The stator is the stationary part of a rotary system, found in electric generators, electric motors, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric motor, the stator provides a rotating magnetic field that drives the rotating armature. In fluid powered devices, the stator guides the flow of fluid to or from the rotating part of the system. Depending on the configuration of a spinning electromotive device the stator may act as the field magnet, interacting with the armature to create motion, or it may act as the armature, receiving its influence from moving field coils on the rotor; the first DC generators and DC motors put the field coils on the stator, the power generation or motive reaction coils on the rotor. This is necessary because a continuously moving power switch known as the commutator is needed to keep the field aligned across the spinning rotor; the commutator must become more robust as the current increases.
The stator of these devices may be either an electromagnet. Where the stator is an electromagnet, the coil which energizes it is known as the field coil or field winding; the coil can be aluminum. To reduce loading losses in motors, manufacturers invariably use copper as the conducting material in windings. Aluminum, because of its lower electrical conductivity, may be an alternate material in fractional horsepower motors when the motors are used for short durations. An AC alternator is able to produce power across multiple high-current power generation coils connected in parallel, eliminating the need for the commutator. Placing the field coils on the rotor allows for an inexpensive slip ring mechanism to transfer high-voltage, low current power to the rotating field coil, it consists of a steel frame enclosing a hollow cylindrical core. The laminations are to reduce eddy current losses. In a turbine, the stator element contains ports used to redirect the flow of fluid; such devices include the torque converter.
In a mechanical siren, the stator contains one or more rows of holes. A stator can be used to great effect to reduce the turbulence and rotational energy introduced by an axial turbine fan, creating a steady column of air with a lower Reynolds number
Lee de Forest
Lee de Forest was an American inventor, self-described "Father of Radio", a pioneer in the development of sound-on-film recording used for motion pictures. He had over 180 patents, but a tumultuous career—he boasted that he made lost, four fortunes, he was involved in several major patent lawsuits, spent a substantial part of his income on legal bills, was tried for mail fraud. His most famous invention, in 1906, was the three-element "Audion" vacuum tube, the first practical amplification device. Although De Forest had only a limited understanding of how it worked, it was the foundation of the field of electronics, making possible radio broadcasting, long distance telephone lines, talking motion pictures, among countless other applications. Lee de Forest was born in 1873 in Council Bluffs, the son of Anna Margaret and Henry Swift DeForest, he was a direct descendant of Jessé de Forest, the leader of a group of Walloon Huguenots who fled Europe in the 17th century due to religious persecution.
De Forest's father was a Congregational Church minister who hoped his son would become a pastor. In 1879 the elder de Forest became president of the American Missionary Association's Talladega College in Talladega, Alabama, a school "open to all of either sex, without regard to sect, race, or color", which educated African-Americans. Many of the local white citizens resented the school and its mission, Lee spent most of his youth in Talladega isolated from the white community, with several close friends among the black children of the town. De Forest prepared for college by attending Mount Hermon Boys' School in Mount Hermon, Massachusetts for two years, beginning in 1891. In 1893, he enrolled in a three-year course of studies at Yale University's Sheffield Scientific School in New Haven, Connecticut, on a $300 per year scholarship, established for relatives of David de Forest. Convinced that he was destined to become a famous—and rich—inventor, perpetually short of funds, he sought to interest companies with a series of devices and puzzles he created, expectantly submitted essays in prize competitions, all with little success.
After completing his undergraduate studies, in September 1896 de Forest began three years of postgraduate work. However, his electrical experiments had a tendency to blow fuses. After being warned to be more careful, he managed to douse the lights during an important lecture by Professor Charles Hastings, who responded by having de Forest expelled from Sheffield. With the outbreak of the Spanish–American War in 1898, de Forest enrolled in the Connecticut Volunteer Militia Battery as a bugler, but the war ended and he was mustered out without leaving the state, he completed his studies at Yale's Sloane Physics Laboratory, earning a Doctorate in 1899 with a dissertation on the "Reflection of Hertzian Waves from the Ends of Parallel Wires", supervised by theoretical physicist Willard Gibbs. De Forest was convinced there was a great future in radiotelegraphic communication, but Italian Guglielmo Marconi, who received his first patent in 1896, was making impressive progress in both Europe and the United States.
One drawback to Marconi's approach was his use of a coherer as a receiver, while providing for permanent records, was slow and not reliable. De Forest was determined to devise a better system, including a self-restoring detector that could receive transmissions by ear, thus making it capable of receiving weaker signals and allowing faster Morse code sending speeds. After making unsuccessful inquiries about employment with Nikola Tesla and Marconi, de Forest struck out on his own, his first job after leaving Yale was with the Western Electric Company's telephone lab in Chicago, Illinois. While there he developed his first receiver, based on findings by two German scientists, Drs. A. Neugschwender and Emil Aschkinass, their original design consisted of a mirror in which a narrow, moistened slit had been cut through the silvered back. Attaching a battery and telephone receiver, they could hear sound changes in response to radio signal impulses. De Forest, along with Ed Smythe, a co-worker who provided financial and technical help, developed variations they called "responders".
A series of short-term positions followed, including three unproductive months with Professor Warren S. Johnson's American Wireless Telegraph Company in Milwaukee and work as an assistant editor of the Western Electrician in Chicago. With radio research his main priority, de Forest next took a night teaching position at the Lewis Institute, which freed him to conduct experiments at the Armour Institute. By 1900, using a spark-coil transmitter and his responder receiver, de Forest expanded his transmitting range to about seven kilometers. Professor Clarence Freeman of the Armour Institute became interested in de Forest's work and developed a new type of spark transmitter. De Forest soon felt that Smythe and Freeman were holding him back, so in the fall of 1901 he made the bold decision to go to New York to compete directly with Marconi in transmitting race results for the International Yacht races. Marconi had made arrangements to provide reports for the Associated Press, which he had done for the 1899 contest.
De Forest contracted to do the same for the smaller Publishers' Press Association. The race effort turned out to be an total failure; the Freeman transmitter broke down — in a fit of rage, de Forest threw it overboard — and had to be replaced by an ordinary spark coil
World War II
World War II known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries; the major participants threw their entire economic and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China, it included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, the only use of nuclear weapons in war. Japan, which aimed to dominate Asia and the Pacific, was at war with China by 1937, though neither side had declared war on the other. World War II is said to have begun on 1 September 1939, with the invasion of Poland by Germany and subsequent declarations of war on Germany by France and the United Kingdom.
From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Finland and the Baltic states. Following the onset of campaigns in North Africa and East Africa, the fall of France in mid 1940, the war continued between the European Axis powers and the British Empire. War in the Balkans, the aerial Battle of Britain, the Blitz, the long Battle of the Atlantic followed. On 22 June 1941, the European Axis powers launched an invasion of the Soviet Union, opening the largest land theatre of war in history; this Eastern Front trapped most crucially the German Wehrmacht, into a war of attrition. In December 1941, Japan launched a surprise attack on the United States as well as European colonies in the Pacific. Following an immediate U. S. declaration of war against Japan, supported by one from Great Britain, the European Axis powers declared war on the U.
S. in solidarity with their Japanese ally. Rapid Japanese conquests over much of the Western Pacific ensued, perceived by many in Asia as liberation from Western dominance and resulting in the support of several armies from defeated territories; the Axis advance in the Pacific halted in 1942. Key setbacks in 1943, which included a series of German defeats on the Eastern Front, the Allied invasions of Sicily and Italy, Allied victories in the Pacific, cost the Axis its initiative and forced it into strategic retreat on all fronts. In 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained its territorial losses and turned toward Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in Central China, South China and Burma, while the Allies crippled the Japanese Navy and captured key Western Pacific islands; the war in Europe concluded with an invasion of Germany by the Western Allies and the Soviet Union, culminating in the capture of Berlin by Soviet troops, the suicide of Adolf Hitler and the German unconditional surrender on 8 May 1945.
Following the Potsdam Declaration by the Allies on 26 July 1945 and the refusal of Japan to surrender under its terms, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August respectively. With an invasion of the Japanese archipelago imminent, the possibility of additional atomic bombings, the Soviet entry into the war against Japan and its invasion of Manchuria, Japan announced its intention to surrender on 15 August 1945, cementing total victory in Asia for the Allies. Tribunals were set up by fiat by the Allies and war crimes trials were conducted in the wake of the war both against the Germans and the Japanese. World War II changed the political social structure of the globe; the United Nations was established to foster international co-operation and prevent future conflicts. The Soviet Union and United States emerged as rival superpowers, setting the stage for the nearly half-century long Cold War. In the wake of European devastation, the influence of its great powers waned, triggering the decolonisation of Africa and Asia.
Most countries whose industries had been damaged moved towards economic expansion. Political integration in Europe, emerged as an effort to end pre-war enmities and create a common identity; the start of the war in Europe is held to be 1 September 1939, beginning with the German invasion of Poland. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred and the two wars merged in 1941; this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935; the British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the fo
The Earth–ionosphere waveguide refers to the phenomenon in which certain radio waves can propagate in the space between the ground and the boundary of the ionosphere. Because the ionosphere contains charged particles, it can behave as a conductor; the earth operates as a ground plane, the resulting cavity behaves as a large waveguide. Low frequency and low frequency signals can propagate efficiently in this waveguide. For instance, lightning strikes launch a signal called radio atmospherics, which can travel many thousands of miles, because they are confined between the Earth and the ionosphere; the round-the-world nature of the waveguide produces resonances, like a cavity. Radio propagation within the ionosphere depends on frequency, angle of incidence, time of day, Earth's magnetic field, solar activity. At vertical incidence, waves with frequencies larger than the electron plasma frequency of the F-layer maximum fe = 9 1/2 kHz can propagate through the ionosphere nearly undisturbed. Waves with frequencies smaller than fe are reflected within the ionospheric D-, E-, F-layers.
Fe is of the order of 8–15 MHz during day time conditions. For oblique incidence, the critical frequency becomes larger. Low frequencies, low frequencies are reflected at the ionospheric D- and lower E-layer. An exception is whistler propagation of lightning signals along the geomagnetic field lines; the wavelengths of VLF waves are comparable with the height of the ionospheric D-layer. Therefore, ray theory is only applicable for propagation over short distances, while mode theory must be used for larger distances; the region between Earth's surface and the ionospheric D-layer behaves thus like a waveguide for VLF- and ELF-waves. In the presence of the ionospheric plasma and the geomagnetic field, electromagnetic waves exist for frequencies which are larger than the gyrofrequency of the ions. Waves with frequencies smaller than the gyrofrequency are called hydromagnetic waves; the geomagnetic pulsations with periods of seconds to minutes as well as Alfvén waves belong to that type of waves. The prototype of a short vertical rod antenna is a vertical electric Hertz dipole in which electric alternating currents of frequency f flow.
Its radiation of electromagnetic waves within the Earth-ionospheric waveguide can be described by a transfer function T: Ez = T Eo where Ez is the vertical component of the electric field at the receiver in a distance ρ from the transmitter, Eo is the electric field of a Hertzian dipole in free space, ω = 2πf the angular frequency. In free space, it is T = 1. Evidently, the Earth–ionosphere waveguide is dispersive because the transfer function depends on frequency; this means that phase- and group velocity of the waves are frequency dependent. In the VLF range, the transfer function is the sum of a ground wave which arrives directly at the receiver and multihop sky waves reflected at the ionospheric D-layer. For the real Earth's surface, the ground wave becomes dissipated and depends of the orography along the ray path. For VLF waves at shorter distances, this effect is, however, of minor importance, the reflection factor of the Earth is Re = 1, in a first approximation. At shorter distances, only the first hop sky wave is of importance.
The D-layer can be simulated by a magnetic wall with a fixed boundary at a virtual height h, which means a phase jump of 180° at the reflection point. In reality, the electron density of the D-layer increases with altitude, the wave is bounded as shown in Figure 2; the sum of ground wave and first hop wave displays an interference pattern with interference minima if the difference between the ray paths of ground and first sky wave is half a wavelength. The last interference minimum on the ground between the ground wave and the first sky wave is at a horizontal distance of ρ1 ≈ 2 f h2/c with c the velocity of light. In the example of Figure 3, this is at about 500 km distance; the theory of ray propagation of VLF waves breaks down at larger distances because in the sum of these waves successive multihop sky waves are involved, the sum diverges. In addition, it becomes necessary to take into account the spherical Earth. Mode theory, the sum of eigen-modes in the Earth–ionosphere waveguide is valid in this range of distances.
The wave modes have fixed vertical structures of their vertical electric field components with maximum amplitudes at the bottom and zero amplitudes at the top of the waveguide. In the case of the fundamental first mode, it is a quarter wavelength. With decreasing frequency, the eigenvalue becomes imaginary at the cutoff frequency, where the mode changes to an evanescent wave. For the first mode, this happens at fco = c / ≈ 1 kHz below; the attenuation of the modes increases with wavenumber n. Therefore only the first two modes are involved in the wave propagation The first interference minimum between these two modes is at the same distance as that of the last interference minimum of ray theory indicating the equivalence of both theories As seen in Figure 3, the spacing between the mode interference minima is constant and about 1000 km in this example; the first mode becomes dominant at distances greater than about 1500 km, because the second mode is more attenuated than the first mode. In the range of ELF waves, only mode theory is appropriate.
The fundamental mode is the zeroth mode. The D-layer becomes here an electric wall (Ri
Long Island is a densely populated island off the East Coast of the United States, beginning at New York Harbor 0.35 miles from Manhattan Island and extending eastward into the Atlantic Ocean. The island comprises four counties in the U. S. state of New York. Kings and Queens Counties and Nassau County share the western third of the island, while Suffolk County occupies the eastern two-thirds. More than half of New York City's residents now live in Brooklyn and Queens. However, many people in the New York metropolitan area colloquially use the term Long Island to refer to Nassau and Suffolk Counties, which are suburban in character, conversely employing the term the City to mean Manhattan alone. Broadly speaking, "Long Island" may refer both to the main island and the surrounding outer barrier islands. North of the island is Long Island Sound, across which lie Westchester County, New York, the state of Connecticut. Across the Block Island Sound to the northeast is the state of Rhode Island. To the west, Long Island is separated from the island of Manhattan by the East River.
To the extreme southwest, it is separated from Staten Island and the state of New Jersey by Upper New York Bay, the Narrows, Lower New York Bay. To the east lie Block Island—which belongs to the State of Rhode Island—and numerous smaller islands. Both the longest and the largest island in the contiguous United States, Long Island extends 118 miles eastward from New York Harbor to Montauk Point, with a maximum north-to-south distance of 23 miles between Long Island Sound and the Atlantic coast. With a land area of 1,401 square miles, Long Island is the 11th-largest island in the United States and the 149th-largest island in the world—larger than the 1,214 square miles of the smallest U. S. state, Rhode Island. With a Census-estimated population of 7,869,820 in 2017, constituting nearly 40% of New York State's population, Long Island is the most populated island in any U. S. state or territory, the 18th-most populous island in the world. Its population density is 5,595.1 inhabitants per square mile.
If Long Island geographically constituted an independent metropolitan statistical area, it would rank fourth most populous in the United States. S. state, Long Island would rank 13th in population and first in population density. Long Island is culturally and ethnically diverse, featuring some of the wealthiest and most expensive neighborhoods in the Western Hemisphere near the shorelines as well as working-class areas in all four counties; as a hub of commercial aviation, Long Island contains two of the New York City metropolitan area's three busiest airports, JFK International Airport and LaGuardia Airport, in addition to Islip MacArthur Airport. Nine bridges and 13 tunnels connect Brooklyn and Queens to the three other boroughs of New York City. Ferries connect Suffolk County northward across Long Island Sound to the state of Connecticut; the Long Island Rail Road is the busiest commuter railroad in North America and operates 24/7. Nassau County high school students feature prominently as winners of the Intel International Science and Engineering Fair and similar STEM-based academic awards.
Biotechnology companies and scientific research play a significant role in Long Island's economy, including research facilities at Brookhaven National Laboratory, Cold Spring Harbor Laboratory, Plum Island Animal Disease Center, State University of New York at Stony Brook, the New York University Tandon School of Engineering, the City University of New York, Hofstra Northwell School of Medicine. Prior to European contact, the Lenape people inhabited the western end of Long Island, spoke the Munsee dialect of Lenape, one of the Algonquian language family. Giovanni da Verrazzano was the first European to record an encounter with the Lenapes, after entering what is now New York Bay in 1524; the eastern portion of the island was inhabited by speakers of the Mohegan-Montauk-Narragansett language group of Algonquian languages. In 1609, the English navigator Henry Hudson explored the harbor and purportedly landed at Coney Island. Adriaen Block followed in 1615, is credited as the first European to determine that both Manhattan and Long Island are islands.
Native American land deeds recorded by the Dutch from 1636 state that the Indians referred to Long Island as Sewanhaka. Sewan was one of the terms for wampum, is translated as "loose" or "scattered", which may refer either to the wampum or to Long Island; the name "'t Lange Eylandt alias Matouwacs" appears in Dutch maps from the 1650s. The English referred to the land as "Nassau Island", after the Dutch Prince William of Nassau, Prince of Orange, it is unclear. Another indigenous name from colonial time, comes from the Native American name for Long Island and means "the island that pays tribute." The first settlements on Long Island were by settlers from England and its colonies in present-day New England. Lion Gardiner settled nearby Gardiners Island. T
Wireless telegraphy means transmission of telegraph signals by radio waves. Before about 1910 when radio became dominant, the term wireless telegraphy was used for various other experimental technologies for transmitting telegraph signals without wires, such as electromagnetic induction, ground conduction telegraph systems. Radiotelegraphy was the first means of radio communication, it continued to be the only type of radio transmission during the first three decades of radio, called the "wireless telegraphy era" up until World War I, when the development of amplitude modulation radiotelephony allowed sound to be transmitted by radio. In radiotelegraphy, information is transmitted by pulses of radio waves of two different lengths called "dots" and "dashes", which spell out text messages in Morse code. In a manual system, the sending operator taps on a switch called a telegraph key which turns the transmitter on and off, producing the pulses of radio waves. At the receiver the pulses are audible in the receiver's speaker as beeps, which are translated back to text by an operator who knows Morse code.
Radiotelegraphy was used for long distance person-to-person commercial and military text communication throughout the first half of the 20th century. It became a strategically important capability during the two world wars, since a nation without long distance radiotelegraph stations could be isolated from the rest of the world by an enemy cutting its submarine telegraph cables. Beginning about 1908, powerful transoceanic radiotelegraphy stations transmitted commercial telegram traffic between countries at rates up to 200 words per minute. Radiotelegraphy was transmitted by several different modulation methods during its history; the primitive spark gap transmitters used until 1920 transmitted damped waves, which had large bandwidth and tended to interfere with other transmissions. This type of emission was banned by 1930; the vacuum tube transmitters which came into use after 1920 transmitted code by pulses of unmodulated sinusoidal carrier wave called continuous waves, still used today. To make CW transmissions audible, the receiver requires a circuit called a beat frequency oscillator.
A third type of modulation, frequency shift keying was used by radioteletypes. Morse code radiotelegraphy was replaced by radioteletype networks in most high volume applications by World War 2. Today it is nearly obsolete, the only remaining users are the radio amateur community and some limited training by the military for emergency use. Wireless telegraphy or radiotelegraphy called CW, ICW transmission, or on-off keying, designated by the International Telecommunication Union as emission type A1A, is a radio communication method in which the sending operator taps on a switch called a telegraph key, which turns the radio transmitter on and off, producing pulses of unmodulated carrier wave of different lengths called "dots" and "dashes", which encode characters of text in Morse code. At the receiving location the code is audible in the radio receiver's earphone or speaker as a sequence of buzzes or beeps, translated back to text by an operator who knows Morse code. Although this type of communication has been replaced since its introduction over 100 years ago by other means of communication it is still used by amateur radio operators as well as some military services.
A CW coastal station, KSM, still exists in California, run as a museum by volunteers, occasional contacts with ships are made. Radio beacons in the aviation service, but as "placeholders" for commercial ship-to-shore systems transmit Morse but at slow speeds; the US Federal Communications Commission issues a lifetime commercial Radiotelegraph Operator License. This requires passing a simple written test on regulations, a more complex written exam on technology, demonstrating Morse reception at 20 words per minute plain language and 16 wpm code groups. Wireless telegraphy is still used today by amateur radio hobbyists where it is referred to as radio telegraphy, continuous wave, or just CW. However, its knowledge is not required to obtain any class of amateur license. Continuous wave radiotelegraphy is regulated by the International Telecommunication Union as emission type A1A. Efforts to find a way to transmit telegraph signals without wires grew out of the success of electric telegraph networks, the first instant telecommunication systems.
Developed beginning in the 1830s, a telegraph line was a person-to-person text message system consisting of multiple telegraph offices linked by an overhead wire supported on telegraph poles. To send a message, an operator at one office would tap on a switch called a telegraph key, creating pulses of electric current which spelled out a message in Morse code; when the key was pressed, it would connect a battery to the telegraph line, sending current down the wire. At the receiving office the current pulses would operate a telegraph sounder, a device which would make a "click" sound when it received each pulse of current; the operator at the receiving station who knew Morse code would translate the clicking sounds to text and write down the message. The ground was used as the return path for current in the telegraph circuit, to avoid having to use a second overhead wire. By the 1860s, telegraph was the standard way to send most urgent commercial and milita
The Atlantic Ocean is the second largest of the world's oceans, with an area of about 106,460,000 square kilometers. It covers 20 percent of the Earth's surface and about 29 percent of its water surface area, it separates the "Old World" from the "New World". The Atlantic Ocean occupies an elongated, S-shaped basin extending longitudinally between Europe and Africa to the east, the Americas to the west; as one component of the interconnected global ocean, it is connected in the north to the Arctic Ocean, to the Pacific Ocean in the southwest, the Indian Ocean in the southeast, the Southern Ocean in the south. The Equatorial Counter Current subdivides it into the North Atlantic Ocean and the South Atlantic Ocean at about 8°N. Scientific explorations of the Atlantic include the Challenger expedition, the German Meteor expedition, Columbia University's Lamont-Doherty Earth Observatory and the United States Navy Hydrographic Office; the oldest known mentions of an "Atlantic" sea come from Stesichorus around mid-sixth century BC: Atlantikoi pelágei and in The Histories of Herodotus around 450 BC: Atlantis thalassa where the name refers to "the sea beyond the pillars of Heracles", said to be part of the sea that surrounds all land.
Thus, on one hand, the name refers to Atlas, the Titan in Greek mythology, who supported the heavens and who appeared as a frontispiece in Medieval maps and lent his name to modern atlases. On the other hand, to early Greek sailors and in Ancient Greek mythological literature such as the Iliad and the Odyssey, this all-encompassing ocean was instead known as Oceanus, the gigantic river that encircled the world. In contrast, the term "Atlantic" referred to the Atlas Mountains in Morocco and the sea off the Strait of Gibraltar and the North African coast; the Greek word thalassa has been reused by scientists for the huge Panthalassa ocean that surrounded the supercontinent Pangaea hundreds of millions of years ago. The term "Aethiopian Ocean", derived from Ancient Ethiopia, was applied to the Southern Atlantic as late as the mid-19th century. During the Age of Discovery, the Atlantic was known to English cartographers as the Great Western Ocean; the term The Pond is used by British and American speakers in context to the Atlantic Ocean, as a form of meiosis, or sarcastic understatement.
The term dates to as early as 1640, first appearing in print in pamphlet released during the reign of Charles I, reproduced in 1869 in Nehemiah Wallington's Historical Notices of Events Occurring Chiefly in The Reign of Charles I, where "great Pond" is used in reference to the Atlantic Ocean by Francis Windebank, Charles I's Secretary of State. The International Hydrographic Organization defined the limits of the oceans and seas in 1953, but some of these definitions have been revised since and some are not used by various authorities and countries, see for example the CIA World Factbook. Correspondingly, the extent and number of oceans and seas varies; the Atlantic Ocean is bounded on the west by South America. It connects to the Arctic Ocean through the Denmark Strait, Greenland Sea, Norwegian Sea and Barents Sea. To the east, the boundaries of the ocean proper are Europe: the Strait of Africa. In the southeast, the Atlantic merges into the Indian Ocean; the 20° East meridian, running south from Cape Agulhas to Antarctica defines its border.
In the 1953 definition it extends south to Antarctica, while in maps it is bounded at the 60° parallel by the Southern Ocean. The Atlantic has irregular coasts indented by numerous bays and seas; these include the Baltic Sea, Black Sea, Caribbean Sea, Davis Strait, Denmark Strait, part of the Drake Passage, Gulf of Mexico, Labrador Sea, Mediterranean Sea, North Sea, Norwegian Sea all of the Scotia Sea, other tributary water bodies. Including these marginal seas the coast line of the Atlantic measures 111,866 km compared to 135,663 km for the Pacific. Including its marginal seas, the Atlantic covers an area of 106,460,000 km2 or 23.5% of the global ocean and has a volume of 310,410,900 km3 or 23.3% of the total volume of the earth's oceans. Excluding its marginal seas, the Atlantic covers 81,760,000 km2 and has a volume of 305,811,900 km3; the North Atlantic covers 41,490,000 km2 and the South Atlantic 40,270,000 km2. The average depth is 3,646 m and the maximum depth, the Milwaukee Deep in the Puerto Rico Trench, is 8,486 m.
The bathymetry of the Atlantic is dominated by a submarine mountain range called the Mid-Atlantic Ridge. It runs from 87°N or 300 km south of the North Pole to the subantarctic Bouvet Island at 42°S; the MAR divides the Atlantic longitudinally into two halves, in each of which a series of basins are delimited by secondary, transverse ridges. The MAR reaches above 2,000 m along most of its length, but is interrupted by larger transform faults at two places: the Romanche Trench near the Equator and the Gibbs Fracture Zone at 53°N; the MAR is a barrier for bottom water, but at these two transform faults deep water currents can pass from one side to the othe