For decades, it was the official policy of the Soviet Union to deny the existence of the secret protocol to the Soviet–German Pact. At the behest of Mikhail Gorbachev, Alexander Nikolaevich Yakovlev headed a commission investigating the existence of such a protocol. In December 1989, the commission concluded that the protocol had existed and revealed its findings to the Congress of People's Deputies of the Soviet Union. As a result, the Congress passed the declaration confirming the existence of the secret protocols, condemning and denouncing them. Both successor-states of the pact parties have declared the secret protocols to be invalid from the moment they were signed. The Federal Republic of Germany declared this on September 1, 1989 and the Soviet Union on December 24, 1989, following an examination of the microfilmed copy of the German originals.


Regarding the timing of German rapprochement, many historians agree that the dismissal of Maxim Litvinov, whose Jewish ethnicity was viewed unfavorably by Nazi Germany, removed an obstacle to negotiations with Germany. Stalin immediately directed Molotov to "purge the ministry of Jews." Given Litvinov's prior attempts to create an anti-fascist coalition, association with the doctrine of collective security with France and Britain, and pro-Western orientation by the standards of the Kremlin, his dismissal indicated the existence of a Soviet option of rapprochement with Germany.[f] Likewise, Molotov's appointment served as a signal to Germany that the USSR was open to offers. The dismissal also signaled to France and Britain the existence of a potential negotiation option with Germany. One British official wrote that Litvinov's disappearance also meant the loss of an admirable technician or shock-absorber, while Molotov's "modus operandi" was "more truly Bolshevik than diplomatic or cosmopolitan." Carr argued that the Soviet Union's replacement of Foreign Minister Litvinov with Molotov on May 3, 1939 indicated not an irrevocable shift towards alignment with Germany, but rather was Stalin's way of engaging in hard bargaining with the British and the French by appointing a proverbial hard man, namely Molotov, to the Foreign Commissariat. Historian Albert Resis stated that the Litvinov dismissal gave the Soviets freedom to pursue faster-paced German negotiations, but that they did not abandon British–French talks. Derek Watson argued that Molotov could get the best deal with Britain and France because he was not encumbered with the baggage of collective security and could negotiate with Germany. Geoffrey Roberts argued that Litvinov's dismissal helped the Soviets with British–French talks, because Litvinov doubted or maybe even opposed such discussions.


Edward Hallett Carr, a frequent defender of Soviet policy, stated: "In return for 'non-intervention' Stalin secured a breathing space of immunity from German attack."[page needed] According to Carr, the "bastion" created by means of the Pact, "was and could only be, a line of defense against potential German attack."[page needed] According to Carr, an important advantage was that "if Soviet Russia had eventually to fight Hitler, the Western Powers would already be involved."[page needed] However, during the last decades, this view has been disputed. Historian Werner Maser stated that "the claim that the Soviet Union was at the time threatened by Hitler, as Stalin supposed ... is a legend, to whose creators Stalin himself belonged. In Maser's view, "neither Germany nor Japan were in a situation [of] invading the USSR even with the least perspective  [sic] of success," and this could not have been unknown to Stalin. Carr further stated that, for a long time, the primary motive of Stalin's sudden change of course was assumed to be the fear of German aggressive intentions.


Some critics of Stalin's policy, such as the popular writer Viktor Suvorov, claim that Stalin's primary motive for signing the Soviet–German non-aggression treaty was his calculation that such a pact could result in a conflict between the capitalist countries of Western Europe.[citation needed] This idea is supported by Albert L. Weeks.[page needed] Claims by Suvorov that Stalin planned to invade Germany in 1941 are debated by historians with, for example, David Glantz opposing such claims, while Mikhail Meltyukhov supports them.[citation needed] The authors of The Black Book of Communism consider the pact a crime against peace and a "conspiracy to conduct war of aggression."


A capacitor (originally known as a condenser) is a passive two-terminal electrical component used to store electrical energy temporarily in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors (plates) separated by a dielectric (i.e. an insulator that can store energy by becoming polarized). The conductors can be thin films, foils or sintered beads of metal or conductive electrolyte, etc. The nonconducting dielectric acts to increase the capacitor's charge capacity. Materials commonly used as dielectrics include glass, ceramic, plastic film, air, vacuum, paper, mica, and oxide layers. Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike a resistor, an ideal capacitor does not dissipate energy. Instead, a capacitor stores energy in the form of an electrostatic field between its plates.


When there is a potential difference across the conductors (e.g., when a capacitor is attached across a battery), an electric field develops across the dielectric, causing positive charge +Q to collect on one plate and negative charge −Q to collect on the other plate. If a battery has been attached to a capacitor for a sufficient amount of time, no current can flow through the capacitor. However, if a time-varying voltage is applied across the leads of the capacitor, a displacement current can flow.


In October 1745, Ewald Georg von Kleist of Pomerania, Germany, found that charge could be stored by connecting a high-voltage electrostatic generator by a wire to a volume of water in a hand-held glass jar. Von Kleist's hand and the water acted as conductors, and the jar as a dielectric (although details of the mechanism were incorrectly identified at the time). Von Kleist found that touching the wire resulted in a powerful spark, much more painful than that obtained from an electrostatic machine. The following year, the Dutch physicist Pieter van Musschenbroek invented a similar capacitor, which was named the Leyden jar, after the University of Leiden where he worked. He also was impressed by the power of the shock he received, writing, "I would not take a second shock for the kingdom of France."


Daniel Gralath was the first to combine several jars in parallel into a "battery" to increase the charge storage capacity. Benjamin Franklin investigated the Leyden jar and came to the conclusion that the charge was stored on the glass, not in the water as others had assumed. He also adopted the term "battery", (denoting the increasing of power with a row of similar units as in a battery of cannon), subsequently applied to clusters of electrochemical cells. Leyden jars were later made by coating the inside and outside of jars with metal foil, leaving a space at the mouth to prevent arcing between the foils.[citation needed] The earliest unit of capacitance was the jar, equivalent to about 1.11 nanofarads.


Since the beginning of the study of electricity non conductive materials like glass, porcelain, paper and mica have been used as insulators. These materials some decades later were also well-suited for further use as the dielectric for the first capacitors. Paper capacitors made by sandwiching a strip of impregnated paper between strips of metal, and rolling the result into a cylinder were commonly used in the late 19century; their manufacture started in 1876, and they were used from the early 20th century as decoupling capacitors in telecommunications (telephony).


Charles Pollak (born Karol Pollak), the inventor of the first electrolytic capacitors, found out that the oxide layer on an aluminum anode remained stable in a neutral or alkaline electrolyte, even when the power was switched off. In 1896 he filed a patent for an "Electric liquid capacitor with aluminum electrodes." Solid electrolyte tantalum capacitors were invented by Bell Laboratories in the early 1950s as a miniaturized and more reliable low-voltage support capacitor to complement their newly invented transistor.


Last but not least the electric double-layer capacitor (now Supercapacitors) were invented. In 1957 H. Becker developed a "Low voltage electrolytic capacitor with porous carbon electrodes". He believed that the energy was stored as a charge in the carbon pores used in his capacitor as in the pores of the etched foils of electrolytic capacitors. Because the double layer mechanism was not known by him at the time, he wrote in the patent: "It is not known exactly what is taking place in the component if it is used for energy storage, but it leads to an extremely high capacity.".


A capacitor consists of two conductors separated by a non-conductive region. The non-conductive region is called the dielectric. In simpler terms, the dielectric is just an electrical insulator. Examples of dielectric media are glass, air, paper, vacuum, and even a semiconductor depletion region chemically identical to the conductors. A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from any external electric field. The conductors thus hold equal and opposite charges on their facing surfaces, and the dielectric develops an electric field. In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device.


The current I(t) through any component in an electric circuit is defined as the rate of flow of a charge Q(t) passing through it, but actual charges—electrons—cannot pass through the dielectric layer of a capacitor. Rather, one electron accumulates on the negative plate for each one that leaves the positive plate, resulting in an electron depletion and consequent positive charge on one electrode that is equal and opposite to the accumulated negative charge on the other. Thus the charge on the electrodes is equal to the integral of the current as well as proportional to the voltage, as discussed above. As with any antiderivative, a constant of integration is added to represent the initial voltage V(t0). This is the integral form of the capacitor equation:


The simplest model capacitor consists of two thin parallel conductive plates separated by a dielectric with permittivity ε . This model may also be used to make qualitative predictions for other device geometries. The plates are considered to extend uniformly over an area A and a charge density ±ρ = ±Q/A exists on their surface. Assuming that the length and width of the plates are much greater than their separation d, the electric field near the centre of the device will be uniform with the magnitude E = ρ/ε. The voltage is defined as the line integral of the electric field between the plates


The maximum energy is a function of dielectric volume, permittivity, and dielectric strength. Changing the plate area and the separation between the plates while maintaining the same volume causes no change of the maximum amount of energy that the capacitor can store, so long as the distance between plates remains much smaller than both the length and width of the plates. In addition, these equations assume that the electric field is entirely concentrated in the dielectric between the plates. In reality there are fringing fields outside the dielectric, for example between the sides of the capacitor plates, which will increase the effective capacitance of the capacitor. This is sometimes called parasitic capacitance. For some simple capacitor geometries this additional capacitance term can be calculated analytically. It becomes negligibly small when the ratios of plate width to separation and length to separation are large.


Capacitors deviate from the ideal capacitor equation in a number of ways. Some of these, such as leakage current and parasitic effects are linear, or can be assumed to be linear, and can be dealt with by adding virtual components to the equivalent circuit of the capacitor. The usual methods of network analysis can then be applied. In other cases, such as with breakdown voltage, the effect is non-linear and normal (i.e., linear) network analysis cannot be used, the effect must be dealt with separately. There is yet another group, which may be linear but invalidate the assumption in the analysis that capacitance is a constant. Such an example is temperature dependence. Finally, combined parasitic effects such as inherent inductance, resistance, or dielectric losses can exhibit non-uniform behavior at variable frequencies of operation.


For air dielectric capacitors the breakdown field strength is of the order 2 to 5 MV/m; for mica the breakdown is 100 to 300 MV/m; for oil, 15 to 25 MV/m; it can be much less when other materials are used for the dielectric. The dielectric is used in very thin layers and so absolute breakdown voltage of capacitors is limited. Typical ratings for capacitors used for general electronics applications range from a few volts to 1 kV. As the voltage increases, the dielectric must be thicker, making high-voltage capacitors larger per capacitance than those rated for lower voltages. The breakdown voltage is critically affected by factors such as the geometry of the capacitor conductive parts; sharp edges or points increase the electric field strength at that point and can lead to a local breakdown. Once this starts to happen, the breakdown quickly tracks through the dielectric until it reaches the opposite plate, leaving carbon behind and causing a short (or relatively low resistance) circuit. The results can be explosive as the short in the capacitor draws current from the surrounding circuitry and dissipates the energy.


Ripple current is the AC component of an applied source (often a switched-mode power supply) whose frequency may be constant or varying. Ripple current causes heat to be generated within the capacitor due to the dielectric losses caused by the changing field strength together with the current flow across the slightly resistive supply lines or the electrolyte in the capacitor. The equivalent series resistance (ESR) is the amount of internal series resistance one would add to a perfect capacitor to model this. Some types of capacitors, primarily tantalum and aluminum electrolytic capacitors, as well as some film capacitors have a specified rating value for maximum ripple current.


The capacitance of certain capacitors decreases as the component ages. In ceramic capacitors, this is caused by degradation of the dielectric. The type of dielectric, ambient operating and storage temperatures are the most significant aging factors, while the operating voltage has a smaller effect. The aging process may be reversed by heating the component above the Curie point. Aging is fastest near the beginning of life of the component, and the device stabilizes over time. Electrolytic capacitors age as the electrolyte evaporates. In contrast with ceramic capacitors, this occurs towards the end of life of the component.


Capacitors, especially ceramic capacitors, and older designs such as paper capacitors, can absorb sound waves resulting in a microphonic effect. Vibration moves the plates, causing the capacitance to vary, in turn inducing AC current. Some dielectrics also generate piezoelectricity. The resulting interference is especially problematic in audio applications, potentially causing feedback or unintended recording. In the reverse microphonic effect, the varying electric field between the capacitor plates exerts a physical force, moving them as a speaker. This can generate audible sound, but drains energy and stresses the dielectric and the electrolyte, if any.


In DC circuits and pulsed circuits, current and voltage reversal are affected by the damping of the system. Voltage reversal is encountered in RLC circuits that are under-damped. The current and voltage reverse direction, forming a harmonic oscillator between the inductance and capacitance. The current and voltage will tend to oscillate and may reverse direction several times, with each peak being lower than the previous, until the system reaches an equilibrium. This is often referred to as ringing. In comparison, critically damped or over-damped systems usually do not experience a voltage reversal. Reversal is also encountered in AC circuits, where the peak current will be equal in each direction.


For maximum life, capacitors usually need to be able to handle the maximum amount of reversal that a system will experience. An AC circuit will experience 100% voltage reversal, while under-damped DC circuits will experience less than 100%. Reversal creates excess electric fields in the dielectric, causes excess heating of both the dielectric and the conductors, and can dramatically shorten the life expectancy of the capacitor. Reversal ratings will often affect the design considerations for the capacitor, from the choice of dielectric materials and voltage ratings to the types of internal connections used.


Capacitors made with any type of dielectric material will show some level of "dielectric absorption" or "soakage". On discharging a capacitor and disconnecting it, after a short time it may develop a voltage due to hysteresis in the dielectric. This effect can be objectionable in applications such as precision sample and hold circuits or timing circuits. The level of absorption depends on many factors, from design considerations to charging time, since the absorption is a time-dependent process. However, the primary factor is the type of dielectric material. Capacitors such as tantalum electrolytic or polysulfone film exhibit very high absorption, while polystyrene or Teflon allow very small levels of absorption. In some capacitors where dangerous voltages and energies exist, such as in flashtubes, television sets, and defibrillators, the dielectric absorption can recharge the capacitor to hazardous voltages after it has been shorted or discharged. Any capacitor containing over 10 joules of energy is generally considered hazardous, while 50 joules or higher is potentially lethal. A capacitor may regain anywhere from 0.01 to 20% of its original charge over a period of several minutes, allowing a seemingly safe capacitor to become surprisingly dangerous.


Leakage is equivalent to a resistor in parallel with the capacitor. Constant exposure to heat can cause dielectric breakdown and excessive leakage, a problem often seen in older vacuum tube circuits, particularly where oiled paper and foil capacitors were used. In many vacuum tube circuits, interstage coupling capacitors are used to conduct a varying signal from the plate of one tube to the grid circuit of the next stage. A leaky capacitor can cause the grid circuit voltage to be raised from its normal bias setting, causing excessive current or signal distortion in the downstream tube. In power amplifiers this can cause the plates to glow red, or current limiting resistors to overheat, even fail. Similar considerations apply to component fabricated solid-state (transistor) amplifiers, but owing to lower heat production and the use of modern polyester dielectric barriers this once-common problem has become relatively rare.


Most types of capacitor include a dielectric spacer, which increases their capacitance. These dielectrics are most often insulators. However, low capacitance devices are available with a vacuum between their plates, which allows extremely high voltage operation and low losses. Variable capacitors with their plates open to the atmosphere were commonly used in radio tuning circuits. Later designs use polymer foil dielectric between the moving and stationary plates, with no significant air space between them.


Several solid dielectrics are available, including paper, plastic, glass, mica and ceramic materials. Paper was used extensively in older devices and offers relatively high voltage performance. However, it is susceptible to water absorption, and has been largely replaced by plastic film capacitors. Plastics offer better stability and ageing performance, which makes them useful in timer circuits, although they may be limited to low operating temperatures and frequencies. Ceramic capacitors are generally small, cheap and useful for high frequency applications, although their capacitance varies strongly with voltage and they age poorly. They are broadly categorized as class 1 dielectrics, which have predictable variation of capacitance with temperature or class 2 dielectrics, which can operate at higher voltage. Glass and mica capacitors are extremely reliable, stable and tolerant to high temperatures and voltages, but are too expensive for most mainstream applications. Electrolytic capacitors and supercapacitors are used to store small and larger amounts of energy, respectively, ceramic capacitors are often used in resonators, and parasitic capacitance occurs in circuits wherever the simple conductor-insulator-conductor structure is formed unintentionally by the configuration of the circuit layout.


Electrolytic capacitors use an aluminum or tantalum plate with an oxide dielectric layer. The second electrode is a liquid electrolyte, connected to the circuit by another foil plate. Electrolytic capacitors offer very high capacitance but suffer from poor tolerances, high instability, gradual loss of capacitance especially when subjected to heat, and high leakage current. Poor quality capacitors may leak electrolyte, which is harmful to printed circuit boards. The conductivity of the electrolyte drops at low temperatures, which increases equivalent series resistance. While widely used for power-supply conditioning, poor high-frequency characteristics make them unsuitable for many applications. Electrolytic capacitors will self-degrade if unused for a period (around a year), and when full power is applied may short circuit, permanently damaging the capacitor and usually blowing a fuse or causing failure of rectifier diodes (for instance, in older equipment, arcing in rectifier tubes). They can be restored before use (and damage) by gradually applying the operating voltage, often done on antique vacuum tube equipment over a period of 30 minutes by using a variable transformer to supply AC power. Unfortunately, the use of this technique may be less satisfactory for some solid state equipment, which may be damaged by operation below its normal power range, requiring that the power supply first be isolated from the consuming circuits. Such remedies may not be applicable to modern high-frequency power supplies as these produce full output voltage even with reduced input.


Several other types of capacitor are available for specialist applications. Supercapacitors store large amounts of energy. Supercapacitors made from carbon aerogel, carbon nanotubes, or highly porous electrode materials, offer extremely high capacitance (up to 5 kF as of 2010[update]) and can be used in some applications instead of rechargeable batteries. Alternating current capacitors are specifically designed to work on line (mains) voltage AC power circuits. They are commonly used in electric motor circuits and are often designed to handle large currents, so they tend to be physically large. They are usually ruggedly packaged, often in metal cases that can be easily grounded/earthed. They also are designed with direct current breakdown voltages of at least five times the maximum AC voltage.


If a capacitor is driven with a time-varying voltage that changes rapidly enough, at some frequency the polarization of the dielectric cannot follow the voltage. As an example of the origin of this mechanism, the internal microscopic dipoles contributing to the dielectric constant cannot move instantly, and so as frequency of an applied alternating voltage increases, the dipole response is limited and the dielectric constant diminishes. A changing dielectric constant with frequency is referred to as dielectric dispersion, and is governed by dielectric relaxation processes, such as Debye relaxation. Under transient conditions, the displacement field can be expressed as (see electric susceptibility):


where a single prime denotes the real part and a double prime the imaginary part, Z(ω) is the complex impedance with the dielectric present, Ccmplx(ω) is the so-called complex capacitance with the dielectric present, and C0 is the capacitance without the dielectric. (Measurement "without the dielectric" in principle means measurement in free space, an unattainable goal inasmuch as even the quantum vacuum is predicted to exhibit nonideal behavior, such as dichroism. For practical purposes, when measurement errors are taken into account, often a measurement in terrestrial vacuum, or simply a calculation of C0, is sufficiently accurate.)


The arrangement of plates and dielectric has many variations depending on the desired ratings of the capacitor. For small values of capacitance (microfarads and less), ceramic disks use metallic coatings, with wire leads bonded to the coating. Larger values can be made by multiple stacks of plates and disks. Larger value capacitors usually use a metal foil or metal film layer deposited on the surface of a dielectric film to make the plates, and a dielectric film of impregnated paper or plastic – these are rolled up to save space. To reduce the series resistance and inductance for long plates, the plates and dielectric are staggered so that connection is made at the common edge of the rolled-up plates, not at the ends of the foil or metalized film strips that comprise the plates.


Capacitors may have their connecting leads arranged in many configurations, for example axially or radially. "Axial" means that the leads are on a common axis, typically the axis of the capacitor's cylindrical body – the leads extend from opposite ends. Radial leads might more accurately be referred to as tandem; they are rarely actually aligned along radii of the body's circle, so the term is inexact, although universal. The leads (until bent) are usually in planes parallel to that of the flat body of the capacitor, and extend in the same direction; they are often parallel as manufactured.


Small, cheap discoidal ceramic capacitors have existed since the 1930s, and remain in widespread use. Since the 1980s, surface mount packages for capacitors have been widely used. These packages are extremely small and lack connecting leads, allowing them to be soldered directly onto the surface of printed circuit boards. Surface mount components avoid undesirable high-frequency effects due to the leads and simplify automated assembly, although manual handling is made difficult due to their small size.


Mechanically controlled variable capacitors allow the plate spacing to be adjusted, for example by rotating or sliding a set of movable plates into alignment with a set of stationary plates. Low cost variable capacitors squeeze together alternating layers of aluminum and plastic with a screw. Electrical control of capacitance is achievable with varactors (or varicaps), which are reverse-biased semiconductor diodes whose depletion region width varies with applied voltage. They are used in phase-locked loops, amongst other applications.


Most capacitors have numbers printed on their bodies to indicate their electrical characteristics. Larger capacitors like electrolytics usually display the actual capacitance together with the unit (for example, 220 μF). Smaller capacitors like ceramics, however, use a shorthand consisting of three numeric digits and a letter, where the digits indicate the capacitance in pF (calculated as XY × 10Z for digits XYZ) and the letter indicates the tolerance (J, K or M for ±5%, ±10% and ±20% respectively).


Capacitors are connected in parallel with the power circuits of most electronic devices and larger systems (such as factories) to shunt away and conceal current fluctuations from the primary power source to provide a "clean" power supply for signal or control circuits. Audio equipment, for example, uses several capacitors in this way, to shunt away power line hum before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power source, and bypass AC currents from the power supply. This is used in car audio applications, when a stiffening capacitor compensates for the inductance and resistance of the leads to the lead-acid car battery.


In electric power distribution, capacitors are used for power factor correction. Such capacitors often come as three capacitors connected as a three phase load. Usually, the values of these capacitors are given not in farads but rather as a reactive power in volt-amperes reactive (var). The purpose is to counteract inductive loading from devices like electric motors and transmission lines to make the load appear to be mostly resistive. Individual motor or lamp loads may have capacitors for power factor correction, or larger sets of capacitors (usually with automatic switching devices) may be installed at a load center within a building or in a large utility substation.


When an inductive circuit is opened, the current through the inductance collapses quickly, creating a large voltage across the open circuit of the switch or relay. If the inductance is large enough, the energy will generate a spark, causing the contact points to oxidize, deteriorate, or sometimes weld together, or destroying a solid-state switch. A snubber capacitor across the newly opened circuit creates a path for this impulse to bypass the contact points, thereby preserving their life; these were commonly found in contact breaker ignition systems, for instance. Similarly, in smaller scale circuits, the spark may not be enough to damage the switch but will still radiate undesirable radio frequency interference (RFI), which a filter capacitor absorbs. Snubber capacitors are usually employed with a low-value resistor in series, to dissipate energy and minimize RFI. Such resistor-capacitor combinations are available in a single package.


In single phase squirrel cage motors, the primary winding within the motor housing is not capable of starting a rotational motion on the rotor, but is capable of sustaining one. To start the motor, a secondary "start" winding has a series non-polarized starting capacitor to introduce a lead in the sinusoidal current. When the secondary (start) winding is placed at an angle with respect to the primary (run) winding, a rotating electric field is created. The force of the rotational field is not constant, but is sufficient to start the rotor spinning. When the rotor comes close to operating speed, a centrifugal switch (or current-sensitive relay in series with the main winding) disconnects the capacitor. The start capacitor is typically mounted to the side of the motor housing. These are called capacitor-start motors, that have relatively high starting torque. Typically they can have up-to four times as much starting torque than a split-phase motor and are used on applications such as compressors, pressure washers and any small device requiring high starting torques.


Capacitors may retain a charge long after power is removed from a circuit; this charge can cause dangerous or even potentially fatal shocks or damage connected equipment. For example, even a seemingly innocuous device such as a disposable-camera flash unit, powered by a 1.5 volt AA battery, has a capacitor which may contain over 15 joules of energy and be charged to over 300 volts. This is easily capable of delivering a shock. Service procedures for electronic devices usually include instructions to discharge large or high-voltage capacitors, for instance using a Brinkley stick. Capacitors may also have built-in discharge resistors to dissipate stored energy to a safe level within a few seconds after power is removed. High-voltage capacitors are stored with the terminals shorted, as protection from potentially dangerous voltages due to dielectric absorption or from transient voltages the capacitor may pick up from static charges or passing weather events.


Capacitors may catastrophically fail when subjected to voltages or currents beyond their rating, or as they reach their normal end of life. Dielectric or metal interconnection failures may create arcing that vaporizes the dielectric fluid, resulting in case bulging, rupture, or even an explosion. Capacitors used in RF or sustained high-current applications can overheat, especially in the center of the capacitor rolls. Capacitors used within high-energy capacitor banks can violently explode when a short in one capacitor causes sudden dumping of energy stored in the rest of the bank into the failing unit. High voltage vacuum capacitors can generate soft X-rays even during normal operation. Proper containment, fusing, and preventive maintenance can help to minimize these hazards.


The history of science is the study of the development of science and scientific knowledge, including both the natural sciences and social sciences. (The history of the arts and humanities is termed as the history of scholarship.) Science is a body of empirical, theoretical, and practical knowledge about the natural world, produced by scientists who emphasize the observation, explanation, and prediction of real world phenomena. Historiography of science, in contrast, often draws on the historical methods of both intellectual history and social history.


The English word scientist is relatively recent—first coined by William Whewell in the 19th century. Previously, people investigating nature called themselves natural philosophers. While empirical investigations of the natural world have been described since classical antiquity (for example, by Thales, Aristotle, and others), and scientific methods have been employed since the Middle Ages (for example, by Ibn al-Haytham, and Roger Bacon), the dawn of modern science is often traced back to the early modern period and in particular to the scientific revolution that took place in 16th- and 17th-century Europe. Scientific methods are considered to be so fundamental to modern science that some consider earlier inquiries into nature to be pre-scientific. Traditionally, historians of science have defined science sufficiently broadly to include those inquiries.


From the 18th century through late 20th century, the history of science, especially of the physical and biological sciences, was often presented in a progressive narrative in which true theories replaced false beliefs. More recent historical interpretations, such as those of Thomas Kuhn, tend to portray the history of science in different terms, such as that of competing paradigms or conceptual systems in a wider matrix that includes intellectual, cultural, economic and political themes outside of science.


The development of writing enabled knowledge to be stored and communicated across generations with much greater fidelity. Combined with the development of agriculture, which allowed for a surplus of food, it became possible for early civilizations to develop, because more time and effort could be devoted to tasks (other than food production) than hunter-gatherers or early subsistence farmers had available. This surplus allowed a community to support individuals who did things other than work towards bare survival. These other tasks included systematic studies of nature, study of written information gathered and recorded by others, and often of adding to that body of information.


Ancient Egypt made significant advances in astronomy, mathematics and medicine. Their development of geometry was a necessary outgrowth of surveying to preserve the layout and ownership of farmland, which was flooded annually by the Nile river. The 3-4-5 right triangle and other rules of thumb were used to build rectilinear structures, and the post and lintel architecture of Egypt. Egypt was also a center of alchemy research for much of the Mediterranean.The Edwin Smith papyrus is one of the first medical documents still extant, and perhaps the earliest document that attempts to describe and analyse the brain: it might be seen as the very beginnings of modern neuroscience. However, while Egyptian medicine had some effective practices, it was not without its ineffective and sometimes harmful practices. Medical historians believe that ancient Egyptian pharmacology, for example, was largely ineffective. Nevertheless, it applies the following components to the treatment of disease: examination, diagnosis, treatment, and prognosis, which display strong parallels to the basic empirical method of science and according to G. E. R. Lloyd played a significant role in the development of this methodology. The Ebers papyrus (c. 1550 BC) also contains evidence of traditional empiricism.


From their beginnings in Sumer (now Iraq) around 3500 BC, the Mesopotamian people began to attempt to record some observations of the world with numerical data. But their observations and measurements were seemingly taken for purposes other than for elucidating scientific laws. A concrete instance of Pythagoras' law was recorded, as early as the 18th century BC: the Mesopotamian cuneiform tablet Plimpton 322 records a number of Pythagorean triplets (3,4,5) (5,12,13). ..., dated 1900 BC, possibly millennia before Pythagoras,  but an abstract formulation of the Pythagorean theorem was not.


In Babylonian astronomy, records of the motions of the stars, planets, and the moon are left on thousands of clay tablets created by scribes. Even today, astronomical periods identified by Mesopotamian proto-scientists are still widely used in Western calendars such as the solar year and the lunar month. Using these data they developed arithmetical methods to compute the changing length of daylight in the course of the year and to predict the appearances and disappearances of the Moon and planets and eclipses of the Sun and Moon. Only a few astronomers' names are known, such as that of Kidinnu, a Chaldean astronomer and mathematician. Kiddinu's value for the solar year is in use for today's calendars. Babylonian astronomy was "the first and highly successful attempt at giving a refined mathematical description of astronomical phenomena." According to the historian A. Aaboe, "all subsequent varieties of scientific astronomy, in the Hellenistic world, in India, in Islam, and in the West—if not indeed all subsequent endeavour in the exact sciences—depend upon Babylonian astronomy in decisive and fundamental ways."


In Classical Antiquity, the inquiry into the workings of the universe took place both in investigations aimed at such practical goals as establishing a reliable calendar or determining how to cure a variety of illnesses and in those abstract investigations known as natural philosophy. The ancient people who are considered the first scientists may have thought of themselves as natural philosophers, as practitioners of a skilled profession (for example, physicians), or as followers of a religious tradition (for example, temple healers).


The earliest Greek philosophers, known as the pre-Socratics, provided competing answers to the question found in the myths of their neighbors: "How did the ordered cosmos in which we live come to be?" The pre-Socratic philosopher Thales (640-546 BC), dubbed the "father of science", was the first to postulate non-supernatural explanations for natural phenomena, for example, that land floats on water and that earthquakes are caused by the agitation of the water upon which the land floats, rather than the god Poseidon. Thales' student Pythagoras of Samos founded the Pythagorean school, which investigated mathematics for its own sake, and was the first to postulate that the Earth is spherical in shape. Leucippus (5th century BC) introduced atomism, the theory that all matter is made of indivisible, imperishable units called atoms. This was greatly expanded by his pupil Democritus.


Subsequently, Plato and Aristotle produced the first systematic discussions of natural philosophy, which did much to shape later investigations of nature. Their development of deductive reasoning was of particular importance and usefulness to later scientific inquiry. Plato founded the Platonic Academy in 387 BC, whose motto was "Let none unversed in geometry enter here", and turned out many notable philosophers. Plato's student Aristotle introduced empiricism and the notion that universal truths can be arrived at via observation and induction, thereby laying the foundations of the scientific method. Aristotle also produced many biological writings that were empirical in nature, focusing on biological causation and the diversity of life. He made countless observations of nature, especially the habits and attributes of plants and animals in the world around him, classified more than 540 animal species, and dissected at least 50. Aristotle's writings profoundly influenced subsequent Islamic and European scholarship, though they were eventually superseded in the Scientific Revolution.


The important legacy of this period included substantial advances in factual knowledge, especially in anatomy, zoology, botany, mineralogy, geography, mathematics and astronomy; an awareness of the importance of certain scientific problems, especially those related to the problem of change and its causes; and a recognition of the methodological importance of applying mathematics to natural phenomena and of undertaking empirical research. In the Hellenistic age scholars frequently employed the principles developed in earlier Greek thought: the application of mathematics and deliberate empirical research, in their scientific investigations. Thus, clear unbroken lines of influence lead from ancient Greek and Hellenistic philosophers, to medieval Muslim philosophers and scientists, to the European Renaissance and Enlightenment, to the secular sciences of the modern day. Neither reason nor inquiry began with the Ancient Greeks, but the Socratic method did, along with the idea of Forms, great advances in geometry, logic, and the natural sciences. According to Benjamin Farrington, former Professor of Classics at Swansea University:


The astronomer Aristarchus of Samos was the first known person to propose a heliocentric model of the solar system, while the geographer Eratosthenes accurately calculated the circumference of the Earth. Hipparchus (c. 190 – c. 120 BC) produced the first systematic star catalog. The level of achievement in Hellenistic astronomy and engineering is impressively shown by the Antikythera mechanism (150-100 BC), an analog computer for calculating the position of planets. Technological artifacts of similar complexity did not reappear until the 14th century, when mechanical astronomical clocks appeared in Europe.


In Hellenistic Egypt, the mathematician Euclid laid down the foundations of mathematical rigor and introduced the concepts of definition, axiom, theorem and proof still in use today in his Elements, considered the most influential textbook ever written. Archimedes, considered one of the greatest mathematicians of all time, is credited with using the method of exhaustion to calculate the area under the arc of a parabola with the summation of an infinite series, and gave a remarkably accurate approximation of Pi. He is also known in physics for laying the foundations of hydrostatics, statics, and the explanation of the principle of the lever.


Theophrastus wrote some of the earliest descriptions of plants and animals, establishing the first taxonomy and looking at minerals in terms of their properties such as hardness. Pliny the Elder produced what is one of the largest encyclopedias of the natural world in 77 AD, and must be regarded as the rightful successor to Theophrastus. For example, he accurately describes the octahedral shape of the diamond, and proceeds to mention that diamond dust is used by engravers to cut and polish other gems owing to its great hardness. His recognition of the importance of crystal shape is a precursor to modern crystallography, while mention of numerous other minerals presages mineralogy. He also recognises that other minerals have characteristic crystal shapes, but in one example, confuses the crystal habit with the work of lapidaries. He was also the first to recognise that amber was a fossilized resin from pine trees because he had seen samples with trapped insects within them.


Mathematics: The earliest traces of mathematical knowledge in the Indian subcontinent appear with the Indus Valley Civilization (c. 4th millennium BC ~ c. 3rd millennium BC). The people of this civilization made bricks whose dimensions were in the proportion 4:2:1, considered favorable for the stability of a brick structure. They also tried to standardize measurement of length to a high degree of accuracy. They designed a ruler—the Mohenjo-daro ruler—whose unit of length (approximately 1.32 inches or 3.4 centimetres) was divided into ten equal parts. Bricks manufactured in ancient Mohenjo-daro often had dimensions that were integral multiples of this unit of length.


Indian astronomer and mathematician Aryabhata (476-550), in his Aryabhatiya (499) introduced a number of trigonometric functions (including sine, versine, cosine and inverse sine), trigonometric tables, and techniques and algorithms of algebra. In 628 AD, Brahmagupta suggested that gravity was a force of attraction. He also lucidly explained the use of zero as both a placeholder and a decimal digit, along with the Hindu-Arabic numeral system now used universally throughout the world. Arabic translations of the two astronomers' texts were soon available in the Islamic world, introducing what would become Arabic numerals to the Islamic World by the 9th century. During the 14th–16th centuries, the Kerala school of astronomy and mathematics made significant advances in astronomy and especially mathematics, including fields such as trigonometry and analysis. In particular, Madhava of Sangamagrama is considered the "founder of mathematical analysis".


Astronomy: The first textual mention of astronomical concepts comes from the Vedas, religious literature of India. According to Sarma (2008): "One finds in the Rigveda intelligent speculations about the genesis of the universe from nonexistence, the configuration of the universe, the spherical self-supporting earth, and the year of 360 days divided into 12 equal parts of 30 days each with a periodical intercalary month.". The first 12 chapters of the Siddhanta Shiromani, written by Bhāskara in the 12th century, cover topics such as: mean longitudes of the planets; true longitudes of the planets; the three problems of diurnal rotation; syzygies; lunar eclipses; solar eclipses; latitudes of the planets; risings and settings; the moon's crescent; conjunctions of the planets with each other; conjunctions of the planets with the fixed stars; and the patas of the sun and moon. The 13 chapters of the second part cover the nature of the sphere, as well as significant astronomical and trigonometric calculations based on it.


Medicine: Findings from Neolithic graveyards in what is now Pakistan show evidence of proto-dentistry among an early farming culture. Ayurveda is a system of traditional medicine that originated in ancient India before 2500 BC, and is now practiced as a form of alternative medicine in other parts of the world. Its most famous text is the Suśrutasamhitā of Suśruta, which is notable for describing procedures on various forms of surgery, including rhinoplasty, the repair of torn ear lobes, perineal lithotomy, cataract surgery, and several other excisions and other surgical procedures.


Mathematics: From the earliest the Chinese used a positional decimal system on counting boards in order to calculate. To express 10, a single rod is placed in the second box from the right. The spoken language uses a similar system to English: e.g. four thousand two hundred seven. No symbol was used for zero. By the 1st century BC, negative numbers and decimal fractions were in use and The Nine Chapters on the Mathematical Art included methods for extracting higher order roots by Horner's method and solving linear equations and by Pythagoras' theorem. Cubic equations were solved in the Tang dynasty and solutions of equations of order higher than 3 appeared in print in 1245 AD by Ch'in Chiu-shao. Pascal's triangle for binomial coefficients was described around 1100 by Jia Xian.


Astronomy: Astronomical observations from China constitute the longest continuous sequence from any civilisation and include records of sunspots (112 records from 364 BC), supernovas (1054), lunar and solar eclipses. By the 12th century, they could reasonably accurately make predictions of eclipses, but the knowledge of this was lost during the Ming dynasty, so that the Jesuit Matteo Ricci gained much favour in 1601 by his predictions. By 635 Chinese astronomers had observed that the tails of comets always point away from the sun.


Seismology: To better prepare for calamities, Zhang Heng invented a seismometer in 132 CE which provided instant alert to authorities in the capital Luoyang that an earthquake had occurred in a location indicated by a specific cardinal or ordinal direction. Although no tremors could be felt in the capital when Zhang told the court that an earthquake had just occurred in the northwest, a message came soon afterwards that an earthquake had indeed struck 400 km (248 mi) to 500 km (310 mi) northwest of Luoyang (in what is now modern Gansu). Zhang called his device the 'instrument for measuring the seasonal winds and the movements of the Earth' (Houfeng didong yi 候风地动仪), so-named because he and others thought that earthquakes were most likely caused by the enormous compression of trapped air. See Zhang's seismometer for further details.


There are many notable contributors to the field of Chinese science throughout the ages. One of the best examples would be Shen Kuo (1031–1095), a polymath scientist and statesman who was the first to describe the magnetic-needle compass used for navigation, discovered the concept of true north, improved the design of the astronomical gnomon, armillary sphere, sight tube, and clepsydra, and described the use of drydocks to repair boats. After observing the natural process of the inundation of silt and the find of marine fossils in the Taihang Mountains (hundreds of miles from the Pacific Ocean), Shen Kuo devised a theory of land formation, or geomorphology. He also adopted a theory of gradual climate change in regions over time, after observing petrified bamboo found underground at Yan'an, Shaanxi province. If not for Shen Kuo's writing, the architectural works of Yu Hao would be little known, along with the inventor of movable type printing, Bi Sheng (990-1051). Shen's contemporary Su Song (1020–1101) was also a brilliant polymath, an astronomer who created a celestial atlas of star maps, wrote a pharmaceutical treatise with related subjects of botany, zoology, mineralogy, and metallurgy, and had erected a large astronomical clocktower in Kaifeng city in 1088. To operate the crowning armillary sphere, his clocktower featured an escapement mechanism and the world's oldest known use of an endless power-transmitting chain drive.


The Jesuit China missions of the 16th and 17th centuries "learned to appreciate the scientific achievements of this ancient culture and made them known in Europe. Through their correspondence European scientists first learned about the Chinese science and culture." Western academic thought on the history of Chinese technology and science was galvanized by the work of Joseph Needham and the Needham Research Institute. Among the technological accomplishments of China were, according to the British scholar Needham, early seismological detectors (Zhang Heng in the 2nd century), the water-powered celestial globe (Zhang Heng), matches, the independent invention of the decimal system, dry docks, sliding calipers, the double-action piston pump, cast iron, the blast furnace, the iron plough, the multi-tube seed drill, the wheelbarrow, the suspension bridge, the winnowing machine, the rotary fan, the parachute, natural gas as fuel, the raised-relief map, the propeller, the crossbow, and a solid fuel rocket, the multistage rocket, the horse collar, along with contributions in logic, astronomy, medicine, and other fields.


With the division of the Roman Empire, the Western Roman Empire lost contact with much of its past. In the Middle East, Greek philosophy was able to find some support under the newly created Arab Empire. With the spread of Islam in the 7th and 8th centuries, a period of Muslim scholarship, known as the Islamic Golden Age, lasted until the 13th century. This scholarship was aided by several factors. The use of a single language, Arabic, allowed communication without need of a translator. Access to Greek texts from the Byzantine Empire, along with Indian sources of learning, provided Muslim scholars a knowledge base to build upon.


Muslim scientists placed far greater emphasis on experiment than had the Greeks. This led to an early scientific method being developed in the Muslim world, where significant progress in methodology was made, beginning with the experiments of Ibn al-Haytham (Alhazen) on optics from c. 1000, in his Book of Optics. The law of refraction of light was known to the Persians. The most important development of the scientific method was the use of experiments to distinguish between competing scientific theories set within a generally empirical orientation, which began among Muslim scientists. Ibn al-Haytham is also regarded as the father of optics, especially for his empirical proof of the intromission theory of light. Some have also described Ibn al-Haytham as the "first scientist" for his development of the modern scientific method.


In mathematics, the Persian mathematician Muhammad ibn Musa al-Khwarizmi gave his name to the concept of the algorithm, while the term algebra is derived from al-jabr, the beginning of the title of one of his publications. What is now known as Arabic numerals originally came from India, but Muslim mathematicians did make several refinements to the number system, such as the introduction of decimal point notation. Sabian mathematician Al-Battani (850-929) contributed to astronomy and mathematics, while Persian scholar Al-Razi contributed to chemistry and medicine.


In astronomy, Al-Battani improved the measurements of Hipparchus, preserved in the translation of Ptolemy's Hè Megalè Syntaxis (The great treatise) translated as Almagest. Al-Battani also improved the precision of the measurement of the precession of the Earth's axis. The corrections made to the geocentric model by al-Battani, Ibn al-Haytham, Averroes and the Maragha astronomers such as Nasir al-Din al-Tusi, Mo'ayyeduddin Urdi and Ibn al-Shatir are similar to Copernican heliocentric model. Heliocentric theories may have also been discussed by several other Muslim astronomers such as Ja'far ibn Muhammad Abu Ma'shar al-Balkhi, Abu-Rayhan Biruni, Abu Said al-Sijzi, Qutb al-Din al-Shirazi, and Najm al-Dīn al-Qazwīnī al-Kātibī.


Ibn Sina (Avicenna) is regarded as the most influential philosopher of Islam. He pioneered the science of experimental medicine and was the first physician to conduct clinical trials. His two most notable works in medicine are the Kitāb al-shifāʾ ("Book of Healing") and The Canon of Medicine, both of which were used as standard medicinal texts in both the Muslim world and in Europe well into the 17th century. Amongst his many contributions are the discovery of the contagious nature of infectious diseases, and the introduction of clinical pharmacology.


An intellectual revitalization of Europe started with the birth of medieval universities in the 12th century. The contact with the Islamic world in Spain and Sicily, and during the Reconquista and the Crusades, allowed Europeans access to scientific Greek and Arabic texts, including the works of Aristotle, Ptolemy, Jābir ibn Hayyān, al-Khwarizmi, Alhazen, Avicenna, and Averroes. European scholars had access to the translation programs of Raymond of Toledo, who sponsored the 12th century Toledo School of Translators from Arabic to Latin. Later translators like Michael Scotus would learn Arabic in order to study these texts directly. The European universities aided materially in the translation and propagation of these texts and started a new infrastructure which was needed for scientific communities. In fact, European university put many works about the natural world and the study of nature at the center of its curriculum, with the result that the "medieval university laid far greater emphasis on science than does its modern counterpart and descendent."


At the beginning of the 13th century, there were reasonably accurate Latin translations of the main works of almost all the intellectually crucial ancient authors, allowing a sound transfer of scientific ideas via both the universities and the monasteries. By then, the natural philosophy contained in these texts began to be extended by notable scholastics such as Robert Grosseteste, Roger Bacon, Albertus Magnus and Duns Scotus. Precursors of the modern scientific method, influenced by earlier contributions of the Islamic world, can be seen already in Grosseteste's emphasis on mathematics as a way to understand nature, and in the empirical approach admired by Bacon, particularly in his Opus Majus. Pierre Duhem's provocative thesis of the Catholic Church's Condemnation of 1277 led to the study of medieval science as a serious discipline, "but no one in the field any longer endorses his view that modern science started in 1277". However, many scholars agree with Duhem's view that the Middle Ages were a period of important scientific developments.


The first half of the 14th century saw much important scientific work being done, largely within the framework of scholastic commentaries on Aristotle's scientific writings. William of Ockham introduced the principle of parsimony: natural philosophers should not postulate unnecessary entities, so that motion is not a distinct thing but is only the moving object and an intermediary "sensible species" is not needed to transmit an image of an object to the eye. Scholars such as Jean Buridan and Nicole Oresme started to reinterpret elements of Aristotle's mechanics. In particular, Buridan developed the theory that impetus was the cause of the motion of projectiles, which was a first step towards the modern concept of inertia. The Oxford Calculators began to mathematically analyze the kinematics of motion, making this analysis without considering the causes of motion.


In 1348, the Black Death and other disasters sealed a sudden end to the previous period of massive philosophic and scientific development. Yet, the rediscovery of ancient texts was improved after the Fall of Constantinople in 1453, when many Byzantine scholars had to seek refuge in the West. Meanwhile, the introduction of printing was to have great effect on European society. The facilitated dissemination of the printed word democratized learning and allowed a faster propagation of new ideas. New ideas also helped to influence the development of European science at this point: not least the introduction of Algebra. These developments paved the way for the Scientific Revolution, which may also be understood as a resumption of the process of scientific inquiry, halted at the start of the Black Death.


The renewal of learning in Europe, that began with 12th century Scholasticism, came to an end about the time of the Black Death, and the initial period of the subsequent Italian Renaissance is sometimes seen as a lull in scientific activity. The Northern Renaissance, on the other hand, showed a decisive shift in focus from Aristoteleian natural philosophy to chemistry and the biological sciences (botany, anatomy, and medicine). Thus modern science in Europe was resumed in a period of great upheaval: the Protestant Reformation and Catholic Counter-Reformation; the discovery of the Americas by Christopher Columbus; the Fall of Constantinople; but also the re-discovery of Aristotle during the Scholastic period presaged large social and political changes. Thus, a suitable environment was created in which it became possible to question scientific doctrine, in much the same way that Martin Luther and John Calvin questioned religious doctrine. The works of Ptolemy (astronomy) and Galen (medicine) were found not always to match everyday observations. Work by Vesalius on human cadavers found problems with the Galenic view of anatomy.


The willingness to question previously held truths and search for new answers resulted in a period of major scientific advancements, now known as the Scientific Revolution. The Scientific Revolution is traditionally held by most historians to have begun in 1543, when the books De humani corporis fabrica (On the Workings of the Human Body) by Andreas Vesalius, and also De Revolutionibus, by the astronomer Nicolaus Copernicus, were first printed. The thesis of Copernicus' book was that the Earth moved around the Sun. The period culminated with the publication of the Philosophiæ Naturalis Principia Mathematica in 1687 by Isaac Newton, representative of the unprecedented growth of scientific publications throughout Europe.


The Age of Enlightenment was a European affair. The 17th century "Age of Reason" opened the avenues to the decisive steps towards modern science, which took place during the 18th century "Age of Enlightenment". Directly based on the works of Newton, Descartes, Pascal and Leibniz, the way was now clear to the development of modern mathematics, physics and technology by the generation of Benjamin Franklin (1706–1790), Leonhard Euler (1707–1783), Mikhail Lomonosov (1711–1765) and Jean le Rond d'Alembert (1717–1783), epitomized in the appearance of Denis Diderot's Encyclopédie between 1751 and 1772. The impact of this process was not limited to science and technology, but affected philosophy (Immanuel Kant, David Hume), religion (the increasingly significant impact of science upon religion), and society and politics in general (Adam Smith, Voltaire), the French Revolution of 1789 setting a bloody cesura indicating the beginning of political modernity[citation needed]. The early modern period is seen as a flowering of the European Renaissance, in what is often known as the Scientific Revolution, viewed as a foundation of modern science.


The Romantic Movement of the early 19th century reshaped science by opening up new pursuits unexpected in the classical approaches of the Enlightenment. Major breakthroughs came in biology, especially in Darwin's theory of evolution, as well as physics (electromagnetism), mathematics (non-Euclidean geometry, group theory) and chemistry (organic chemistry). The decline of Romanticism occurred because a new movement, Positivism, began to take hold of the ideals of the intellectuals after 1840 and lasted until about 1880.


The scientific revolution is a convenient boundary between ancient thought and classical physics. Nicolaus Copernicus revived the heliocentric model of the solar system described by Aristarchus of Samos. This was followed by the first known model of planetary motion given by Johannes Kepler in the early 17th century, which proposed that the planets follow elliptical orbits, with the Sun at one focus of the ellipse. Galileo ("Father of Modern Physics") also made use of experiments to validate physical theories, a key element of the scientific method.


In 1687, Isaac Newton published the Principia Mathematica, detailing two comprehensive and successful physical theories: Newton's laws of motion, which led to classical mechanics; and Newton's Law of Gravitation, which describes the fundamental force of gravity. The behavior of electricity and magnetism was studied by Faraday, Ohm, and others during the early 19th century. These studies led to the unification of the two phenomena into a single theory of electromagnetism, by James Clerk Maxwell (known as Maxwell's equations).


The beginning of the 20th century brought the start of a revolution in physics. The long-held theories of Newton were shown not to be correct in all circumstances. Beginning in 1900, Max Planck, Albert Einstein, Niels Bohr and others developed quantum theories to explain various anomalous experimental results, by introducing discrete energy levels. Not only did quantum mechanics show that the laws of motion did not hold on small scales, but even more disturbingly, the theory of general relativity, proposed by Einstein in 1915, showed that the fixed background of spacetime, on which both Newtonian mechanics and special relativity depended, could not exist. In 1925, Werner Heisenberg and Erwin Schrödinger formulated quantum mechanics, which explained the preceding quantum theories. The observation by Edwin Hubble in 1929 that the speed at which galaxies recede positively correlates with their distance, led to the understanding that the universe is expanding, and the formulation of the Big Bang theory by Georges Lemaître.


In 1938 Otto Hahn and Fritz Strassmann discovered nuclear fission with radiochemical methods, and in 1939 Lise Meitner and Otto Robert Frisch wrote the first theoretical interpretation of the fission process, which was later improved by Niels Bohr and John A. Wheeler. Further developments took place during World War II, which led to the practical application of radar and the development and use of the atomic bomb. Though the process had begun with the invention of the cyclotron by Ernest O. Lawrence in the 1930s, physics in the postwar period entered into a phase of what historians have called "Big Science", requiring massive machines, budgets, and laboratories in order to test their theories and move into new frontiers. The primary patron of physics became state governments, who recognized that the support of "basic" research could often lead to technologies useful to both military and industrial applications. Currently, general relativity and quantum mechanics are inconsistent with each other, and efforts are underway to unify the two.


Modern chemistry emerged from the sixteenth through the eighteenth centuries through the material practices and theories promoted by alchemy, medicine, manufacturing and mining. A decisive moment came when 'chymistry' was distinguished from alchemy by Robert Boyle in his work The Sceptical Chymist, in 1661; although the alchemical tradition continued for some time after his work. Other important steps included the gravimetric experimental practices of medical chemists like William Cullen, Joseph Black, Torbern Bergman and Pierre Macquer and through the work of Antoine Lavoisier (Father of Modern Chemistry) on oxygen and the law of conservation of mass, which refuted phlogiston theory. The theory that all matter is made of atoms, which are the smallest constituents of matter that cannot be broken down without losing the basic chemical and physical properties of that matter, was provided by John Dalton in 1803, although the question took a hundred years to settle as proven. Dalton also formulated the law of mass relationships. In 1869, Dmitri Mendeleev composed his periodic table of elements on the basis of Dalton's discoveries.


The synthesis of urea by Friedrich Wöhler opened a new research field, organic chemistry, and by the end of the 19th century, scientists were able to synthesize hundreds of organic compounds. The later part of the 19th century saw the exploitation of the Earth's petrochemicals, after the exhaustion of the oil supply from whaling. By the 20th century, systematic production of refined materials provided a ready supply of products which provided not only energy, but also synthetic materials for clothing, medicine, and everyday disposable resources. Application of the techniques of organic chemistry to living organisms resulted in physiological chemistry, the precursor to biochemistry. The 20th century also saw the integration of physics and chemistry, with chemical properties explained as the result of the electronic structure of the atom. Linus Pauling's book on The Nature of the Chemical Bond used the principles of quantum mechanics to deduce bond angles in ever-more complicated molecules. Pauling's work culminated in the physical modelling of DNA, the secret of life (in the words of Francis Crick, 1953). In the same year, the Miller–Urey experiment demonstrated in a simulation of primordial processes, that basic constituents of proteins, simple amino acids, could themselves be built up from simpler molecules.


Geology existed as a cloud of isolated, disconnected ideas about rocks, minerals, and landforms long before it became a coherent science. Theophrastus' work on rocks, Peri lithōn, remained authoritative for millennia: its interpretation of fossils was not overturned until after the Scientific Revolution. Chinese polymath Shen Kua (1031–1095) first formulated hypotheses for the process of land formation. Based on his observation of fossils in a geological stratum in a mountain hundreds of miles from the ocean, he deduced that the land was formed by erosion of the mountains and by deposition of silt.


Geology did not undergo systematic restructuring during the Scientific Revolution, but individual theorists made important contributions. Robert Hooke, for example, formulated a theory of earthquakes, and Nicholas Steno developed the theory of superposition and argued that fossils were the remains of once-living creatures. Beginning with Thomas Burnet's Sacred Theory of the Earth in 1681, natural philosophers began to explore the idea that the Earth had changed over time. Burnet and his contemporaries interpreted Earth's past in terms of events described in the Bible, but their work laid the intellectual foundations for secular interpretations of Earth history.


Modern geology, like modern chemistry, gradually evolved during the 18th and early 19th centuries. Benoît de Maillet and the Comte de Buffon saw the Earth as much older than the 6,000 years envisioned by biblical scholars. Jean-Étienne Guettard and Nicolas Desmarest hiked central France and recorded their observations on some of the first geological maps. Aided by chemical experimentation, naturalists such as Scotland's John Walker, Sweden's Torbern Bergman, and Germany's Abraham Werner created comprehensive classification systems for rocks and minerals—a collective achievement that transformed geology into a cutting edge field by the end of the eighteenth century. These early geologists also proposed a generalized interpretations of Earth history that led James Hutton, Georges Cuvier and Alexandre Brongniart, following in the steps of Steno, to argue that layers of rock could be dated by the fossils they contained: a principle first applied to the geology of the Paris Basin. The use of index fossils became a powerful tool for making geological maps, because it allowed geologists to correlate the rocks in one locality with those of similar age in other, distant localities. Over the first half of the 19th century, geologists such as Charles Lyell, Adam Sedgwick, and Roderick Murchison applied the new technique to rocks throughout Europe and eastern North America, setting the stage for more detailed, government-funded mapping projects in later decades.


Midway through the 19th century, the focus of geology shifted from description and classification to attempts to understand how the surface of the Earth had changed. The first comprehensive theories of mountain building were proposed during this period, as were the first modern theories of earthquakes and volcanoes. Louis Agassiz and others established the reality of continent-covering ice ages, and "fluvialists" like Andrew Crombie Ramsay argued that river valleys were formed, over millions of years by the rivers that flow through them. After the discovery of radioactivity, radiometric dating methods were developed, starting in the 20th century. Alfred Wegener's theory of "continental drift" was widely dismissed when he proposed it in the 1910s, but new data gathered in the 1950s and 1960s led to the theory of plate tectonics, which provided a plausible mechanism for it. Plate tectonics also provided a unified explanation for a wide range of seemingly unrelated geological phenomena. Since 1970 it has served as the unifying principle in geology.


In 1847, Hungarian physician Ignác Fülöp Semmelweis dramatically reduced the occurrency of puerperal fever by simply requiring physicians to wash their hands before attending to women in childbirth. This discovery predated the germ theory of disease. However, Semmelweis' findings were not appreciated by his contemporaries and came into use only with discoveries by British surgeon Joseph Lister, who in 1865 proved the principles of antisepsis. Lister's work was based on the important findings by French biologist Louis Pasteur. Pasteur was able to link microorganisms with disease, revolutionizing medicine. He also devised one of the most important methods in preventive medicine, when in 1880 he produced a vaccine against rabies. Pasteur invented the process of pasteurization, to help prevent the spread of disease through milk and other foods.


Perhaps the most prominent, controversial and far-reaching theory in all of science has been the theory of evolution by natural selection put forward by the British naturalist Charles Darwin in his book On the Origin of Species in 1859. Darwin proposed that the features of all living things, including humans, were shaped by natural processes over long periods of time. The theory of evolution in its current form affects almost all areas of biology. Implications of evolution on fields outside of pure science have led to both opposition and support from different parts of society, and profoundly influenced the popular understanding of "man's place in the universe". In the early 20th century, the study of heredity became a major investigation after the rediscovery in 1900 of the laws of inheritance developed by the Moravian monk Gregor Mendel in 1866. Mendel's laws provided the beginnings of the study of genetics, which became a major field of research for both scientific and industrial research. By 1953, James D. Watson, Francis Crick and Maurice Wilkins clarified the basic structure of DNA, the genetic material for expressing life in all its forms. In the late 20th century, the possibilities of genetic engineering became practical for the first time, and a massive international effort began in 1990 to map out an entire human genome (the Human Genome Project).


The discipline of ecology typically traces its origin to the synthesis of Darwinian evolution and Humboldtian biogeography, in the late 19th and early 20th centuries. Equally important in the rise of ecology, however, were microbiology and soil science—particularly the cycle of life concept, prominent in the work Louis Pasteur and Ferdinand Cohn. The word ecology was coined by Ernst Haeckel, whose particularly holistic view of nature in general (and Darwin's theory in particular) was important in the spread of ecological thinking. In the 1930s, Arthur Tansley and others began developing the field of ecosystem ecology, which combined experimental soil science with physiological concepts of energy and the techniques of field biology. The history of ecology in the 20th century is closely tied to that of environmentalism; the Gaia hypothesis, first formulated in the 1960s, and spreading in the 1970s, and more recently the scientific-religious movement of Deep Ecology have brought the two closer together.


Political science is a late arrival in terms of social sciences[citation needed]. However, the discipline has a clear set of antecedents such as moral philosophy, political philosophy, political economy, history, and other fields concerned with normative determinations of what ought to be and with deducing the characteristics and functions of the ideal form of government. The roots of politics are in prehistory. In each historic period and in almost every geographic area, we can find someone studying politics and increasing political understanding.


In Western culture, the study of politics is first found in Ancient Greece. The antecedents of European politics trace their roots back even earlier than Plato and Aristotle, particularly in the works of Homer, Hesiod, Thucydides, Xenophon, and Euripides. Later, Plato analyzed political systems, abstracted their analysis from more literary- and history- oriented studies and applied an approach we would understand as closer to philosophy. Similarly, Aristotle built upon Plato's analysis to include historical empirical evidence in his analysis.


An ancient Indian treatise on statecraft, economic policy and military strategy by Kautilya and Viṣhṇugupta, who are traditionally identified with Chāṇakya (c. 350–-283 BCE). In this treatise, the behaviors and relationships of the people, the King, the State, the Government Superintendents, Courtiers, Enemies, Invaders, and Corporations are analysed and documented. Roger Boesche describes the Arthaśāstra as "a book of political realism, a book analysing how the political world does work and not very often stating how it ought to work, a book that frequently discloses to a king what calculating and sometimes brutal measures he must carry out to preserve the state and the common good."


With the fall of the Western Roman Empire, there arose a more diffuse arena for political studies. The rise of monotheism and, particularly for the Western tradition, Christianity, brought to light a new space for politics and political action[citation needed]. During the Middle Ages, the study of politics was widespread in the churches and courts. Works such as Augustine of Hippo's The City of God synthesized current philosophies and political traditions with those of Christianity, redefining the borders between what was religious and what was political. Most of the political questions surrounding the relationship between Church and State were clarified and contested in this period.


Historical linguistics emerged as an independent field of study at the end of the 18th century. Sir William Jones proposed that Sanskrit, Persian, Greek, Latin, Gothic, and Celtic languages all shared a common base. After Jones, an effort to catalog all languages of the world was made throughout the 19th century and into the 20th century. Publication of Ferdinand de Saussure's Cours de linguistique générale created the development of descriptive linguistics. Descriptive linguistics, and the related structuralism movement caused linguistics to focus on how language changes over time, instead of just describing the differences between languages. Noam Chomsky further diversified linguistics with the development of generative linguistics in the 1950s. His effort is based upon a mathematical model of language that allows for the description and prediction of valid syntax. Additional specialties such as sociolinguistics, cognitive linguistics, and computational linguistics have emerged from collaboration between linguistics and other disciplines.


The basis for classical economics forms Adam Smith's An Inquiry into the Nature and Causes of the Wealth of Nations, published in 1776. Smith criticized mercantilism, advocating a system of free trade with division of labour. He postulated an "invisible hand" that regulated economic systems made up of actors guided only by self-interest. Karl Marx developed an alternative economic theory, called Marxian economics. Marxian economics is based on the labor theory of value and assumes the value of good to be based on the amount of labor required to produce it. Under this assumption, capitalism was based on employers not paying the full value of workers labor to create profit. The Austrian school responded to Marxian economics by viewing entrepreneurship as driving force of economic development. This replaced the labor theory of value by a system of supply and demand.


In the 1920s, John Maynard Keynes prompted a division between microeconomics and macroeconomics. Under Keynesian economics macroeconomic trends can overwhelm economic choices made by individuals. Governments should promote aggregate demand for goods as a means to encourage economic expansion. Following World War II, Milton Friedman created the concept of monetarism. Monetarism focuses on using the supply and demand of money as a method for controlling economic activity. In the 1970s, monetarism has adapted into supply-side economics which advocates reducing taxes as a means to increase the amount of money available for economic expansion.


The above "history of economics" reflects modern economic textbooks and this means that the last stage of a science is represented as the culmination of its history (Kuhn, 1962). The "invisible hand" mentioned in a lost page in the middle of a chapter in the middle of the to "Wealth of Nations", 1776, advances as Smith's central message.[clarification needed] It is played down that this "invisible hand" acts only "frequently" and that it is "no part of his [the individual's] intentions" because competition leads to lower prices by imitating "his" invention. That this "invisible hand" prefers "the support of domestic to foreign industry" is cleansed—often without indication that part of the citation is truncated. The opening passage of the "Wealth" containing Smith's message is never mentioned as it cannot be integrated into modern theory: "Wealth" depends on the division of labour which changes with market volume and on the proportion of productive to Unproductive labor.


The end of the 19th century marks the start of psychology as a scientific enterprise. The year 1879 is commonly seen as the start of psychology as an independent field of study. In that year Wilhelm Wundt founded the first laboratory dedicated exclusively to psychological research (in Leipzig). Other important early contributors to the field include Hermann Ebbinghaus (a pioneer in memory studies), Ivan Pavlov (who discovered classical conditioning), William James, and Sigmund Freud. Freud's influence has been enormous, though more as cultural icon than a force in scientific psychology.


The final decades of the 20th century have seen the rise of a new interdisciplinary approach to studying human psychology, known collectively as cognitive science. Cognitive science again considers the mind as a subject for investigation, using the tools of psychology, linguistics, computer science, philosophy, and neurobiology. New methods of visualizing the activity of the brain, such as PET scans and CAT scans, began to exert their influence as well, leading some researchers to investigate the mind by investigating the brain, rather than cognition. These new forms of investigation assume that a wide understanding of the human mind is possible, and that such an understanding may be applied to other research domains, such as artificial intelligence.


Ibn Khaldun can be regarded as the earliest scientific systematic sociologist. The modern sociology, emerged in the early 19th century as the academic response to the modernization of the world. Among many early sociologists (e.g., Émile Durkheim), the aim of sociology was in structuralism, understanding the cohesion of social groups, and developing an "antidote" to social disintegration. Max Weber was concerned with the modernization of society through the concept of rationalization, which he believed would trap individuals in an "iron cage" of rational thought. Some sociologists, including Georg Simmel and W. E. B. Du Bois, utilized more microsociological, qualitative analyses. This microlevel approach played an important role in American sociology, with the theories of George Herbert Mead and his student Herbert Blumer resulting in the creation of the symbolic interactionism approach to sociology.


American sociology in the 1940s and 1950s was dominated largely by Talcott Parsons, who argued that aspects of society that promoted structural integration were therefore "functional". This structural functionalism approach was questioned in the 1960s, when sociologists came to see this approach as merely a justification for inequalities present in the status quo. In reaction, conflict theory was developed, which was based in part on the philosophies of Karl Marx. Conflict theorists saw society as an arena in which different groups compete for control over resources. Symbolic interactionism also came to be regarded as central to sociological thinking. Erving Goffman saw social interactions as a stage performance, with individuals preparing "backstage" and attempting to control their audience through impression management. While these theories are currently prominent in sociological thought, other approaches exist, including feminist theory, post-structuralism, rational choice theory, and postmodernism.


Computer science, built upon a foundation of theoretical linguistics, discrete mathematics, and electrical engineering, studies the nature and limits of computation. Subfields include computability, computational complexity, database design, computer networking, artificial intelligence, and the design of computer hardware. One area in which advances in computing have contributed to more general scientific development is by facilitating large-scale archiving of scientific data. Contemporary computer science typically distinguishes itself by emphasising mathematical 'theory' in contrast to the practical emphasis of software engineering.


As an academic field, history of science began with the publication of William Whewell's History of the Inductive Sciences (first published in 1837). A more formal study of the history of science as an independent discipline was launched by George Sarton's publications, Introduction to the History of Science (1927) and the Isis journal (founded in 1912). Sarton exemplified the early 20th-century view of the history of science as the history of great men and great ideas. He shared with many of his contemporaries a Whiggish belief in history as a record of the advances and delays in the march of progress. The history of science was not a recognized subfield of American history in this period, and most of the work was carried out by interested scientists and physicians rather than professional historians. With the work of I. Bernard Cohen at Harvard, the history of science became an established subdiscipline of history after 1945.


Much of the study of the history of science has been devoted to answering questions about what science is, how it functions, and whether it exhibits large-scale patterns and trends. The sociology of science in particular has focused on the ways in which scientists work, looking closely at the ways in which they "produce" and "construct" scientific knowledge. Since the 1960s, a common trend in science studies (the study of the sociology and history of science) has been to emphasize the "human component" of scientific knowledge, and to de-emphasize the view that scientific data are self-evident, value-free, and context-free. The field of Science and Technology Studies, an area that overlaps and often informs historical studies of science, focuses on the social context of science in both contemporary and historical periods.


Humboldtian science refers to the early 19th century approach of combining scientific field work with the age of Romanticism sensitivity, ethics and aesthetic ideals. It helped to install natural history as a separate field, gave base for ecology and was based on the role model of scientist, naturalist and explorer Alexander von Humboldt. The later 19th century positivism asserted that all authentic knowledge allows verification and that all authentic knowledge assumes that the only valid knowledge is scientific.


The mid 20th century saw a series of studies relying to the role of science in a social context, starting from Thomas Kuhn's The Structure of Scientific Revolutions in 1962. It opened the study of science to new disciplines by suggesting that the evolution of science was in part sociologically determined and that positivism did not explain the actual interactions and strategies of the human participants in science. As Thomas Kuhn put it, the history of science may be seen in more nuanced terms, such as that of competing paradigms or conceptual systems in a wider matrix that includes intellectual, cultural, economic and political themes outside of science. "Partly by selection and partly by distortion, the scientists of earlier ages are implicitly presented as having worked upon the same set of fixed problems and in accordance with the same set of fixed canons that the most recent revolution in scientific theory and method made seem scientific."


Further studies, e.g. Jerome Ravetz 1971 Scientific Knowledge and its Social Problems referred to the role of the scientific community, as a social construct, in accepting or rejecting (objective) scientific knowledge. The Science wars of the 1990 were about the influence of especially French philosophers, which denied the objectivity of science in general or seemed to do so. They described as well differences between the idealized model of a pure science and the actual scientific practice; while scientism, a revival of the positivism approach, saw in precise measurement and rigorous calculation the basis for finally settling enduring metaphysical and moral controversies. However, more recently some of the leading critical theorists have recognized that their postmodern deconstructions have at times been counter-productive, and are providing intellectual ammunition for reactionary interests. Bruno Latour noted that "dangerous extremists are using the very same argument of social construction to destroy hard-won evidence that could save our lives. Was I wrong to participate in the invention of this field known as science studies? Is it enough to say that we did not really mean what we meant?"


(デジモン Dejimon, branded as Digimon: Digital Monsters, stylized as DIGIMON), short for "Digital Monsters" (デジタルモンスター Dejitaru Monsutā), is a Japanese media franchise encompassing virtual pet toys, anime, manga, video games, films and a trading card game. The franchise focuses on Digimon creatures, which are monsters living in a "Digital World", a parallel universe that originated from Earth's various communication networks. In many incarnations, Digimon are raised by humans called "Digidestined" or "Tamers", and they team up to defeat evil Digimon and human villains who are trying to destroy the fabric of the Digital world.


The franchise was first created in 1997 as a series of virtual pets, akin to—and influenced in style by—the contemporary Tamagotchi or nano Giga Pet toys. The creatures were first designed to look cute and iconic even on the devices' small screens; later developments had them created with a harder-edged style influenced by American comics. The franchise gained momentum with its first anime incarnation, Digimon Adventure, and an early video game, Digimon World, both released in 1999. Several seasons of the anime and films based on them have aired, and the video game series has expanded into genres such as role-playing, racing, fighting, and MMORPGs. Other media forms have also been released.


Digimon was first conceived as a virtual pet toy in the vein of Tamagotchis and, as such, took influence from Tamagotchis' cute and round designs. The small areas of the screens (16 by 16 pixels) meant that character designers had to create monsters whose forms would be easily recognizable. As such, many of the early Digimon—including Tyrannomon, the first one ever created—were based on dinosaurs. Many further designs were created by Kenji Watanabe, who was brought in to help with the "X-Antibody" creatures and art for the Digimon collectible card game. Watanabe was one influenced by American comics, which were beginning to gain popularity in Japan, and as such began to make his characters look stronger and "cool." The character creation process, however, has for most of the franchise's history been collaborative and reliant on conversation and brainstorming.


Digimon hatch from types of eggs which are called Digi-Eggs (デジタマ, Dejitama?). In the English iterations of the franchise there is another type of Digi-Egg that can be used to digivolve, or transform, Digimon. This second type of Digi-Egg is called a Digimental (デジメンタル, Dejimentaru?) in Japanese. (This type of Digi-Egg was also featured as a major object throughout season 2 as a way of Digivolution available only to certain characters at certain points throughout the season.) They age via a process called "Digivolution" which changes their appearance and increases their powers. The effect of Digivolution, however, is not permanent in the partner Digimon of the main characters in the anime, and Digimon who have digivolved will most of the time revert to their previous form after a battle or if they are too weak to continue. Some Digimon act feral. Most, however, are capable of intelligence and human speech. They are able to digivolve by the use of Digivices that their human partners have. In some cases, as in the first series, the DigiDestined (known as the 'Chosen Children' in the original Japanese) had to find some special items such as crests and tags so the Digimon could digivolve into further stages of evolution known as Ultimate and Mega in the dub.


The first Digimon anime introduced the Digimon life cycle: They age in a similar fashion to real organisms, but do not die under normal circumstances because they are made of reconfigurable data, which can be seen throughout the show. Any Digimon that receives a fatal wound will dissolve into infinitesimal bits of data. The data then recomposes itself as a Digi-Egg, which will hatch when rubbed gently, and the Digimon goes through its life cycle again. Digimon who are reincarnated in this way will sometimes retain some or all their memories of their previous life. However, if a Digimon's data is completely destroyed, they will die.


Digimon started out as digital pets called "Digital Monsters", similar in style and concept to the Tamagotchi. It was planned by WiZ and released by Bandai on June 26, 1997. The toy began as the simple concept of a Tamagotchi mainly for boys. The V-Pet is similar to its predecessors, with the exceptions of being more difficult and being able to fight other Digimon v-pets. Every owner would start with a Baby Digimon, train it, evolve it, take care of it, and then have battles with other Digimon owners to see who was stronger. The Digimon pet had several evolution capabilities and abilities too, so many owners had different Digimon. In December, the second generation of Digital Monster was released, followed by a third edition in 1998.


"Digimon" are "Digital Monsters". According to the stories, they are inhabitants of the "DigiWorld", a manifestation of Earth's communication network. The stories tell of a group of mostly pre-teens, who accompany special Digimon born to defend their world (and ours) from various evil forces. To help them surmount the most difficult obstacles found within both realms, the Digimon have the ability to evolve (Digivolve) In this process, the Digimon change appearance and become much stronger, often changing in personality as well. The group of children who come in contact with the Digital World changes from series to series.


As of 2011, there have been six series — Digimon Adventure, the follow-up sequel Digimon Adventure 02, Digimon Tamers, Digimon Frontier, Digimon Data Squad and Digimon Fusion. The first two series take place in the same fictional universe, but the third, fourth, fifth and sixth each occupy their own unique world. Each series is commonly based on the original storyline but things are added to make them unique. However, in Tamers, the Adventure universe is referred to as a commercial enterprise — a trading card game in Japan, plus a show-within-a-show in the English dub. It also features an appearance by a character from the Adventure universe. In addition, each series has spawned assorted feature films. Digimon still shows popularity, as new card series, video games, and movies are still being produced and released: new card series include Eternal Courage, Hybrid Warriors, Generations, and Operation X; the video game, Digimon Rumble Arena 2; and the previously unreleased movies Revenge of Diaboromon, Runaway Locomon, Battle of Adventurers, and Island of Lost Digimon. In Japan, Digital Monster X-Evolution, the eighth TV movie, was released on January 3, 2005, and on December 23, 2005 at Jump Festa 2006, the fifth series, Digimon Savers was announced for Japan to begin airing after a three-year hiatus of the show. A sixth television series, Digimon Xros Wars, began airing in 2010, and was followed by a second season, which started on October 2, 2011 as a direct sequel to Digimon Xros Wars.


The first Digimon television series, which began airing on March 7, 1999 in Japan on Fuji TV and Kids Station and on August 14, 1999 in the United States on Fox Kids dubbed by Saban Entertainment for the North American English version. Its premise is a group of 7 kids who, while at summer camp, travel to the Digital World, inhabited by creatures known as Digital Monsters, or Digimon, learning they are chosen to be "DigiDestined" ("Chosen Children" in the Japanese version) to save both the Digital and Real World from evil. Each Kid was given a Digivice which selected them to be transported to the DigiWorld and was destined to be paired up with a Digimon Partner, such as Tai being paired up with Agumon and Matt with Gabumon. The children are helped by a mysterious man/digimon named Gennai, who helps them via hologram. The Digivices help their Digimon allies to Digivolve into stronger creatures in times of peril. The Digimon usually reached higher forms when their human partners are placed in dangerous situations, such as fighting the evil forces of Devimon, Etemon and Myotismon in their Champion forms. Later, each character discovered a crest that each belonged to a person; Tai the Crest of Courage, Matt the Crest of Friendship, Sora the Crest of Love, Izzy the Crest of Knowledge, Mimi the Crest of Sincerity, Joe the Crest of Reliability, T.K. the Crest of Hope, and later Kari the Crest of Light which allowed their Digimon to digivolve into their Ultimate forms. The group consisted of seven original characters: Taichi "Tai" Kamiya, Yamato "Matt" Ishida, Sora Takenouchi, Koushiro "Izzy" Izumi, Mimi Tachikawa, Joe Kido, and Takeru "T.K." Takaishi. Later on in the series, an eighth character was introduced: Hikari "Kari" Kamiya (who is Taichi's younger sister).