document_title: Speed of light

question_text: who discovered that light is faster than sound

question_tokens: who discovered that light is faster than sound

text: Speed of light

text: Numerical value, notation, and units

text: The speed of light in vacuum is usually denoted by a lowercase c, for "constant" or the Latin celeritas (meaning "swiftness, celerity"). In 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch had used c for a different constant later shown to equal √2 times the speed of light in vacuum. Historically, the symbol V was used as an alternative symbol for the speed of light, introduced by James Clerk Maxwell in 1865. In 1894, Paul Drude redefined c with its modern meaning. Einstein used V in his original German-language papers on special relativity in 1905, but in 1907 he switched to c, which by then had become the standard symbol for the speed of light.[7][8]

text: Sometimes c is used for the speed of waves in any material medium, and c0 for the speed of light in vacuum.[9] This subscripted notation, which is endorsed in official SI literature,[6] has the same form as other related constants: namely, μ0 for the vacuum permeability or magnetic constant, ε0 for the vacuum permittivity or electric constant, and Z0 for the impedance of free space. This article uses c exclusively for the speed of light in vacuum.

text: Since 1983, the metre has been defined in the International System of Units (SI) as the distance light travels in vacuum in  1⁄7008299792458000000♠299792458 of a second. This definition fixes the speed of light in vacuum at exactly 7008299792458000000♠299,792,458 m/s.[10][11][12] As a dimensional physical constant, the numerical value of c is different for different unit systems.[Note 3] In branches of physics in which c appears often, such as in relativity, it is common to use systems of natural units of measurement or the geometrized unit system where c = 1.[14][15] Using these units, c does not appear explicitly because multiplication or division by 1 does not affect the result.

text: Fundamental role in physics

text: The speed at which light waves propagate in vacuum is independent both of the motion of the wave source and of the inertial frame of reference of the observer.[Note 4] This invariance of the speed of light was postulated by Einstein in 1905,[5] after being motivated by Maxwell's theory of electromagnetism and the lack of evidence for the luminiferous aether;[16] it has since been consistently confirmed by many experiments. It is only possible to verify experimentally that the two-way speed of light (for example, from a source to a mirror and back again) is frame-independent, because it is impossible to measure the one-way speed of light (for example, from a source to a distant detector) without some convention as to how clocks at the source and at the detector should be synchronized. However, by adopting Einstein synchronization for the clocks, the one-way speed of light becomes equal to the two-way speed of light by definition.[17][18] The special theory of relativity explores the consequences of this invariance of c with the assumption that the laws of physics are the same in all inertial frames of reference.[19][20] One consequence is that c is the speed at which all massless particles and waves, including light, must travel in vacuum.

text: Special relativity has many counterintuitive and experimentally verified implications.[21] These include the equivalence of mass and energy (E = mc2), length contraction (moving objects shorten),[Note 5] and time dilation (moving clocks run more slowly). The factor γ by which lengths contract and times dilate is known as the Lorentz factor and is given by γ = (1 − v2/c2)−1/2, where v is the speed of the object. The difference of γ from 1 is negligible for speeds much slower than c, such as most everyday speeds—in which case special relativity is closely approximated by Galilean relativity—but it increases at relativistic speeds and diverges to infinity as v approaches c. For example, a time dilation factor of γ = 2 occurs at a relative velocity of 86.6% of the speed of light (v = .866c). Similarly, a time dilation factor of γ = 10 occurs at v = 99.5% c.

text: The results of special relativity can be summarized by treating space and time as a unified structure known as spacetime (with c relating the units of space and time), and requiring that physical theories satisfy a special symmetry called Lorentz invariance, whose mathematical formulation contains the parameter c.[24] Lorentz invariance is an almost universal assumption for modern physical theories, such as quantum electrodynamics, quantum chromodynamics, the Standard Model of particle physics, and general relativity. As such, the parameter c is ubiquitous in modern physics, appearing in many contexts that are unrelated to light. For example, general relativity predicts that c is also the speed of gravity and of gravitational waves.[25][26] In non-inertial frames of reference (gravitationally curved spacetime or accelerated reference frames), the local speed of light is constant and equal to c, but the speed of light along a trajectory of finite length can differ from c, depending on how distances and times are defined.[27]

text: It is generally assumed that fundamental constants such as c have the same value throughout spacetime, meaning that they do not depend on location and do not vary with time. However, it has been suggested in various theories that the speed of light may have changed over time.[28][29] No conclusive evidence for such changes has been found, but they remain the subject of ongoing research.[30][31]

text: It also is generally assumed that the speed of light is isotropic, meaning that it has the same value regardless of the direction in which it is measured. Observations of the emissions from nuclear energy levels as a function of the orientation of the emitting nuclei in a magnetic field (see Hughes–Drever experiment), and of rotating optical resonators (see Resonator experiments) have put stringent limits on the possible two-way anisotropy.[32][33]

text: Upper limit on speeds

text: According to special relativity, the energy of an object with rest mass m and speed v is given by γmc2, where γ is the Lorentz factor defined above. When v is zero, γ is equal to one, giving rise to the famous E = mc2 formula for mass–energy equivalence. The γ factor approaches infinity as v approaches c, and it would take an infinite amount of energy to accelerate an object with mass to the speed of light. The speed of light is the upper limit for the speeds of objects with positive rest mass, and individual photons cannot travel faster than the speed of light.[34][35] This is experimentally established in many tests of relativistic energy and momentum.[36]

text: More generally, it is normally impossible for information or energy to travel faster than c. One argument for this follows from the counter-intuitive implication of special relativity known as the relativity of simultaneity. If the spatial distance between two events A and B is greater than the time interval between them multiplied by c then there are frames of reference in which A precedes B, others in which B precedes A, and others in which they are simultaneous. As a result, if something were travelling faster than c relative to an inertial frame of reference, it would be travelling backwards in time relative to another frame, and causality would be violated.[Note 6][38] In such a frame of reference, an "effect" could be observed before its "cause". Such a violation of causality has never been recorded,[18] and would lead to paradoxes such as the tachyonic antitelephone.[39]

text: Faster-than-light observations and experiments

text: There are situations in which it may seem that matter, energy, or information travels at speeds greater than c, but they do not. For example, as is discussed in the propagation of light in a medium section below, many wave velocities can exceed c. For example, the phase velocity of X-rays through most glasses can routinely exceed c,[40] but phase velocity does not determine the velocity at which waves convey information.[41]

text: If a laser beam is swept quickly across a distant object, the spot of light can move faster than c, although the initial movement of the spot is delayed because of the time it takes light to get to the distant object at the speed c. However, the only physical entities that are moving are the laser and its emitted light, which travels at the speed c from the laser to the various positions of the spot. Similarly, a shadow projected onto a distant object can be made to move faster than c, after a delay in time.[42] In neither case does any matter, energy, or information travel faster than light.[43]

text: The rate of change in the distance between two objects in a frame of reference with respect to which both are moving (their closing speed) may have a value in excess of c. However, this does not represent the speed of any single object as measured in a single inertial frame.[43]

text: Certain quantum effects appear to be transmitted instantaneously and therefore faster than c, as in the EPR paradox. An example involves the quantum states of two particles that can be entangled. Until either of the particles is observed, they exist in a superposition of two quantum states. If the particles are separated and one particle's quantum state is observed, the other particle's quantum state is determined instantaneously (i.e., faster than light could travel from one particle to the other). However, it is impossible to control which quantum state the first particle will take on when it is observed, so information cannot be transmitted in this manner.[43][44]

text: Another quantum effect that predicts the occurrence of faster-than-light speeds is called the Hartman effect; under certain conditions the time needed for a virtual particle to tunnel through a barrier is constant, regardless of the thickness of the barrier.[45][46] This could result in a virtual particle crossing a large gap faster-than-light. However, no information can be sent using this effect.[47]

text: So-called superluminal motion is seen in certain astronomical objects,[48] such as the relativistic jets of radio galaxies and quasars. However, these jets are not moving at speeds in excess of the speed of light: the apparent superluminal motion is a projection effect caused by objects moving near the speed of light and approaching Earth at a small angle to the line of sight: since the light which was emitted when the jet was farther away took longer to reach the Earth, the time between two successive observations corresponds to a longer time between the instants at which the light rays were emitted.[49]

text: In models of the expanding universe, the farther galaxies are from each other, the faster they drift apart. This receding is not due to motion through space, but rather to the expansion of space itself.[43] For example, galaxies far away from Earth appear to be moving away from the Earth with a speed proportional to their distances. Beyond a boundary called the Hubble sphere, the rate at which their distance from Earth increases becomes greater than the speed of light.[50]

text: Propagation of light

text: In classical physics, light is described as a type of electromagnetic wave. The classical behaviour of the electromagnetic field is described by Maxwell's equations, which predict that the speed c with which electromagnetic waves (such as light) propagate through the vacuum is related to the electric constant ε0 and the magnetic constant μ0 by the equation[51]

text: In modern quantum physics, the electromagnetic field is described by the theory of quantum electrodynamics (QED). In this theory, light is described by the fundamental excitations (or quanta) of the electromagnetic field, called photons. In QED, photons are massless particles and thus, according to special relativity, they travel at the speed of light in vacuum.

text: Extensions of QED in which the photon has a mass have been considered. In such a theory, its speed would depend on its frequency, and the invariant speed c of special relativity would then be the upper limit of the speed of light in vacuum.[27] No variation of the speed of light with frequency has been observed in rigorous testing,[52][53][54] putting stringent limits on the mass of the photon. The limit obtained depends on the model used: if the massive photon is described by Proca theory,[55] the experimental upper bound for its mass is about 10−57 grams;[56] if photon mass is generated by a Higgs mechanism, the experimental upper limit is less sharp, m ≤ 10−14 eV/c2 [55] (roughly 2 × 10−47 g).

text: Another reason for the speed of light to vary with its frequency would be the failure of special relativity to apply to arbitrarily small scales, as predicted by some proposed theories of quantum gravity. In 2009, the observation of the spectrum of gamma-ray burst GRB 090510 did not find any difference in the speeds of photons of different energies, confirming that Lorentz invariance is verified at least down to the scale of the Planck length (lP = √ħG/c3 ≈ 6965161630000000000♠1.6163×10−35 m) divided by 1.2.[57]

text: In a medium

text: In a medium, light usually does not propagate at a speed equal to c; further, different types of light wave will travel at different speeds. The speed at which the individual crests and troughs of a plane wave (a wave filling the whole space, with only one frequency) propagate is called the phase velocity vp. An actual physical signal with a finite extent (a pulse of light) travels at a different speed. The largest part of the pulse travels at the group velocity vg, and its earliest part travels at the front velocity vf.

text: The phase velocity is important in determining how a light wave travels through a material or from one material to another. It is often represented in terms of a refractive index. The refractive index of a material is defined as the ratio of c to the phase velocity vp in the material: larger indices of refraction indicate lower speeds. The refractive index of a material may depend on the light's frequency, intensity, polarization, or direction of propagation; in many cases, though, it can be treated as a material-dependent constant. The refractive index of air is approximately 1.0003.[58] Denser media, such as water,[59] glass,[60] and diamond,[61] have refractive indexes of around 1.3, 1.5 and 2.4, respectively, for visible light. In exotic materials like Bose–Einstein condensates near absolute zero, the effective speed of light may be only a few metres per second. However, this represents absorption and re-radiation delay between atoms, as do all slower-than-c speeds in material substances. As an extreme example of light "slowing" in matter, two independent teams of physicists claimed to bring light to a "complete standstill" by passing it through a Bose–Einstein condensate of the element rubidium, one team at Harvard University and the Rowland Institute for Science in Cambridge, Mass., and the other at the Harvard–Smithsonian Center for Astrophysics, also in Cambridge. However, the popular description of light being "stopped" in these experiments refers only to light being stored in the excited states of atoms, then re-emitted at an arbitrarily later time, as stimulated by a second laser pulse. During the time it had "stopped," it had ceased to be light. This type of behaviour is generally microscopically true of all transparent media which "slow" the speed of light.[62]

text: In transparent materials, the refractive index generally is greater than 1, meaning that the phase velocity is less than c. In other materials, it is possible for the refractive index to become smaller than 1 for some frequencies; in some exotic materials it is even possible for the index of refraction to become negative.[63] The requirement that causality is not violated implies that the real and imaginary parts of the dielectric constant of any material, corresponding respectively to the index of refraction and to the attenuation coefficient, are linked by the Kramers–Kronig relations.[64] In practical terms, this means that in a material with refractive index less than 1, the absorption of the wave is so quick that no signal can be sent faster than c.

text: A pulse with different group and phase velocities (which occurs if the phase velocity is not the same for all the frequencies of the pulse) smears out over time, a process known as dispersion. Certain materials have an exceptionally low (or even zero) group velocity for light waves, a phenomenon called slow light, which has been confirmed in various experiments.[65][66][67][68] The opposite, group velocities exceeding c, has also been shown in experiment.[69] It should even be possible for the group velocity to become infinite or negative, with pulses travelling instantaneously or backwards in time.[70]

text: None of these options, however, allow information to be transmitted faster than c. It is impossible to transmit information with a light pulse any faster than the speed of the earliest part of the pulse (the front velocity). It can be shown that this is (under certain assumptions) always equal to c.[70]

text: It is possible for a particle to travel through a medium faster than the phase velocity of light in that medium (but still slower than c). When a charged particle does that in a dielectric material, the electromagnetic equivalent of a shock wave, known as Cherenkov radiation, is emitted.[71]

text: Practical effects of finiteness

text: The speed of light is of relevance to communications: the one-way and round-trip delay time are greater than zero. This applies from small to astronomical scales. On the other hand, some techniques depend on the finite speed of light, for example in distance measurements.

text: Small scales

text: In supercomputers, the speed of light imposes a limit on how quickly data can be sent between processors. If a processor operates at 1 gigahertz, a signal can only travel a maximum of about 30 centimetres (1 ft) in a single cycle. Processors must therefore be placed close to each other to minimize communication latencies; this can cause difficulty with cooling. If clock frequencies continue to increase, the speed of light will eventually become a limiting factor for the internal design of single chips.[72]

text: Large distances on Earth

text: For example, given the equatorial circumference of the Earth is about 7007400750000000000♠40075 km and c about 7008300000000000000♠300000 km/s, the theoretical shortest time for a piece of information to travel half the globe along the surface is about 67 milliseconds. When light is travelling around the globe in an optical fibre, the actual transit time is longer, in part because the speed of light is slower by about 35% in an optical fibre, depending on its refractive index n.[73] Furthermore, straight lines rarely occur in global communications situations, and delays are created when the signal passes through an electronic switch or signal regenerator.[74]

text: Spaceflights and astronomy

text: Similarly, communications between the Earth and spacecraft are not instantaneous. There is a brief delay from the source to the receiver, which becomes more noticeable as distances increase. This delay was significant for communications between ground control and Apollo 8 when it became the first manned spacecraft to orbit the Moon: for every question, the ground control station had to wait at least three seconds for the answer to arrive.[75] The communications delay between Earth and Mars can vary between five and twenty minutes depending upon the relative positions of the two planets. As a consequence of this, if a robot on the surface of Mars were to encounter a problem, its human controllers would not be aware of it until at least five minutes later, and possibly up to twenty minutes later; it would then take a further five to twenty minutes for instructions to travel from Earth to Mars.

text: NASA must wait several hours for information from a probe orbiting Jupiter, and if it needs to correct a navigation error, the fix will not arrive at the spacecraft for an equal amount of time, creating a risk of the correction not arriving in time.

text: Receiving light and other signals from distant astronomical sources can even take much longer. For example, it has taken 13 billion (13×109) years for light to travel to Earth from the faraway galaxies viewed in the Hubble Ultra Deep Field images.[76][77] Those photographs, taken today, capture images of the galaxies as they appeared 13 billion years ago, when the universe was less than a billion years old.[76] The fact that more distant objects appear to be younger, due to the finite speed of light, allows astronomers to infer the evolution of stars, of galaxies, and of the universe itself.

text: Astronomical distances are sometimes expressed in light-years, especially in popular science publications and media.[78] A light-year is the distance light travels in one year, around 9461 billion kilometres, 5879 billion miles, or 0.3066 parsecs. In round figures, a light year is nearly 10 trillion kilometres or nearly 6 trillion miles. Proxima Centauri, the closest star to Earth after the Sun, is around 4.2 light-years away.[79]

text: Distance measurement

text: Radar systems measure the distance to a target by the time it takes a radio-wave pulse to return to the radar antenna after being reflected by the target: the distance to the target is half the round-trip transit time multiplied by the speed of light. A Global Positioning System (GPS) receiver measures its distance to GPS satellites based on how long it takes for a radio signal to arrive from each satellite, and from these distances calculates the receiver's position. Because light travels about 7005300000000000000♠300000 kilometres (7008299337984000000♠186000 mi) in one second, these measurements of small fractions of a second must be very precise. The Lunar Laser Ranging Experiment, radar astronomy and the Deep Space Network determine distances to the Moon,[80] planets[81] and spacecraft,[82] respectively, by measuring round-trip transit times.

text: High-frequency trading

text: The speed of light has become important in high-frequency trading, where traders seek to gain minute advantages by delivering their trades to exchanges fractions of a second ahead of other traders. For example, traders have been switching to microwave communications between trading hubs, because of the advantage which microwaves travelling at near to the speed of light in air, have over fibre optic signals which travel 30–40% slower at the speed of light through glass.[83]

text: Measurement

text: There are different ways to determine the value of c. One way is to measure the actual speed at which light waves propagate, which can be done in various astronomical and earth-based setups. However, it is also possible to determine c from other physical laws where it appears, for example, by determining the values of the electromagnetic constants ε0 and μ0 and using their relation to c. Historically, the most accurate results have been obtained by separately determining the frequency and wavelength of a light beam, with their product equalling c.

text: In 1983 the metre was defined as "the length of the path travelled by light in vacuum during a time interval of  1⁄7008299792458000000♠299792458 of a second",[84] fixing the value of the speed of light at 7008299792458000000♠299792458 m/s by definition, as described below. Consequently, accurate measurements of the speed of light yield an accurate realization of the metre rather than an accurate value of c.

text: Astronomical measurements

text: Outer space is a convenient setting for measuring the speed of light because of its large scale and nearly perfect vacuum. Typically, one measures the time needed for light to traverse some reference distance in the solar system, such as the radius of the Earth's orbit. Historically, such measurements could be made fairly accurately, compared to how accurately the length of the reference distance is known in Earth-based units. It is customary to express the results in astronomical units (AU) per day.

text: Ole Christensen Rømer used an astronomical measurement to make the first quantitative estimate of the speed of light.[85][86] When measured from Earth, the periods of moons orbiting a distant planet are shorter when the Earth is approaching the planet than when the Earth is receding from it. The distance travelled by light from the planet (or its moon) to Earth is shorter when the Earth is at the point in its orbit that is closest to its planet than when the Earth is at the farthest point in its orbit, the difference in distance being the diameter of the Earth's orbit around the Sun. The observed change in the moon's orbital period is caused by the difference in the time it takes light to traverse the shorter or longer distance. Rømer observed this effect for Jupiter's innermost moon Io and deduced that light takes 22 minutes to cross the diameter of the Earth's orbit.

text: Another method is to use the aberration of light, discovered and explained by James Bradley in the 18th century.[87] This effect results from the vector addition of the velocity of light arriving from a distant source (such as a star) and the velocity of its observer (see diagram on the right). A moving observer thus sees the light coming from a slightly different direction and consequently sees the source at a position shifted from its original position. Since the direction of the Earth's velocity changes continuously as the Earth orbits the Sun, this effect causes the apparent position of stars to move around. From the angular difference in the position of stars (maximally 20.5 arcseconds)[88] it is possible to express the speed of light in terms of the Earth's velocity around the Sun, which with the known length of a year can be converted to the time needed to travel from the Sun to the Earth. In 1729, Bradley used this method to derive that light travelled 10,210 times faster than the Earth in its orbit (the modern figure is 10,066 times faster) or, equivalently, that it would take light 8 minutes 12 seconds to travel from the Sun to the Earth.[87]

text: Astronomical unit

text: An astronomical unit (AU) is approximately the average distance between the Earth and Sun. It was redefined in 2012 as exactly 7011149597870700000♠149597870700 m.[89][90] Previously the AU was not based on the International System of Units but in terms of the gravitational force exerted by the Sun in the framework of classical mechanics.[Note 7] The current definition uses the recommended value in metres for the previous definition of the astronomical unit, which was determined by measurement.[89] This redefinition is analogous to that of the metre, and likewise has the effect of fixing the speed of light to an exact value in astronomical units per second (via the exact speed of light in metres per second).

text: Previously, the inverse of c expressed in seconds per astronomical unit was measured by comparing the time for radio signals to reach different spacecraft in the Solar System, with their position calculated from the gravitational effects of the Sun and various planets. By combining many such measurements, a best fit value for the light time per unit distance could be obtained. For example, in 2009, the best estimate, as approved by the International Astronomical Union (IAU), was:[92][93]

text: The relative uncertainty in these measurements is 0.02 parts per billion (6989200000000000000♠2×10−11), equivalent to the uncertainty in Earth-based measurements of length by interferometry.[94] Since the metre is defined to be the length travelled by light in a certain time interval, the measurement of the light time in terms of the previous definition of the astronomical unit can also be interpreted as measuring the length of an AU (old definition) in metres.[Note 8]

text: Time of flight techniques

text: A method of measuring the speed of light is to measure the time needed for light to travel to a mirror at a known distance and back. This is the working principle behind the Fizeau–Foucault apparatus developed by Hippolyte Fizeau and Léon Foucault.

text: The setup as used by Fizeau consists of a beam of light directed at a mirror 8 kilometres (5 mi) away. On the way from the source to the mirror, the beam passes through a rotating cogwheel. At a certain rate of rotation, the beam passes through one gap on the way out and another on the way back, but at slightly higher or lower rates, the beam strikes a tooth and does not pass through the wheel. Knowing the distance between the wheel and the mirror, the number of teeth on the wheel, and the rate of rotation, the speed of light can be calculated.[95]

text: The method of Foucault replaces the cogwheel by a rotating mirror. Because the mirror keeps rotating while the light travels to the distant mirror and back, the light is reflected from the rotating mirror at a different angle on its way out than it is on its way back. From this difference in angle, the known speed of rotation and the distance to the distant mirror the speed of light may be calculated.[96]

text: Nowadays, using oscilloscopes with time resolutions of less than one nanosecond, the speed of light can be directly measured by timing the delay of a light pulse from a laser or an LED reflected from a mirror. This method is less precise (with errors of the order of 1%) than other modern techniques, but it is sometimes used as a laboratory experiment in college physics classes.[97][98][99]

text: Electromagnetic constants

text: An option for deriving c that does not directly depend on a measurement of the propagation of electromagnetic waves is to use the relation between c and the vacuum permittivity ε0 and vacuum permeability μ0 established by Maxwell's theory: c2 = 1/(ε0μ0). The vacuum permittivity may be determined by measuring the capacitance and dimensions of a capacitor, whereas the value of the vacuum permeability is fixed at exactly 6993400000000000000♠4π×10−7 H·m−1 through the definition of the ampere. Rosa and Dorsey used this method in 1907 to find a value of 7008299710000000000♠299710±22 km/s.[100][101]

text: Cavity resonance

text: Another way to measure the speed of light is to independently measure the frequency f and wavelength λ of an electromagnetic wave in vacuum. The value of c can then be found by using the relation c = fλ. One option is to measure the resonance frequency of a cavity resonator. If the dimensions of the resonance cavity are also known, these can be used to determine the wavelength of the wave. In 1946, Louis Essen and A.C. Gordon-Smith established the frequency for a variety of normal modes of microwaves of a microwave cavity of precisely known dimensions. The dimensions were established to an accuracy of about ±0.8 μm using gauges calibrated by interferometry.[100] As the wavelength of the modes was known from the geometry of the cavity and from electromagnetic theory, knowledge of the associated frequencies enabled a calculation of the speed of light.[100][102]

text: The Essen–Gordon-Smith result, 7008299792000000000♠299792±9 km/s, was substantially more precise than those found by optical techniques.[100] By 1950, repeated measurements by Essen established a result of 7008299792500000000♠299792.5±3.0 km/s.[103]

text: A household demonstration of this technique is possible, using a microwave oven and food such as marshmallows or margarine: if the turntable is removed so that the food does not move, it will cook the fastest at the antinodes (the points at which the wave amplitude is the greatest), where it will begin to melt. The distance between two such spots is half the wavelength of the microwaves; by measuring this distance and multiplying the wavelength by the microwave frequency (usually displayed on the back of the oven, typically 2450 MHz), the value of c can be calculated, "often with less than 5% error".[104][105]

text: Interferometry

text: Interferometry is another method to find the wavelength of electromagnetic radiation for determining the speed of light.[106] A coherent beam of light (e.g. from a laser), with a known frequency (f), is split to follow two paths and then recombined. By adjusting the path length while observing the interference pattern and carefully measuring the change in path length, the wavelength of the light (λ) can be determined. The speed of light is then calculated using the equation c = λf.

text: Before the advent of laser technology, coherent radio sources were used for interferometry measurements of the speed of light.[107] However interferometric determination of wavelength becomes less precise with wavelength and the experiments were thus limited in precision by the long wavelength (~0.4 cm) of the radiowaves. The precision can be improved by using light with a shorter wavelength, but then it becomes difficult to directly measure the frequency of the light. One way around this problem is to start with a low frequency signal of which the frequency can be precisely measured, and from this signal progressively synthesize higher frequency signals whose frequency can then be linked to the original signal. A laser can then be locked to the frequency, and its wavelength can be determined using interferometry.[108] This technique was due to a group at the National Bureau of Standards (NBS) (which later became NIST). They used it in 1972 to measure the speed of light in vacuum with a fractional uncertainty of 6991350000000000000♠3.5×10−9.[108][109]

text: History

text:
History of measurements of c (in km/s)

<1638
Galileo, covered lanterns
inconclusive[Note 9]

<1667
Accademia del Cimento, covered lanterns
inconclusive[Note 10]

1675
Rømer and Huygens, moons of Jupiter
7005220000000000000♠220000[86][114]

1729
James Bradley, aberration of light
7005301000000000000♠301000[95]

1849
Hippolyte Fizeau, toothed wheel
7005315000000000000♠315000[95]

1862
Léon Foucault, rotating mirror
7005298000000000000♠298000±500[95]

1907
Rosa and Dorsey, EM constants
7005299710000000000♠299710±30[100][101]

1926
Albert A. Michelson, rotating mirror
7005299796000000000♠299796±4[115]

1950
Essen and Gordon-Smith, cavity resonator
7005299792500000000♠299792.5±3.0[103]

1958
K.D. Froome, radio interferometry
7005299792500000000♠299792.50±0.10[107]

1972
Evenson et al., laser interferometry
7005299792456200000♠299792.4562±0.0011[109]

1983
17th CGPM, definition of the metre
7005299792458000000♠299792.458 (exact)[84]

text: Until the early modern period, it was not known whether light travelled instantaneously or at a very fast finite speed. The first extant recorded examination of this subject was in ancient Greece. The ancient Greeks, Muslim scholars, and classical European scientists long debated this until Rømer provided the first calculation of the speed of light. Einstein's Theory of Special Relativity concluded that the speed of light is constant regardless of one's frame of reference. Since then, scientists have provided increasingly accurate measurements.

text: Early history

text: Empedocles (c. 490–430 BC) was the first to propose a theory of light[116] and claimed that light has a finite speed.[117] He maintained that light was something in motion, and therefore must take some time to travel. Aristotle argued, to the contrary, that "light is due to the presence of something, but it is not a movement".[118] Euclid and Ptolemy advanced Empedocles' emission theory of vision, where light is emitted from the eye, thus enabling sight. Based on that theory, Heron of Alexandria argued that the speed of light must be infinite because distant objects such as stars appear immediately upon opening the eyes. Early Islamic philosophers initially agreed with the Aristotelian view that light had no speed of travel. In 1021, Alhazen (Ibn al-Haytham) published the Book of Optics, in which he presented a series of arguments dismissing the emission theory of vision in favour of the now accepted intromission theory, in which light moves from an object into the eye.[119] This led Alhazen to propose that light must have a finite speed,[118][120][121] and that the speed of light is variable, decreasing in denser bodies.[121][122] He argued that light is substantial matter, the propagation of which requires time, even if this is hidden from our senses.[123] Also in the 11th century, Abū Rayhān al-Bīrūnī agreed that light has a finite speed, and observed that the speed of light is much faster than the speed of sound.[124]

text: In the 13th century, Roger Bacon argued that the speed of light in air was not infinite, using philosophical arguments backed by the writing of Alhazen and Aristotle.[125][126] In the 1270s, Witelo considered the possibility of light travelling at infinite speed in vacuum, but slowing down in denser bodies.[127]

text: In the early 17th century, Johannes Kepler believed that the speed of light was infinite, since empty space presents no obstacle to it. René Descartes argued that if the speed of light were to be finite, the Sun, Earth, and Moon would be noticeably out of alignment during a lunar eclipse. Since such misalignment had not been observed, Descartes concluded the speed of light was infinite. Descartes speculated that if the speed of light were found to be finite, his whole system of philosophy might be demolished.[118] In Descartes' derivation of Snell's law, he assumed that even though the speed of light was instantaneous, the denser the medium, the faster was light's speed.[128] Pierre de Fermat derived Snell's law using the opposing assumption, the denser the medium the slower light traveled. Fermat also argued in support of a finite speed of light.[129]

text: First measurement attempts

text: In 1629, Isaac Beeckman proposed an experiment in which a person observes the flash of a cannon reflecting off a mirror about one mile (1.6 km) away. In 1638, Galileo Galilei proposed an experiment, with an apparent claim to having performed it some years earlier, to measure the speed of light by observing the delay between uncovering a lantern and its perception some distance away. He was unable to distinguish whether light travel was instantaneous or not, but concluded that if it were not, it must nevertheless be extraordinarily rapid.[110][111] In 1667, the Accademia del Cimento of Florence reported that it had performed Galileo's experiment, with the lanterns separated by about one mile, but no delay was observed. The actual delay in this experiment would have been about 11 microseconds.

text: The first quantitative estimate of the speed of light was made in 1676 by Rømer (see Rømer's determination of the speed of light).[85][86] From the observation that the periods of Jupiter's innermost moon Io appeared to be shorter when the Earth was approaching Jupiter than when receding from it, he concluded that light travels at a finite speed, and estimated that it takes light 22 minutes to cross the diameter of Earth's orbit. Christiaan Huygens combined this estimate with an estimate for the diameter of the Earth's orbit to obtain an estimate of speed of light of 7008220000000000000♠220000 km/s, 26% lower than the actual value.[114]

text: In his 1704 book Opticks, Isaac Newton reported Rømer's calculations of the finite speed of light and gave a value of "seven or eight minutes" for the time taken for light to travel from the Sun to the Earth (the modern value is 8 minutes 19 seconds).[130] Newton queried whether Rømer's eclipse shadows were coloured; hearing that they were not, he concluded the different colours travelled at the same speed. In 1729, James Bradley discovered stellar aberration.[87] From this effect he determined that light must travel 10,210 times faster than the Earth in its orbit (the modern figure is 10,066 times faster) or, equivalently, that it would take light 8 minutes 12 seconds to travel from the Sun to the Earth.[87]

text: Connections with electromagnetism

text: In the 19th century Hippolyte Fizeau developed a method to determine the speed of light based on time-of-flight measurements on Earth and reported a value of 7008315000000000000♠315000 km/s.[131] His method was improved upon by Léon Foucault who obtained a value of 7008298000000000000♠298000 km/s in 1862.[95] In the year 1856, Wilhelm Eduard Weber and Rudolf Kohlrausch measured the ratio of the electromagnetic and electrostatic units of charge, 1/√ε0μ0, by discharging a Leyden jar, and found that its numerical value was very close to the speed of light as measured directly by Fizeau. The following year Gustav Kirchhoff calculated that an electric signal in a resistanceless wire travels along the wire at this speed.[132] In the early 1860s, Maxwell showed that, according to the theory of electromagnetism he was working on, electromagnetic waves propagate in empty space[133][134][135] at a speed equal to the above Weber/Kohrausch ratio, and drawing attention to the numerical proximity of this value to the speed of light as measured by Fizeau, he proposed that light is in fact an electromagnetic wave.[136]

text: "Luminiferous aether"

text: It was thought at the time that empty space was filled with a background medium called the luminiferous aether in which the electromagnetic field existed. Some physicists thought that this aether acted as a preferred frame of reference for the propagation of light and therefore it should be possible to measure the motion of the Earth with respect to this medium, by measuring the isotropy of the speed of light. Beginning in the 1880s several experiments were performed to try to detect this motion, the most famous of which is the experiment performed by Albert A. Michelson and Edward W. Morley in 1887.[137] The detected motion was always less than the observational error. Modern experiments indicate that the two-way speed of light is isotropic (the same in every direction) to within 6 nanometres per second.[138] Because of this experiment Hendrik Lorentz proposed that the motion of the apparatus through the aether may cause the apparatus to contract along its length in the direction of motion, and he further assumed, that the time variable for moving systems must also be changed accordingly ("local time"), which led to the formulation of the Lorentz transformation. Based on Lorentz's aether theory, Henri Poincaré (1900) showed that this local time (to first order in v/c) is indicated by clocks moving in the aether, which are synchronized under the assumption of constant light speed. In 1904, he speculated that the speed of light could be a limiting velocity in dynamics, provided that the assumptions of Lorentz's theory are all confirmed. In 1905, Poincaré brought Lorentz's aether theory into full observational agreement with the principle of relativity.[139][140]

text: Special relativity

text: In 1905 Einstein postulated from the outset that the speed of light in vacuum, measured by a non-accelerating observer, is independent of the motion of the source or observer. Using this and the principle of relativity as a basis he derived the special theory of relativity, in which the speed of light in vacuum c featured as a fundamental constant, also appearing in contexts unrelated to light. This made the concept of the stationary aether (to which Lorentz and Poincaré still adhered) useless and revolutionized the concepts of space and time.[141][142]

text: Increased accuracy of c and redefinition of the metre and second

text: In the second half of the 20th century much progress was made in increasing the accuracy of measurements of the speed of light, first by cavity resonance techniques and later by laser interferometer techniques. These were aided by new, more precise, definitions of the metre and second. In 1950, Louis Essen determined the speed as 7008299792500000000♠299792.5±1 km/s, using cavity resonance. This value was adopted by the 12th General Assembly of the Radio-Scientific Union in 1957. In 1960, the metre was redefined in terms of the wavelength of a particular spectral line of krypton-86, and, in 1967, the second was redefined in terms of the hyperfine transition frequency of the ground state of caesium-133.

text: In 1972, using the laser interferometer method and the new definitions, a group at the US National Bureau of Standards in Boulder, Colorado determined the speed of light in vacuum to be c = 7008299792456200000♠299792456.2±1.1 m/s. This was 100 times less uncertain than the previously accepted value. The remaining uncertainty was mainly related to the definition of the metre.[Note 11][109] As similar experiments found comparable results for c, the 15th General Conference on Weights and Measures in 1975 recommended using the value 7008299792458000000♠299792458 m/s for the speed of light.[145]

text: Defining the speed of light as an explicit constant

text: In 1983 the 17th CGPM found that wavelengths from frequency measurements and a given value for the speed of light are more reproducible than the previous standard. They kept the 1967 definition of second, so the caesium hyperfine frequency would now determine both the second and the metre. To do this, they redefined the metre as: "The metre is the length of the path travelled by light in vacuum during a time interval of 1/7008299792458000000♠299792458 of a second."[84] As a result of this definition, the value of the speed of light in vacuum is exactly 7008299792458000000♠299792458 m/s[146][147] and has become a defined constant in the SI system of units.[12] Improved experimental techniques that prior to 1983 would have measured the speed of light, no longer affect the known value of the speed of light in SI units, but instead allow a more precise realization of the metre by more accurately measuring the wavelength of Krypton-86 and other light sources.[148][149]

text: In 2011, the CGPM stated its intention to redefine all seven SI base units using what it calls "the explicit-constant formulation", where each "unit is defined indirectly by specifying explicitly an exact value for a well-recognized fundamental constant", as was done for the speed of light. It proposed a new, but completely equivalent, wording of the metre's definition: "The metre, symbol m, is the unit of length; its magnitude is set by fixing the numerical value of the speed of light in vacuum to be equal to exactly 7008299792458000000♠299792458 when it is expressed in the SI unit m s−1."[150] This is one of the proposed changes to be incorporated in the next revision of the SI also termed the New SI.


document_title: The Fat Controller

question_text: when did the fat controller became sir topham hatt

root

text: The Fat Controller

text: Origin of nickname[edit]

text: The character is first seen in "The Sad Story of Henry" in the first book in the Railway Series, The Three Railway Engines. When Henry refused to leave a tunnel, the story says "a Fat Director who was on the train told the guard to get a rope". The character is referred to as the Fat Director/Controller for the remainder of the Railway Series, both in the narrative and by the other characters. The name Sir Topham Hatt is first mentioned in the Foreword to Henry the Green Engine and also appears on his luggage trunk in the same book in the story "Percy and the Trousers". The first use of the name Sir Topham Hatt in the narrative comes in the episode 'Come Out Henry!' when Ringo Starr introduces him to the audience.

tag: p

text: Biography (Railway Series)[edit]

text: There have been three Fat Controllers. This is not revealed directly in the stories, as they all look very similar and are all known as Sir Topham Hatt. However, the books The Island of Sodor: Its People, History and Railways (written by Rev. W. Awdry and George Awdry) and Sodor: Reading Between the Lines (by Christopher Awdry) make this clear.

text: The Fat Controller, 1st Bt[edit]

text: He was a talented engineer who was apprenticed with Sir William Stanier at the Great Western Railway's Swindon works, which gave him a great love of all things Great Western. He went on to assist A. W. Dry in the construction of the Tidmouth, Knapford and Elsbridge Light Railway, which became the branch line, and designed the locomotives that ran upon it.

text: When the standard gauge railways of the Island were merged into the North Western Railway in 1914, Topham Hatt was called upon for his engineering skill. He constructed a bridge to link Sodor with the Mainland, as well as a number of branch lines and improvements to locomotive facilities. He was immediately made a Director of the railway.

text: Topham married Jane Brown and fathered a son (Charles Topham Hatt) and a daughter (Barbara Jane Hatt). Jane was sister to Sir Handel Brown, Liberal MP for Sodor East and owner of the Skarloey Railway, making all successive descendants of the two railway families cousins. Charles wed Amanda Croarie, daughter of the owner of the Ffarquhar Quarry Company, and Barbara married Henry Regaby, the Viscount Harwick. In light of this, Topham's family unit can be seen as an alliance of several of the most prominent families in Sodor.

text: When the North Western Railway was nationalised and became part of British Railways in 1948, Topham Hatt was made Controller of the railway. 1948 also saw him made a baronet for his services to the railways of Sodor.

text: This Fat Controller appears to be the one shown in the series.

text: The Fat Controller, 2nd Bt[edit]

text: Charles Topham Hatt was the son of the first Sir Topham Hatt and the second Controller of the NWR. He too served an apprenticeship with Stanier, this time working under the locomotive designer. Like his father, he was an innovative engineer and made a number of improvements to the railway and its engines. He was also the originator of the scheme to construct the Arlesdale Railway and the ballast consortium that used it.

text: He was responsible for the line's policy of retaining steam locomotives long after they had been abolished on the rest of British Railways, and while Dr Beeching was closing down branch lines on the Mainland, Charles was reopening them on Sodor.

text: The Fat Controller, 3rd Bt[edit]

text: Stephen Topham Hatt was first seen as a child in the book Toby the Tram Engine. As an adult, he was made the third Controller of the North Western Railway. His son, Richard Topham Hatt, is tipped to be the next Fat Controller on Stephen's retirement and at Stephen's death he will inherit the family's baronetcy and the title 'Sir Topham Hatt'.

text: Biography (television series)[edit]

text: In the television series, The Fat Controller is always the same man, with the same wife and grandchildren. He is in his mid 60s (as evident in a newspaper article in the Great Discovery), although his voice in the UK versions sometimes hint at old age, and he has even appeared with a white moustache in certain episodes. Very little of his history is revealed, although we do see more of his extended family, including his mother (Dowager Hatt), and his mischievous brother (Sir Lowham Hatt). In the first season, he and all the other human characters were made out of lead. From the second season onwards, they were made out of resin so they could move around more easily.

text: He is shown to be a qualified railway engine driver when he brings Percy to the yard for the first time. He is in charge of all the engines on Sodor and seemingly has a great deal of say over other vehicles. As a young man, he learnt to drive in Elizabeth the vintage Sentinel lorry. He has overseen the construction of a number of lines, railway services, and has been involved with the opening of several tourist attractions on Sodor.

text: UK Narrator Michael Angelis portrayed the character with a strong Yorkshire accent, with a low gruff voice a trait of which has been continued when Pierce Brosnan briefly took over the mantle, and also when individual voice artists were brought in to voice the characters, The Fat Controller being voiced by Keith Wickham in both the UK and US versions as of 2015 onwards. Kerry Shale initially voiced him in the US prior to 2015. In the American version, he has always been referred to by his actual name, Sir Topham Hatt, possibly because "fat" is a much more pejorative term in the US than in the UK.

text: The Fat Controller's name was revealed to be Bertram by Alicia Botti, the famous opera singer, in the series 13 episode "Play Time", and by his mother Dowager Hatt in the series 13 episode "Percy's Parcel", the series 14 episode "Jitters and Japes", and the series 15 episodes "Edward the Hero" and "Stop that Bus!".

text: Mode of dress[edit]

text: In his iconic top hat and morning suit, the Fat Controller looks rather old-fashioned and formal. However, until at least the late 1950s it was customary for railway officials in Britain to be so dressed – for Sir Topham to be dressed any other way would be far more unusual.

text: In the television series, Sir Topham's suit has often been used for comic effect, being augmented with scarf and mittens in winter. The series plays on the outdated nature of this outfit, giving Sir Topham an entire wardrobe of old-fashioned and formal clothes for occasions when he is not "on duty". In the Series 8 episode "Halloween", he is shown wearing pyjamas and a nightcap, and in the Series 9 and 10 episodes "Flour Power" and "Sticky Toffee Thomas" he is briefly shown wearing a wizard costume. In yet another episode, he is shown wearing a kilt, a gift from a visiting Scottish Lord. In various CGI episodes, he dresses like Santa Claus.

text: Sir Topham's household[edit]

text: Wife: Lady Hatt[edit]

text: Lady Jane Brown Hatt helps her husband run the railway, and is happiest when she sees new lines opened, and has had some special birthday parties. She likes the railway, but had a certain dislike of Annie and Clarabel, calling them beach huts. Later, she took a liking to them, after they got new coats of paint. Although her husband runs a railway, she likes a day out on a boat or in their car.

text: Mother: Dowager Hatt[edit]

text: Dowager Hatt visits Sodor occasionally, and on her first appearance in a TV episode, her son held a party for her. On this occasion, her Dalmatian dog (soon to be named Gremlin) ran away after being frightened by Gordon's whistle, and ended up in Thomas' cab, where he greatly enjoyed a long ride to the docks. She says the railway is really useful, and the Fat Controller says she is always right.

text: Dowager Hatt has appeared in:

text:
Series 5 - Gordon and the Gremlin (not named)
Series 6 - It's Only Snow (cameo) and Thomas the Jet Engine/Thomas and the Jet Engine (cameo)
Series 9 - Thomas and the Birthday Picnic (not named in the US narration)
Series 11 - Percy and the Left Luggage/Percy and the Baggage (not named in the US narration)
Series 12 - Excellent Emily (does not speak)
Series 13 - Percy's Parcel
Series 14 - Jitters and Japes
Series 15 - Gordon and Ferdinand, Percy's New Friends (cameo), Edward the Hero, Up, Up and Away!, Stop that Bus!, Wonky Whistle (cameo), Tree Trouble and Fiery Flynn
Series 16 - Express Coming Through, Thomas and the Sounds of Sodor (cameo), Muddy Matters (cameo) and Happy Birthday Sir! (does not speak)
Series 18 - Toad's Adventure and Millie and the Volcano
Series 19 - Diesel's Ghostly Christmas (cameo), The Beast of Sodor and Reds Vs. Blues (cameo)
Series 20 - Engine of the Future and Buckled Tracks and Bumpy Trucks/Bumpy Tracks and Bumpy Cars
Series 21 - Dowager Hatt's Busy Day, Terence Breaks the Ice (cameo) and Confused Coaches
Specials - Day of the Diesels, The Adventure Begins (portrait cameo), Sodor's Legend of the Lost Treasure (cameo) and The Great Race (cameo)

tag: ul

text: She was mentioned in:

text:
Series 16 - Percy and the Monster of Brendam
Series 18 - Samson Sent for Scrap (not named)
Series 21 - A Shed for Edward

text: She is the only member of the household to originate in the television series, never having appeared in the books.

text: Grandson: Stephen Hatt[edit]

text: Stephen Topham Hatt lives on the Island of Sodor, and regularly has outings and holidays with his grandparents and his sister. Stephen loves trains, and was excited when he first met Toby the Tram Engine. Stephen also has a bit of knowledge about the Island, of which is the reason they discovered the Old Castle and the mine (in which Bertram was found).

text: In the Railway Series, Stephen ultimately took the railway over, and is the current Fat Controller. In the television series he has always remained a child.

text: Granddaughter: Bridget Hatt[edit]

text: Bridget Amanda Hatt lives on Sodor, and regularly goes for outings and holidays with her grandparents and her brother, Stephen. On one occasion they went to Toby the Tram Engine's old line, where she thought Toby was an electric tram and was reprimanded by her brother for offending him.

text: Her parents (mentioned only in the book 'Sodor: Reading Between the Lines') are Charles and Amanda Hatt.

text: Brother: Lowham Hatt[edit]

text: Sir Lowham Hatt is the jolly brother of Sir Topham Hatt, the son of Dowager Hatt, the great-uncle of Stephen and Bridget Hatt, and the brother-in-law of Lady Hatt.

text: Sir Lowham Hatt is mischievous and enjoys playing with the children. He seems to know little or nothing about railways. He played hide-and-seek with the children and then went into a signal box and pulled the lever, switching Gordon to the branchline. He dresses exactly like Sir Topham but has a moustache. It is unknown how and why he got his knighthood.

text: Sir Lowham Hatt only appears in the series 13 episode "Double Trouble".

text: Butler[edit]

text: Sir Topham Hatt has a butler who is featured in the Thomas the Tank Engine and Friends TV Series. He has appeared in only two stories, "Thomas Breaks the Rules" ("Thomas in Trouble" in the United Kingdom) in Season 1, and "Thomas and the Search for Fergus" ("Fergus Breaks The Rules" in the United Kingdom), in Season 7.

text: In real life[edit]

text: "Day out with Thomas" events are a popular way of raising money for heritage railways. These events are an opportunity for children to meet characters from the books and television series (or at least, engines that have been "dressed up" to resemble them). These events are invariably presided over by a Fat Controller, played by a railway volunteer of appropriate age and build. The copyright holders are strict about how these volunteers should appear: the South Devon Railway's Fat Controller was forced to either quit or shave off his beard,[1] and it is absolutely forbidden for a Fat Controller to be too thin. In the United States, on the other hand, he is often portrayed by a person in a costume.

text: Other uses of the name "Fat Controller"[edit]

text:
In Series 3, Episode 2 of To the Manor Born, during a meeting to protest the closing of the local railway station, the Rector loses his temper with an overweight representative of British Rail, played by Richard Thorp, and refers to him as "the Fat Controller".
In Australia the term 'fat controller' is also used to describe someone working within the finance industry,[citation needed] usually the financial manager of a company similar to the terminology 'fat cat' being used to describe people relating to government.
The name "Fat Controller" has also been given to a student magazine, an electronic snow glove[2] and at least one public house[3] in the United Kingdom.
It is also the nickname of Samuel Northcliffe, the malevolent influence on the life of protagonist Ian Wharton in British novelist Will Self's 1993 novel My Idea of Fun.
The British alternative rock band Catherine Wheel recorded the song "Here Comes the Fat Controller" on their 1997 album, Adam and Eve.
Electronic musician Squarepusher has a song called "Fat Controller" on his album Hard Normal Daddy.
In software development, "Fat Controller" is the name of an antipattern (The Fat Controller) related to MVC; opposite of Skinny Controller.
"The Fat Controller" is an epithet given to Superintendent Andy Dalziel (played on TV by Warren Clarke) by his subordinates in the British detective series Dalziel and Pascoe.
In the fantasy novel Railsea by China Miéville, That Apt Ohm is a deity of the rails. His name is an anagram of Topham Hatt.


document_title: Philosopher king

question_text: who believed that a government should be run by philosopher kings

text: Philosopher king

text: In Book VI of The Republic[edit]

text: Plato defined a philosopher firstly as its eponymous occupation: "wisdom-lover". He then distinguishes between one who loves true knowledge (as opposed to mere experience or education) by saying that the philosopher is the only person who has access to ideas – the archetypal entities that exist behind all representations of the form (such as Beauty itself as opposed to any one particular instance of beauty). It is next and in support of the idea that philosophers are the best rulers that Plato fashions the Ship of State metaphor, one of his most often cited ideas (along with his allegory of the cave): a "true pilot must of necessity pay attention to the seasons, the heavens, the stars, the winds, and everything proper to the craft if he is really to rule a ship" (The Republic, 6.488d).

text: Examples[edit]

text: Magna Graecia[edit]

text: Archytas was a Pythagorean philosopher and political leader in the ancient Greek city of Tarentum, in Italy. He was a close friend of Plato, and some scholars assert that he may have been an inspiration for Plato's concept of a philosopher-king.

text: Dion of Syracuse was a disciple of Plato. He overthrew the tyrant Dionysius II of Syracuse and was installed as leader in the city, only to be made to leave by the Syracusans who were unhappy with his opposition to democratic reforms. He was later re-invited to the city, where he attempted to establish an aristocracy along Platonic lines, but he was assassinated by plotters in the pay of the former tyrant.

text: Roman Empire[edit]

text: Marcus Aurelius was the first prominent example of a philosopher king. His Stoic tome Meditations, written in Greek while on campaign between 170 and 180, is still revered as a literary monument to a philosophy of service and duty, describing how to find and preserve equanimity in the midst of conflict by following nature as a source of guidance and inspiration.

text: Hungary and Croatia[edit]

text: Matthias Corvinus (1443–1490), who was king of Hungary and Croatia from 1458, was influenced by the Italian Renaissance and strongly endeavored to follow in practice the model and ideas of the philosopher-king as described in The Republic.[1]

text: Revolutionary Iran[edit]

text: Ayatollah Khomeini is said to have been inspired by the Platonic vision of the philosopher king while in Qum in the 1920s when he became interested in Islamic mysticism and Plato's Republic. As such, it has been speculated that he was inspired by Plato's philosopher king, and subsequently based elements of his Islamic republic on it, despite it being a republic which deposed the former Pahlavi dynasty.[2]

text: Others[edit]

text: Alexander the Great, king of the Macedonians, and Khusraw I, king of the Sassanian Empire, are known by some to be examples of the philosopher king.

text: Criticism[edit]

text: Karl Popper blamed Plato for the rise of totalitarianism in the 20th century, seeing Plato's philosopher kings, with their dreams of 'social engineering' and 'idealism', as leading directly to Adolf Hitler and Joseph Stalin (via Georg Wilhelm Friedrich Hegel and Karl Marx respectively).[3]


document_title: APA style

question_text: what is the most current edition of apa

question_tokens: what is the most current edition of apa

text: APA style

text: History[edit]

text: The APA got involved in journal publishing in 1923.[3] In 1929, an APA committee had a seven-page writer's guide published in the Psychological Bulletin.[4][5] In 1944, a 32-page guide appeared as an article in the same journal.[3] The first edition of the APA Publication Manual was published in 1952 as a 61-page supplement to the Psychological Bulletin,[6]  marking the beginning of a recognized “APA style.”[3] In response to the growing complexities of scientific reporting, subsequent editions were released in 1974, 1983, 1994, 2001, and 2009.

text: Primarily known for the simplicity of its reference citation style, the Manual also established standards for language use that had far-reaching effects.  Particularly influential were the "Guidelines for Nonsexist Language in APA Journals," first published as a modification to the 1974 edition, which provided practical alternatives to sexist language then in common usage.[7][8] The guidelines for reducing bias in language have been updated over the years and presently provide practical guidance for writing about race, ethnicity, age, gender, sexual orientation, and disability status (APA, 2009, pp. 70–77; see also APA, 2009b).[9]

text: Sixth edition of the Publication Manual[edit]

text: The sixth edition of the Publication Manual of the American Psychological Association is the most current. It was released in July 2009 after four years of development. The Publication Manual Revision Task Force of the American Psychological Association established parameters for the revision based on published critique; user comments; commissioned reviews; and input from psychologists, nurses, librarians, business leaders, publishing professionals, and APA governance groups (APA, 2007a, 2007b).[10][11]  To accomplish these revisions, the Task Force appointed working groups of four to nine members in seven areas: bias-free language, ethics, graphics, Journal Article Reporting Standards,[12] references, statistics, and writing style (APA, 2009, pp. XVII–XVIII).

text: The APA explained the issuing of a new edition only eight years after the fifth edition by pointing to the increased use of online source or online access to academic journals (6th edition, p. XV). The sixth edition is accompanied by a style website, apastyle.org as well as the APA Style Blog, which answers many common questions from users.

text: Errors in the first printing[edit]

text: Sample papers in the first printing of the sixth edition contained errors. APA staff posted all of the corrections online for free in a single document on October 1, 2009, and shortly thereafter alerted users to the existence of the corrections in an APA blog entry.[13] These errors attracted significant attention from the scholarly community and nearly two weeks later, on October 13, 2009, the article "Correcting a Style Guide" was published in the online newspaper Inside Higher Ed that included interviews with several individuals, one of whom described the errors as "egregious".[14] All copies of the printing with errors were soon after recalled in 2009 (including those from major retailers such as Amazon.com) and all manuals currently in circulation are unaffected.

text: Characteristics of APA Style Citation[edit]

text: In-text citations[edit]

text: APA Style uses an author-date reference citation system in the text with an accompanying reference list. That means that to cite any reference in a paper, the writer should cite the author and year of the work, either by putting both in parentheses separated by a comma (parenthetical citation) or by putting the author in the narrative of the sentence and the year in parentheses (narrative citation).

text: Example narrative citation: Schmidt and Oh (2016) described a fear among the public that the findings of science are not actually real.

text: Example parenthetical citation: In our postfactual era, many members of the public fear that the findings of science are not real (Schmidt & Oh, 2016).

text: Reference list[edit]

text: In the APA reference list, the writer should provide the author, year, title, and source of the cited work in an alphabetical list of references. If a reference is not cited in the text, it should not be included in the reference list. The reference format varies slightly depending on the document type (e.g., journal article, edited book chapter, blog post), but broadly speaking always follows the same pattern of author, date, title, source.

text:
Reference type

Template

Example

Journal article

Author, A., & Author, B. (year). Title of article. Journal Title, Volume, page range. DOI

Schmidt, F. L., & Oh, I.-S. (2016). The crisis of confidence in research findings in psychology: Is lack of replication the real problem? Or is it something else? Archives of Scientific Psychology, 4, 32–37. https://dx.doi.org/10.1037/arc0000029

Whole book

Author, A., & Author, B. (year). Title of book. Publisher location: Publisher Name. DOI

Brown, B. (2010). The gifts of imperfection: Let go of who you think you're supposed to be and embrace who you are. Center City, MN: Hazelden.

Edited book chapter

Author, A., & Author, B. (year). Title of chapter. In E. Editor & A. Editor (Eds.), Title of book (pp. xx-xx). Publisher location: Publisher Name. DOI

Singh, A. A., Hwahng, S. J., Chang, S. C., White, B. (2017). Affirmative counseling with trans/gender-variant people of color. In A. Singh & L. M. Dickey (Eds.), Affirmative counseling and psychological practice with transgender and gender nonconforming clients (pp. 41–68). Washington, DC: American Psychological Association. https://dx.doi.org/10.1037/14957-003

Website

Group Author. (year). Title of page. Retrieved from http://xxxxxxx on date

American Psychological Association. (n.d.). Divisions. Retrieved from http://www.apa.org/about/division/ on 2011-07-23

tag: table

text: Note that the title of a website reference may be italic or not italic. If the work stands alone, italicize the title; if it is part of a greater whole, do not italicize the title.


document_title: 2018 FIFA World Cup broadcasting rights

question_text: which channels will telecast fifa world cup 2018 in india

text: 2018 FIFA World Cup broadcasting rights

text: FIFA, through several companies, sold the broadcasting rights for the 2018 FIFA World Cup[1] to the following broadcasters.

text: Television[edit]

text:
Country/Region

Broadcaster

Ref.

 Afghanistan

ATN

[1][2]

 Albania

RTSH

[1]

 Andorra

TF1, France Télévisions, TVE, beIN Sports

[1]

 Angola

TPA, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Argentina

TV Pública, TyC Sports, DirecTV

[1]

 Armenia

ARMTV

[1]

 Australia

SBS, Optus Sport

[3][4][5]

 Austria

ORF, OE24, DAZN

[1]

 Azerbaijan

İTV, AzTV

[1]

 Bangladesh

BTV, Maasranga TV,  Nagorik TV, Sony Pictures Networks

[1][2][6]

 Bahamas

ZNS, DirecTV

[1]

 Belarus

BTRC

[1]

 Belgium

VRT, RTBF

[1]

 Benin

ORTB, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Bermuda

BBC, DirecTV

[1]

 Bhutan

Sony Pictures Networks

[1]

 Bolivia

Unitel, Red Uno, DirecTV

[1]

 Bosnia and Herzegovina

BHRT

[1]

 Brazil

Globo, SporTV, Fox Sports

[7][8][9]

 Brunei

Astro

[1]

 Bulgaria

BNT

[1]

 Burkina Faso

RTB, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Cambodia

CBS

[1][2]

 Cameroon

CRTV, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Canada

CBC, Sportsnet, TVA Sports

[4][10][1]

 Chad

ORTNV, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Chile

Canal 13, TVN, Mega, DirecTV, Movistar

[1]

 China

CCTV, Migu, Youku

[2][11][12]

 Colombia

Caracol TV, RCN TV, DirecTV

[1]

 Congo

Télé Congo, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Costa Rica

Teletica, Sky, Movistar

[1][13]

 Côte d'Ivoire

RTI, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Croatia

HRT

[1]

 Cuba

ICRT

[1]

 Cyprus

CyBC

[1]

 Czech Republic

ČT

[1]

 Denmark

DR, TV 2

[1]

 Dominica

Sky, DirecTV

[1]

 Dominican Republic

Antena 7, Sky

[14]

 Ecuador

RTS, DirecTV

[1]

 El Salvador

TCS, Sky

[1]

 Estonia

ERR

[1]

 Faroe Islands

DR, TV 2

[1]

 Finland

Yle

[1][15]

 France

TF1, France Télévisions, beIN Sports

[1]

 Gabon

RTG, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Gambia

GRTS, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Germany

ARD, ZDF, Sky Sport, DAZN

[16][17][18][19][20]

 Georgia

GPB

[1]

 Ghana

GBC, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Greece

ERT

[1]

 Greenland

DR, TV 2

[1]

 Guatemala

TV Azteca, Tigo Sports, Sky, Movistar

[1]

 Guinea

RTG, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Honduras

TVC, Sky, Movistar

[1]

 Hong Kong

ViuTV,  Now TV

[1][2][21][22]

 Hungary

MTVA

[1]

 Iceland

RÚV

[1]

 India

Jio TV, AirTel TV, Sony Pictures Networks

[1][23]

 Indonesia

Trans Media, K-Vision, SuperPass, USeeTV

[2][24][25][26][27]

 Iran

IRIB, beIN Sports

[28]

 Ireland

RTÉ

[1]

 Israel

KAN, Keshet, Sport 5, Charlton

[1]

 Italy

Mediaset

[1]

 Jamaica

TVJ, DirecTV

[1]

 Japan

NHK, NTV, TV Asahi, TBS, Fuji TV

[1]

 Kazakhstan

Qazaqstan

[1]

 Kenya

NTV, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Kosovo

RTK

[1]

 Kyrgyzstan

KTRK

[1]

 Laos

TVLAO

[1][2]

 Latvia

LTV

[1]

 Lebanon

Télé Liban, beIN Sports

[1][29][30]

 Liechtenstein

SRG SSR

[31]

 Lithuania

LRT

[1]

 Macau

TDM

[2][32]

 Madagascar

ORTM, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Malaysia

Astro, RTM

[1][33][34][35]

 Maldives

PSM, Sony Pictures Networks

[1]

 Mali

Africable, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Malta

PBS

[1]

 Mauritius

MBC, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Mexico

Televisa, TV Azteca, Sky México

[1]

 Moldova

TRM

[1]

 Monaco

TF1, France Télévisions, beIN Sports

[1]

 Mongolia

NTV, MNB

[1][2]

 Montenegro

RTCG

[1]

 Morocco

SNRT, beIN Sports

[1][36]

 Mozambique

TVM, TV Miramar, TV Sucesso, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Myanmar

Skynet Sports

[1][2]

 Namibia

NBC, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

   Nepal

NTV, Kantipur TV, Sony Pictures Networks

[1]

 Netherlands

NOS

[1]

 New Zealand

Sky Sport

[1][37]

 Nicaragua

Ratensa, Sky, Movistar

[1]

 Niger

ORTN, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Nigeria

NTA, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 North Korea

KCTV

[1]

 Norway

NRK, TV 2

[1]

 Pakistan

PTV, Sony Pictures Networks

[1]

 Panama

Corporación Medcom, Televisora Nacional, Sky, Movistar

[1]

 Papua New Guinea

EM TV, Sky Pacific

[1]

 Paraguay

SNT, Telefuturo, TyC, DirecTV

[1]

 Peru

Latina, DirecTV

[1]

 Philippines

ABS-CBN

[1][2][38]

 Poland

TVP, NC+

[1]

 Portugal

RTP, SIC, SportTV

[39][40][41]

 Romania

TVR

[1]

 Rwanda

RBA, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Russia

Perviy Kanal, VGTRK, Match TV

[42]

 San Marino

Mediaset

[1]

 Senegal

RTS, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Serbia

RTS

[1]

 Seychelles

SBC, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Singapore

Mediacorp, Singtel, StarHub

[2][43]

 Slovakia

RTVS

[1]

 Slovenia

RTVSLO

[1]

 Solomon Islands

Our Telekom, Sky Pacific

[1]

 South Africa

SABC, SuperSport, StarTimes

[1][44]

 South Korea

KBS, MBC, SBS

[1]

 Spain

TVE

[1]

 Sri Lanka

Sri Lanka Rupavahini Corporation, Sony Pictures Networks

[1]

 Suriname

SCCN, DirecTV

[1]

 Sweden

SVT, TV4

[16][18]

  Switzerland

SRG SSR, DAZN

[31]

 Taiwan

ELTA, CTS

[1][2][45]

 Tajikistan

Varzish TV

[1]

 Tanzania

TBC, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Thailand

TrueVisions, Channel 5, Amarin TV

[2][46][47][48]

 Timor Leste

ETO Telco

[1][2]

 Togo

TVT, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Trinidad & Tobago

CNC3, DirecTV

[1]

 Tunisia

ERTT, beIN Sports

[1]

 Turkey

TRT

[1]

 Uganda

BBS, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

 Ukraine

Inter, NTN

[1][49]

 United KingdomshowHome Nations/Territories
 Channel Islands
 England
 Isle of Man
 Northern Ireland
 Scotland
 Wales

BBC, ITV

[17]

 United Statesshowand territories
 American Samoa
 Guam
 Northern Mariana Islands
 Puerto Rico
 Baker Island
 Howland Island
 Jarvis Island
 Johnston Atoll
 Kingman Reef
 Midway Islands
 Navassa Island
 Palmyra Atoll
 Wake Island

NBC, Telemundo

[50][51]

 Uruguay

Monte Carlo, Canal 10, Teledoce, TyC, DirecTV

[1]

 Uzbekistan

Uzreport TV, Futbol TV

[2][52]

  Vatican City

RAI, Sky Sport

[1]

 Venezuela

Venevisión, TVes, Meridiano Televisión, VC Sports, DirecTV

[1]

 Vietnam

VTV

[2][53][54]

 Zambia

Muvi TV, Kwesé Sports, SuperSport, StarTimes, Canal+

[1]

text:
Region

Broadcaster

Ref.

CaribbeanshowCountries/Territories
 Antigua & Barbuda
 Anguilla
 Aruba
 Barbados
 Belize
 British Virgin Islands
 Cayman Islands
 Curaçao
 Dominican Republic
 Grenada
 Guyana
 Haiti
 Montserrat
 St. Lucia
 St. Kitts & Nevis
 St. Vincent & the Grenadines
 Turks and Caicos
 U.S. Virgin Islands

DirecTV

[1][55][1]

Middle East and North AfricashowCountries
 Algeria
 Bahrain
 Comoros
 Djibouti
 Egypt
 Iraq
 Jordan
 Kuwait
 Libya
 Mauritania
 Oman
 Palestinian Authority
 Qatar
 Saudi Arabia
 Somalia
 South Sudan
 Sudan
 Syria
 United Arab Emirates
 Yemen

beIN Sports

[1][56][57][58]

OceaniashowCountries/Territories
 Cook Islands
 Fiji
 Kiribati
 Micronesia
 Nauru
 Palau
 Samoa
 Tonga
 Tuvalu
 Vanuatu

Sky Pacific

[1]

Sub-Saharan AfricashowCountries
 Botswana
 Burundi
 Cape Verde
 Central African Republic
 DR Congo
 Equatorial Guinea
 Eritrea
 Ethiopia
 Guinea-Bissau
 Lesotho
 Liberia
 Malawi
 Sierra Leone
 Swaziland
 Zimbabwe

Kwesé Sports, SuperSport, StarTimes, Canal+

[1][59]

text: Radio[edit]

text:
Nation/Territory

Broadcaster

Ref

 Albania

RTSH

[1]

 Australia

SBS, ABC

[1]

 Austria

ORF

[1]

 Belarus

BTRC

[1]

 Belgium

VRT, RTBF

[1]

 Bosnia and Herzegovina

BHRT

[1]

 Brazil

Rádio Bandeirantes, Rádio Gaúcha, Rádio Itatiaia, Rádio Jovem Pan, Rádio Verdes Mares, Radio Sagres 730, Sistema Globo de Rádio, Super Rádio Tupi

[1]

 Bulgaria

BNR

[1]

 Chile

ADN Radio, Radio Bío-Bío, Radio Cooperativa, UCV Radio

[1]

 Colombia

Blu Radio, Caracol Radio, RCN Radio

[1]

 Costa Rica

Radio Columbia, Radio Monumental, Teletica Radio

[1]

 Croatia

HRT

[1]

 Cyprus

CyBC

[1]

 Denmark

DR

[1]

 Ecuador

RTS

[1]

 Estonia

ERR

[1]

 France

Europe 1, RTL, Radio France, RMC

[1]

 Finland

Yle

[1]

 Georgia

GPB

[1]

 Germany

ARD, RTL Radio, Radio Hamburg, Radio NRW, Hitradio RTL Sachsen, Hitradio FFH, Antenne Bayern, 89.0 RTL

[1]

 Guatemala

Emisoras Unidas, La Red Deportes 106.1

[1]

 Hong Kong

RTHK

[60]

 Iceland

RÚV

[1]

 Indonesia

RRI

[61]

 Iran

IRIB

[1]

 Ireland

RTÉ

[1]

 Israel

KAN

[1]

 Italy

RAI, Mediaset

[1][62]

 Jamaica

RJR 94 FM

[1]

 Kosovo

RTK

[1]

 Liechtenstein

SRG SSR

[1]

 Lithuania

LT

[1]

 Macau

TDM

[1]

 Macedonia

MRT

[1]

 Moldova

TeleRadio-Moldova

[1]

 Monaco

RMC Sport

[1]

 Montenegro

RTCG

[1]

 Morocco

SNRT,Radio Mars

[1][36]

 Netherlands

NOS

[1]

 Norway

NRK

[1]

 Peru

RPP

[1]

 Portugal

RTP, TSF, Rádio Renascença

[1]

 Portuguese-speaking AfricashowCountries
 Cape Verde
 Guinea-Bissau
 Mozambique
 São Tomé and Príncipe

RTP

[63]

 Russia

VGTRK

[1]

 Serbia

RTS

[1]

 Slovenia

RTVSLO

[1]

 South Africa

SABC

[1]

 South Korea

SBS

[1]

 Spain

RTVE, Cadena COPE, Cadena SER, Onda Cero, Radio Marca

[1]

 Sub-Saharan AfricashowCountries
 Angola
 Benin
 Botswana
 Burkina Faso
 Burundi
 Cameroon
 Cape Verde
 Central African Republic
 Chad
 Congo
 Côte d'Ivoire
 DR Congo
 Equatorial Guinea
 Eritrea
 Ethiopia
 Gabon
 Gambia
 Ghana
 Guinea
 Guinea-Bissau
 Kenya
 Lesotho
 Liberia
 Madagascar
 Malawi
 Mali
 Mauritius
 Mozambique
 Namibia
 Niger
 Nigeria
 Rwanda
 São Tomé and Príncipe
 Senegal
 Seychelles
 Sierra Leone
 Swaziland
 Tanzania
 Togo
 Uganda
 Zambia
 Zimbabwe

France Médias Monde

[1]

 Sweden

SR

[1]

  Switzerland

SRG SSR

[1]

 Turkey

TRT

[1]

 United KingdomshowHome Nations/Territories
 England
 Scotland
 Wales
 Northern Ireland
 Gibraltar
 Channel Islands
 Isle of Man

BBC, talkSPORT

[1]

 United States showand territories
 American Samoa
 Guam
 Northern Mariana Islands
 Puerto Rico
 U.S. Virgin Islands
 Baker Island
 Howland Island
 Jarvis Island
 Johnston Atoll
 Kingman Reef
 Midway Islands
 Navassa Island
 Palmyra Atoll
 Wake Island

ESPN Radio, Fútbol de Primera

[1][64]

 Uruguay

770 AM Oriental, 810 AM El Espectador, 850 AM Carve, 890 AM Sarandí Sport, 930 AM Monte Carlo, 970 AM Radio Universal, 1090 AM Radio Imparcial, 1410 AM Radio LaCatorce10, 99.5 FM Del Sol

[1]

 Vietnam

VOV

[1][65]


question_text: who put the overalls in mrs murphys chowder

text: Who Threw the Overalls in Mrs. Murphy's Chowder? is a popular song, sometimes known as "Who Threw the Overalls in Mistress Murphy's Chowder". It was written by George L. Giefer in 1898 and originally recorded by Edward M. Favor in 1901.[1] It was later recorded by Bing Crosby on December 6, 1945[2] and included in his album St. Patrick's Day. Julie Andrews included the song in her album Don't Go in the Lion's Cage Tonight (1962).[3]

text: The song describes an incident in which a pair of worn-out overalls are found in a batch of Mrs. Murphy's large pot of chowder. Tim Nolan, who discovered the overalls, immediately assumes it was a prank, and promises to inflict pain on "the mick that threw the overalls ... ". Mistress Murphy, upon realizing the ruckus, admits that she forgot to take the overalls out of the pot after she had been using it for laundry earlier in the day, at which point Nolan apologizes and the group puts music to his words and sing (the chorus).

text: The song has enjoyed some popularity with Irish-Americans and association with the Saint Patrick's Day holiday and is sometimes played during the holiday, sometimes edited to remove elements of the song that can be construed to disparage the Irish.

text: The song was used in the 1943 film Coney Island when it was performed by Charles Winninger, Phil Silvers, George Montgomery and Frank Orth and later reprised by Winninger at the piano.[4]


document_title: Numismatic history of the United States

question_text: what was the first coin minted in the united states

text: Numismatic history of the United States

text: American coinage (1792 - c. 1837)[edit]

text: The Coinage Act of 1792 established the United States Mint and regulated the coinage of the United States.[3]  The act created coins in the denominations of Half Cent (1/200 of a dollar), Cent (1/100 of a dollar, or a cent), Half Dime (also known as a half disme) (five cents), Dime (also known as a disme) (10 cents), Quarter (25 cents), Half Dollar (50 cents), Dollar, Quarter Eagle ($2.50), Half Eagle ($5), and Eagle ($10).

text: The first coin minted under the act, and therefore the first official coin of the United States, was the half disme. According to legend these first half disme coins were minted from Martha Washington's silverware.[4]

text: The half cent and cent were made of pure copper, the half dime, dime, quarter, half, and dollar in 90% silver, and the quarter, half and full eagle in .9167 gold (later changed to .8992 in 1834, and then 90% gold in 1837). All of the coins featured Liberty on the front and a bald eagle on the back.

text: This period of coinage covers several designs.  The Draped Bust design was featured on all copper and silver coins minted between 1796-1807.  On silver coins other than the dollar this design was followed by the Capped Bust.

text: In the early days, often years went by without a certain denomination being minted.

text: Seated Liberty era and introduction of the Double Eagle, Nickel and small cent (1836 - 1891)[edit]

text: United States Seated Liberty coinage was the silver coin design minted in the mid-to-late 19th century. It was the first seated-portrait U.S. coin, now-scarce Seated Liberty Dollar, and debuted in 1836. The seated liberty dime and seated liberty half dime followed the next year in 1837 and the seated liberty quarter and seated liberty half dollar in 1839.

text: In 1849, in the wake of the California Gold Rush, the Double Eagle, or $20 gold denomination was added [5] This coin contains nearly a pure ounce of gold and were minted in large quantities; many still exist today and are used as bullion coins and command only a modest premium over spot price, though many dates are rare as well. The Liberty Head Double Eagle was minted up to 1907.

text: Rising copper prices caused the reduction of the size of the large cent. Originally, cent coins were large and heavy. This changed between 1856 and 1857 when they were replaced by the small-sized Flying Eagle cent, which was made of 88% copper and 12% nickel, and had a somewhat pale brown color. In 1859 this was replaced by the Indian Head cent, and by 1864, the Civil War increased nickel and copper prices and the cent was made thinner and the nickel removed; the cent was thus now a small, thin bronze coin.

text: The five cent nickel coin was introduced in 1866, and gradually it made the half dime obsolete. To this day, the nickel, though the design has changed, retains the same metallic content it had from its inception: ~25% nickel, ~75% copper.[6]

text: The second half of the 19th century saw several odd coin denominations. The two cent piece was minted from 1864 to 1873. It was the first American coin to display the phrase In God We Trust, a result of the increased wartime religiosity during the Civil War. Three cent pieces made of silver, and later copper-nickel, were also made around this era. From 1875 to 1878, Twenty cent pieces were made in the Seated Liberty design. A Three-dollar piece of gold was minted from 1854 to 1889.

text: In 1878, the first Morgan Silver Dollars were minted; this series lasted until 1904 and was revived for several months in 1921.

text: Turn of the 20th century coinage, the introduction of paper money and the end of gold coins (1892 - 1932)[edit]

text: The year 1892 saw the designs of Charles E. Barber adorn the dime, quarter and half dollar. His Liberty Head nickel had debuted in 1883, and thus from the years 1892 to 1904, his designs were featured on every denomination from 5 cents up to one dollar. The Barber design would last on dimes and quarters up to 1916, on half dollars up to 1915, and on the nickel up to the extremely rare and famous 1913 Liberty Head nickels.

text: Federal Reserve Notes were issued for the first time in 1917. Originally, these were backed by gold, and a note could be, at least in theory, exchanged for gold coin at a bank until 1933 when gold was confiscated from the general public. Silver certificates were exchangeable for silver coin up to June 1968.

text: The design of the American One dollar bill has stayed almost the same since 1935, and the other denominations had a similar appearance until their redesign in the late 1990s.

text: The Gold Eagle was re-designed in 1907 as the Indian Head eagle and the $2.50 and $5 pieces followed in 1908. The Liberty Head Double Eagle was replaced with the St. Gaudens Double Eagle in 1907. The wheat penny, with the head of Lincoln on the obverse, was introduced in 1909. The wheat penny was the first American coin that featured the face of an actual person (rather than Liberty). Also, the Buffalo nickel and Mercury dime were both introduced in the 1910s (1913 and 1916, respectively).

text: The Peace Dollar was minted from 1921 to 1935. After 1935, no more silver dollars would be minted for circulation by the US Mint. 90% silver dimes, quarters and half dollars were replaced with copper-nickel coins after 1964. From 1965 to 1976, 40% silver coins were issued in certain denominations. Of these, only the 1965 to 1969 dated Kennedy Half Dollars were minted for general circulation. No precious metals were present in any coins issued after 1977 by the US Mint until the bullion and commemorative series that began in the 1980s and continue to the present day.

text: Mid-to-late 20th century and the end of silver coinage (1933 - c. 1998)[edit]

text: As there were no more gold coins or silver dollars after the Executive Order 6102 of 1933 minted in the United States, paper notes took place of the coin denominations above 50 cents. Up to 1964, dimes, quarters and half dollars were still minted in 90% silver; halves would contain 40% silver from 1965 to 1970.

text: The new tradition of placing past presidents and Founding Fathers on coins, which had begun with the 1909 Lincoln cent, continued in the 1930s and 1940s, with the introduction of the Washington quarter in 1932, the Jefferson nickel in 1938, the Roosevelt dime in 1946, and the Franklin half dollar in 1948. The original Washington quarter design remained unchanged, aside from the removal of silver content and finer details, up to 1998, the Jefferson nickel up to 2003, and the Roosevelt dime to the present day. The Franklin half was replaced by the John F. Kennedy half dollar in 1964 to commemorate him after his murder. The composition of the Kennedy half dollar was changed from 90% silver to 40% silver in 1965 and remained that way through 1970. After 1970, Kennedy half dollars were made of the same copper-nickel alloy as the other denominations.

text: The last 90% silver circulated coins are dated 1964,[7] though they were actually minted for several years later dated as 1964. In 1982, the penny had most of its copper content removed, and is now made primarily of zinc, with a thin copper plating.

text: The paper money of the United States was re-designed to deter counterfeit through the late 1990s and early to mid-2000s.

text: Contemporary (1999 to present)[edit]

text: American coinage and paper money has gone through significant changes since the late 1990s. Up to the mid-1990s, American money had changed little since the end of silver coins in the mid-1960s, and some of the denominations, including the paper notes and the nickel, had barely changed since the 1930s.

text: Beginning in 1996 with the $100 and $50 bills, paper money was redesigned to deter counterfeit. In 1999, the State Quarter program ended the classic design of the Washington quarter. Next came the 2004 nickels, meant to commemorate Lewis and Clark's 200th anniversary. The cent was re-designed in 2009 to commemorate Abraham Lincoln's 200th birthday. After 2009, the Shield Penny design, representing how Lincoln preserved the Union, appeared on the reverse of pennies.

text: The dollar coin returned in 1999, in a case very similar to the 1921 Morgan dollar, with the Susan B. Anthony dollar, to fill in until the Sacagawea Dollar came about in 2000. Concurrent is the Presidential Dollar series, which, as of March 2016, is set to end in fall 2016.

text:
hidevteCoinage of the United StatesCent (1¢)
Fugio Cent (1787)
Chain (1793)
Wreath (1793)
Liberty Cap (1793–1796)
Draped Bust (1796–1807)
Classic Head (1808–1814)
Matron Head (1816–1839)
Large cent (Braided Hair) (1835–57; 1868)
Flying Eagle cent (1856–1858)
Indian Head (1859–1909)
Lincoln cent (1909–present)
1943 steel cent
1955 doubled die cent
1974 aluminum cent
Nickel (5¢)Half dime
Flowing Hair (1794–95)
Draped Bust (1796–97, 1800–1805)
Capped Bust (1829–1837)
Seated Liberty (1837–1873)
Shield (1866–1883)
Liberty Head (1883–1913)
Buffalo (1913–1938)
Jefferson (1938–present)
Dime (10¢)
Disme (1792)
Draped Bust (1796–1807)
Capped Bust (1809–1837)
Seated Liberty (1837–1891)
Barber (1892–1916)
Mercury (1916–1945)
Roosevelt (1946–present)
Quarter dollar (25¢)
Draped Bust (1796–1807)
Capped Bust (1815–1839)
Seated Liberty (1839–1891)
Barber (1892–1916)
Standing Liberty (1916–1930)
Washington (1932–1998)
50 State Quarters (1999–2008)
District of Columbia and United States Territories Quarters (2009)
America the Beautiful Quarters (2010–present)
Half dollar (50¢)
Flowing Hair (1794–95)
Draped Bust (1796–1807)
Capped Bust (1807–1839)
Seated Liberty (1839–1891)
Barber (1892–1915)
Walking Liberty (1916–1947)
Franklin (1948–1963)
Kennedy (1964–present)
Dollar ($1)
Flowing Hair (1794–95)
Draped Bust (1795–1804)
1804 (1834, c. 1858–1860)
Gobrecht (1836–1839)
Seated Liberty (1840–1873)
Gold (1849–1889)
Trade (1873–1885)
Morgan (1878–1904; 1921)
Peace (1921–1935)
Eisenhower (1971–1978)
Susan B. Anthony (1979–1981; 1999)
Silver Eagle (1986–present)
Sacagawea (2000–present)
Presidential (2007–2016)
Gold
Turban Head eagle (1795–1804)
Half eagle (1795–1929)
Eagle (1795–1933)
Quarter eagle (1796–1929)
Gold dollar (1849–1889)
Three-dollar piece (1854–1889)
Liberty Head double eagle (1849–1907)
Double eagle (1849–1933)
Saint-Gaudens double eagle (1907–1933)
1933 double eagle
Indian Head eagle (1907–1933)
Indian Head gold pieces (1908–1929)
Gold Eagle (1986–present)
Gold Buffalo (2006–present)
First Spouse gold bullion coins (2007–2016)
CommemorativeEarly(1892–1954)
Columbian half dollar (1892–93)
Isabella quarter (1893)
Lafayette dollar (1900)
Louisiana Purchase Exposition dollar (1903)
Lewis and Clark Exposition dollar (1904–05)
Panama–Pacific commemorative coins (1915)
McKinley Birthplace Memorial dollar (1916–17)
Illinois Centennial half dollar (1918)
Maine Centennial half dollar (1920)
Pilgrim Tercentenary half dollar (1920–21)
Missouri Centennial half dollar (1921)
Alabama Centennial half dollar (1921)
Monroe Doctrine Centennial half dollar (1923)
Huguenot-Walloon half dollar (1924)
Stone Mountain Memorial half dollar (1925)
Lexington-Concord Sesquicentennial half dollar (1925)
California Diamond Jubilee half dollar (1925)
Fort Vancouver Centennial half dollar (1925)
United States Sesquicentennial coinage (1926)
Oregon Trail Memorial half dollar (1926–1939)
Vermont Sesquicentennial half dollar (1927)
Hawaii Sesquicentennial half dollar (1928)
Texas Centennial half dollar (1934–1938)
Hudson Sesquicentennial half dollar (1935)
Connecticut Tercentenary half dollar (1935)
California Pacific International Exposition half dollar (1935–36)
Rhode Island Tercentenary half dollar (1936)
Cincinnati Musical Center half dollar (1936)
Cleveland Centennial half dollar (1936)
Bridgeport half dollar (1936)
Elgin, Illinois, Centennial half dollar (1936)
Modern(1982–present)
Los Angeles XXIII Olympiad dollar (1984)
Eisenhower commemorative dollar (1990)
Library of Congress ten dollar coin (2000)
John Marshall commemorative dollar (2005)
Marine Corps 230th Anniversary silver dollar (2005)
Boy Scouts of America centennial silver dollar (2010)
Patterns
Two-cent billon (1836)
Three-cent bronze (1863)
Stella (1879–80)
Half-union (1877)
Other
Half cent (1793–1857)
Two-cent piece (1864–1873)
Three-cent silver (1851–1873)
Three-cent nickel (1865–1889)
Twenty-cent piece (1875–1878)
United States Bicentennial coinage (1975–76)
Platinum Eagle (1997–present)
Palladium Eagle (2017–present)
America the Beautiful Silver Bullion Coins (2010–present)
Norse-American medal (1925)