Air conditioning is the process of removing heat and moisture from the interior of an occupied space, to improve the comfort of occupants. Air conditioning can be used in both commercial environments; this process is most used to achieve a more comfortable interior environment for humans and other animals. Air conditioners use a fan to distribute the conditioned air to an occupied space such as a building or a car to improve thermal comfort and indoor air quality. Electric refrigerant-based AC units range from small units that can cool a small bedroom, which can be carried by a single adult, to massive units installed on the roof of office towers that can cool an entire building; the cooling is achieved through a refrigeration cycle, but sometimes evaporation or free cooling is used. Air conditioning systems can be made based on desiccants; some AC systems store heat in subterranean pipes. In the most general sense, air conditioning can refer to any form of technology that modifies the condition of air.
In common usage, though, "air conditioning" refers to systems. In construction, a complete system of heating and air conditioning is referred to as HVAC. Since prehistoric times and ice were used for cooling; the business of harvesting ice during winter and storing for use in summer became popular towards the late 17th century. This practice was replaced by mechanical ice-making machines; the basic concept behind air conditioning is said to have been applied in ancient Egypt, where reeds were hung in windows and were moistened with trickling water. The evaporation of water cooled the air blowing through the window; this process made the air more humid, which can be beneficial in a dry desert climate. Other techniques in medieval Persia involved the use of cisterns and wind towers to cool buildings during the hot season; the 2nd-century Chinese mechanical engineer and inventor Ding Huan of the Han Dynasty invented a rotary fan for air conditioning, with seven wheels 3 m in diameter and manually powered by prisoners of the time.
In 747, Emperor Xuanzong of the Tang Dynasty had the Cool Hall built in the imperial palace, which the Tang Yulin describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song Dynasty, written sources mentioned the air conditioning rotary fan as more used. In the 17th century, the Dutch inventor Cornelis Drebbel demonstrated "Turning Summer into Winter" as an early form of modern air conditioning for James I of England by adding salt to water. Modern air conditioning emerged from advances in chemistry during the 19th century, the first large-scale electrical air conditioning was invented and used in 1902 by US inventor Willis Carrier; the introduction of residential air conditioning in the 1920s helped enable the great migration to the Sun Belt in the United States. In 1758, Benjamin Franklin and John Hadley, a chemistry professor at Cambridge University, conducted an experiment to explore the principle of evaporation as a means to cool an object.
Franklin and Hadley confirmed that evaporation of volatile liquids could be used to drive down the temperature of an object past the freezing point of water. They conducted their experiment with the bulb of a mercury thermometer as their object and with a bellows used to speed up the evaporation, they lowered the temperature of the thermometer bulb down to −14 °C while the ambient temperature was 18 °C. Franklin noted that, soon after they passed the freezing point of water 0 °C, a thin film of ice formed on the surface of the thermometer's bulb and that the ice mass was about 6 mm thick when they stopped the experiment upon reaching −14 °C. Franklin concluded: "From this experiment one may see the possibility of freezing a man to death on a warm summer's day."In 1820, English scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida.
He hoped to use his ice-making machine to regulate the temperature of buildings. He envisioned centralized air conditioning that could cool entire cities. Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. Though his process improved the artificial production of ice, his hopes for its success vanished soon afterwards when his chief financial backer died and Gorrie did not get the money he needed to develop the machine. According to his biographer, Vivian M. Sherlock, he blamed the "Ice King", Frederic Tudor, for his failure, suspecting that Tudor had launched a smear campaign against his invention. Dr. Gorrie died impoverished in 1855, the dream of commonplace air conditioning went away for 50 years. James Harrison's first mechanical ice-making machine began operation in 1851 on the banks of the Barwon River at Rocky Point in Geelong, Australia, his first commercial ice-making machine followed in 1853, his patent for an ether vapor compression refrigeration system was granted in 1855.
This novel system used a compres
A picnic is a meal taken outdoors as part of an excursion – ideally in scenic surroundings, such as a park, lakeside, or other place affording an interesting view, or else in conjunction with a public event such as preceding an open-air theatre performance, in summer. Picnics are meant for the late mornings or midday breakfasts, but could be held as a luncheonette or a dinner event. Descriptions of picnics show that the idea of a meal, jointly contributed and was enjoyed out-of-doors was essential to a picnic from the early 19th century. Picnics are family oriented but can be an intimate occasion between two people or a large get together such as company picnics and church picnics, it is sometimes combined with a cookout a form of barbecue: either grilling, baking, or a combination of all of the above. On romantic and family picnics, a picnic basket and a blanket are brought along. Outdoor games or some other form of entertainment are common at large picnics. In established public parks, a picnic area includes picnic tables and other items related to eating outdoors, such as built-in grills, water faucets, garbage containers, restrooms.
Some picnics are a potluck, an entertainment at which each person contributed some dish to a common table for all to share. When the picnic is not a cookout, the food eaten is hot, instead taking the form of deli sandwiches, finger food, fresh fruit, cold meats and accompanied by chilled wine or champagne or soft drinks; the first usage of the word is traced to the 1692 edition of Tony Willis, Origines de la Langue Française, which mentions pique-nique as being of recent origin. The term was used to describe a group of people dining in a restaurant; the concept of a picnic long retained the connotation of a meal to which everyone contributed something. Whether picnic is based on the verb piquer which means'pick' or'peck' with the rhyming nique meaning "thing of little importance" is doubted. Picnicking was common in France after the French Revolution, when it became possible for ordinary people to visit and mingle in the country’s royal parks. In 18th and 19th centuries, picnics were elaborate social events with complex meals and fancy drinks that sometimes took days to prepare.
The word picnic first appeared in English in a letter of the Gallicized Lord Chesterfield in 1748, who associates it with card-playing and conversation, may have entered the English language from this French word. The practice of an elegant meal eaten out-of-doors, rather than an agricultural worker's dinner in a field, was connected with respite from hunting from the Middle Ages. Though it may have appeared in a 17th-century dictionary as "pique-nique," the actual usage began as "pique un niche" meaning to "pick a place," an isolated spot where family or friends could enjoy a jolly meal together away from the distractions and public nature of a communal life; the term after years of usage entered the official French language. Despite having been debunked, a spurious etymology linking the origin of the word to lynchings of African-Americans in the American South continues to resurface from time to time. After the French Revolution in 1789, royal parks became open to the public for the first time.
Picnicking in the parks became a popular activity amongst the newly enfranchised citizens. Early in the 19th century, a fashionable group of Londoners formed the'Picnic Society'. Members met in the Pantheon on Oxford Street; each member was expected to provide a share of the entertainment and of the refreshments with no one particular host. Interest in the society waned in the 1850s. From the 1830s, Romantic American landscape painting of spectacular scenery included a group of picnickers in the foreground. An early American illustration of the picnic is Thomas Cole's The Pic-Nic of 1846. In it, a guitarist serenades the genteel social group in the Hudson River Valley with the Catskills visible in the distance. Cole's well-dressed young picnickers having finished their repast, served from splint baskets on blue-and-white china, stroll about in the woodland and boat on the lake; the image of picnics as a peaceful social activity can be utilised for political protest, too. In this context, a picnic functions as a temporary occupation of significant public territory.
A famous example of this is the Pan-European Picnic held on both sides of the Hungarian/Austrian border on the 19 August 1989 as part of the struggle towards German reunification. In 2000, a 600-mile-long picnic took place from coast to coast in France to celebrate the first Bastille Day of the new Millennium. In the United States the 4 July celebration of American independence is a popular day for a picnic. In Italy, the favorite picnic day is Easter Monday; the 1955 film Picnic, based on the Pulitzer Prize-winning play by William Inge, was a multiple Oscar winner. The film has been remade twice, in 1986 and 2000. Picnickers are used to illustrate the scale of one metre in the film Powers of Ten; the Office Picnic is a dark comedy set in an Australian Public Service office. It was written and produced by filmmaker Tom Cowan, now famous for his work on the series Survivor. In Peter Weir's myst
A train station, railway station, railroad station, or depot is a railway facility or area where trains stop to load or unload passengers or freight. It consists of at least one track-side platform and a station building providing such ancillary services as ticket sales and waiting rooms. If a station is on a single-track line, it has a passing loop to facilitate traffic movements; the smallest stations are most referred to as "stops" or, in some parts of the world, as "halts". Stations elevated. Connections may be available to intersecting rail lines or other transport modes such as buses, trams or other rapid transit systems. In British English, traditional usage favours railway station or station though train station, perceived as an Americanism, is now about as common as railway station in writing. In British usage, the word station is understood to mean a railway station unless otherwise qualified. In American English, the most common term in contemporary usage is train station. In North America, the term depot is sometimes used as an alternative name for station, along with the compound forms train depot, railway depot, railroad depot, but applicable for goods, the term depot is not used in reference to vehicle maintenance facilities in American English.
The world's first recorded railway station was The Mount on the Oystermouth Railway in Swansea, which began passenger service in 1807, although the trains were horsedrawn rather than by locomotives. The two-storey Mount Clare station in Baltimore, which survives as a museum, first saw passenger service as the terminus of the horse-drawn Baltimore and Ohio Railroad on 22 May 1830; the oldest terminal station in the world was Crown Street railway station in Liverpool, built in 1830, on the locomotive hauled Liverpool to Manchester line. As the first train on the Liverpool-Manchester line left Liverpool, the station is older than the Manchester terminal at Liverpool Road; the station was the first to incorporate a train shed. The station was demolished in 1836 as the Liverpool terminal station moved to Lime Street railway station. Crown Street station was converted to a goods station terminal; the first stations had little in the way of amenities. The first stations in the modern sense were on the Liverpool and Manchester Railway, opened in 1830.
Manchester's Liverpool Road Station, the second oldest terminal station in the world, is preserved as part of the Museum of Science and Industry in Manchester. It resembles a row of Georgian houses. Early stations were sometimes built with both passenger and goods facilities, though some railway lines were goods-only or passenger-only, if a line was dual-purpose there would be a goods depot apart from the passenger station. Dual-purpose stations can sometimes still be found today, though in many cases goods facilities are restricted to major stations. In rural and remote communities across Canada and the United States, passengers wanting to board the train had to flag the train down in order for it to stop; such stations were known as "flag stops" or "flag stations". Many stations date from the 19th century and reflect the grandiose architecture of the time, lending prestige to the city as well as to railway operations. Countries where railways arrived may still have such architecture, as stations imitated 19th-century styles.
Various forms of architecture have been used in the construction of stations, from those boasting grand, Baroque- or Gothic-style edifices, to plainer utilitarian or modernist styles. Stations in Europe tended to follow British designs and were in some countries, like Italy, financed by British railway companies. Stations built more often have a similar feel to airports, with a simple, abstract style. Examples of modern stations include those on newer high-speed rail networks, such as the Shinkansen in Japan, THSR in Taiwan, TGV lines in France and ICE lines in Germany. Stations have staffed ticket sales offices, automated ticket machines, or both, although on some lines tickets are sold on board the trains. Many stations include a convenience store. Larger stations have fast-food or restaurant facilities. In some countries, stations may have a bar or pub. Other station facilities may include: toilets, left-luggage, lost-and-found and arrivals boards, luggage carts, waiting rooms, taxi ranks, bus bays and car parks.
Larger or manned stations tend to have a greater range of facilities including a station security office. These are open for travellers when there is sufficient traffic over a long enough period of time to warrant the cost. In large cities this may mean facilities available around the clock. A basic station might only have platforms, though it may still be distinguished from a halt, a stopping or halting place that may not have platforms. Many stations, either larger or smaller, offer interchange with local transportation. In many African, South American countries, Asian countries, stations are used as a place for public markets and other informal businesses; this is true on tourist routes or stations near tourist destinations. As well as providing services for passengers and loading facilities for goods, stations can sometimes have locomotive and rolling stock depots (usually with facilities for storing and refuelling rolling stock an
Clergy are some of the main and important formal leaders within certain religions. The roles and functions of clergy vary in different religious traditions but these involve presiding over specific rituals and teaching their religion's doctrines and practices; some of the terms used for individual clergy are clergyman and churchman. Less common terms are churchwoman and cleric. In Christianity the specific names and roles of clergy vary by denomination and there is a wide range of formal and informal clergy positions, including deacons, priests, preachers, pastors and the Pope. In Islam, a religious leader is known formally or informally as an imam, mufti, mullah or ayatollah. In Jewish tradition, a religious leader is a rabbi or hazzan; the word "Cleric" comes from the ecclesiastical Latin Clericus, for those belonging to the priestly class. In turn, the source of the Latin word is from the Ecclesiastical Greek Clericus, meaning appertaining to an inheritance, in reference to the fact that the Levitical priests of the Old Testament had no inheritance except the Lord.
"Clergy" is from two Old French words, clergié and clergie, which refer to those with learning and derive from Medieval Latin clericatus, from Late Latin clericus. "Clerk", which used to mean one ordained to the ministry derives from clericus. In the Middle Ages and writing were exclusively the domain of the priestly class, this is the reason for the close relationship of these words. Within Christianity in Eastern Christianity and in Western Roman Catholicism, the term cleric refers to any individual, ordained, including deacons and bishops. In Latin Roman Catholicism, the tonsure was a prerequisite for receiving any of the minor orders or major orders before the tonsure, minor orders, the subdiaconate were abolished following the Second Vatican Council. Now, the clerical state is tied to reception of the diaconate. Minor Orders are still given in the Eastern Catholic Churches, those who receive those orders are'minor clerics.'The use of the word "Cleric" is appropriate for Eastern Orthodox minor clergy who are tonsured in order not to trivialize orders such as those of Reader in the Eastern Church, or for those who are tonsured yet have no minor or major orders.
It is in this sense that the word entered the Arabic language, most in Lebanon from the French, as kleriki meaning "seminarian." This is all in keeping with Eastern Orthodox concepts of clergy, which still include those who have not yet received, or do not plan to receive, the diaconate. A priesthood is a body of priests, shamans, or oracles who have special religious authority or function; the term priest is derived from the Greek presbyter, but is used in the sense of sacerdos in particular, i.e. for clergy performing ritual within the sphere of the sacred or numinous communicating with the gods on behalf of the community. Buddhist clergy are collectively referred to as the Sangha, consist of various orders of male and female monks; this diversity of monastic orders and styles was one community founded by Gautama Buddha during the 5th century BC living under a common set of rules. According to scriptural records, these celibate monks and nuns in the time of the Buddha lived an austere life of meditation, living as wandering beggars for nine months out of the year and remaining in retreat during the rainy season.
However, as Buddhism spread geographically over time - encountering different cultures, responding to new social and physical environments - this single form of Buddhist monasticism diversified. The interaction between Buddhism and Tibetan Bon led to a uniquely Tibetan Buddhism, within which various sects, based upon certain teacher-student lineages arose; the interaction between Indian Buddhist monks and Chinese Confucian and Taoist monks from c200-c900AD produced the distinctive Ch'an Buddhism. Ch'an, like the Tibetan style, further diversified into various sects based upon the transmission style of certain teachers, as well as in response to particular political developments such as the An Lushan Rebellion and the Buddhist persecutions of Emperor Wuzong. In these ways, manual labour was introduced to a practice where monks survived on alms; this adaptation of form and roles of Buddhist monastic practice continued after the transmission to Japan. For example, monks took on administrative functions for the Emperor in particular secular communities, thereby creating Buddhist'priests'.
Again, in response to various historic attempts to suppress Buddhism, the practice of celibacy was relaxed and Japanese monks allowed to marry. This form was transmitted to Korea, during Japanese occupation, where celibate and non-celibate monks today exist in the same sects.. As these varied styles of Buddhist monasticism are transmitted to Western cultures, still more new forms are being created. In general, the Mahayana schools of Buddhism tend to be mo
A firearm is a portable gun that inflicts damage on targets by launching one or more projectiles driven by expanding high-pressure gas produced chemically by exothermic combustion of propellant within an ammunition cartridge. If gas pressurization is achieved through mechanical gas compression rather than through chemical propellant combustion the gun is technically an air gun, not a firearm; the first primitive firearms originated in 10th-century China when bamboo tubes containing gunpowder and pellet projectiles were mounted on spears into the one-person-portable fire lance, used as a shock weapon to good effect in the Siege of De'an in 1132. In the 13th century the Chinese invented the metal-barrelled hand cannon considered the true ancestor of all firearms; the technology spread through the rest of East Asia, South Asia, the Middle East, Europe. Older firearms used black powder as a propellant, but modern firearms use smokeless powder or other propellants. Most modern firearms have rifled barrels to impart spin to the projectile for improved flight stability.
Modern firearms can be described in the case of shotguns by their gauge. Further classification may make reference to the type of barrel used and to the barrel length, to the firing mechanism, to the design's primary intended use, or to the accepted name for a particular variation. Shooters aim firearms at their targets with hand-eye coordination, using either iron sights or optical sights; the accurate range of pistols does not exceed 110 yards, while most rifles are accurate to 550 yards using iron sights, or to longer ranges using optical sights. Purpose-built sniper rifles and anti-materiel rifles are accurate to ranges of more than 2,200 yards. Firearms include a variety of ranged weapons and there is no agreed upon definition. Many soldiers consider a firearm to be any ranged weapon that uses gunpowder or a derivative as a propellant. Small arms include handguns and long guns, such as rifles, submachine guns, personal defense weapons, squad automatic weapons, light machine guns; the world's top small arms manufacturing companies are Browning, Colt, Smith & Wesson, Mossberg, Heckler & Koch, SIG Sauer, Walther, ČZUB, Steyr-Mannlicher, FN Herstal, Norinco, Tula Arms and Kalashnikov, while former top producers were Mauser, Springfield Armory, Rock Island Armory under Armscor.
In 2018, Small Arms Survey reported that there are over one billion small arms distributed globally, of which 857 million are in civilian hands. U. S. civilians alone account for 393 million of the worldwide total of civilian held firearms. This amounts to "120.5 firearms for every 100 residents." The world's armed forces control about 133 million of the global total of small arms, of which over 43 percent belong to two countries: the Russian Federation and China. Law enforcement agencies control about 23 million of the global total of small arms; the smallest of all firearms is the handgun. There are two common types of handguns: semi-automatic pistols. Revolvers have "charge holes" in a revolving cylinder. Semi-automatic pistols have a single fixed firing chamber machined into the rear of the barrel, a magazine so they can be used to fire more than one round; each press of the trigger fires a cartridge, using the energy of the cartridge to activate the mechanism so that the next cartridge may be fired immediately.
This is opposed to "double-action" revolvers which accomplish the same end using a mechanical action linked to the trigger pull. Prior to the 19th century all handguns were single-shot muzzleloaders. With the invention of the revolver in 1818, handguns capable of holding multiple rounds became popular. Certain designs of auto-loading pistol appeared beginning in the 1870s and had supplanted revolvers in military applications by the end of World War I. By the end of the 20th century, most handguns carried by military and civilians were semi-automatic, although revolvers were still used. Speaking and police forces use semi-automatic pistols due to their high magazine capacities and ability to reload by removing the empty magazine and inserting a loaded one. Revolvers are common among handgun hunters because revolver cartridges are more powerful than similar caliber semi-automatic pistol cartridges and the strength and durability of the revolver design is well-suited to outdoor use. Revolvers in.22 LR and 38 Special/357 Magnum, are common concealed weapons in j
A town is a human settlement. Towns are larger than villages but smaller than cities, though the criteria to distinguish them vary between different parts of the world; the word town shares an origin with the German word Zaun, the Dutch word tuin, the Old Norse tun. The German word Zaun comes closest to the original meaning of the word: a fence of any material. An early borrowing from Celtic *dunom. In English and Dutch, the meaning of the word took on the sense of the space which these fences enclosed. In England, a town was a small community that could not afford or was not allowed to build walls or other larger fortifications, built a palisade or stockade instead. In the Netherlands, this space was a garden, more those of the wealthy, which had a high fence or a wall around them. In Old Norse tun means a place between farmhouses, the word is still used in a similar meaning in modern Norwegian. In Old English and Early and Middle Scots, the words ton, etc. could refer to diverse kinds of settlements from agricultural estates and holdings picking up the Norse sense at one end of the scale, to fortified municipalities.
If there was any distinction between toun and burgh as claimed by some, it did not last in practice as burghs and touns developed. For example, "Edina Burgh" or "Edinburgh" was built around a fort and came to have a defensive wall. In some cases, "town" is an alternative name for "city" or "village". Sometimes, the word "town" is short for "township". In general, today towns can be differentiated from townships, villages, or hamlets on the basis of their economic character, in that most of a town's population will tend to derive their living from manufacturing industry and public services rather than primary industry such as agriculture or related activities. A place's population size is not a reliable determinant of urban character. In many areas of the world, e.g. in India at least until recent times, a large village might contain several times as many people as a small town. In the United Kingdom, there are historical cities; the modern phenomenon of extensive suburban growth, satellite urban development, migration of city dwellers to villages has further complicated the definition of towns, creating communities urban in their economic and cultural characteristics but lacking other characteristics of urban localities.
Some forms of non-rural settlement, such as temporary mining locations, may be non-rural, but have at best a questionable claim to be called a town. Towns exist as distinct governmental units, with defined borders and some or all of the appurtenances of local government. In the United States these are referred to as "incorporated towns". In other cases the town lacks its own governance and is said to be "unincorporated". Note that the existence of an unincorporated town may be set out by other means, e.g. zoning districts. In the case of some planned communities, the town exists in the form of covenants on the properties within the town; the United States Census identifies many census-designated places by the names of unincorporated towns which lie within them. The distinction between a town and a city depends on the approach: a city may be an administrative entity, granted that designation by law, but in informal usage, the term is used to denote an urban locality of a particular size or importance: whereas a medieval city may have possessed as few as 10,000 inhabitants, today some consider an urban place of fewer than 100,000 as a town though there are many designated cities that are much smaller than that.
Australian geographer Thomas Griffith Taylor proposed a classification of towns based on their age and pattern of land use. He identified five types of town: Infantile towns, with no clear zoning Juvenile towns, which have developed an area of shops Adolescent towns, where factories have started to appear Early mature towns, with a separate area of high-class housing Mature towns, with defined industrial and various types of residential area In Afghanistan and cities are known as shār; as the country is an rural society with few larger settlements, with major cities never holding more than a few hundred thousand inhabitants before the 2000s, the lingual tradition of the country does not discriminate between towns and cities. In Albania "qytezë" means town, similar with the word for city. Although there is no official use of the term for any settlement. In Albanian "qytezë" means "small city" or "new city", while in ancient times "small residential center within the walls of a castle"; the center is a population group, larger than a village, smaller than a city.
Though the village is bigger than a hamlet In Australia, towns or "urban centre localities" are understood to be those centers of population not formally declared to be cities and having a population in excess of about 200 people. Centers too small to be called towns are understood to be a township. In addition, some local government entities are styled as towns in Queensland, Western Australia and the Northern Territory, before the statewide amalgamations of th
Video is an electronic medium for the recording, playback and display of moving visual media. Video was first developed for mechanical television systems, which were replaced by cathode ray tube systems which were replaced by flat panel displays of several types. Video systems vary in display resolution, aspect ratio, refresh rate, color capabilities and other qualities. Analog and digital variants exist and can be carried on a variety of media, including radio broadcast, magnetic tape, optical discs, computer files, network streaming. Video technology was first developed for mechanical television systems, which were replaced by cathode ray tube television systems, but several new technologies for video display devices have since been invented. Video was exclusively a live technology. Charles Ginsburg led an Ampex research team developing one of the first practical video tape recorder. In 1951 the first video tape recorder captured live images from television cameras by converting the camera's electrical impulses and saving the information onto magnetic video tape.
Video recorders were sold for US $50,000 in 1956, videotapes cost US $300 per one-hour reel. However, prices dropped over the years; the use of digital techniques in video created digital video, which allows higher quality and much lower cost than earlier analog technology. After the invention of the DVD in 1997 and Blu-ray Disc in 2006, sales of videotape and recording equipment plummeted. Advances in computer technology allows inexpensive personal computers and smartphones to capture, store and transmit digital video, further reducing the cost of video production, allowing program-makers and broadcasters to move to tapeless production; the advent of digital broadcasting and the subsequent digital television transition is in the process of relegating analog video to the status of a legacy technology in most parts of the world. As of 2015, with the increasing use of high-resolution video cameras with improved dynamic range and color gamuts, high-dynamic-range digital intermediate data formats with improved color depth, modern digital video technology is converging with digital film technology.
Frame rate, the number of still pictures per unit of time of video, ranges from six or eight frames per second for old mechanical cameras to 120 or more frames per second for new professional cameras. PAL standards and SECAM specify 25 frame/s. Film is shot at the slower frame rate of 24 frames per second, which complicates the process of transferring a cinematic motion picture to video; the minimum frame rate to achieve a comfortable illusion of a moving image is about sixteen frames per second. Video can be progressive. In progressive scan systems, each refresh period updates all scan lines in each frame in sequence; when displaying a natively progressive broadcast or recorded signal, the result is optimum spatial resolution of both the stationary and moving parts of the image. Interlacing was invented as a way to reduce flicker in early mechanical and CRT video displays without increasing the number of complete frames per second. Interlacing retains detail while requiring lower bandwidth compared to progressive scanning.
In interlaced video, the horizontal scan lines of each complete frame are treated as if numbered consecutively, captured as two fields: an odd field consisting of the odd-numbered lines and an field consisting of the even-numbered lines. Analog display devices reproduce each frame doubling the frame rate as far as perceptible overall flicker is concerned; when the image capture device acquires the fields one at a time, rather than dividing up a complete frame after it is captured, the frame rate for motion is doubled as well, resulting in smoother, more lifelike reproduction of moving parts of the image when viewed on an interlaced CRT display. NTSC, PAL and SECAM are interlaced formats. Abbreviated video resolution specifications include an i to indicate interlacing. For example, PAL video format is described as 576i50, where 576 indicates the total number of horizontal scan lines, i indicates interlacing, 50 indicates 50 fields per second; when displaying a natively interlaced signal on a progressive scan device, overall spatial resolution is degraded by simple line doubling—artifacts such as flickering or "comb" effects in moving parts of the image which appear unless special signal processing eliminates them.
A procedure known as deinterlacing can optimize the display of an interlaced video signal from an analog, DVD or satellite source on a progressive scan device such as an LCD television, digital video projector or plasma panel. Deinterlacing cannot, produce video quality, equivalent to true progressive scan source material. Aspect ratio describes the proportional relationship between the width and height of video screens and video picture elements. All popular video formats are rectangular, so can be described by a ratio between width and height; the ratio width to height for a traditional television screen is 4:3, or about 1.33:1. High definition televisions use an aspect ratio of 16:9, or about 1.78:1. The aspect ratio of a full 35 mm film frame with soundtrack is 1.375:1. Pixels on computer monitors are square, but pixels used in digital video have non-square aspect ratios, such as those used in the PAL and NTSC variants of the CCIR 601 digital video