A lifeboat is a small, rigid or inflatable boat carried for emergency evacuation in the event of a disaster aboard a ship. Lifeboat drills are required by law on larger commercial ships. Rafts are used. In the military, a lifeboat may double as a whaleboat, dinghy, or gig; the ship's tenders of cruise ships double as lifeboats. Recreational sailors carry inflatable life rafts, though a few prefer small proactive lifeboats that are harder to sink and can be sailed to safety. Inflatable lifeboats may be equipped with auto-inflation canisters or mechanical pumps. A quick release and pressure release mechanism is fitted on ships so that the canister or pump automatically inflates the lifeboat, the lifeboat breaks free of the sinking vessel. Commercial aircraft are required to carry auto-inflating life rafts in case of an emergency water landing. Ship-launched lifeboats are lowered from davits on a ship's deck, are hard to sink in normal circumstances; the cover serves as protection from sun and rain, can be used to collect rainwater, is made of a reflective or fluorescent material, visible.
Lifeboats have oars and mirrors for signaling, first aid supplies, food and water for several days. Some lifeboats are more capably equipped to permit self-rescue, with supplies such as a radio, an engine and sail, navigational equipment, solar water stills, rainwater catchments and fishing equipment; the International Convention for the Safety of Life at Sea and the International Life-Saving Appliance Code requires certain emergency equipment be carried on each lifeboat and liferaft used on international voyages. Modern lifeboats carry an Emergency Position-Indicating Radio Beacon and either a radar reflector or Search and Rescue Transponder. During the Age of Sail, the ship's boats were also used as lifeboats in case of emergency. In March 1870, answering a question at the House of Commons of the United Kingdom about the sinking of PS Normandy, George Shaw-Lefevre said that...in the opinion of the Board of Trade, it will not be possible to compel the passenger steamers running between England and France to have boats sufficient for the numerous passengers they carry.
They would encumber the decks, rather add to the danger than detract from it. In the late 1880s, Maria Beasley improved the design of life rafts, she patented a life-saving raft in both the United States and England in 1880. By the turn of the 20th century larger ships meant more people could travel, but safety rules regarding lifeboats remained out of date: for example, British legislation concerning the number of lifeboats was based on the tonnage of a vessel and only encompassed vessels of "10,000 gross register tons and over", it was not until after the sinking of RMS Titanic on April 15, 1912, that a broader movement began to require a sufficient number of lifeboats on passenger ships for all people on board. Titanic, with a gross tonnage of 46,000 tonnes and carrying 20 lifeboats, exceeded the regulations laid down by the Board of Trade, which required a ship of her size to carry boats capable of carrying a total of 1,060 people. Titanic's boats had a capacity of 1,178 people on a ship capable of carrying 3,330 people.
The type of life raft used on Titanic were the ones patented by Beasley. The need for so many more lifeboats on the decks of passenger ships after 1912 led to the use of most of the deck space available on the large ships, creating the problem of restricted passageways; this was resolved by the wider use of collapsible lifeboats, a number of, carried on Titanic. During World War II and the Battle of the Atlantic with convoys going to northern Russia through the Arctic Ocean it was found that the chance of the crews of merchant ships surviving in open lifeboats was not good unless they were rescued in a couple of hours; the US Navy asked various groups and manufacturers to suggest solutions. The result was the first enclosed, self-righting lifeboat, manufactured in Delanco, New Jersey; these radically new lifeboats were 24 feet in length and weighed 5,000 lb. They had two enclosed cabins which could hold a total of 25 persons; the space in between was designed to help persons in the water be pulled aboard, could be enclosed with a canvas top.
The new type lifeboat could be driven either by a small motor or sail. In 1943 the US developed a balsa wood liferaft that would not sink, irrespective of the number of holes in it; these balsa liferafts were designed to hold five to ten men on a platform suspended on the inside or fifteen to twenty-five hanging lines placed on the outsides. They were inexpensive, during the war thousands were stored in any space possible on US warships and merchant ships; these liferafts were intended only for use during a short term before lifeboats or another ship in the convoy or group could bring them aboard. When USS Indianapolis, a cruiser operating alone, was sunk in 1945, none of its larger lifeboats were launched, the survivors had to rely on balsa liferafts automatically released as the ship sank. Today, enclosed lifeboats are the preferred lifeboats fitted on modern merchant ships because of their superior protection against the elements; each merchant ship has one lifeboat fitted on the port side and one on the starboard side, so that a lifeboat is always available if the ship is listing to one side.
Lifeboat capacity is specified
Surveying or land surveying is the technique and science of determining the terrestrial or three-dimensional positions of points and the distances and angles between them. A land surveying professional is called a land surveyor; these points are on the surface of the Earth, they are used to establish maps and boundaries for ownership, such as building corners or the surface location of subsurface features, or other purposes required by government or civil law, such as property sales. Surveyors work with elements of geometry, regression analysis, engineering, programming languages, the law, they use equipment, such as total stations, robotic total stations, theodolites, GNSS receivers, retroreflectors, 3D scanners, handheld tablets, digital levels, subsurface locators, drones, GIS, surveying software. Surveying has been an element in the development of the human environment since the beginning of recorded history; the planning and execution of most forms of construction require it. It is used in transport, communications and the definition of legal boundaries for land ownership.
It is an important tool for research in many other scientific disciplines. The International Federation of Surveyors defines the function of surveying as: A surveyor is a professional person with the academic qualifications and technical expertise to conduct one, or more, of the following activities. Surveying has occurred since humans built the first large structures. In ancient Egypt, a rope stretcher would use simple geometry to re-establish boundaries after the annual floods of the Nile River; the perfect squareness and north-south orientation of the Great Pyramid of Giza, built c. 2700 BC, affirm the Egyptians' command of surveying. The Groma instrument originated in Mesopotamia; the prehistoric monument at Stonehenge was set out by prehistoric surveyors using peg and rope geometry. The mathematician Liu Hui described ways of measuring distant objects in his work Haidao Suanjing or The Sea Island Mathematical Manual, published in 263 AD; the Romans recognized land surveying as a profession.
They established the basic measurements under which the Roman Empire was divided, such as a tax register of conquered lands. Roman surveyors were known as Gromatici. In medieval Europe, beating the bounds maintained the boundaries of a village or parish; this was the practice of gathering a group of residents and walking around the parish or village to establish a communal memory of the boundaries. Young boys were included to ensure the memory lasted as long as possible. In England, William the Conqueror commissioned the Domesday Book in 1086, it recorded the names of all the land owners, the area of land they owned, the quality of the land, specific information of the area's content and inhabitants. It did not include maps showing exact locations. Abel Foullon described a plane table in 1551, but it is thought that the instrument was in use earlier as his description is of a developed instrument. Gunter's chain was introduced in 1620 by English mathematician Edmund Gunter, it enabled plots of land to be surveyed and plotted for legal and commercial purposes.
Leonard Digges described a Theodolite that measured horizontal angles in his book A geometric practice named Pantometria. Joshua Habermel created a theodolite with a compass and tripod in 1576. Johnathon Sission was the first to incorporate a telescope on a theodolite in 1725. In the 18th century, modern techniques and instruments for surveying began to be used. Jesse Ramsden introduced the first precision theodolite in 1787, it was an instrument for measuring angles in vertical planes. He created his great theodolite using an accurate dividing engine of his own design. Ramsden's theodolite represented a great step forward in the instrument's accuracy. William Gascoigne invented an instrument that used a telescope with an installed crosshair as a target device, in 1640. James Watt developed an optical meter for the measuring of distance in 1771. Dutch mathematician Willebrord Snellius introduced the modern systematic use of triangulation. In 1615 he surveyed the distance from Alkmaar to Breda 72 miles.
He underestimated this distance by 3.5%. The survey was a chain of quadrangles containing 33 triangles in all. Snell showed, he showed how to resection, or calculate, the position of a point inside a triangle using the angles cast between the vertices at the unknown point. These could be measured more than bearings of the vertices, which depended on a compass, his work established the idea of surveying a primary network of control points, locating subsidiary points inside the primary network later. Between 1733 and 1740, Jacques Cassini and his son César undertook the first triangulation of France, they included a re-surveying of the meridian arc, leading to the publication in 1745 of the first map of France constructed on rigorous principles. By this time triangulation methods were well established for local map-making, it was only towards the end of the 18th century that detailed triangulation network surveys mapped whole countries. In 1784, a team from Gene
Lunar Laser Ranging experiment
The ongoing Lunar Laser Ranging experiment or Apollo landing mirror measures the distance between surfaces of Earth and the Moon using laser ranging. Lasers at observatories on Earth are aimed at retroreflectors planted on the Moon during the Apollo program, the two Lunokhod missions. Laser light pulses are transmitted and reflected back to Earth, the round-trip duration is measured; the lunar distance is calculated from this value. The first successful tests were carried out in 1962 when a team from the Massachusetts Institute of Technology succeeded in observing laser pulses reflected from the Moon's surface using a laser with a millisecond pulse length. Similar measurements were obtained the same year by a Soviet team at the Crimean Astrophysical Observatory using a Q-switched ruby laser. Greater accuracy was achieved following the installation of a retroreflector array on 21 July 1969, by the crew of Apollo 11, two more retroreflector arrays left by the Apollo 14 and Apollo 15 missions have contributed to the experiment.
Successful lunar laser range measurements to the retroreflectors were first reported by the 3.1 m telescope at Lick Observatory, Air Force Cambridge Research Laboratories Lunar Ranging Observatory in Arizona, the Pic du Midi Observatory in France, the Tokyo Astronomical Observatory, McDonald Observatory in Texas. The unmanned Soviet Lunokhod 1 and Lunokhod 2 rovers carried smaller arrays. Reflected signals were received from Lunokhod 1, but no return signals were detected after 1971 until a team from University of California rediscovered the array in April 2010 using images from NASA's Lunar Reconnaissance Orbiter. Lunokhod 2's array continues to return signals to Earth; the Lunokhod arrays suffer from decreased performance in direct sunlight—a factor considered in reflector placement during the Apollo missions. The Apollo 15 array is three times the size of the arrays left by the two earlier Apollo missions, its size made it the target of three-quarters of the sample measurements taken in the first 25 years of the experiment.
Improvements in technology since have resulted in greater use of the smaller arrays, by sites such as the Côte d'Azur Observatory in Grasse, France. The distance to the Moon is calculated using the equation: distance = / 2 To compute the lunar distance many factors must be considered in addition to the round-trip time of about 2.5 seconds. These factors include the location of the Moon in the sky, the relative motion of Earth and the Moon, Earth's rotation, lunar libration, polar motion, velocity of light in various parts of air, propagation delay through Earth's atmosphere, the location of the observing station and its motion due to crustal motion and tides, relativistic effects; the distance continually changes for a number of reasons, but averages 385,000.6 km between the center of the Earth and the center of the Moon. At the Moon's surface, the beam is about 6.5 kilometers wide and scientists liken the task of aiming the beam to using a rifle to hit a moving dime 3 kilometers away. The reflected light is too weak to see with the human eye.
Out of 1017 photons aimed at the reflector, only one is received back on Earth under good conditions. They can be identified as originating from the laser because the laser is monochromatic; this is one of the most precise distance measurements made, is equivalent in accuracy to determining the distance between Los Angeles and New York to within 0.25 mm. The upcoming MoonLIGHT reflector, that will be placed in 2019 by the private MX-1E lander, is designed to increase measurement accuracy 100 times over existing systems. Lunar laser ranging measurement data is available from the Paris Observatory Lunar Analysis Center, the active stations; some of the findings of this long-term experiment are: The Moon is spiraling away from Earth at a rate of 3.8 cm/year. This rate has been described as anomalously high; the Moon has a liquid core of about 20% of the Moon's radius. The universal force of gravity is stable; the experiments have constrained the change in Newton's gravitational constant G to a factor of ×10−13 per year.
The likelihood of any Nordtvedt effect has been ruled out to high precision supporting the validity of the strong equivalence principle. Einstein's theory of gravity predicts the Moon's orbit to within the accuracy of the laser ranging measurements. Gauge freedom plays a major role in a correct physical interpretation of the relativistic effects in the Earth-Moon system observed with LLR technique; the distance to the Moon can be measured with millimeter precision. Apache Point Observatory Lunar Laser-ranging Operation Apollo Lunar Surface Experiments Package Tom Murphy Carroll Alley Earth–Moon–Earth communication Lidar Lunar distance Lunokhod programme Satellite laser ranging Space geodesy Third-party evidence for Apollo Moon landings List of retroreflectors on the Moon "Theory and Model for the New Generation of the Lunar Laser Ranging Data" by Sergei Kopeikin Apollo 15 Experiments - Laser Ranging Retroreflector by the Lunar and Planetary Institute "History of Laser Ranging and MLRS" by the University of Texas at Austin, Center for Space Research "Lunar Retroreflectors" by Tom Murphy Station de Télémétrie Laser-Lune in Grasse, France Lu
Boeing B-52 Stratofortress
The Boeing B-52 Stratofortress is an American long-range, jet-powered strategic bomber. The B-52 was built by Boeing, which has continued to provide support and upgrades, it has been operated by the United States Air Force since the 1950s. The bomber is capable of carrying up to 70,000 pounds of weapons, has a typical combat range of more than 8,800 miles without aerial refueling. Beginning with the successful contract bid in June 1946, the B-52 design evolved from a straight wing aircraft powered by six turboprop engines to the final prototype YB-52 with eight turbojet engines and swept wings; the B-52 took its maiden flight in April 1952. Built to carry nuclear weapons for Cold War-era deterrence missions, the B-52 Stratofortress replaced the Convair B-36. A veteran of several wars, the B-52 has dropped only conventional munitions in combat; the B-52's official name Stratofortress is used. The B-52 has been in active service with the USAF since 1955; as of December 2015, 58 were in active service with 18 in reserve.
The bombers flew under the Strategic Air Command until it was disestablished in 1992 and its aircraft absorbed into the Air Combat Command. Superior performance at high subsonic speeds and low operating costs have kept the B-52 in service despite the advent of more advanced aircraft, including the canceled Mach 3 B-70 Valkyrie, the variable-geometry B-1 Lancer, the stealth B-2 Spirit; the B-52 completed sixty years of continuous service with its original operator in 2015. After being upgraded between 2013 and 2015, it is expected to serve into the 2050s. On 23 November 1945, Air Materiel Command issued desired performance characteristics for a new strategic bomber "capable of carrying out the strategic mission without dependence upon advanced and intermediate bases controlled by other countries"; the aircraft was to have a crew of five or more turret gunners, a six-man relief crew. It was required to cruise at 300 mph at 34,000 feet with a combat radius of 5,000 miles; the armament was to consist of 10,000 pounds of bombs.
On 13 February 1946, the Air Force issued bid invitations for these specifications, with Boeing, Consolidated Aircraft, Glenn L. Martin Company submitting proposals. On 5 June 1946, Boeing's Model 462, a straight-wing aircraft powered by six Wright T35 turboprops with a gross weight of 360,000 pounds and a combat radius of 3,110 miles, was declared the winner. On 28 June 1946, Boeing was issued a letter of contract for US$1.7 million to build a full-scale mock-up of the new XB-52 and do preliminary engineering and testing. However, by October 1946, the air force began to express concern about the sheer size of the new aircraft and its inability to meet the specified design requirements. In response, Boeing produced Model 464, a smaller four-engine version with a 230,000 pound gross weight, deemed acceptable. Subsequently, in November 1946, the Deputy Chief of Air Staff for Research and Development, General Curtis LeMay, expressed the desire for a cruising speed of 400 miles per hour, to which Boeing responded with a 300,000 lb aircraft.
In December 1946, Boeing was asked to change their design to a four-engine bomber with a top speed of 400 miles per hour, range of 12,000 miles, the ability to carry a nuclear weapon. Boeing responded with two models powered by T35 turboprops; the Model 464-16 was a "nuclear only" bomber with a 10,000 pound payload, while the Model 464-17 was a general purpose bomber with a 9,000 pound payload. Due to the cost associated with purchasing two specialized aircraft, the air force selected Model 464-17 with the understanding that it could be adapted for nuclear strikes. In June 1947, the military requirements were updated and the Model 464-17 met all of them except for the range, it was becoming obvious to the Air Force that with the updated performance, the XB-52 would be obsolete by the time it entered production and would offer little improvement over the Convair B-36. During this time, Boeing continued to perfect the design, which resulted in the Model 464-29 with a top speed of 455 miles per hour and a 5,000-mile range.
In September 1947, the Heavy Bombardment Committee was convened to ascertain performance requirements for a nuclear bomber. Formalized on 8 December 1947, these requirements called for a top speed of 500 miles per hour and an 8,000 mile range, far beyond the capabilities of 464–29; the outright cancellation of the Boeing contract on 11 December 1947 was staved off by a plea from its president William McPherson Allen to the Secretary of the Air Force Stuart Symington. Allen reasoned that the design was capable of being adapted to new aviation technology and more stringent requirements. In January 1948 Boeing was instructed to explore recent technological innovations, including aerial refueling and the flying wing. Noting stability and control problems Northrop was experiencing with their YB-35 and YB-49 flying wing bombers, Boeing insisted on a conventional aircraft, in April 1948 presented a US$30 million proposal for design and testing of two Model 464-35 prototypes. Furth
Clothing is a collective term for items worn on the body. Clothing can be made of animal skin, or other thin sheets of materials put together; the wearing of clothing is restricted to human beings and is a feature of all human societies. The amount and type of clothing worn depend on body type and geographic considerations; some clothing can be gender-specific. Physically, clothing serves many purposes: it can serve as protection from the elements and can enhance safety during hazardous activities such as hiking and cooking, it protects the wearer from rough surfaces, rash-causing plants, insect bites, splinters and prickles by providing a barrier between the skin and the environment. Clothes can insulate against cold or hot conditions, they can provide a hygienic barrier, keeping infectious and toxic materials away from the body. Clothing provides protection from ultraviolet radiation. Wearing clothes is a social norm, being deprived of clothing in front of others may be embarrassing, or not wearing clothes in public such that genitals, breasts or buttocks are visible could be seen as indecent exposure.
There is no easy way to determine when clothing was first developed, but some information has been inferred by studying lice which estimates the introduction of clothing at 42,000–72,000 years ago. The most obvious function of clothing is to improve the comfort of the wearer, by protecting the wearer from the elements. In hot climates, clothing provides protection from sunburn or wind damage, while in cold climates its thermal insulation properties are more important. Shelter reduces the functional need for clothing. For example, hats and other outer layers are removed when entering a warm home if one is living or sleeping there. Clothing has seasonal and regional aspects, so that thinner materials and fewer layers of clothing are worn in warmer regions and seasons than in colder ones. Clothing performs a range of social and cultural functions, such as individual and gender differentiation, social status. In many societies, norms about clothing reflect standards of modesty, religion and social status.
Clothing may function as a form of adornment and an expression of personal taste or style. Clothing can be and has in the past been made from a wide variety of materials. Materials have ranged from leather and furs to woven materials, to elaborate and exotic natural and synthetic fabrics. Not all body coverings are regarded as clothing. Articles carried rather than worn, worn on a single part of the body and removed, worn purely for adornment, or those that serve a function other than protection, are considered accessories rather than clothing, except for shoes. Clothing protects against many things. Clothes protect people from the elements, including rain, snow and other weather, as well as from the sun. However, clothing, too sheer, small, etc. offers less protection. Appropriate clothes can reduce risk during activities such as work or sport; some clothing protects from specific hazards, such as insects, noxious chemicals, weather and contact with abrasive substances. Conversely, clothing may protect the environment from the clothing wearer: for instance doctors wear medical scrubs.
Humans have been ingenious in devising clothing solutions to environmental or other hazards: such as space suits, air conditioned clothing, diving suits, bee-keeper gear, motorcycle leathers, high-visibility clothing, other pieces of protective clothing. Meanwhile, the distinction between clothing and protective equipment is not always clear-cut, since clothes designed to be fashionable have protective value and clothes designed for function consider fashion in their design; the choice of clothes has social implications. They cover parts of the body that social norms require to be covered, act as a form of adornment, serve other social purposes. Someone who lacks the means to procure reasonable clothing due to poverty or affordability, or lack of inclination, is sometimes said to be scruffy, ragged, or shabby. Serious books on clothing and its functions appear from the 19th century as imperialists dealt with new environments such as India and the tropics; some scientific research into the multiple functions of clothing in the first half of the 20th century, with publications such as J.
C. Flügel's Psychology of Clothes in 1930, Newburgh's seminal Physiology of Heat Regulation and The Science of Clothing in 1949. By 1968, the field of environmental physiology had advanced and expanded but the science of clothing in relation to environmental physiology had changed little. There has since been considerable research, the knowledge base has grown but the main concepts remain unchanged, indeed Newburgh's book is still cited by contemporary authors, including those attempting to develop thermoregulatory models of clothing development. In most cultures, gender differentiation of clothing is considered appropriate; the differences are in styles and fabrics. In Western societies, skirts and high-heeled shoes are seen as women's clothing, while neckties are seen as men's clothing. Trousers were once seen as male clothing, but can nowadays be worn by both genders. Male clothes are more practical, but a wider range of clothing styles are available for females. Males are allowed to bare their chests in a greater variety of public places.
LAGEOS, Laser Geodynamics Satellite or Laser Geometric Environmental Observation Survey, are a series of two scientific research satellites designed to provide an orbiting laser ranging benchmark for geodynamical studies of the Earth. Each satellite is a high-density passive laser reflector in a stable medium Earth orbit; the spacecraft are aluminum-covered brass spheres with diameters of 60 centimetres and masses of 400 and 411 kilograms, covered with 426 cube-corner retroreflectors, giving them the appearance of giant golf balls. Of these retroreflectors, 422 are made from fused silica glass while the remaining 4 are made from germanium to obtain measurements in the infrared for experimental studies of reflectivity and satellite orientation, they have no on-board sensors or electronics, are not altitude-controlled. They orbit at an altitude of 5,900 kilometres, well above low earth orbit and well below geostationary orbit, at orbital inclinations of 109.8 and 52.6 degrees. Measurements are made by transmitting pulsed laser beams from Earth ground stations to the satellites.
The laser beams return to Earth after hitting the reflecting surfaces. The LAGEOS satellites make it possible to determine positions of points on the Earth with high accuracy due to the stability of their orbits; the high mass-to-area ratio and the precise, stable geometry of the LAGEOS spacecraft, together with their regular orbits, make these satellites the most precise position references available. The LAGEOS mission consists of the following key goals: Provide an accurate measurement of the satellite's position with respect to Earth. Determine the planet's shape. Determine tectonic plate movements associated with continental drift. Ground tracking stations located in many countries have ranged to the satellites and data from these stations are available worldwide to investigators studying crustal dynamics. There are two LAGEOS spacecraft, LAGEOS-1 launched in 1976, LAGEOS-2 launched in 1992; as of May 2011, both LAGEOS spacecraft are tracked by the ILRS network. LAGEOS-1 contains a plaque designed by Carl Sagan to indicate to future humanity when LAGEOS-1 was launched.
The plaque includes the numbers 1 to 10 in binary. In the upper right is a diagram of the Earth orbiting the Sun, with a binary number 1 indicating one revolution, equaling one year, it shows 268435456 years in the past, indicated by a left arrow and the arrangement of the Earth's continents at that time. The present arrangement of the Earth's continents is indicated with a 0 and both forward and backward arrows; the estimated arrangement of the continents in 8.4 million years with a right facing arrow and 8388608 in binary. LAGEOS itself is shown at launch on the 0 year, falling to the Earth in the 8.4 million year diagram. LAGEOS 1, launched 4 May 1976, NSSDC ID 1976-039A, NORAD number 8820 LAGEOS 2, deployed 23 October 1992 from STS-52, NSSDC ID 1992-070B, NORAD number 22195 GEOS-3 PAGEOS Geodesy Post-glacial rebound List of laser articles List of laser ranging satellites LARES a similar object made of tungsten Sagan, Carl. Murmurs of Earth: The Voyager Interstellar Record. Random House. Pp. 8–9.
The Conversation Space bling: ‘jewelled’ LAGEOS satellites help us to measure the Earth, Official website LAGEOS-1, -2 LAGEOS-1 page at US National Space Science Data Center LAGEOS-2 page at US National Space Science Data Center LAGEOS-1, -2 LAGEOS video at AParchive.com
A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light, such as flat-white paint; the most familiar type of mirror is the plane mirror. Curved mirrors are used, to produce magnified or diminished images or focus light or distort the reflected image. Mirrors are used for personal grooming or admiring oneself, for viewing the area behind and on the sides on motor vehicles while driving, for decoration, architecture. Mirrors are used in scientific apparatus such as telescopes and lasers and industrial machinery. Most mirrors are designed for visible light. There are many types of glass mirrors, each representing a different manufacturing process and reflection type.
An aluminium glass mirror is made of a float glass manufactured using vacuum coating, i.e. aluminium powder is evaporated onto the exposed surface of the glass in a vacuum chamber and coated with two or more layers of waterproof protective paint. A low aluminium glass mirror is manufactured by coating silver and two layers of protective paint on the back surface of glass. A low aluminium glass mirror is clear, light transmissive and reflects accurate natural colors; this type of glass is used for framing presentations and exhibitions in which a precise color representation of the artwork is essential or when the background color of the frame is predominantly white. A safety glass mirror is made by adhering a special protective film to the back surface of a silver glass mirror, which prevents injuries in case the mirror is broken; this kind of mirror is used for furniture, glass walls, commercial shelves, or public areas. A silkscreen printed glass mirror is produced using inorganic color ink that prints patterns through a special screen onto glass.
Various colors and glass shapes are available. Such a glass mirror is durable and more moisture resistant than ordinary printed glass and can serve for over 20 years; this type of glass is used for decorative purposes. A silver glass mirror is an ordinary mirror, coated on its back surface with silver, which produces images by reflection; this kind of glass mirror is produced by coating a silver, copper film and two or more layers of waterproof paint on the back surface of float glass, which resists acid and moisture. A silver glass mirror provides clear and actual images, is quite durable, is used for furniture and other decorative purposes. Decorative glass mirrors are handcrafted. A variety of shades and glass thickness are available. A beam of light reflects off a mirror at an angle of reflection equal to its angle of incidence; that is, if the beam of light is shining on a mirror's surface, at a θ ° angle vertically it reflects from the point of incidence at a θ ° angle, vertically in the opposite direction.
This law mathematically follows from the interference of a plane wave on a flat boundary. In a plane mirror, a parallel beam of light changes its direction as a whole, while still remaining parallel. In a concave mirror, parallel beams of light become a convergent beam, whose rays intersect in the focus of the mirror. Known as converging mirror In a convex mirror, parallel beams become divergent, with the rays appearing to diverge from a common point of intersection "behind" the mirror. Spherical concave and convex mirrors do not focus parallel rays to a single point due to spherical aberration. However, the ideal of focusing to a point is a used approximation. Parabolic reflectors resolve this. Parabolic reflectors are not suitable for imaging nearby objects because the light rays are not parallel. Objects viewed in a mirror will appear not vertically inverted. However, a mirror does not "swap" left and right any more than it swaps top and bottom. A mirror reverses the forward/backward axis. To be precise, it reverses the object in the direction perpendicular to the mirror surface.
Because left and right are defined relative to front-back and top-bottom, the "flipping" of front and back results in the perception of a left-right reversal in the image. Looking at an image of oneself with the front-back axis flipped results in the perception of an image with its left-right axis flipped; when reflected in the mirror, your right hand remains directly opposite your real right hand, but it is perceived as the left hand of your image. When a person looks into a mirror, the image is front-back reversed, an effect similar to the holl