Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics describes the behaviour of visible and infrared light; because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays and radio waves exhibit similar properties. Most optical phenomena can be accounted for using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however difficult to apply in practice. Practical optics is done using simplified models; the most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be accounted for in geometric optics; the ray-based model of light was developed first, followed by the wave model of light.
Progress in electromagnetic theory in the 19th century led to the discovery that light waves were in fact electromagnetic radiation. Some phenomena depend on the fact that light has both particle-like properties. Explanation of these effects requires quantum mechanics; when considering light's particle-like properties, the light is modelled as a collection of particles called "photons". Quantum optics deals with the application of quantum mechanics to optical systems. Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields and medicine. Practical applications of optics are found in a variety of technologies and everyday objects, including mirrors, telescopes, microscopes and fibre optics. Optics began with the development of lenses by Mesopotamians; the earliest known lenses, made from polished crystal quartz, date from as early as 700 BC for Assyrian lenses such as the Layard/Nimrud lens. The ancient Romans and Greeks filled glass spheres with water to make lenses.
These practical developments were followed by the development of theories of light and vision by ancient Greek and Indian philosophers, the development of geometrical optics in the Greco-Roman world. The word optics comes from the ancient Greek word ὀπτική, meaning "appearance, look". Greek philosophy on optics broke down into two opposing theories on how vision worked, the "intromission theory" and the "emission theory"; the intro-mission approach saw vision as coming from objects casting off copies of themselves that were captured by the eye. With many propagators including Democritus, Epicurus and their followers, this theory seems to have some contact with modern theories of what vision is, but it remained only speculation lacking any experimental foundation. Plato first articulated the emission theory, the idea that visual perception is accomplished by rays emitted by the eyes, he commented on the parity reversal of mirrors in Timaeus. Some hundred years Euclid wrote a treatise entitled Optics where he linked vision to geometry, creating geometrical optics.
He based his work on Plato's emission theory wherein he described the mathematical rules of perspective and described the effects of refraction qualitatively, although he questioned that a beam of light from the eye could instantaneously light up the stars every time someone blinked. Ptolemy, in his treatise Optics, held an extramission-intromission theory of vision: the rays from the eye formed a cone, the vertex being within the eye, the base defining the visual field; the rays were sensitive, conveyed information back to the observer's intellect about the distance and orientation of surfaces. He summarised much of Euclid and went on to describe a way to measure the angle of refraction, though he failed to notice the empirical relationship between it and the angle of incidence. During the Middle Ages, Greek ideas about optics were resurrected and extended by writers in the Muslim world. One of the earliest of these was Al-Kindi who wrote on the merits of Aristotelian and Euclidean ideas of optics, favouring the emission theory since it could better quantify optical phenomena.
In 984, the Persian mathematician Ibn Sahl wrote the treatise "On burning mirrors and lenses" describing a law of refraction equivalent to Snell's law. He used this law to compute optimum shapes for curved mirrors. In the early 11th century, Alhazen wrote the Book of Optics in which he explored reflection and refraction and proposed a new system for explaining vision and light based on observation and experiment, he rejected the "emission theory" of Ptolemaic optics with its rays being emitted by the eye, instead put forward the idea that light reflected in all directions in straight lines from all points of the objects being viewed and entered the eye, although he was unable to explain how the eye captured the rays. Alhazen's work was ignored in the Arabic world but it was anonymously translated into Latin around 1200 A. D. and further summarised and expanded on by the Polish monk Witelo making it a standard text on optics in Europe for the next 400 years. In the 13th century in medieval Europe, English bishop Robert Grosseteste wrote on a wide range of scientific topics, discussed light from four different perspectives: an epistemology of light, a metaphysics or cosmogony of light, an etiology or physics of light, a theology of light, basing it on the works Aristotle and Platonism.
Grosseteste's most famous disciple, Roger Bacon, wrote w
The Shuttle Remote Manipulator System known as Canadarm, is a series of robotic arms that were used on the Space Shuttle orbiters to deploy and capture payloads. After the Space Shuttle Columbia disaster, the Canadarm was always paired with the Orbiter Boom Sensor System, used to inspect the exterior of the Shuttle for damage to the thermal protection system. In 1969, Canada was invited by the National Aeronautics and Space Administration to participate in the Space Shuttle program. At the time what that participation would entail had not yet been decided but a manipulator system was identified as an important component. Canadian company DSMA ATCON had developed a robot to load fuel into CANDU nuclear reactors. In 1975, NASA and the Canadian National Research Council signed a memorandum of understanding that Canada would develop and construct the Shuttle Remote Manipulator System. NRC awarded the manipulator contract to Spar Aerospace. Three systems were constructed within this design, development and evaluation contract: an engineering model to assist in the design and testing of the Canadarm, a qualification model, subjected to environmental testing to qualify the design for use in space, a flight unit.
Anthony "Tony" Zubrzycki, a design engineer at DSMA ATCON, while seconded to SPAR, originated the concept for the Canadarm End Effector, inspired by an elastic band around his fingers. Tony formally presented this concept to NASA officials. Frank Mee, head of the SPAR mechanical development laboratory, built the end effector prototype based on Tony's concept and is credited by SPAR as the inventor of the Canadarm End Effector; the three-wire crossover design won over the claw-like mechanisms and others, such as the camera iris model, that were being considered. The main controls algorithms were developed by subcontractor Dynacon Inc. of Toronto. CAE Electronics Ltd. in Montreal provided the display and control panel and the hand controllers located in the Shuttle aft flight deck. Other electronic interfaces and power conditioners located on the Canadarm were designed and built by SPAR at its Montreal factory; the graphite composite boom that provides the structural connection between the shoulder and the elbow joint and the similar boom that connects the elbow to the wrist were produced by General Dynamics in the United States.
Dilworth, Secord and Associates, Ltd. in Toronto was contracted to produce the engineering model end effector SPAR evolved the design and produced the qualification and flight units. The shuttle flight software that monitors and controls the Canadarm was developed in Houston, Texas, by the Federal Systems Division of IBM. Rockwell International's Space Transportation Systems Division designed, developed and built the systems used to attach the Canadarm to the payload bay of the orbiter. An acceptance ceremony for NASA was held at Spar's RMS Division in Toronto on the 11th of February 1981. Here Larkin Kerwin the head of the NRC, gave the SRMS the informal name, Canadarm; the first remote manipulator system was delivered to NASA in April 1981. Astronaut Judith Resnik onboard operating procedures for the system. In all, five arms—Nos. 201, 202, 301, 302, 303—were built and delivered to NASA. Arm 302 was lost in the Challenger accident. During STS-61.]] The original Canadarm was capable of deploying and retrieving payloads weighing up to 332.5 kg in space.
In the mid-1990s the arm control system was redesigned to increase the payload capability to 3,293 kg in order to support space station assembly operations. While able to maneuver payloads with the mass of a loaded bus in space, the arm motors cannot lift the arm's own weight when on the ground. NASA therefore developed a model of the arm for use at its training facility within the Johnson Space Center located in Houston, Texas; the Canadarm can retrieve and deploy satellites, provide a mobile extension ladder for extravehicular activity crew members for work stations or foot restraints, be used as an inspection aid to allow the flight crew members to view the orbiter's or payload's surfaces through a television camera on the Canadarm. The basic Canadarm configuration consists of a manipulator arm, a Canadarm display and control panel, including rotational and translational hand controllers at the orbiter aft flight deck flight crew station, a manipulator controller interface unit that interfaces with the orbiter computer.
Most of the time, the arm operators see what they are doing by looking at|The Canadarm 1 End Effector.]] One crew member operates the Canadarm from the aft flight deck control station, a second crew member assists with television camera operations. This allows the Canadarm operator to view Canadarm operations through the aft flight deck payload and overhead windows and through the closed-circuit television monitors at the aft flight deck station; the Canadarm is outfitted with an explosive-based mechanism to allow the arm to be jettisoned. This safety system would have allowed the Orbiter's payload bay doors to be closed in the event that the arm failed in an extended position and was not able to be retracted; the Canadarm is 38 cm diameter with six degrees of freedom. It weighs 410 kg by itself, 450 kg as part of the total system; the Canadarm has six joints that correspond to the joints of the human arm, with shoulder yaw and pitch joints, an elbow pitch joint, wrist pitch and roll joints. The end effector is the unit at the end of the wrist.
The two lightweight boom segments are called the upper an
Langley Research Center
Langley Research Center located in Hampton, United States, is the oldest of NASA's field centers. It directly borders the Back River on the Chesapeake Bay. LaRC has focused on aeronautical research, but has tested space hardware at the facility, such as the Apollo Lunar Module. In addition, a number of the earliest high-profile space missions were designed on-site. Established in 1917 by the National Advisory Committee for Aeronautics, the research center devotes two-thirds of its programs to aeronautics, the rest to space. LaRC researchers use more than 40 wind tunnels to study and improve aircraft and spacecraft safety and efficiency. Between 1958 and 1963, when NASA started Project Mercury, LaRC served as the main office of the Space Task Group. In June 2015, after serving as associate director deputy director, Dr. David E. Bowles was appointed director of NASA Langley. After US-German relations had deteriorated from neutral to hostile around 1916, the prospect of U. S. war entry became possible.
On February 15, 1917, the newly established Aviation Week warned that the U. S. military aviation capability was less than. President Woodrow Wilson sent Jerome Hunsaker to Europe to investigate, Hunsaker's report prompted Wilson to command the creation of the nation's first aeronautics laboratory, which became NASA Langley. In 1917, less than three years after it was created, the NACA established Langley Memorial Aeronautical Laboratory on Langley Field. Both Langley Field and the Langley Laboratory are named for aviation pioneer Samuel Pierpont Langley; the Aviation Section, U. S. Signal Corps had established a base there earlier that same year; the first research facilities were in place and aeronautical research was started by 1920. The laboratory included four researchers and 11 technicians. Langley Field and NACA began parallel growth as air power proved its utility during World War I; the center was established to explore the field of aerodynamic research involving airframe and propulsion engine design and performance.
In 1934 the world's largest wind tunnel was constructed at Langley Field with a 30 × 60 foot test section. It remained the world's largest wind tunnel until the 1940s, when a 40 × 80 foot tunnel was built at NASA Ames Research Center in California. Early in 1945, the center expanded to include rocket research, leading to the establishment of a flight station at Wallops Island, Virginia. A further expansion of the research program permitted Langley Research Center to orbit payloads, starting with NASA's Explorer 9 balloon satellite in mid-February 1961; as rocket research grew, aeronautics research continued to expand and played an important part when subsonic flight was advanced and supersonic and hypersonic flight were introduced. Langley Research Center can claim many historic firsts, some of which have proven to be revolutionary scientific breakthroughs; these accomplishments include the development of the concept of research aircraft leading to supersonic flight, the world's first transonic wind tunnels, the Lunar Landing Facility providing the simulation of lunar gravity, the Viking program for Mars exploration.
The center developed standards for the grooving of aircraft runways based on a previous British design used at Washington National Airport. Grooved runways reduce aquaplaning; this grooving is now the international standard for all runways around the world. Langley Research Center performs critical research on aeronautics, including wake vortex behavior, fixed-wing aircraft, rotary wing aircraft, aviation safety, human factors and aerospace engineering. LaRC supported the design and testing of the hypersonic X-43, which achieved a world speed record of Mach 9.6. LaRC assisted the NTSB in the investigation of the crash of American Airlines Flight 587. Work began in July 2011 to remove the 1940s era 16 feet transonic wind tunnel; the facility supported development and propulsion integration research for many military aircraft including all fighters since 1960 but had been inactive since 2004. Langley retained transonic wind tunnel testing capabilities facilities in the National Transonic Facility, a high pressure, cryogenically cooled 8.2 feet closed loop wind tunnel.
The EBF³ process produces structural metallic parts with immense strength, useful in performing repairs in remote locations. Additionally, the ability to build functionally graded, unitized parts directly from CAD data offers enhanced performance in numerous applications. LaRC has become home to this new type of machining process, used by their new room-sized electron-emitting device, which uses a High Frequency 42 kW, X-ray emitting electron gun, which melts either aluminum or titanium wire into the desired 3-dimensional metallic parts with a material strength comparable to that of wrought products; the machine's deposition rate is 150 in³/h, equivalent to its plastic-fabricating counterpart. Metallic parts are built directly from CAD without molds or tools, leaving the end product with no porosity. Other properties include: 6-axis positioning Heated or cooled platen 1×10−6 torr vacuum capability 72 × 24 × 24 inch build envelope Power efficiency in excess of 90% Near 100% feedstock efficiency Can deposit reflective materials not processable with lasers Potential portable EBF³ system (Unde
The Milky Way is the galaxy that contains our Solar System. The name describes the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye; the term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος. From Earth, the Milky Way appears as a band. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610; until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies; the Milky Way is a barred spiral galaxy with a diameter between 200,000 light-years. It is estimated to contain 100 -- more than 100 billion planets; the Solar System is located at a radius of 26,490 light-years from the Galactic Center, on the inner edge of the Orion Arm, one of the spiral-shaped concentrations of gas and dust.
The stars in the innermost 10,000 light-years form a bulge and one or more bars that radiate from the bulge. The galactic center is an intense radio source known as Sagittarius A*, assumed to be a supermassive black hole of 4.100 million solar masses. Stars and gases at a wide range of distances from the Galactic Center orbit at 220 kilometers per second; the constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way is invisible to telescopes, neither emitting nor absorbing electromagnetic radiation. This conjectural mass has been termed "dark matter"; the rotational period is about 240 million years at the radius of the Sun. The Milky Way as a whole is moving at a velocity of 600 km per second with respect to extragalactic frames of reference; the oldest stars in the Milky Way are nearly as old as the Universe itself and thus formed shortly after the Dark Ages of the Big Bang. The Milky Way has several satellite galaxies and is part of the Local Group of galaxies, which form part of the Virgo Supercluster, itself a component of the Laniakea Supercluster.
The Milky Way is visible from Earth as a hazy band of white light, some 30° wide, arching across the night sky. In night sky observing, although all the individual naked-eye stars in the entire sky are part of the Milky Way, the term “Milky Way” is limited to this band of light; the light originates from the accumulation of unresolved stars and other material located in the direction of the galactic plane. Dark regions within the band, such as the Great Rift and the Coalsack, are areas where interstellar dust blocks light from distant stars; the area of sky that the Milky Way obscures is called the Zone of Avoidance. The Milky Way has a low surface brightness, its visibility can be reduced by background light, such as light pollution or moonlight. The sky needs to be darker than about 20.2 magnitude per square arcsecond in order for the Milky Way to be visible. It should be visible if the limiting magnitude is +5.1 or better and shows a great deal of detail at +6.1. This makes the Milky Way difficult to see from brightly lit urban or suburban areas, but prominent when viewed from rural areas when the Moon is below the horizon.
Maps of artificial night sky brightness show that more than one-third of Earth's population cannot see the Milky Way from their homes due to light pollution. As viewed from Earth, the visible region of the Milky Way's galactic plane occupies an area of the sky that includes 30 constellations; the Galactic Center lies in the direction of Sagittarius. From Sagittarius, the hazy band of white light appears to pass around to the galactic anticenter in Auriga; the band continues the rest of the way around the sky, back to Sagittarius, dividing the sky into two equal hemispheres. The galactic plane is inclined by about 60° to the ecliptic. Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic, relative to the galactic plane; the north galactic pole is situated at right ascension 12h 49m, declination +27.4° near β Comae Berenices, the south galactic pole is near α Sculptoris.
Because of this high inclination, depending on the time of night and year, the arch of the Milky Way may appear low or high in the sky. For observers from latitudes 65° north to 65° south, the Milky Way passes directly overhead twice a day; the Milky Way is the second-largest galaxy in the Local Group, with its stellar disk 100,000 ly in diameter and, on average 1,000 ly thick. The Milky Way is 1.5 trillion times the mass of the Sun. To compare the relative physical scale of the Milky Way, if the Solar System out to Neptune were the size of a US quarter, the Milky Way would be the size of the contiguous United States. There is a ring-like filament of stars rippling above and below the flat galactic plane, wrapping around the Milky Way at a diameter of 150,000–180,000 light-years, which may be part of the Milky Way itself. Estimates of the mass of the Milky Way vary, depending upon the method and data used; the low end of the estimate range is 5.8×1011 solar masses, somewhat less than that of the Andromeda Galaxy.
Measurements using the Very Long Baseline Array in 2009 found
Canada is a country in the northern part of North America. Its ten provinces and three territories extend from the Atlantic to the Pacific and northward into the Arctic Ocean, covering 9.98 million square kilometres, making it the world's second-largest country by total area. Canada's southern border with the United States is the world's longest bi-national land border, its capital is Ottawa, its three largest metropolitan areas are Toronto and Vancouver. As a whole, Canada is sparsely populated, the majority of its land area being dominated by forest and tundra, its population is urbanized, with over 80 percent of its inhabitants concentrated in large and medium-sized cities, many near the southern border. Canada's climate varies across its vast area, ranging from arctic weather in the north, to hot summers in the southern regions, with four distinct seasons. Various indigenous peoples have inhabited what is now Canada for thousands of years prior to European colonization. Beginning in the 16th century and French expeditions explored, settled, along the Atlantic coast.
As a consequence of various armed conflicts, France ceded nearly all of its colonies in North America in 1763. In 1867, with the union of three British North American colonies through Confederation, Canada was formed as a federal dominion of four provinces; this began an accretion of provinces and territories and a process of increasing autonomy from the United Kingdom. This widening autonomy was highlighted by the Statute of Westminster of 1931 and culminated in the Canada Act of 1982, which severed the vestiges of legal dependence on the British parliament. Canada is a parliamentary democracy and a constitutional monarchy in the Westminster tradition, with Elizabeth II as its queen and a prime minister who serves as the chair of the federal cabinet and head of government; the country is a realm within the Commonwealth of Nations, a member of the Francophonie and bilingual at the federal level. It ranks among the highest in international measurements of government transparency, civil liberties, quality of life, economic freedom, education.
It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many other countries. Canada's long and complex relationship with the United States has had a significant impact on its economy and culture. A developed country, Canada has the sixteenth-highest nominal per capita income globally as well as the twelfth-highest ranking in the Human Development Index, its advanced economy is the tenth-largest in the world, relying chiefly upon its abundant natural resources and well-developed international trade networks. Canada is part of several major international and intergovernmental institutions or groupings including the United Nations, the North Atlantic Treaty Organization, the G7, the Group of Ten, the G20, the North American Free Trade Agreement and the Asia-Pacific Economic Cooperation forum. While a variety of theories have been postulated for the etymological origins of Canada, the name is now accepted as coming from the St. Lawrence Iroquoian word kanata, meaning "village" or "settlement".
In 1535, indigenous inhabitants of the present-day Quebec City region used the word to direct French explorer Jacques Cartier to the village of Stadacona. Cartier used the word Canada to refer not only to that particular village but to the entire area subject to Donnacona. From the 16th to the early 18th century "Canada" referred to the part of New France that lay along the Saint Lawrence River. In 1791, the area became two British colonies called Upper Canada and Lower Canada collectively named the Canadas. Upon Confederation in 1867, Canada was adopted as the legal name for the new country at the London Conference, the word Dominion was conferred as the country's title. By the 1950s, the term Dominion of Canada was no longer used by the United Kingdom, which considered Canada a "Realm of the Commonwealth"; the government of Louis St. Laurent ended the practice of using'Dominion' in the Statutes of Canada in 1951. In 1982, the passage of the Canada Act, bringing the Constitution of Canada under Canadian control, referred only to Canada, that year the name of the national holiday was changed from Dominion Day to Canada Day.
The term Dominion was used to distinguish the federal government from the provinces, though after the Second World War the term federal had replaced dominion. Indigenous peoples in present-day Canada include the First Nations, Métis, the last being a mixed-blood people who originated in the mid-17th century when First Nations and Inuit people married European settlers; the term "Aboriginal" as a collective noun is a specific term of art used in some legal documents, including the Constitution Act 1982. The first inhabitants of North America are hypothesized to have migrated from Siberia by way of the Bering land bridge and arrived at least 14,000 years ago; the Paleo-Indian archeological sites at Old Crow Flats and Bluefish Caves are two of the oldest sites of human habitation in Canada. The characteristics of Canadian indigenous societies included permanent settlements, complex societal hierarchies, trading networks; some of these cultures had collapsed by the time European explorers arrived in the late 15th and early 16th centuries and have only been discovered through archeological investigations.
The indigenous population at the time of the first European settlements is estimated to have been between 200,000
Switzerland the Swiss Confederation, is a country situated in western and southern Europe. It consists of 26 cantons, the city of Bern is the seat of the federal authorities; the sovereign state is a federal republic bordered by Italy to the south, France to the west, Germany to the north, Austria and Liechtenstein to the east. Switzerland is a landlocked country geographically divided between the Alps, the Swiss Plateau and the Jura, spanning a total area of 41,285 km2. While the Alps occupy the greater part of the territory, the Swiss population of 8.5 million people is concentrated on the plateau, where the largest cities are to be found: among them are the two global cities and economic centres Zürich and Geneva. The establishment of the Old Swiss Confederacy dates to the late medieval period, resulting from a series of military successes against Austria and Burgundy. Swiss independence from the Holy Roman Empire was formally recognized in the Peace of Westphalia in 1648; the country has a history of armed neutrality going back to the Reformation.
It pursues an active foreign policy and is involved in peace-building processes around the world. In addition to being the birthplace of the Red Cross, Switzerland is home to numerous international organisations, including the second largest UN office. On the European level, it is a founding member of the European Free Trade Association, but notably not part of the European Union, the European Economic Area or the Eurozone. However, it participates in the Schengen Area and the European Single Market through bilateral treaties. Spanning the intersection of Germanic and Romance Europe, Switzerland comprises four main linguistic and cultural regions: German, French and Romansh. Although the majority of the population are German-speaking, Swiss national identity is rooted in a common historical background, shared values such as federalism and direct democracy, Alpine symbolism. Due to its linguistic diversity, Switzerland is known by a variety of native names: Schweiz. On coins and stamps, the Latin name – shortened to "Helvetia" – is used instead of the four national languages.
Switzerland is one of the most developed countries in the world, with the highest nominal wealth per adult and the eighth-highest per capita gross domestic product according to the IMF. Switzerland ranks at or near the top globally in several metrics of national performance, including government transparency, civil liberties, quality of life, economic competitiveness and human development. Zürich and Basel have all three been ranked among the top ten cities in the world in terms of quality of life, with the first ranked second globally, according to Mercer in 2018; the English name Switzerland is a compound containing Switzer, an obsolete term for the Swiss, in use during the 16th to 19th centuries. The English adjective Swiss is a loan from French Suisse in use since the 16th century; the name Switzer is from the Alemannic Schwiizer, in origin an inhabitant of Schwyz and its associated territory, one of the Waldstätten cantons which formed the nucleus of the Old Swiss Confederacy. The Swiss began to adopt the name for themselves after the Swabian War of 1499, used alongside the term for "Confederates", used since the 14th century.
The data code for Switzerland, CH, is derived from Latin Confoederatio Helvetica. The toponym Schwyz itself was first attested in 972, as Old High German Suittes perhaps related to swedan ‘to burn’, referring to the area of forest, burned and cleared to build; the name was extended to the area dominated by the canton, after the Swabian War of 1499 came to be used for the entire Confederation. The Swiss German name of the country, Schwiiz, is homophonous to that of the canton and the settlement, but distinguished by the use of the definite article; the Latin name Confoederatio Helvetica was neologized and introduced after the formation of the federal state in 1848, harking back to the Napoleonic Helvetic Republic, appearing on coins from 1879, inscribed on the Federal Palace in 1902 and after 1948 used in the official seal.. Helvetica is derived from the Helvetii, a Gaulish tribe living on the Swiss plateau before the Roman era. Helvetia appears as a national personification of the Swiss confederacy in the 17th century with a 1672 play by Johann Caspar Weissenbach.
Switzerland has existed as a state in its present form since the adoption of the Swiss Federal Constitution in 1848. The precursors of Switzerland established a protective alliance at the end of the 13th century, forming a loose confederation of states which persisted for centuries; the oldest traces of hominid existence in Switzerland date back about 150,000 years. The oldest known farming settlements in Switzerland, which were found at Gächlingen, have been dated to around 5300 BC; the earliest known cultural tribes of the area were members of the Hallstatt and La Tène cultures, named after the archaeological site of La Tène on the north side of Lake Neuchâtel. La Tène culture developed and flourished during the late Iron Age from around 450 BC under some influence from the Gree