International Organization for Standardization
The International Organization for Standardization is an international standard-setting body composed of representatives from various national standards organizations. Founded on 23 February 1947, the organization promotes worldwide proprietary and commercial standards, it is headquartered in Geneva and works in 164 countries. It was one of the first organizations granted general consultative status with the United Nations Economic and Social Council; the International Organization for Standardization is an independent, non-governmental organization, the members of which are the standards organizations of the 164 member countries. It is the world's largest developer of voluntary international standards and facilitates world trade by providing common standards between nations. Over twenty thousand standards have been set covering everything from manufactured products and technology to food safety and healthcare. Use of the standards aids in the creation of products and services that are safe, reliable and of good quality.
The standards help businesses increase productivity while minimizing errors and waste. By enabling products from different markets to be directly compared, they facilitate companies in entering new markets and assist in the development of global trade on a fair basis; the standards serve to safeguard consumers and the end-users of products and services, ensuring that certified products conform to the minimum standards set internationally. The three official languages of the ISO are English and Russian; the name of the organization in French is Organisation internationale de normalisation, in Russian, Международная организация по стандартизации. ISO is not an acronym; the organization adopted ISO as its abbreviated name in reference to the Greek word isos, as its name in the three official languages would have different acronyms. During the founding meetings of the new organization, the Greek word explanation was not invoked, so this meaning may have been made public later. ISO gives this explanation of the name: "Because'International Organization for Standardization' would have different acronyms in different languages, our founders decided to give it the short form ISO.
ISO is derived from the Greek isos, meaning equal. Whatever the country, whatever the language, the short form of our name is always ISO."Both the name ISO and the ISO logo are registered trademarks, their use is restricted. The organization today known as ISO began in 1928 as the International Federation of the National Standardizing Associations, it was suspended in 1942 during World War II, but after the war ISA was approached by the formed United Nations Standards Coordinating Committee with a proposal to form a new global standards body. In October 1946, ISA and UNSCC delegates from 25 countries met in London and agreed to join forces to create the new International Organization for Standardization. ISO is a voluntary organization whose members are recognized authorities on standards, each one representing one country. Members meet annually at a General Assembly to discuss ISO's strategic objectives; the organization is coordinated by a Central Secretariat based in Geneva. A Council with a rotating membership of 20 member bodies provides guidance and governance, including setting the Central Secretariat's annual budget.
The Technical Management Board is responsible for over 250 technical committees, who develop the ISO standards. ISO has formed two joint committees with the International Electrotechnical Commission to develop standards and terminology in the areas of electrical and electronic related technologies. ISO/IEC Joint Technical Committee 1 was created in 1987 to "evelop, maintain and facilitate IT standards", where IT refers to information technology. ISO/IEC Joint Technical Committee 2 was created in 2009 for the purpose of "tandardization in the field of energy efficiency and renewable energy sources". ISO has 163 national members. ISO has three membership categories: Member bodies are national bodies considered the most representative standards body in each country; these are the only members of ISO. Correspondent members are countries; these members do not participate in standards promulgation. Subscriber members are countries with small economies, they can follow the development of standards. Participating members are called "P" members, as opposed to observing members, who are called "O" members.
ISO is funded by a combination of: Organizations that manage the specific projects or loan experts to participate in the technical work. Subscriptions from member bodies; these subscriptions are in proportion to each country's gross national trade figures. Sale of standards. ISO's main products are international standards. ISO publishes technical reports, technical specifications, publicly available specifications, technical corrigenda, guides. International standards These are designated using the format ISO nnnnn: Title, where nnnnn is the number of the standard, p is an optional part number, yyyy is the year published, Title describes the subject. IEC for International Electrotechnical Commission is included if the standard results from the work of ISO/IEC JTC1. ASTM is used for standards developed in cooperation with ASTM International. Yyyy and IS are not used for an incomplete or unpublished standard and may under some
Mathematics includes the study of such topics as quantity, structure and change. Mathematicians use patterns to formulate new conjectures; when mathematical structures are good models of real phenomena mathematical reasoning can provide insight or predictions about nature. Through the use of abstraction and logic, mathematics developed from counting, calculation and the systematic study of the shapes and motions of physical objects. Practical mathematics has been a human activity from as far back; the research required to solve mathematical problems can take years or centuries of sustained inquiry. Rigorous arguments first appeared in Greek mathematics, most notably in Euclid's Elements. Since the pioneering work of Giuseppe Peano, David Hilbert, others on axiomatic systems in the late 19th century, it has become customary to view mathematical research as establishing truth by rigorous deduction from appropriately chosen axioms and definitions. Mathematics developed at a slow pace until the Renaissance, when mathematical innovations interacting with new scientific discoveries led to a rapid increase in the rate of mathematical discovery that has continued to the present day.
Mathematics is essential in many fields, including natural science, medicine and the social sciences. Applied mathematics has led to new mathematical disciplines, such as statistics and game theory. Mathematicians engage in pure mathematics without having any application in mind, but practical applications for what began as pure mathematics are discovered later; the history of mathematics can be seen as an ever-increasing series of abstractions. The first abstraction, shared by many animals, was that of numbers: the realization that a collection of two apples and a collection of two oranges have something in common, namely quantity of their members; as evidenced by tallies found on bone, in addition to recognizing how to count physical objects, prehistoric peoples may have recognized how to count abstract quantities, like time – days, years. Evidence for more complex mathematics does not appear until around 3000 BC, when the Babylonians and Egyptians began using arithmetic and geometry for taxation and other financial calculations, for building and construction, for astronomy.
The most ancient mathematical texts from Mesopotamia and Egypt are from 2000–1800 BC. Many early texts mention Pythagorean triples and so, by inference, the Pythagorean theorem seems to be the most ancient and widespread mathematical development after basic arithmetic and geometry, it is in Babylonian mathematics that elementary arithmetic first appear in the archaeological record. The Babylonians possessed a place-value system, used a sexagesimal numeral system, still in use today for measuring angles and time. Beginning in the 6th century BC with the Pythagoreans, the Ancient Greeks began a systematic study of mathematics as a subject in its own right with Greek mathematics. Around 300 BC, Euclid introduced the axiomatic method still used in mathematics today, consisting of definition, axiom and proof, his textbook Elements is considered the most successful and influential textbook of all time. The greatest mathematician of antiquity is held to be Archimedes of Syracuse, he developed formulas for calculating the surface area and volume of solids of revolution and used the method of exhaustion to calculate the area under the arc of a parabola with the summation of an infinite series, in a manner not too dissimilar from modern calculus.
Other notable achievements of Greek mathematics are conic sections, trigonometry (Hipparchus of Nicaea, the beginnings of algebra. The Hindu–Arabic numeral system and the rules for the use of its operations, in use throughout the world today, evolved over the course of the first millennium AD in India and were transmitted to the Western world via Islamic mathematics. Other notable developments of Indian mathematics include the modern definition of sine and cosine, an early form of infinite series. During the Golden Age of Islam during the 9th and 10th centuries, mathematics saw many important innovations building on Greek mathematics; the most notable achievement of Islamic mathematics was the development of algebra. Other notable achievements of the Islamic period are advances in spherical trigonometry and the addition of the decimal point to the Arabic numeral system. Many notable mathematicians from this period were Persian, such as Al-Khwarismi, Omar Khayyam and Sharaf al-Dīn al-Ṭūsī. During the early modern period, mathematics began to develop at an accelerating pace in Western Europe.
The development of calculus by Newton and Leibniz in the 17th century revolutionized mathematics. Leonhard Euler was the most notable mathematician of the 18th century, contributing numerous theorems and discoveries; the foremost mathematician of the 19th century was the German mathematician Carl Friedrich Gauss, who made numerous contributions to fields such as algebra, differential geometry, matrix theory, number theory, statistics. In the early 20th century, Kurt Gödel transformed mathematics by publishing his incompleteness theorems, which show that any axiomatic system, consistent will contain unprovable propositions. Mathematics has since been extended, there has been a fruitful interaction between mathematics and science, to
An equator of a rotating spheroid is its zeroth circle of latitude. It is the imaginary line on the spheroid, equidistant from its poles, dividing it into northern and southern hemispheres. In other words, it is the intersection of the spheroid with the plane perpendicular to its axis of rotation and midway between its geographical poles. On Earth, the Equator is 21.3 % over land. Indonesia is the country straddling the greatest length of the equatorial line across both land and sea; the name is derived from medieval Latin word aequator, in the phrase circulus aequator diei et noctis, meaning ‘circle equalizing day and night’, from the Latin word aequare meaning ‘make equal’. The latitude of the Earth's equator is, by definition, 0° of arc; the Equator is one of the five notable circles of latitude on Earth. The Equator is the only line of latitude, a great circle — that is, one whose plane passes through the center of the globe; the plane of Earth's equator, when projected outwards to the celestial sphere, defines the celestial equator.
In the cycle of Earth's seasons, the equatorial plane runs through the Sun twice per year: on the equinoxes in March and September. To a person on Earth, the Sun appears to travel above the Equator at these times. Light rays from the Sun's center are perpendicular to Earth's surface at the point of solar noon on the Equator. Locations on the Equator experience the shortest sunrises and sunsets because the Sun's daily path is nearly perpendicular to the horizon for most of the year; the length of daylight is constant throughout the year. Earth bulges at the Equator. Sites near the Equator, such as the Guiana Space Centre in Kourou, French Guiana, are good locations for spaceports as they have a faster rotational speed than other latitudes. Since Earth rotates eastward, spacecraft must be launched eastward to take advantage of this Earth-boost of speed; the precise location of the Equator is not fixed. This effect must be accounted for in detailed geophysical measurements; the International Association of Geodesy and the International Astronomical Union have chosen to use an equatorial radius of 6,378.1366 kilometres.
This equatorial radius is in the 2003 and 2010 IERS Conventions. It is the equatorial radius used for the IERS 2003 ellipsoid. If it were circular, the length of the Equator would be 2π times the radius, namely 40,075.0142 kilometres. The GRS 80 as approved and adopted by the IUGG at its Canberra, Australia meeting of 1979 has an equatorial radius of 6,378.137 kilometres. The WGS 84, a standard for use in cartography and satellite navigation including GPS has an equatorial radius of 6,378.137 kilometres. For both GRS 80 and WGS 84, this results in a length for the Equator of 40,075.0167 km. The geographical mile is defined as one arc-minute of the Equator, so it has different values depending on which radius is assumed. For example, by WSG-84, the distance is 1,855.3248 metres, while by IAU-2000, it is 1,855.3257 metres. This is a difference of less than one millimetre over the total distance; the earth is modeled as a sphere flattened 0.336% along its axis. This makes the Equator 0.16% longer than a meridian.
The IUGG standard meridian is, to the nearest millimetre, 40,007.862917 kilometres, one arc-minute of, 1,852.216 metres, explaining the SI standardization of the nautical mile as 1,852 metres, more than 3 metres less than the geographical mile. The sea-level surface of the Earth is irregular, so the actual length of the Equator is not so easy to determine. Aviation Week and Space Technology on 9 October 1961 reported that measurements using the Transit IV-A satellite had shown the equatorial "diameter" from longitude 11° West to 169° East to be 1,000 feet greater than its "diameter" ninety degrees away; the Equator passes through the land of 11 countries. Starting at the Prime Meridian and heading eastwards, the Equator passes through: Despite its name, no part of Equatorial Guinea lies on the Equator. However, its island of Annobón is 155 km south of the Equator, the rest of the country lies to the north. Seasons result from the tilt of the Earth's axis compared to the plane of its revolution around the Sun.
Throughout the year the northern and southern hemispheres are alternately turned either toward or away from the sun depending on Earth's position in its orbit. The hemisphere turned toward the sun receives more sunlight and is in summer, while the other hemisphere receives less sun and is in winter. At the equinoxes, the Earth's axis
Video game development
Video game development is the process of creating a video game. The effort is undertaken by a developer, ranging from a single person to an international team dispersed across the globe. Development of traditional commercial PC and console games is funded by a publisher, can take several years to reach completion. Indie games take less time and money and can be produced by individuals and smaller developers; the independent game industry has been on the rise, facilitated by the growth of new online distribution systems such as Steam and Uplay, as well as the mobile game market for Android and iOS devices. The first video games, developed in the 1960s, were noncommercial, they were not available to the general public. Commercial game development began in the'70s with the advent of first-generation video game consoles and early home computers like the Apple I. At that time, owing to low costs and low capabilities of computers, a lone programmer could develop a full and complete game. However, in the late'80s and'90s, ever-increasing computer processing power and heightened expectations from gamers made it difficult for a single person to produce a mainstream console or PC game.
The average cost of producing a triple-A video game rose, from US$1–4 million in 2000, to over $5 million in 2006 to over $20 million by 2010. Mainstream commercial PC and console games are developed in phases: first, in pre-production, pitches and game design documents are written; the development of a complete game involves a team of 20–100 individuals with various responsibilities, including designers, artists and testers. Games are produced through the software development process. Games are developed as a creative outlet. Development is funded by a publisher. Well-made games bring profit more readily. However, it is important to estimate a game's financial requirements, such as development costs of individual features. Failing to provide clear implications of game's expectations may result in exceeding allocated budget. In fact, the majority of commercial games do not produce profit. Most developers cannot afford changing development schedule and require estimating their capabilities with available resources before production.
The game industry requires innovations, as publishers cannot profit from constant release of repetitive sequels and imitations. Every year new independent development companies open and some manage to develop hit titles. Many developers close down because they cannot find a publishing contract or their production is not profitable, it is difficult to start a new company due to high initial investment required. Growth of casual and mobile game market has allowed developers with smaller teams to enter the market. Once the companies become financially stable, they may expand to develop larger games. Most developers start small and expand their business. A developer receiving profit from a successful title may store up capital to expand and re-factor their company, as well as tolerate more failed deadlines. An average development budget for a multiplatform game is US$18-28M, with high-profile games exceeding $40M. In the early era of home computers and video game consoles in the early 1980s, a single programmer could handle all the tasks of developing a game — programming, graphical design, sound effects, etc.
It could take as little as six weeks to develop a game. However, the high user expectations and requirements of modern commercial games far exceed the capabilities of a single developer and require the splitting of responsibilities. A team of over a hundred people can be employed full-time for a single project. Game development, production, or design is a process that starts from an concept; the idea is based on a modification of an existing game concept. The game idea may fall within one or several genres. Designers experiment with different combinations of genres. A game designer writes an initial game proposal document, that describes the basic concept, feature list and story, target audience and schedule, staff and budget estimates. Different companies have different formal procedures and philosophies regarding game design and development. There is no standardized development method. A game developer may range from a single individual to a large multinational company. There are both publisher-owned studios.
Independent developers rely on financial support from a game publisher. They have to develop a game from concept to prototype without external funding; the formal game proposal is submitted to publishers, who may finance the game development from several months to years. The publisher would retain exclusive rights to distribute and market the game and would own the intellectual property rights for the game franchise. Publisher's company may own the developer's company, or it may have internal development studio; the publisher is the one who owns the game's intellectual property rights. All but the smallest developer companies work on several titles at once; this is necessary because of the time taken between shipping a game and receiving royalty payments, which may be between 6 and 18 months. Small companies may structure contracts, ask for advances on royalties, use shareware distribution, employ part-time workers and use other methods to meet payroll demands. Console manufacturers, such as Microsoft, Nintendo, or Sony, have a standard set of technical requirements that a game must conform to in order to be approved.
Additionally, the gam
An azimuth is an angular measurement in a spherical coordinate system. The vector from an observer to a point of interest is projected perpendicularly onto a reference plane; when used as a celestial coordinate, the azimuth is the horizontal direction of a star or other astronomical object in the sky. The star is the point of interest, the reference plane is the local area around an observer on Earth's surface, the reference vector points to true north; the azimuth is the star's vector on the horizontal plane. Azimuth is measured in degrees; the concept is used in navigation, engineering, mapping and ballistics. In land navigation, azimuth is denoted alpha, α, defined as a horizontal angle measured clockwise from a north base line or meridian. Azimuth has been more defined as a horizontal angle measured clockwise from any fixed reference plane or established base direction line. Today, the reference plane for an azimuth is true north, measured as a 0° azimuth, though other angular units can be used.
Moving clockwise on a 360 degree circle, east has azimuth 90°, south 180°, west 270°. There are exceptions: some navigation systems use south as the reference vector. Any direction can be the reference vector, as long as it is defined. Quite azimuths or compass bearings are stated in a system in which either north or south can be the zero, the angle may be measured clockwise or anticlockwise from the zero. For example, a bearing might be described as " south, thirty degrees east", abbreviated "S30°E", the bearing 30 degrees in the eastward direction from south, i.e. the bearing 150 degrees clockwise from north. The reference direction, stated first, is always north or south, the turning direction, stated last, is east or west; the directions are chosen so that the angle, stated between them, is positive, between zero and 90 degrees. If the bearing happens to be in the direction of one of the cardinal points, a different notation, e.g. "due east", is used instead. The cartographical azimuth can be calculated when the coordinates of 2 points are known in a flat plane: α = 180 π atan2 Remark that the reference axes are swapped relative to the mathematical polar coordinate system and that the azimuth is clockwise relative to the north.
This is the reason why the Y axis in the above formula are swapped. If the azimuth becomes negative, one can always add 360°; the formula in radians would be easier: α = atan2 Caveat: Most computer libraries reverse the order of the atan2 parameters. When the coordinates of one point, the distance L, the azimuth α to another point are known, one can calculate its coordinates: X 2 = X 1 + L sin α Y 2 = Y 1 + L cos α This is used in triangulation. We are standing at latitude φ 1, longitude zero. We can get a fair approximation by assuming the Earth is a sphere, in which case the azimuth α is given by tan α = sin L cos φ 1 tan φ 2 − sin φ 1 cos L A better approximation assumes the Earth is a slightly-squashed sphere. Normal-section azimuth is the angle measured at our viewpoint by a theodolite whose axis is perpendicular to the surface of the spheroid; the difference is immeasurably small. Various websites will calculate geodetic azimuth. Formulas for calculating geodetic azimuth are linked in the distance
A prime meridian is a meridian in a geographic coordinate system at which longitude is defined to be 0°. Together, a prime meridian and its anti-meridian form a great circle; this great circle divides e.g. Earth, into two hemispheres. If one uses directions of East and West from a defined prime meridian they can be called the Eastern Hemisphere and the Western Hemisphere. A prime meridian is arbitrary, unlike an equator, determined by the axis of rotation—and various conventions have been used or advocated in different regions and throughout history; the most used modern meridian is the IERS Reference Meridian. It is derived but deviates from the Greenwich Meridian, selected as an international standard in 1884; the notion of longitude was developed by the Greek Eratosthenes in Alexandria, Hipparchus in Rhodes, applied to a large number of cities by the geographer Strabo. But it was Ptolemy. Ptolemy used as his basis the "Fortunate Isles", a group of islands in the Atlantic which are associated with the Canary Islands, although his maps correspond more to the Cape Verde islands.
The main point is to be comfortably west of the western tip of Africa as negative numbers were not yet in use. His prime meridian corresponds to 18° 40' west of Winchester today. At that time the chief method of determining longitude was by using the reported times of lunar eclipses in different countries. Ptolemy's Geographia was first printed with maps at Bologna in 1477, many early globes in the 16th century followed his lead, but there was still a hope. Christopher Columbus reported that the compass pointed due north somewhere in mid-Atlantic, this fact was used in the important Treaty of Tordesillas of 1494 which settled the territorial dispute between Spain and Portugal over newly discovered lands; the Tordesillas line was settled at 370 leagues west of Cape Verde. This is shown in Diogo Ribeiro's 1529 map. São Miguel Island in the Azores was still used for the same reason as late as 1594 by Christopher Saxton, although by it had been shown that the zero magnetic deviation line did not follow a line of longitude.
In 1541, Mercator produced his famous 41 cm terrestrial globe and drew his prime meridian through Fuerteventura in the Canaries. His maps used the Azores, following the magnetic hypothesis, but by the time that Ortelius produced the first modern atlas in 1570, other islands such as Cape Verde were coming into use. In his atlas longitudes were counted from 0° to 360°, not 180°W to 180°E as is usual today; this practice was followed by navigators well into the 18th century. In 1634, Cardinal Richelieu used the westernmost island of the Canaries, Ferro, 19° 55' west of Paris, as the choice of meridian; the geographer Delisle decided to round this off to 20°, so that it became the meridian of Paris disguised. In the early 18th century the battle was on to improve the determination of longitude at sea, leading to the development of the marine chronometer by John Harrison, but it was the development of accurate star charts, principally by the first British Astronomer Royal, John Flamsteed between 1680 and 1719 and disseminated by his successor Edmund Halley, that enabled navigators to use the lunar method of determining longitude more using the octant developed by Thomas Godfrey and John Hadley.
Between 1765 and 1811, Nevil Maskelyne published 49 issues of the Nautical Almanac based on the meridian of the Royal Observatory, Greenwich. "Maskelyne's tables not only made the lunar method practicable, they made the Greenwich meridian the universal reference point. The French translations of the Nautical Almanac retained Maskelyne's calculations from Greenwich—in spite of the fact that every other table in the Connaissance des Temps considered the Paris meridian as the prime." In 1884, at the International Meridian Conference in Washington, D. C. 22 countries voted to adopt the Greenwich meridian as the prime meridian of the world. The French argued for a neutral line, mentioning the Azores and the Bering Strait, but abstained and continued to use the Paris meridian until 1911. In October 1884 the Greenwich Meridian was selected by delegates to the International Meridian Conference held in Washington, D. C. United States to be the common zero of longitude and standard of time reckoning throughout the world.
The modern prime meridian, the IERS Reference Meridian, is placed near this meridian and is the prime meridian that has the widest use. The modern prime meridian, based at the Royal Observatory, was established by Sir George Airy in 1851; the position of the Greenwich Meridian has been defined by the location of the Airy Transit Circle since the first observation was taken with it by Sir George Airy in 1851. Prior to that, it was defined by a succession of earlier transit instruments, the first of, acquired by the second Astronomer Royal, Edmond Halley in 1721, it was set up in the extreme north-west corner of the Observatory between Flamsteed House and the Western Summer House. This spot, now subsumed into Flamsteed House, is 43 metres to the west of the Airy Transit Circle, a distance equivalent to 0.15 seconds of time. It was Airy's transit circle, adopted in principle as the Prime Meridian of th
A loudspeaker is an electroacoustic transducer. The most used type of speaker in the 2010s is the dynamic speaker, invented in 1925 by Edward W. Kellogg and Chester W. Rice; the dynamic speaker operates on the same basic principle as a dynamic microphone, but in reverse, to produce sound from an electrical signal. When an alternating current electrical audio signal is applied to its voice coil, a coil of wire suspended in a circular gap between the poles of a permanent magnet, the coil is forced to move back and forth due to Faraday's law of induction, which causes a diaphragm attached to the coil to move back and forth, pushing on the air to create sound waves. Besides this most common method, there are several alternative technologies that can be used to convert an electrical signal into sound; the sound source must be amplified or strengthened with an audio power amplifier before the signal is sent to the speaker. Speakers are housed in a speaker enclosure or speaker cabinet, a rectangular or square box made of wood or sometimes plastic.
The enclosure's materials and design play an important role in the quality of the sound. Where high fidelity reproduction of sound is required, multiple loudspeaker transducers are mounted in the same enclosure, each reproducing a part of the audible frequency range. In this case the individual speakers are referred to as "drivers" and the entire unit is called a loudspeaker. Drivers made for reproducing high audio frequencies are called tweeters, those for middle frequencies are called mid-range drivers, those for low frequencies are called woofers. Smaller loudspeakers are found in devices such as radios, portable audio players and electronic musical instruments. Larger loudspeaker systems are used for music, sound reinforcement in theatres and concerts, in public address systems; the term "loudspeaker" may refer to individual transducers or to complete speaker systems consisting of an enclosure including one or more drivers. To adequately reproduce a wide range of frequencies with coverage, most loudspeaker systems employ more than one driver for higher sound pressure level or maximum accuracy.
Individual drivers are used to reproduce different frequency ranges. The drivers are named subwoofers; the terms for different speaker drivers differ, depending on the application. In two-way systems there is no mid-range driver, so the task of reproducing the mid-range sounds falls upon the woofer and tweeter. Home stereos use the designation "tweeter" for the high frequency driver, while professional concert systems may designate them as "HF" or "highs"; when multiple drivers are used in a system, a "filter network", called a crossover, separates the incoming signal into different frequency ranges and routes them to the appropriate driver. A loudspeaker system with n separate frequency bands is described as "n-way speakers": a two-way system will have a woofer and a tweeter. Loudspeaker driver of the type pictured are termed "dynamic" to distinguish them from earlier drivers, or speakers using piezoelectric or electrostatic systems, or any of several other sorts. Johann Philipp Reis installed an electric loudspeaker in his telephone in 1861.
Alexander Graham Bell patented his first electric loudspeaker as part of his telephone in 1876, followed in 1877 by an improved version from Ernst Siemens. During this time, Thomas Edison was issued a British patent for a system using compressed air as an amplifying mechanism for his early cylinder phonographs, but he settled for the familiar metal horn driven by a membrane attached to the stylus. In 1898, Horace Short patented a design for a loudspeaker driven by compressed air. A few companies, including the Victor Talking Machine Company and Pathé, produced record players using compressed-air loudspeakers. However, these designs were limited by their poor sound quality and their inability to reproduce sound at low volume. Variants of the system were used for public address applications, more other variations have been used to test space-equipment resistance to the loud sound and vibration levels that the launching of rockets produces; the first experimental moving-coil loudspeaker was invented by Oliver Lodge in 1898.
The first practical moving-coil loudspeakers were manufactured by Danish engineer Peter L. Jensen and Edwin Pridham in 1915, in Napa, California. Like previous loudspeakers these used horns to amplify the sound produced by a small diaphragm. Jensen was denied patents. Being unsuccessful in selling their product to telephone companies, in 1915 they changed their target market to radios and public address systems, named their product Magnavox. Jensen was, for years after the invention of a part owner of The Magnavox Company; the moving-coil principle used today in speakers was patented in 1924 by Chester W. Rice and Edward W. Kellogg; the key difference between previous attempts and the patent by Rice and Kell