A balance style weighing scale is a device that compares the weights of two object in the same gravitational field: it determines whether one object is heavier or lighter than the other.

Weight is variable
Weight is not an intrinsic property of matter because the local gravitational field that generates the force called weight is variable in space and time:
 Since the Earth's attraction decreases as the square of the distance to its center, the weight of an object is slightly smaller at high altitude (e.g., at the top of a mountain) than at sea level, or at the equator than at the poles (because the Earth is slightly bulging).
 An arbitrary object on Earth is also attracted by all other celestial bodies, such as the Moon, for instance. Hence, its weight will be less with the Moon overhead than with the Moon on the other side of the Earth.
 Weight is not defined exclusively to Earth: An astronaut weighs 6 times less on the surface of the Moon than on the surface of the Earth.
 Weightlessness is an apparent condition experienced by astronauts or satellites in orbit around a planet. In reality their weight (gravitational pull) is the force that keeps them in orbit. Objects in orbit travel with very high speed. For satellites orbiting 300 - 500 kilometres above the Earth this speed is about 27,000 kph. Without the gravitational pull of the Earth they would fly off in a straight line. The gravitational pull keeps them falling towards the planet. The combination of high sideways velocity and constant pull toward the centre of the Earth bends their path so they stay in orbit.

Related pages
 Difference between Weight and Mass
 Center of mass
 Gravity
 Density

Physical quantity
Basic English 850 words
Basic physics ideas

Weight


The Internet Protocol (IP) is the most important communications protocol in the Internet protocol suite for relaying data across network boundaries. It establishes the Internet. In the past, IP did not provide the connectivity; It only specified how packets are supposed to be created. The Transmission Control Protocol (TCP) allowed this functionality. Since one could not perform its task without the other, they earned the name TCP/IP to show how they depend on each other.

Think of IP as something like the postal system. It allows you to address a package and drop it into the system, but there is no actual direct link between you and the recipient. Instead, there is a "web" of links interconnecting with each other. This is where IP and TCP come in. IP tells packets what their destination is and how to get there; TCP ensures a reliable connection, checking packets for errors, requesting a "re-transmission" if it detects one.

Function
The Internet Protocol gets information from a source computer to a destination computer. It sends this information in the form of packets.

There are two versions of the Internet Protocol currently in use: IPv4 and IPv6, with IPv4 being the version most used. IP also gives computers an IP address to identify each other, much like a typical physical address.

IP is the primary protocol in the Internet Layer of the Internet Protocol Suite, which is a set of communications protocols consisting of seven abstraction layers (see OSI model),

The main purpose and task of IP is the delivery of datagrams from the source host (source computer) to the destination host (receiving computer) based on their addresses. To achieve this, IP includes methods and structures for putting tags (address information, which is part of metadata) within datagrams. The process of putting these tags on datagrams is called encapsulation. Think of the analogy of the postal system. IP is similar in that it allows a package (a datagram) to be addressed (encapsulation) and put into the system (the Internet) by the sender (source host). However, there is no direct link between sender and receiver.

The package (datagram) is almost always divided into pieces, but each piece contains the address of the receiver (destination host). Eventually, each piece arrives at the receiver, often by different routes and at different times. These routes and times are also determined by the Postal System, which is the IP. However, the Postal System (in the transport and application layers) puts all the pieces back together before delivery to the receiver (destination host).

Note: IP is actually a connectionless protocol, meaning that the circuit to the receiver (destination host) does not need be set up before transmission (by the source host). Continuing the analogy, there does not need to be a direct connection between the physical return address on the letter/package and the recipient address before the letter/package is sent.

Originally, IP was a connectionless datagram service in a transmission control program created by Vint Cerf and Bob Kahn in 1974. When format and rules were applied to allow connections, the connection-oriented Transmission Control Protocol was created. The two together form the Internet Protocol Suite, often referred to as TCP/IP.

Internet Protocol version 4 (IPv4) was the first major version of IP. This is the dominant protocol of the Internet. However, IPv6 is active and in use, and its deployment is increasing all over the world.

Addressing and routing are the most complex aspects of IP. However, intelligence in the network is located at nodes (network interconnection points) in the form of routers which forward datagrams to the next known gateway on the route to the final destination. The routers use interior gateway protocols (IGPs) or external gateway protocols (EGPs) to help with making forwarding route decisions. Routes are determined by the routing prefix within the datagrams. The routing process can therefore become complex. But at the speed of light (or nearly so) the routing intelligence determines the best route, and the datagram pieces and datagram all eventually arrive at their destination

IP Packets
IP packets or datagram has two parts. The first part is the header, which is like a label on an envelope. The second part is the payload, which is like the letter inside an envelope. The header contains the source and destination IP addresses, and some extra information. This information is called metadata, and is about the packet itself. Putting data in a packet with a header is encapsulation.

Routing
Every computer on a network does some kind of routing. Dedicated computers talk with each other to figure out where to send packets. These computers are called routers, and talk using routing protocols.

Along every hop in a packet's journey, a computer reads the header. The computer sees the destination IP address and figures out where to send the packet.

Reliability
ARPANET, the early ancestor of the internet, was designed to survive a nuclear war. If one computer was destroyed, communication between all the other computers would still work. Computer networks still follow this same design.

Computers talking to each other handle the "smart" functions to simplify computer networks. The end nodes will check for errors instead of a central authority. Keeping the "smart" things on the end computers or nodes follows the end-to-end principle.

The Internet Protocol sends packets out without ensuring they arrive safely. This is best-effort delivery, and is unreliable. Packets could get messed up, lost, duplicated, or received out of order. Higher level protocols like the Transmission Control Protocol (TCP) ensure packets are delivered correctly. IP is also connectionless, so it does not keep track of communications. It assumes that another protocol such as TCP will keep track of connections.

Internet Protocol Version 4 (IPv4) uses a checksum to check for errors in an IP header. Every checksum is unique to a source/destination combination. A routing node generates a new checksum when it gets a packet. If the new checksum is different from the old one, the routing node knows the packet is bad and throws it out. IPv6 assumes another protocol will check for errors and leaves out the checksum. This is to improve performance.

History
In 1974, the Institute of Electrical and Electronics Engineers published a paper called "A Protocol for Packet Network Intercommunication". The paper described a way for computers to talk to each other using Packet Switching. A big part of this idea was the "Transmission Control Program". The Transmission Control Program was too big, so it split into TCP and IP. This model is now called the DoD Internet Model and Internet Protocol Suite, or the TCP/IP Model.

Versions 0 to 3 of IP were experimental, and used between 1977 and 1979. Versions 2 and 3, and a draft of version 4, allowed an address length of up to 128 bits, but this was mistakenly reduced to 32 bits in the final version of IPv4. Versions 7-9 were prototypes of what eventually became IPv6.

IPv4 addresses will run out, because the number of possible addresses is running out. To fix this, the IEEE made IPv6 which had even more addresses. While IPv4 has 4.3 Billion addresses, IPv6 has 340 undecillion of them. This means we will never run out of IPv6 addresses. IPv5 was reserved for the Internet Stream Protocol, which was only used experimentally.

References

Internet protocols

Internet Protocol