title: The Love Song of J. Alfred Prufrock

text: The intended audience is not evident. Some believe that Prufrock is talking to another person or directly to the reader, while others believe Prufrock's monologue is internal. Perrine writes "The 'you and I' of the first line are divided parts of Prufrock's own nature", while professor emerita of English Mutlu Konuk Blasing suggests that the "you and I" refers to the relationship between the dilemmas of the character and the author. Similarly, critics dispute whether Prufrock is going somewhere during the course of the poem. In the first half of the poem, Prufrock uses various outdoor images (the sky, streets, cheap restaurants and hotels, fog), and talks about how there will be time for various things before "the taking of a toast and tea", and "time to turn back and descend the stair." This has led many to believe that Prufrock is on his way to an afternoon tea, where he is preparing to ask this "overwhelming question". Others, however, believe that Prufrock is not physically going anywhere, but rather, is playing through it in his mind.


title: The Love Song of J. Alfred Prufrock

text: Perhaps the most significant dispute lies over the "overwhelming question" that Prufrock is trying to ask. Many believe that Prufrock is trying to tell a woman of his romantic interest in her, pointing to the various images of women's arms and clothing and the final few lines in which Prufrock laments that the mermaids will not sing to him. Others, however, believe that Prufrock is trying to express some deeper philosophical insight or disillusionment with society, but fears rejection, pointing to statements that express a disillusionment with society, such as "I have measured out my life with coffee spoons" (line 51). Many believe that the poem is a criticism of Edwardian society and Prufrock's dilemma represents the inability to live a meaningful existence in the modern world. McCoy and Harlan wrote "For many readers in the 1920s, Prufrock seemed to epitomize the frustration and impotence of the modern individual. He seemed to represent thwarted desires and modern disillusionment."


title: The Love Song of J. Alfred Prufrock

text: In general, Eliot uses imagery which is indicative of Prufrock's character, representing aging and decay. For example, "When the evening is spread out against the sky / Like a patient etherized upon a table" (lines 2–3), the "sawdust restaurants" and "cheap hotels", the yellow fog, and the afternoon "Asleep...tired... or it malingers" (line 77), are reminiscent of languor and decay, while Prufrock's various concerns about his hair and teeth, as well as the mermaids "Combing the white hair of the waves blown back / When the wind blows the water white and black," show his concern over aging.


title: The Love Song of J. Alfred Prufrock

text: Like many of Eliot's poems, "The Love Song of J. Alfred Prufrock" makes numerous allusions to other works, which are often symbolic themselves.


title: William M. Tweed

text: William Magear Tweed (April 3, 1823 – April 12, 1878), often erroneously referred to as William "Marcy" Tweed (see below), and widely known as "Boss" Tweed, was an American politician most notable for being the political boss of Tammany Hall, the Democratic Party's political machine that played a major role in the politics of 19th-century New York City and state. At the height of his influence, Tweed was the third-largest landowner in New York City, a director of the Erie Railroad, a director of the Tenth National Bank, a director of the New-York Printing Company, the proprietor of the Metropolitan Hotel, a significant stockholder in iron mines and gas companies, a board member of the Harlem Gas Light Company, a board member of the Third Avenue Railway Company, a board member of the Brooklyn Bridge Company, and the president of the Guardian Savings Bank.


title: William M. Tweed

text: Tweed was elected to the United States House of Representatives in 1852 and the New York County Board of Supervisors in 1858, the year that he became the head of the Tammany Hall political machine. He was also elected to the New York State Senate in 1867. However, Tweed's greatest influence came from being an appointed member of a number of boards and commissions, his control over political patronage in New York City through Tammany, and his ability to ensure the loyalty of voters through jobs he could create and dispense on city-related projects.


title: William M. Tweed

text: Tweed was convicted for stealing an amount estimated by an aldermen's committee in 1877 at between $25 million and $45 million from New York City taxpayers from political corruption, but later estimates ranged as high as $200 million. Unable to make bail, he escaped from jail once but was returned to custody. He died in the Ludlow Street Jail.


title: William M. Tweed

text: Tweed was born April 3, 1823, at 1 Cherry Street, on the Lower East Side of Manhattan. The son of a third-generation Scottish chair-maker, Tweed grew up on Cherry Street. His grandfather arrived in the United States from a town near the River Tweed close to Edinburgh. Tweed's religious affiliation was not widely known in his lifetime, but at the time of his funeral "The New York Times", quoting a family friend, reported that his parents had been Quakers and "members of the old Rose Street Meeting house". At the age of 11, he left school to learn his father's trade, and then became an apprentice to a saddler. He also studied to be a bookkeeper and worked as a brushmaker for a company he had invested in, before eventually joining in the family business in 1852. On September 29, 1844, he married Mary Jane C. Skaden and lived with her family on Madison Street for two years.


title: William M. Tweed

text: Tweed became a member of the Odd Fellows and the Masons, and joined a volunteer fire company, Engine No. 12. In 1848, at the invitation of state assemblyman John J. Reilly, he and some friends organized the Americus Fire Company No. 6, also known as the "Big Six", as a volunteer fire company, which took as its symbol a snarling red Bengal tiger from a French lithograph, a symbol which remained associated with Tweed and Tammany Hall for many years. At the time, volunteer fire companies competed vigorously with each other; some were connected with street gangs and had strong ethnic ties to various immigrant communities. The competition could become so fierce, that burning buildings would sometimes be ignored as the fire companies fought each other. Tweed became known for his ax-wielding violence, and was soon elected the Big Six foreman. Pressure from Alfred Carlson, the chief engineer, got him thrown out of the crew. However, fire companies were also recruiting grounds for political parties at the time, thus Tweed's exploits came to the attention of the Democratic politicians who ran the Seventh Ward. The Seventh Ward put him up for Alderman in 1850, when Tweed was 26. He lost that election to the Whig candidate Morgan Morgans, but ran again the next year and won, garnering his first political position. Tweed then became associated with the "Forty Thieves", the group of aldermen and assistant aldermen who, up to that point, were known as some of the most corrupt politicians in the city's history.


title: William M. Tweed

text: Tweed was elected to the United States House of Representatives in 1852, but his two-year term was undistinguished. In an attempt by Republican reformers in Albany, the state capital, to control the Democratic-dominated New York City government, the power of the New York County Board of Supervisors was beefed up. The board had 12 members, six appointed by the mayor and six elected, and in 1858 Tweed was appointed to the board, which became his first vehicle for large-scale graft; Tweed and other supervisors forced vendors to pay a 15% overcharge to their "ring" in order to do business with the city. By 1853, Tweed was running the seventh ward for Tammany. The board also had six Democrats and six Republicans, but Tweed often just bought off one Republican to sway the board. One such Republican board member was Peter P. Voorhis, a coal dealer by profession who absented himself from a board meeting in exchange for $2,500 so that the board could appoint city inspectors. Henry Smith was another Republican that was a part of the Tweed ring.


title: William M. Tweed

text: Although he was not trained as a lawyer, Tweed's friend, Judge George G. Barnard, certified him as an attorney, and Tweed opened a law office on Duane Street. He ran for sheriff in 1861 and was defeated, but became the chairman of the Democratic General Committee shortly after the election, and was then chosen to be the head of Tammany's general committee in January 1863. Several months later, in April, he became "Grand Sachem", and began to be referred to as "Boss", especially after he tightened his hold on power by creating a small executive committee to run the club. Tweed then took steps to increase his income: he used his law firm to extort money, which was then disguised as legal services; he had himself appointed deputy street commissioner – a position with considerable access to city contractors and funding; he bought the New-York Printing Company, which became the city's official printer, and the city's stationery supplier, the Manufacturing Stationers' Company, and had both companies begin to overcharge the city government for their goods and services. Among other legal services he provided, he accepted almost $100,000 from the Erie Railroad in return for favors. He also became one of the largest owners of real estate in the city. He also started to form what became known as the "Tweed Ring", by having his friends elected to office: George G. Barnard was elected Recorder of New York City; Peter B. Sweeny was elected New York County District Attorney; and Richard B. Connolly was elected City Comptroller. Other judicial members of the Tweed ring included Albert Cardozo, John McCunn, and John K. Hackett.


title: William M. Tweed

text: When Grand Sachem Isaac Fowler, who had produced the $2,500 to buy off the Republican Voorhis on the Board of Supervisors, was found to have stolen $150,000 in post office receipts, the responsibility for Fowler's arrest was given to Isaiah Rynders, another Tammany operative who was serving as a United States marshal at the time. Rynders made enough ruckus upon entering the hotel where Fowler was staying that Fowler was able to escape to Mexico.


title: William M. Tweed

text: With his new position and wealth came a change in style: Tweed began to favor wearing a large diamond in his shirtfront – a habit that Thomas Nast used to great effect in his attacks on Tweed in "Harper's Weekly" beginning in 1869 – and he bought a brownstone to live in at 41 West 36th Street, then a very fashionable area. He invested his now considerable illegal income in real estate, so that by the late 1860s he ranked among the biggest landowners in New York City.


title: William M. Tweed

text: Tweed became involved in the operation of the New York Mutuals, an early professional baseball club, in the 1860s. He brought in thousands of dollars per home game by dramatically increasing the cost of admission and gambling on the team. He has been credited with originating the practice of spring training in 1869 by sending the club south to New Orleans to prepare for the season.


title: William M. Tweed

text: Tweed was a member of the New York State Senate (4th D.) from 1868 to 1873, sitting in the 91st, 92nd, 93rd, and 94th New York State Legislatures, but not taking his seat in the 95th and 96th New York State Legislatures. While serving in the State Senate, he split his time between Albany, New York and New York City. While in Albany, he stayed in a suite of seven rooms in Delevan House. Accompanying him in his rooms were his favorite canaries. Guests are presumed to have included members of the Black Horse Cavalry, thirty state legislators whose votes were up for sale. In the Senate he helped financiers Jay Gould and Big Jim Fisk to take control of the Erie Railroad from Cornelius Vanderbilt by arranging for legislation that legitimized fake Erie stock certificates that Gould and Fisk had issued. In return, Tweed received a large block of stock and was made a director of the company.


title: William M. Tweed

text: After the election of 1869, Tweed took control of the New York City government. His protégé, John T. Hoffman, the former mayor of the city, won election as governor, and Tweed garnered the support of good-government reformers like Peter Cooper and the Union League Club, by proposing a new city charter which returned power to City Hall at the expense of the Republican-inspired state commissions. The new charter passed, thanks in part to $600,000 in bribes Tweed paid to Republicans, and was signed into law by Hoffman in 1870. Mandated new elections allowed Tammany to take over the city's Common Council when they won all fifteen aldermanic contests.


title: William M. Tweed

text: The new charter put control of the city's finances in the hands of a Board of Audit, which consisted of Tweed, who was Commissioner of Public Works, Mayor A. Oakey Hall and Comptroller Richard "Slippery Dick" Connolly, both Tammany men. Hall also appointed other Tweed associates to high offices – such as Peter B. Sweeny, who took over the Department of Public Parks – providing what became known as the Tweed Ring with even firmer control of the New York City government and enabling them to defraud the taxpayers of many more millions of dollars. In the words of Albert Bigelow Paine, "their methods were curiously simple and primitive. There were no skilful manipulations of figures, making detection difficult ... Connolly, as Controller, had charge of the books, and declined to show them. With his fellows, he also 'controlled' the courts and most of the bar." Crucially, the new city charter allowed the Board of Audit to issue bonds for debt in order to finance opportunistic capital expenditures the city otherwise could not afford. This ability to float debt was enabled by Tweed's guidance and passage of the Adjusted Claims Act in 1868. Contractors working for the city – "Ring favorites, most of them – were told to multiply the amount of each bill by five, or ten, or a hundred, after which, with Mayor Hall's 'O. K.' and Connolly's endorsement, it was paid ... through a go-between, who cashed the check, settled the original bill and divided the remainder ... between Tweed, Sweeny, Connolly and Hall".


title: William M. Tweed

text: For example, the construction cost of the New York County Courthouse, begun in 1861, grew to nearly $13 million—about $178 million in 2017 dollars, and nearly twice the cost of the Alaska Purchase in 1867.


title: William M. Tweed

text: "A carpenter was paid $360,751 (roughly $4.9 million today) for one month's labor in a building with very little woodwork ... a plasterer got $133,187 ($1.82 million) for two days' work". Tweed bought a marble quarry in Sheffield, Massachusetts, to provide much of the marble for the courthouse at great profit to himself. After the Tweed Charter to reorganize the city's government was passed in 1870, four commissioners for the construction of the New York County Courthouse were appointed. The commission never held a meeting, though each commissioner received a 20% kickback from the bills for the supplies.


title: William M. Tweed

text: Tweed and his friends also garnered huge profits from the development of the Upper East Side, especially Yorkville and Harlem. They would buy up undeveloped property, then use the resources of the city to improve the area – for instance by installing pipes to bring in water from the Croton Aqueduct – thus increasing the value of the land, after which they sold and took their profits. The focus on the east side also slowed down the development of the west side, the topography of which made it more expensive to improve. The ring also took their usual percentage of padded contracts, as well as raking off money from property taxes. Despite the corruption of Tweed and Tammany Hall, they did accomplish the development of upper Manhattan, though at the cost of tripling the city's bond debt to almost $90 million.


title: William M. Tweed

text: During the Tweed era, the proposal to build a suspension bridge between New York and Brooklyn, then an independent city, was floated by Brooklyn-boosters, who saw the ferry connections as a bottleneck to Brooklyn's further development. In order to ensure that the Brooklyn Bridge project would go forward, State Senator Henry Cruse Murphy approached Tweed to find out whether New York's aldermen would approve the proposal. Tweed's response was that $60,000 for the aldermen would close the deal, and contractor William C. Kingsley put up the cash, which was delivered in a carpet bag. Tweed and two others from Tammany also received over half the private stock of the Bridge Company, the charter of which specified that only private stockholders had voting rights, so that even though the cities of Brooklyn and Manhattan put up most of the money, they essentially had no control over the project.


title: William M. Tweed

text: Tweed bought a mansion on Fifth Avenue and 43rd Street, and stabled his horses, carriages and sleighs on 40th Street. By 1871, he was a member of the board of directors of not only the Erie Railroad and the Brooklyn Bridge Company, but also the Third Avenue Railway Company and the Harlem Gas Light Company. He was president of the Guardian Savings Banks and he and his confederates set up the Tenth National Bank to better control their fortunes.


title: William M. Tweed

text: Tweed's downfall began in 1871. James Watson, who was a county auditor in Comptroller Dick Connolly's office and who also held and recorded the ring's books, died a week after his head was smashed by a horse in a sleigh accident on January 21, 1871. Although Tweed guarded Watson's estate in the week prior to Watson's death, and although another ring member attempted to destroy Watson's records, a replacement auditor, Matthew O'Rourke, associated with former sheriff James O'Brien, provided city accounts to O'Brien. The Orange riot of 1871 in the summer of that year did not help the ring's popularity. The riot was prompted after Tammany Hall banned a parade of Irish Protestants celebrating a historical victory against Catholicism, namely the Battle of the Boyne. The parade was banned because of a riot the previous year in which eight people died when a crowd of Irish Catholic laborers attacked the paraders. Under strong pressure from the newspapers and the Protestant elite of the city, Tammany reversed course, and the march was allowed to proceed, with protection from city policemen and state militia. The result was an even larger riot in which over 60 people were killed and more than 150 injured.


title: William M. Tweed

text: Although Tammany's electoral power base was largely centered in the Irish immigrant population, it also needed both the city's general population and elite to acquiesce in its rule, and this was conditional on the machine's ability to control the actions of its people. The July riot showed that this capability was not nearly as strong as had been supposed.


title: William M. Tweed

text: Tweed had for months been under attack from "The New York Times" and Thomas Nast, the cartoonist from "Harper's Weekly" – regarding Nast's cartoons, Tweed reportedly said, "Stop them damned pictures. I don't care so much what the papers say about me. My constituents don't know how to read, but they can't help seeing them damned pictures!" – but their campaign had only limited success in gaining traction. They were able to force an examination of the city's books, but the blue-ribbon commission of six businessmen appointed by Mayor A. Oakey Hall, a Tammany man, which included John Jacob Astor III, banker Moses Taylor and others who benefited from Tammany's actions, found that the books had been "faithfully kept", letting the air out of the effort to dethrone Tweed.


title: William M. Tweed

text: The response to the Orange riot changed everything, and only days afterwards the "Times"/Nast campaign began to garner popular support. More important, the "Times" started to receive inside information from County Sheriff James O'Brien, whose support for Tweed had fluctuated during Tammany's reign. O'Brien had tried to blackmail Tammany by threatening to expose the ring's embezzlement to the press, and when this failed he provided the evidence he had collected to the "Times". Shortly afterward, county auditor Matthew J. O'Rourke supplied additional details to the "Times", which was reportedly offered $5 million to not publish the evidence. The "Times" also obtained the accounts of the recently deceased James Watson, who was the Tweed Ring's bookkeeper, and these were published daily, culminating in a special four-page supplement on July 29 headlined "Gigantic Frauds of the Ring Exposed". In August, Tweed began to transfer ownership in his real-estate empire and other investments to his family members.


title: William M. Tweed

text: The exposé provoked an international crisis of confidence in New York City's finances, and, in particular, in its ability to repay its debts. European investors were heavily positioned in the city's bonds and were already nervous about its management – only the reputations of the underwriters were preventing a run on the city's securities. New York's financial and business community knew that if the city's credit were to collapse, it could potentially bring down every bank in the city with it.


title: William M. Tweed

text: Thus, the city's elite met at Cooper Union in September to discuss political reform: but for the first time, the conversation included not only the usual reformers, but also Democratic bigwigs such as Samuel J. Tilden, who had been thrust aside by Tammany. The consensus was that the "wisest and best citizens" should take over the governance of the city and attempt to restore investor confidence. The result was the formation of the Executive Committee of Citizens and Taxpayers for Financial Reform of the city (also known as "the Committee of Seventy"), which attacked Tammany by cutting off the city's funding. Property owners refused to pay their municipal taxes, and a judge—Tweed's old friend George Barnard—enjoined the city Comptroller from issuing bonds or spending money. Unpaid workers turned against Tweed, marching to City Hall demanding to be paid. Tweed doled out some funds from his own purse—$50,000—but it was not sufficient to end the crisis, and Tammany began to lose its essential base.


title: William M. Tweed

text: Shortly thereafter, the Comptroller resigned, appointing Andrew Haswell Green, an associate of Tilden, as his replacement. Green loosened the purse strings again, allowing city departments not under Tammany control to borrow money to operate. Green and Tilden had the city's records closely examined, and discovered money that went directly from city contractors into Tweed's pocket. The following day, they had Tweed arrested.


title: William M. Tweed

text: Tweed was released on $1 million bail, and Tammany set to work to recover its position through the ballot box. Tweed was re-elected to the state senate in November 1871, due to his personal popularity and largesse in his district, but in general Tammany did not do well, and the members of the Tweed Ring began to flee the jurisdiction, many going overseas. Tweed was re-arrested, forced to resign his city positions, and was replaced as Tammany's leader. Once again, he was released on bail—$8 million this time—but Tweed's supporters, such as Jay Gould, felt the repercussions of his fall from power.


title: William M. Tweed

text: Tweed's first trial, in January 1873, ended when the jury was unable to deliver a verdict. Tweed's defense counsel included David Dudley Field II and Elihu Root. His retrial in November resulted in convictions on 204 of 220 counts, a fine of $12,750 (the equivalent of $ today) and a prison sentence of 12 years; a higher court, however, reduced Tweed's sentence to one year. After his release from The Tombs prison, New York State filed a civil suit against Tweed, attempting to recover $6 million in embezzled funds. Unable to put up the $3 million bail, Tweed was locked up in the Ludlow Street Jail, although he was allowed home visits. During one of these on December 4, 1875, Tweed escaped and fled to Spain, where he worked as a common seaman on a Spanish ship. The U.S. government discovered his whereabouts and arranged for his arrest once he reached the Spanish border, where he was recognized from Nast's political cartoons. He was turned over to an American warship, the , which delivered him to authorities in New York City on November 23, 1876, and he was returned to prison.


title: William M. Tweed

text: Desperate and broken, Tweed now agreed to testify about the inner workings of the Tweed Ring to a special committee set up by the Board of Aldermen in return for his release, but after he did so, Tilden, now governor of New York, refused to abide by the agreement, and Tweed remained incarcerated. He died in the Ludlow Street Jail on April 12, 1878, from severe pneumonia, and was buried in Brooklyn's Green-Wood Cemetery. Mayor Smith Ely would not allow the flag at City Hall to be flown at half staff.


title: William M. Tweed

text: According to Tweed biographer Kenneth D. Ackerman:It's hard not to admire the skill behind Tweed's system ... The Tweed ring at its height was an engineering marvel, strong and solid, strategically deployed to control key power points: the courts, the legislature, the treasury and the ballot box. Its frauds had a grandeur of scale and an elegance of structure: money-laundering, profit sharing and organization.


title: William M. Tweed

text: A minority view that Tweed was mostly innocent is presented in a scholarly biography by history professor Leo Hershkowitz. He states:Except for Tweed’s own very questionable "confession," there really was no evidence of a "Tweed Ring," no direct evidence of Tweed’s thievery, no evidence, excepting the testimony of the informer contractors, of "wholesale" plunder by Tweed...[Instead there was] a conspiracy of self-justification of the corruption of the law by the upholders of that law, of a venal irresponsible press and a citizenry delighting in the exorcism of witchery.


title: William M. Tweed

text: In depictions of Tweed and the Tammany Hall organization, most historians have emphasized the thievery and conspiratorial nature of Boss Tweed, along with lining his own pockets and those of his friends and allies. The theme is that the sins of corruption so violated American standards of political rectitude that they far overshadow Tweed's positive contributions to New York City.


title: William M. Tweed

text: Although he held numerous important public offices and was one of a handful of senior leaders of Tammany Hall, as well as the state legislature and the state Democratic Party, Tweed was never the sole "boss" of New York City. He shared control of the city with numerous less famous people, such as the villains depicted in Nast's famous circle of guilt cartoon shown above. Seymour J. Mandelbaum has argued that, apart from the corruption he engaged in, Tweed was a modernizer who prefigured certain elements of the Progressive Era in terms of more efficient city management. Much of the money he siphoned off from the city treasury went to needy constituents who appreciated the free food at Christmas time and remembered it at the next election, and to precinct workers who provided the muscle of his machine. As a legislator he worked to expand and strengthen welfare programs, especially those by private charities, schools, and hospitals. With a base in the Irish Catholic community, he opposed efforts of Protestants to require the reading of the King James Bible in public schools, which was done deliberately to keep out Catholics. He facilitated the founding of the New York Public Library, even though one of its founders, Samuel Tilden, was Tweed's sworn enemy in the Democratic Party.


title: William M. Tweed

text: Tweed recognized that the support of his constituency was necessary for him to remain in power, and as a consequence he used the machinery of the city's government to provide numerous social services, including building more orphanages, almshouses and public baths. Tweed also fought for the New York State Legislature to donate to private charities of all religious denominations, and subsidize Catholic schools and hospitals. From 1869 to 1871, under Tweed's influence, the state of New York spent more on charities than for the entire time period from 1852 to 1868 combined. Tweed also pushed through funding for a teachers college and prohibition of corporal punishment in schools, as well as salary increases for school teachers.


title: William M. Tweed

text: During Tweed's regime, the main business thoroughfare Broadway was widened between 34th Street and 59th Street, land was secured for the Metropolitan Museum of Art, and the Upper East Side and Upper West Side were developed and provided the necessary infrastructure – all to the benefit of the purses of the Tweed Ring, but also, ultimately, to the benefit of the people of the city.


title: William M. Tweed

text: Hershkowitz blames the implications of Thomas Nast in "Harper's Weekly" and the editors of "The New York Times", which both had ties to the Republican party. In part, the campaign against Tweed diverted public attention from Republican scandals such as the Whiskey Ring.


title: William M. Tweed

text: Tweed himself wanted no particular recognition of his achievements, such as they were. When it was proposed, in March 1871, when he was at the height of his power, that a statue be erected in his honor, he declared: "Statues are not erected to living men ... I claim to be a live man, and hope (Divine Providence permitting) to survive in all my vigor, politically and physically, some years to come." One of Tweed's unwanted legacies is that he has become "the archetype of the bloated, rapacious, corrupt city boss".


title: William M. Tweed

text: Tweed never signed his name with anything other than a plain "M.", and his middle name is often mistakenly listed as "Marcy". His actual middle name was "Magear", his mother's maiden name. Tweed's son's name was William Magear Tweed Jr.


title: William M. Tweed

text: Confusion derived from a Nast cartoon with a picture of Tweed supplemented with a quote from William L. Marcy, the former governor of New York.


title: Solar wind

text: The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the solar wind plasma also includes a mixture of materials found in the solar plasma: trace amounts of heavy ions and atomic nuclei such as C, N, O, Ne, Mg, Si, S, and Fe. There are also rarer traces of some other nuclei and isotopes such as P, Ti, Cr, Fe and Fe, and Ni, Ni, and Ni. Superposed with the solar-wind plasma is the interplanetary magnetic field. The solar wind varies in density, temperature and speed over time and over solar latitude and longitude. Its particles can escape the Sun's gravity because of their high energy resulting from the high temperature of the corona, which in turn is a result of the coronal magnetic field. The boundary separating the corona from the solar wind is called the Alfvén surface.


title: Solar wind

text: At a distance of more than a few solar radii from the Sun, the solar wind reaches speeds of 250–750 km/s and is supersonic, meaning it moves faster than the speed of the fast magnetosonic wave. The flow of the solar wind is no longer supersonic at the termination shock. Other related phenomena include the aurora (northern and southern lights), the plasma tails of comets that always point away from the Sun, and geomagnetic storms that can change the direction of magnetic field lines.


title: Solar wind

text: The existence of particles flowing outward from the Sun to the Earth was first suggested by British astronomer Richard C. Carrington. In 1859, Carrington and Richard Hodgson independently made the first observations of what would later be called a solar flare. This is a sudden, localised increase in brightness on the solar disc, which is now known to often occur in conjunction with an episodic ejection of material and magnetic flux from the Sun's atmosphere, known as a coronal mass ejection. The following day, a powerful geomagnetic storm was observed, and Carrington suspected that there might be a connection; the geomagnetic storm is now attributed to the arrival of the coronal mass ejection in near-Earth space and its subsequent interaction with the Earth's magnetosphere. Irish academic George FitzGerald later suggested that matter was being regularly accelerated away from the Sun, reaching the Earth after several days.


title: Solar wind

text: In 1910, British astrophysicist Arthur Eddington essentially suggested the existence of the solar wind, without naming it, in a footnote to an article on Comet Morehouse. Eddington's proposition was never fully embraced, even though he had also made a similar suggestion at a Royal Institution address the previous year, in which he had postulated that the ejected material consisted of electrons, whereas in his study of Comet Morehouse he had supposed them to be ions.


title: Solar wind

text: The idea that the ejected material consisted of both ions and electrons was first suggested by Norwegian scientist Kristian Birkeland. His geomagnetic surveys showed that auroral activity was almost uninterrupted. As these displays and other geomagnetic activity were being produced by particles from the Sun, he concluded that the Earth was being continually bombarded by "rays of electric corpuscles emitted by the Sun". He proposed in 1916 that, "From a physical point of view it is most probable that solar rays are neither exclusively negative nor positive rays, but of both kinds"; in other words, the solar wind consists of both negative electrons and positive ions. Three years later, in 1919, British physicist Frederick Lindemann also suggested that the Sun ejects particles of both polarities: protons as well as electrons.


title: Solar wind

text: Around the 1930s, scientists had concluded that the temperature of the solar corona must be a million degrees Celsius because of the way it extended into space (as seen during a total solar eclipse). Later spectroscopic work confirmed this extraordinary temperature to be the case. In the mid-1950s, British mathematician Sydney Chapman calculated the properties of a gas at such a temperature and determined that the corona being such a superb conductor of heat, it must extend way out into space, beyond the orbit of Earth. Also in the 1950s, German astronomer Ludwig Biermann became interested in the fact that the tail of a comet always points away from the Sun, regardless of the direction in which the comet is travelling. Biermann postulated that this happens because the Sun emits a steady stream of particles that pushes the comet's tail away. German astronomer Paul Ahnert is credited (by Wilfried Schröder) as being the first to relate solar wind to the direction of a comet's tail based on observations of the comet Whipple-Fedke (1942g).


title: Solar wind

text: American astrophysicist Eugene Parker realised that heat flowing from the Sun in Chapman's model, and the comet tail blowing away from the Sun in Biermann's hypothesis, had to be the result of the same phenomenon which he termed the "solar wind". In 1957, Parker showed that although the Sun's corona is strongly attracted by solar gravity, it is such a good conductor of heat that it is still very hot at large distances from the Sun. As solar gravity weakens with increasing distance from the Sun, the outer coronal atmosphere is able to escape supersonically into interstellar space. Parker was also the first person to notice that the weakening influence of the Sun's gravity has the same effect on hydrodynamic flow as a de Laval nozzle, inciting a transition from subsonic to supersonic flow. There was strong opposition to Parker's hypothesis on the solar wind; the paper he submitted to "The Astrophysical Journal" in 1958 was rejected by two reviewers, before being accepted by the editor Subrahmanyan Chandrasekhar.


title: Solar wind

text: In January 1959, the Soviet spacecraft "Luna 1" first directly observed the solar wind and measured its strength, using hemispherical ion traps. The discovery, made by , was verified by "Luna 2", "Luna 3", and the more distant measurements of "Venera 1". Three years later, a similar measurement was performed by American geophysicist Marcia Neugebauer and collaborators using the "Mariner 2" spacecraft.


title: Solar wind

text: The first numerical simulation of the solar wind in the solar corona, including closed and open field lines, was performed by Pneuman and Kopp in 1971. The magnetohydrodynamics equations in steady state were solved iteratively starting with an initial dipolar configuration.


title: Solar wind

text: In 1990, the "Ulysses" probe was launched to study the solar wind from high solar latitudes. All prior observations had been made at or near the Solar System's ecliptic plane.


title: Solar wind

text: In the late 1990s, the Ultraviolet Coronal Spectrometer (UVCS) instrument on board the SOHO spacecraft observed the acceleration region of the fast solar wind emanating from the poles of the Sun and found that the wind accelerates much faster than can be accounted for by thermodynamic expansion alone. Parker's model predicted that the wind should make the transition to supersonic flow at an altitude of about four solar radii (approx. 3,000,000 km) from the photosphere (surface); but the transition (or "sonic point") now appears to be much lower, perhaps only one solar radius (approx. 700,000 km) above the photosphere, suggesting that some additional mechanism accelerates the solar wind away from the Sun. The acceleration of the fast wind is still not understood and cannot be fully explained by Parker's theory. However, the gravitational and electromagnetic explanation for this acceleration is detailed in an earlier paper by 1970 Nobel laureate in Physics, Hannes Alfvén.


title: Solar wind

text: The STEREO mission was launched in 2006 to study coronal mass ejections and the solar corona, using stereoscopy from two widely separated imaging systems. Each STEREO spacecraft carried two heliospheric imagers: highly sensitive wide-field cameras capable of imaging the solar wind itself, via Thomson scattering of sunlight off of free electrons. Movies from STEREO revealed the solar wind near the ecliptic, as a large-scale turbulent flow.


title: Solar wind

text: The "Voyager 1" probe reached the end of the solar-wind "bubble" in 2012, at which time the detection of solar wind dropped off precipitously. A similar observation was made six years later by "Voyager 2".


title: Solar wind

text: In 2018, NASA launched the "Parker Solar Probe", named in honor of American astrophysicist Eugene Parker, on a mission to study the structure and dynamics of the solar corona, in an attempt to understand the mechanisms that cause particles to be heated and accelerated as solar wind. During its seven-year mission, the probe will make twenty-four orbits of the Sun, passing further into the corona with each orbit's perihelion, ultimately passing within 0.04 astronomical units of the Sun's surface. It is the first NASA spacecraft named for a living person, and Parker, at age 91, was on hand to observe the launch.


title: Solar wind

text: While early models of the solar wind relied primarily on thermal energy to accelerate the material, by the 1960s it was clear that thermal acceleration alone cannot account for the high speed of solar wind. An additional unknown acceleration mechanism is required and likely relates to magnetic fields in the solar atmosphere.


title: Solar wind

text: The Sun's corona, or extended outer layer, is a region of plasma that is heated to over a megakelvin. As a result of thermal collisions, the particles within the inner corona have a range and distribution of speeds described by a Maxwellian distribution. The mean velocity of these particles is about , which is well below the solar escape velocity of . However, a few of the particles achieve energies sufficient to reach the terminal velocity of , which allows them to feed the solar wind. At the same temperature, electrons, due to their much smaller mass, reach escape velocity and build up an electric field that further accelerates ions away from the Sun.


title: Solar wind

text: The total number of particles carried away from the Sun by the solar wind is about per second. Thus, the total mass loss each year is about solar masses, or about 1.3–1.9 Million tonnes per second. This is equivalent to losing a mass equal to the Earth every 150 million years. However, since the Sun's formation, only about 0.01% of its initial mass has been lost through the solar wind. Other stars have much stronger stellar winds that result in significantly higher mass-loss rates.


title: Solar wind

text: The solar wind is observed to exist in two fundamental states, termed the slow solar wind and the fast solar wind, though their differences extend well beyond their speeds. In near-Earth space, the slow solar wind is observed to have a velocity of , a temperature of ~100 MK and a composition that is a close match to the corona. By contrast, the fast solar wind has a typical velocity of , a temperature of 800 MK and it nearly matches the composition of the Sun's photosphere. The slow solar wind is twice as dense and more variable in nature than the fast solar wind.


title: Solar wind

text: The slow solar wind appears to originate from a region around the Sun's equatorial belt that is known as the "streamer belt", where coronal streamers are produced by magnetic flux open to the heliosphere draping over closed magnetic loops. The exact coronal structures involved in slow solar wind formation and the method by which the material is released is still under debate. Observations of the Sun between 1996 and 2001 showed that emission of the slow solar wind occurred at latitudes up to 30–35° during the solar minimum (the period of lowest solar activity), then expanded toward the poles as the solar cycle approached maximum. At solar maximum, the poles were also emitting a slow solar wind.


title: Solar wind

text: The fast solar wind originates from coronal holes, which are funnel-like regions of open field lines in the Sun's magnetic field. Such open lines are particularly prevalent around the Sun's magnetic poles. The plasma source is small magnetic fields created by convection cells in the solar atmosphere. These fields confine the plasma and transport it into the narrow necks of the coronal funnels, which are located only 20,000 km above the photosphere. The plasma is released into the funnel when these magnetic field lines reconnect.


title: Solar wind

text: Near the Earth's orbit at 1 Astronomical Unit (AU) the plasma flows at speeds ranging from 250–750 km/s (155-404 mi/s) with a density ranging between 3-10 particles per cubic centimeter and temperature ranging from 10 to 10 degrees Kelvin.


title: Solar wind

text: On average, the plasma density decreases with the square of the distance from the Sun while the velocity is nearly constant, see Figure 4.2.


title: Solar wind

text: At , the wind exerts a pressure typically in the range of (), although it can readily vary outside that range.


title: Solar wind

text: where "m" is the proton mass, pressure "P" is in nPa (nanopascals), "n" is the density in particles/cm and "V" is the speed in km/s of the solar wind.


title: Solar wind

text: Both the fast and slow solar wind can be interrupted by large, fast-moving bursts of plasma called coronal mass ejections, or CMEs. CMEs are caused by a release of magnetic energy at the Sun. CMEs are often called "solar storms" or "space storms" in the popular media. They are sometimes, but not always, associated with solar flares, which are another manifestation of magnetic energy release at the Sun. CMEs cause shock waves in the thin plasma of the heliosphere, launching electromagnetic waves and accelerating particles (mostly protons and electrons) to form showers of ionizing radiation that precede the CME.


title: Solar wind

text: When a CME impacts the Earth's magnetosphere, it temporarily deforms the Earth's magnetic field, changing the direction of compass needles and inducing large electrical ground currents in Earth itself; this is called a geomagnetic storm and it is a global phenomenon. CME impacts can induce magnetic reconnection in Earth's magnetotail (the midnight side of the magnetosphere); this launches protons and electrons downward toward Earth's atmosphere, where they form the aurora.


title: Solar wind

text: CMEs are not the only cause of space weather. Different patches on the Sun are known to give rise to slightly different speeds and densities of wind depending on local conditions. In isolation, each of these different wind streams would form a spiral with a slightly different angle, with fast-moving streams moving out more directly and slow-moving streams wrapping more around the Sun. Fast-moving streams tend to overtake slower streams that originate westward of them on the Sun, forming turbulent co-rotating interaction regions that give rise to wave motions and accelerated particles, and that affect Earth's magnetosphere in the same way as, but more gently than, CMEs.


title: Solar wind

text: Magnetic switchbacks are sudden reversals in the magnetic field of the solar wind. They can also be described as traveling disturbances in the solar wind that caused the magnetic field to bend back on itself. They were first observed by the NASA-ESA mission "Ulysses", the first spacecraft to fly over the Sun's poles. Parker Solar Probe observed first switchbacks in 2018.


title: Solar wind

text: Over the Sun's lifetime, the interaction of its surface layers with the escaping solar wind has significantly decreased its surface rotation rate. The wind is considered responsible for comets' tails, along with the Sun's radiation. The solar wind contributes to fluctuations in celestial radio waves observed on the Earth, through an effect called interplanetary scintillation.


title: Solar wind

text: Where the solar wind intersects with a planet that has a well-developed magnetic field (such as Earth, Jupiter or Saturn), the particles are deflected by the Lorentz force. This region, known as the magnetosphere, causes the particles to travel around the planet rather than bombarding the atmosphere or surface. The magnetosphere is roughly shaped like a hemisphere on the side facing the Sun, then is drawn out in a long wake on the opposite side. The boundary of this region is called the magnetopause, and some of the particles are able to penetrate the magnetosphere through this region by partial reconnection of the magnetic field lines.


title: Solar wind

text: The solar wind is responsible for the overall shape of Earth's magnetosphere. Fluctuations in its speed, density, direction, and entrained magnetic field strongly affect Earth's local space environment. For example, the levels of ionizing radiation and radio interference can vary by factors of hundreds to thousands; and the shape and location of the magnetopause and bow shock wave upstream of it can change by several Earth radii, exposing geosynchronous satellites to the direct solar wind. These phenomena are collectively called space weather.


title: Solar wind

text: From the European Space Agency's Cluster mission, a new study has taken place that proposes that it is easier for the solar wind to infiltrate the magnetosphere than previously believed. A group of scientists directly observed the existence of certain waves in the solar wind that were not expected. A recent study shows that these waves enable incoming charged particles of solar wind to breach the magnetopause. This suggests that the magnetic bubble forms more as a filter than a continuous barrier. This latest discovery occurred through the distinctive arrangement of the four identical Cluster spacecraft, which fly in a controlled configuration through near-Earth space. As they sweep from the magnetosphere into interplanetary space and back again, the fleet provides exceptional three-dimensional insights on the phenomena that connect the sun to Earth.


title: Solar wind

text: The research characterised variances in formation of the interplanetary magnetic field (IMF) largely influenced by Kelvin–Helmholtz instability (which occur at the interface of two fluids) as a result of differences in thickness and numerous other characteristics of the boundary layer. Experts believe that this was the first occasion that the appearance of Kelvin–Helmholtz waves at the magnetopause had been displayed at high latitude downward orientation of the IMF. These waves are being seen in unforeseen places under solar wind conditions that were formerly believed to be undesired for their generation. These discoveries show how Earth's magnetosphere can be penetrated by solar particles under specific IMF circumstances. The findings are also relevant to studies of magnetospheric progressions around other planetary bodies. This study suggests that Kelvin–Helmholtz waves can be a somewhat common, and possibly constant, instrument for the entrance of solar wind into terrestrial magnetospheres under various IMF orientations.


title: Solar wind

text: The solar wind affects other incoming cosmic rays interacting with planetary atmospheres. Moreover, planets with a weak or non-existent magnetosphere are subject to atmospheric stripping by the solar wind.


title: Solar wind

text: Venus, the nearest and most similar planet to Earth, has 100 times denser atmosphere, with little or no geo-magnetic field. Space probes discovered a comet-like tail that extends to Earth's orbit.


title: Solar wind

text: Earth itself is largely protected from the solar wind by its magnetic field, which deflects most of the charged particles; however, some of the charged particles are trapped in the Van Allen radiation belt. A smaller number of particles from the solar wind manage to travel, as though on an electromagnetic energy transmission line, to the Earth's upper atmosphere and ionosphere in the auroral zones. The only time the solar wind is observable on the Earth is when it is strong enough to produce phenomena such as the aurora and geomagnetic storms. Bright auroras strongly heat the ionosphere, causing its plasma to expand into the magnetosphere, increasing the size of the plasma geosphere and injecting atmospheric matter into the solar wind. Geomagnetic storms result when the pressure of plasmas contained inside the magnetosphere is sufficiently large to inflate and thereby distort the geomagnetic field.


title: Solar wind

text: Although Mars is larger than Mercury and four times farther from the Sun, it is thought that the solar wind has stripped away up to a third of its original atmosphere, leaving a layer 1/100th as dense as the Earth's. It is believed the mechanism for this atmospheric stripping is gas caught in bubbles of the magnetic field, which are ripped off by the solar wind. In 2015 the NASA Mars Atmosphere and Volatile Evolution (MAVEN) mission measured the rate of atmospheric stripping caused by the magnetic field carried by the solar wind as it flows past Mars, which generates an electric field, much as a turbine on Earth can be used to generate electricity. This electric field accelerates electrically charged gas atoms, called ions, in Mars' upper atmosphere and shoots them into space. The MAVEN mission measured the rate of atmospheric stripping at about 100 grams (≈1/4 lb) per second.


title: Solar wind

text: Mercury, the nearest planet to the Sun, bears the full brunt of the solar wind, and since its atmosphere is vestigial and transient, its surface is bathed in radiation.


title: Solar wind

text: Mercury has an intrinsic magnetic field, so under normal solar wind conditions, the solar wind cannot penetrate its magnetosphere and particles only reach the surface in the cusp regions. During coronal mass ejections, however, the magnetopause may get pressed into the surface of the planet, and under these conditions, the solar wind may interact freely with the planetary surface.


title: Solar wind

text: The Earth's Moon has no atmosphere or intrinsic magnetic field, and consequently its surface is bombarded with the full solar wind. The Project Apollo missions deployed passive aluminum collectors in an attempt to sample the solar wind, and lunar soil returned for study confirmed that the lunar regolith is enriched in atomic nuclei deposited from the solar wind. These elements may prove useful resources for future lunar colonies.


title: Solar wind

text: The Alfvén surface is the boundary separating the corona from the solar wind defined as where the coronal plasma's Alfvén speed and the large-scale solar wind speed are equal.


title: Solar wind

text: Researchers were unsure exactly where the Alfvén critical surface of the Sun lay. Based on remote images of the corona, estimates had put it somewhere between 10 to 20 solar radii from the surface of the Sun. On April 28, 2021, during its eighth flyby of the Sun, NASA's Parker Solar Probe encountered the specific magnetic and particle conditions at 18.8 solar radii that indicated that it penetrated the Alfvén surface.


title: Solar wind

text: The solar wind "blows a bubble" in the interstellar medium (the rarefied hydrogen and helium gas that permeates the galaxy). The point where the solar wind's strength is no longer great enough to push back the interstellar medium is known as the heliopause and is often considered to be the outer border of the Solar System. The distance to the heliopause is not precisely known and probably depends on the current velocity of the solar wind and the local density of the interstellar medium, but it is far outside Pluto's orbit. Scientists hope to gain perspective on the heliopause from data acquired through the Interstellar Boundary Explorer (IBEX) mission, launched in October 2008.


title: Solar wind

text: The end of the heliosphere is noted as one of the ways defining the extent of the Solar System, along with the Kuiper Belt, and finally the radius at which of the Sun's gravitational influence is matched by other stars. The maximum extent of that influence has been estimated at between 50,000 AU and 2 light-years, compared to the edge of the heliopause (the outer edge of the heliosphere), which has been detected to end about 120 AU by the "Voyager 1" spacecraft.


title: Solar wind

text: The "Voyager 2" spacecraft crossed the shock more than five times between August 30 and December 10, 2007. "Voyager 2" crossed the shock about a Tm closer to the Sun than the 13.5 Tm distance where "Voyager 1" came upon the termination shock. The spacecraft moved outward through the termination shock into the heliosheath and onward toward the interstellar medium.


title: Solar wind

text: S.Cuperman and N. Metzler, Role of fluctuations in the interplanetary magnetic field on the heat conduction in the Solar Wind.J.Geophys. Res. 78 (16), 3167–3168, 1973.


title: Solar wind

text: S. Cuperman and N. Metzler, Solution of 3-fluid model equations with anomalous transport coefficients for thequiet Solar Wind. Astrophys.J., 196 (1) 205–219, 1975


title: Solar wind

text: S.Cuperman and N. Metzler, Relative magnitude of streaming velocities of alpha particles and protons at 1AU. Astrophys. and Space Sci. 45 (2) 411–417,1976.


title: Solar wind

text: N. Metzler. A multi-fluid model for stellar winds. Proceedings of the L.D.de Feiter Memorial Symposium on the Study of Traveling Interplanetary Phenomena. AFGL-TR-77-0309, Air Force Systems Command, USAF, 1978.


title: Solar wind

text: N. Metzler and M. Dryer, A self-consistent solution of the three-fluid model of the Solar Wind. Astrophys. J., 222 (2), 689–695, 1978.


title: Solar wind

text: S. Cuperman and N. Metzler, Comments on Acceleration of Solar Wind He++3 effects of Resonant and nonresonant interactions with transverse waves. J. Geophys. Res. 84 (NA5), 2139–2140 (1979)


title: New York City draft riots

text: The New York City draft riots (July 13–16, 1863), sometimes referred to as the Manhattan draft riots and known at the time as Draft Week, were violent disturbances in Lower Manhattan, widely regarded as the culmination of white working-class discontent with new laws passed by Congress that year to draft men to fight in the ongoing American Civil War. The riots remain the largest civil and most racially charged urban disturbance in American history. According to Toby Joyce, the riot represented a "civil war" inside the Irish Catholic community, in that "mostly Irish American rioters confronted police, [while] soldiers, and pro-war politicians ... were also to a considerable extent from the local Irish immigrant community."


title: New York City draft riots

text: President Abraham Lincoln diverted several regiments of militia and volunteer troops after the Battle of Gettysburg to control the city. The rioters were overwhelmingly Irish working-class men who did not want to fight in the Civil War and resented that wealthier men, who could afford to pay a $300 ( though a typical laborer's wage was between $1.00 and $2.00 a day in 1863) commutation fee to hire a substitute, were spared from the draft.


title: New York City draft riots

text: Initially intended to express anger at the draft, the protests turned into a race riot, with white rioters attacking black people, in violence throughout the city. The official death toll was listed at either 119 or 120 individuals. Conditions in the city were such that Major General John E. Wool, commander of the Department of the East, said on July 16 that, "Martial law ought to be proclaimed, but I have not a sufficient force to enforce it."


title: New York City draft riots

text: The military did not reach the city until the second day of rioting, by which time the mobs had ransacked or destroyed numerous public buildings, two Protestant churches, the homes of various abolitionists or sympathizers, many black homes, and the Colored Orphan Asylum at 44th Street and Fifth Avenue, which was burned to the ground. The area's demographics changed as a result of the riot. Many black residents left Manhattan permanently with many moving to Brooklyn. By 1865, the black population had fallen below 11,000 for the first time since 1820.


title: New York City draft riots

text: New York's economy was tied to the South; by 1822, nearly half of its exports were cotton shipments. In addition, upstate textile mills processed cotton in manufacturing. New York had such strong business connections to the South that on January 7, 1861, Mayor Fernando Wood, a Democrat, called on the city's Board of Aldermen to "declare the city's independence from Albany and from Washington"; he said it "would have the whole and united support of the Southern States." When the Union entered the war, New York City had many sympathizers with the South.


title: New York City draft riots

text: The city was also a continuing destination of immigrants. Since the 1840s, most were from Ireland and Germany. In 1860, nearly 25 percent of the New York City population was German-born, and many did not speak English. During the 1840s and 1850s, journalists had published sensational accounts, directed at the white working class, dramatizing the evils of interracial socializing, relationships, and marriages. Reformers joined the effort. Newspapers carried derogatory portrayals of black people and ridiculed "black aspirations for equal rights in voting, education, and employment".


title: New York City draft riots

text: The Democratic Party's Tammany Hall political machine had been working to enroll immigrants as U.S. citizens so they could vote in local elections and had strongly recruited Irish. In March 1863, with the war continuing, Congress passed the Enrollment Act to establish a draft for the first time, as more troops were needed. In New York City and other locations, new citizens learned they were expected to register for the draft to fight for their new country. Black men were excluded from the draft as they were largely not considered citizens, and wealthier white men could pay for substitutes.


title: New York City draft riots

text: New York political offices, including the mayor, were historically held by Democrats before the war, but the election of Abraham Lincoln as president had demonstrated the rise in Republican political power nationally. Newly elected New York City Republican Mayor George Opdyke was mired in profiteering scandals in the months leading up to the riots. The Emancipation Proclamation of January 1863 alarmed much of the white working class in New York, who feared that freed slaves would migrate to the city and add further competition to the labor market. There had already been tensions between black and white workers since the 1850s, particularly at the docks, with free blacks and immigrants competing for low-wage jobs in the city. In March 1863, white longshoremen refused to work with black laborers and rioted, attacking 200 black men.


title: New York City draft riots

text: There were reports of rioting in Buffalo, New York, and certain other cities, but the first drawing of draft numbers—on July 11, 1863—occurred peaceably in Manhattan. The second drawing was held on Monday, July 13, 1863, ten days after the Union victory at Gettysburg. At 10 a.m., a furious crowd of around 500, led by the volunteer firemen of Engine Company 33 (known as the "Black Joke"), attacked the assistant Ninth District provost marshal's office, at Third Avenue and 47th Street, where the draft was taking place.


title: New York City draft riots

text: The crowd threw large paving stones through windows, burst through the doors, and set the building ablaze. When the fire department responded, rioters broke up their vehicles. Others killed horses that were pulling streetcars and smashed the cars. To prevent other parts of the city being notified of the riot, they cut telegraph lines.


title: New York City draft riots

text: Since the New York State Militia had been sent to assist Union troops at Gettysburg, the local New York Metropolitan Police Department was the only force on hand to try to suppress the riots. Police Superintendent John Kennedy arrived at the site on Monday to check on the situation. Although he was not in uniform, people in the mob recognized him and attacked him. Kennedy was left nearly unconscious, his face bruised and cut, his eye injured, his lips swollen, and his hand cut with a knife. He had been beaten to a mass of bruises and blood all over his body.


title: New York City draft riots

text: Police drew their clubs and revolvers and charged the crowd but were overpowered. The police were badly outnumbered and unable to quell the riots, but they kept the rioting out of Lower Manhattan below Union Square. Inhabitants of the "Bloody Sixth" Ward, around the South Street Seaport and Five Points areas, refrained from involvement in the rioting. The 19th Company/1st Battalion US Army Invalid Corps which was part of the Provost Guard tried to disperse the mob with a volley of gunfire but were overwhelmed and suffered over 14 injured with 1 soldier missing (believed killed).


title: New York City draft riots

text: The Bull's Head hotel on 44th Street, which refused to provide alcohol to the rioters, was burned. The mayor's residence on Fifth Avenue was spared by words of Judge George Gardner Barnard, and the crowd of about 500 turned to another location of pillage. The Eighth and Fifth District police stations, and other buildings were attacked and set on fire. Other targets included the office of the "New York Times". The mob was turned back at the "Times" office by staff manning Gatling guns, including "Times" founder Henry Jarvis Raymond. Fire engine companies responded, but some firefighters were sympathetic to the rioters because they had also been drafted on Saturday. The "New York Tribune" was attacked, being looted and burned; not until police arrived and extinguished the flames, dispersing the crowd. Later in the afternoon, authorities shot and killed a man as a crowd attacked the armory at Second Avenue and 21st Street. The mob broke all the windows with paving stones ripped from the street. The mob beat, tortured and/or killed numerous black civilians, including one man who was attacked by a crowd of 400 with clubs and paving stones, then lynched, hanged from a tree and set alight.


title: New York City draft riots

text: The Colored Orphan Asylum at 43rd Street and Fifth Avenue, a "symbol of white charity to blacks and of black upward mobility" that provided shelter for 233 children, was attacked by a mob at around 4 p.m. A mob of several thousand, including many women and children, looted the building of its food and supplies. However, the police were able to secure the orphanage for enough time to allow the orphans to escape before the building burned down. Throughout the areas of rioting, mobs attacked and killed numerous black civilians and destroyed their known homes and businesses, such as James McCune Smith's pharmacy at 93 West Broadway, believed to be the first owned by a black man in the United States.


title: New York City draft riots

text: Near the midtown docks, tensions brewing since the mid-1850s boiled over. As recently as March 1863, white employers had hired black longshoremen, with whom many White men refused to work. Rioters went into the streets in search of "all the negro porters, cartmen and laborers" to attempt to remove all evidence of a black and interracial social life from the area near the docks. White dockworkers attacked and destroyed brothels, dance halls, boarding houses, and tenements that catered to black people. Mobs stripped the clothing off the white owners of these businesses.


title: New York City draft riots

text: Heavy rain fell on Monday night, helping to abate the fires and sending rioters home, but the crowds returned the next day. Rioters burned down the home of Abby Gibbons, a prison reformer and the daughter of abolitionist Isaac Hopper. They also attacked white "amalgamationists", such as Ann Derrickson and Ann Martin, two white women who were married to black men, and Mary Burke, a white prostitute who catered to black men.


title: New York City draft riots

text: Governor Horatio Seymour arrived on Tuesday and spoke at City Hall, where he attempted to assuage the crowd by proclaiming that the Conscription Act was unconstitutional. General John E. Wool, commander of the Eastern District, brought approximately 800 soldiers and Marines in from forts in New York Harbor, West Point, and the Brooklyn Navy Yard. He ordered the militias to return to New York.


title: New York City draft riots

text: The situation improved July 15 when assistant provost-marshal-general Robert Nugent received word from his superior officer, Colonel James Barnet Fry, to postpone the draft. As this news appeared in newspapers, some rioters stayed home. But some of the militias began to return and used harsh measures against the remaining rioters. The rioting spread to Brooklyn and Staten Island.


title: New York City draft riots

text: Order began to be restored on July 16. The New York State Militia and some federal troops were returned to New York, including the 152nd New York Volunteers, the 26th Michigan Volunteers, the 27th Indiana Volunteers and the 7th Regiment New York State Militia from Frederick, Maryland, after a forced march. In addition, the governor sent in the 74th and 65th regiments of the New York State Militia, which had not been in federal service, and a section of the 20th Independent Battery, New York Volunteer Artillery from Fort Schuyler in Throggs Neck. The New York State Militia units were the first to arrive. There were several thousand militia and Federal troops in the city.


title: New York City draft riots

text: A final confrontation occurred in the evening near Gramercy Park. According to Adrian Cook, twelve people died on this last day of the riots in skirmishes between rioters, the police, and the Army.


title: New York City draft riots

text: "The New York Times" reported on Thursday that Plug Uglies and Blood Tubs gang members from Baltimore, as well as "Scuykill Rangers [sic] and other rowdies of Philadelphia", had come to New York during the unrest to participate in the riots alongside the Dead Rabbits and "Mackerelvillers". The "Times" editorialized that "the scoundrels cannot afford to miss this golden opportunity of indulging their brutal natures, and at the same time serving their colleagues the Copperheads and secesh [secessionist] sympathizers."


title: New York City draft riots

text: The exact death toll during the New York draft riots is unknown, but according to historian James M. McPherson, 119 or 120 people were killed. Violence by longshoremen against black men was especially fierce in the docks area:


title: New York City draft riots

text: In all, eleven black men were hanged over five days. Among the murdered blacks was the seven-year-old nephew of Bermudian First Sergeant Robert John Simmons of the 54th Massachusetts Infantry Regiment, whose account of fighting in South Carolina, written on the approach to Fort Wagner July 18, 1863, was to be published in the "New York Tribune" on December 23, 1863 (Simmons having died in August of wounds received in the attack on Fort Wagner).


title: New York City draft riots

text: The most reliable estimates indicate at least 2,000 people were injured. Herbert Asbury, the author of the 1928 book "Gangs of New York", upon which the 2002 film was based, puts the figure much higher, at 2,000 killed and 8,000 wounded, a number that some dispute. Total property damage was about $1–5 million (equivalent to $ – $ in ). The city treasury later indemnified one-quarter of the amount.


title: New York City draft riots

text: Historian Samuel Eliot Morison wrote that the riots were "equivalent to a Confederate victory". Fifty buildings, including two Protestant churches and the Colored Orphan Asylum, were burned to the ground. 4,000 federal troops had to be pulled out of the Gettysburg Campaign to suppress the riots, troops that could have aided in pursuing the battered Army of Northern Virginia as it retreated out of Union territory. During the riots, landlords, fearing that the mob would destroy their buildings, drove black residents from their homes. As a result of the violence against them, hundreds of black people left New York, including physician James McCune Smith and his family, moving to Williamsburg, Brooklyn, or New Jersey.


title: New York City draft riots

text: The white elite in New York organized to provide relief to black riot victims, helping them find new work and homes. The Union League Club and the Committee of Merchants for the Relief of Colored People provided nearly $40,000 to 2,500 victims of the riots. By 1865 the black population in the city had dropped to under 10,000, the lowest since 1820. The white working-class riots had changed the demographics of the city, and white residents exerted their control in the workplace; they became "unequivocally divided" from the black population.


title: New York City draft riots

text: On August 19, the government resumed the draft in New York. It was completed within 10 days without further incident. Fewer men were drafted than had been feared by the white working class: of the 750,000 selected nationwide for conscription, only about 45,000 were sent into active duty.


title: New York City draft riots

text: While the rioting mainly involved the white working class, middle and upper-class New Yorkers had split sentiments on the draft and use of federal power or martial law to enforce it. Many wealthy Democratic businessmen sought to have the draft declared unconstitutional. Tammany Democrats did not seek to have the draft declared unconstitutional, but they helped pay the commutation fees for those who were drafted.


title: New York City draft riots

text: In December 1863, the Union League Club recruited more than 2,000 black soldiers, outfitted and trained them, honoring and sending men off with a parade through the city to the Hudson River docks in March 1864. A crowd of 100,000 watched the procession, which was led by police and members of the Union League Club.


title: New York City draft riots

text: New York's support for the Union cause continued, however grudgingly, and gradually Southern sympathies declined in the city. New York banks eventually financed the Civil War, and the state's industries were more productive than those of the entire Confederacy. By the end of the war, more than 450,000 soldiers, sailors, and militia had enlisted from New York State, which was the most populous state at the time. A total of 46,000 military men from New York State died during the war, more from disease than wounds, as was typical of most combatants.


title: New York City draft riots

text:
New York Metropolitan Police Department under the command of Superintendent John A. Kennedy.
Commissioners Thomas Coxon Acton and John G. Bergen took command when Kennedy was seriously injured by a mob during the early stages of the riots.


title: New York City draft riots

text: Secretary of War Edwin M. Stanton authorized five regiments from Gettysburg, mostly federalized state militia and volunteer units from the Army of the Potomac, to reinforce the New York City Police Department. By the end of the riots, there were more than 4,000 soldiers garrisoned in the troubled area.


title: Fiber-optic communication

text: Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of infrared light through an optical fiber. The light is a form of carrier wave that is modulated to carry information. Fiber is preferred over electrical cabling when high bandwidth, long distance, or immunity to electromagnetic interference is required. This type of communication can transmit voice, video, and telemetry through local area networks or across long distances.


title: Fiber-optic communication

text: Optical fiber is used by many telecommunications companies to transmit telephone signals, internet communication, and cable television signals. Researchers at Bell Labs have reached a record bandwidth–distance product of over kilometers per second using fiber-optic communication.


title: Fiber-optic communication

text: First developed in the 1970s, fiber-optics have revolutionized the telecommunications industry and have played a major role in the advent of the Information Age. Because of its advantages over electrical transmission, optical fibers have largely replaced copper wire communications in backbone networks in the developed world.


title: Fiber-optic communication

text: Optical fiber is used by telecommunications companies to transmit telephone signals, Internet communication and cable television signals. It is also used in other industries, including medical, defense, government, industrial and commercial. In addition to serving the purposes of telecommunications, it is used as light guides, for imaging tools, lasers, hydrophones for seismic waves, SONAR, and as sensors to measure pressure and temperature.


title: Fiber-optic communication

text: Due to lower attenuation and interference, optical fiber has advantages over copper wire in long-distance, high-bandwidth applications. However, infrastructure development within cities is relatively difficult and time-consuming, and fiber-optic systems can be complex and expensive to install and operate. Due to these difficulties, early fiber-optic communication systems were primarily installed in long-distance applications, where they can be used to their full transmission capacity, offsetting the increased cost. The prices of fiber-optic communications have dropped considerably since 2000.


title: Fiber-optic communication

text: The price for rolling out fiber to homes has currently become more cost-effective than that of rolling out a copper-based network. Prices have dropped to $850 per subscriber in the US and lower in countries like The Netherlands, where digging costs are low and housing density is high.


title: Fiber-optic communication

text: Since 1990, when optical-amplification systems became commercially available, the telecommunications industry has laid a vast network of intercity and transoceanic fiber communication lines. By 2002, an intercontinental network of 250,000 km of submarine communications cable with a capacity of 2.56 Tb/s was completed, and although specific network capacities are privileged information, telecommunications investment reports indicate that network capacity has increased dramatically since 2004. As of 2020, over 5 billion kilometers of fiber-optic cable has been deployed around the globe.


title: Fiber-optic communication

text: In 1880 Alexander Graham Bell and his assistant Charles Sumner Tainter created a very early precursor to fiber-optic communications, the Photophone, at Bell's newly established Volta Laboratory in Washington, D.C. Bell considered it his most important invention. The device allowed for the transmission of sound on a beam of light. On June 3, 1880, Bell conducted the world's first wireless telephone transmission between two buildings, some 213 meters apart. Due to its use of an atmospheric transmission medium, the Photophone would not prove practical until advances in laser and optical fiber technologies permitted the secure transport of light. The Photophone's first practical use came in military communication systems many decades later.


title: Fiber-optic communication

text: In 1954 Harold Hopkins and Narinder Singh Kapany showed that rolled fiber glass allowed light to be transmitted. Jun-ichi Nishizawa, a Japanese scientist at Tohoku University, proposed the use of optical fibers for communications in 1963. Nishizawa invented the PIN diode and the static induction transistor, both of which contributed to the development of optical fiber communications.


title: Fiber-optic communication

text: In 1966 Charles K. Kao and George Hockham at Standard Telecommunication Laboratories showed that the losses of 1,000 dB/km in existing glass (compared to 5–10 dB/km in coaxial cable) were due to contaminants which could potentially be removed.


title: Fiber-optic communication

text: Optical fiber with attenuation low enough for communication purposes (about 20 dB/km) was developed in 1970 by Corning Glass Works. At the same time, GaAs semiconductor lasers were developed that were compact and therefore suitable for transmitting light through fiber optic cables for long distances.


title: Fiber-optic communication

text: In 1973, Optelecom, Inc., co-founded by the inventor of the laser, Gordon Gould, received a contract from ARPA for one of the first optical communication systems. Developed for Army Missile Command in Huntsville, Alabama, the system was intended to allow a short-range missile with video processing to communicate by laser to the ground by means of a five-kilometer long optical fiber that unspooled from the missile as it flew. Optelecom then delivered the first commercial optical communications system to Chevron.


title: Fiber-optic communication

text: After a period of research starting from 1975, the first commercial fiber-optic telecommunications system was developed which operated at a wavelength around 0.8 μm and used GaAs semiconductor lasers. This first-generation system operated at a bit rate of 45 Mbit/s with repeater spacing of up to 10 km. Soon on 22 April 1977, General Telephone and Electronics sent the first live telephone traffic through fiber optics at a 6 Mbit/s throughput in Long Beach, California.


title: Fiber-optic communication

text: In October 1973, Corning Glass signed a development contract with CSELT and Pirelli aimed to test fiber optics in an urban environment: in September 1977, the second cable in this test series, named COS-2, was experimentally deployed in two lines (9 km) in Turin, for the first time in a big city, at a speed of 140 Mbit/s.


title: Fiber-optic communication

text: The second generation of fiber-optic communication was developed for commercial use in the early 1980s, operated at 1.3 μm and used InGaAsP semiconductor lasers. These early systems were initially limited by multi-mode fiber dispersion, and in 1981 the single-mode fiber was revealed to greatly improve system performance, however practical connectors capable of working with single mode fiber proved difficult to develop. Canadian service provider SaskTel had completed construction of what was then the world's longest commercial fiber optic network, which covered and linked 52 communities. By 1987, these systems were operating at bit rates of up to with repeater spacing up to .


title: Fiber-optic communication

text: The first transatlantic telephone cable to use optical fiber was TAT-8, based on Desurvire optimized laser amplification technology. It went into operation in 1988.


title: Fiber-optic communication

text: Third-generation fiber-optic systems operated at 1.55 μm and had losses of about 0.2 dB/km. This development was spurred by the discovery of indium gallium arsenide and the development of the indium gallium arsenide photodiode by Pearsall. Engineers overcame earlier difficulties with pulse-spreading using conventional InGaAsP semiconductor lasers at that wavelength by using dispersion-shifted fibers designed to have minimal dispersion at 1.55 μm or by limiting the laser spectrum to a single longitudinal mode. These developments eventually allowed third-generation systems to operate commercially at with repeater spacing in excess of .


title: Fiber-optic communication

text: The fourth generation of fiber-optic communication systems used optical amplification to reduce the need for repeaters and wavelength-division multiplexing (WDM) to increase data capacity. The introduction of WDM was the start of optical networking, as WDM became the technology of choice for fiber-optic bandwidth expansion. The first to market with a dense WDM system was Ciena Corp., in June 1996. The introduction of optical amplifiers and WDM caused system capacity to double every six months from 1992 until a bit rate of was reached by 2001. In 2006 a bit-rate of was reached over a single line using optical amplifiers. , Japanese scientists transmitted 319 terabits per second over 3,000 kilometers with four-core fiber cables with standard cable diameter.


title: Fiber-optic communication

text: The focus of development for the fifth generation of fiber-optic communications is on extending the wavelength range over which a WDM system can operate. The conventional wavelength window, known as the C band, covers the wavelength range 1525–1565 nm, and "dry fiber" has a low-loss window promising an extension of that range to 1300–1650 nm. Other developments include the concept of "optical solitons", pulses that preserve their shape by counteracting the effects of dispersion with the nonlinear effects of the fiber by using pulses of a specific shape.


title: Fiber-optic communication

text: In the late 1990s through 2000, industry promoters, and research companies such as KMI, and RHK predicted massive increases in demand for communications bandwidth due to increased use of the Internet, and commercialization of various bandwidth-intensive consumer services, such as video on demand. Internet protocol data traffic was increasing exponentially, at a faster rate than integrated circuit complexity had increased under Moore's Law. From the bust of the dot-com bubble through 2006, however, the main trend in the industry has been consolidation of firms and offshoring of manufacturing to reduce costs. Companies such as Verizon and AT&T have taken advantage of fiber-optic communications to deliver a variety of high-throughput data and broadband services to consumers' homes.


title: Fiber-optic communication

text: Modern fiber-optic communication systems generally include optical transmitters that convert electrical signals into optical signals, optical fiber cables to carry the signal, optical amplifiers, and optical receivers to convert the signal back into an electrical signal. The information transmitted is typically digital information generated by computers or telephone systems.


title: Fiber-optic communication

text: The most commonly used optical transmitters are semiconductor devices such as light-emitting diodes (LEDs) and laser diodes. The difference between LEDs and laser diodes is that LEDs produce incoherent light, while laser diodes produce coherent light. For use in optical communications, semiconductor optical transmitters must be designed to be compact, efficient and reliable, while operating in an optimal wavelength range and directly modulated at high frequencies.


title: Fiber-optic communication

text: In its simplest form, an LED emits light through spontaneous emission, a phenomenon referred to as electroluminescence. The emitted light is incoherent with a relatively wide spectral width of 30–60 nm. The large spectrum width of LEDs is subject to higher fiber dispersion, considerably limiting their bit rate-distance product (a common measure of usefulness). LEDs are suitable primarily for local-area-network applications with bit rates of 10–100 Mbit/s and transmission distances of a few kilometers.


title: Fiber-optic communication

text: LED light transmission is inefficient, with only about 1% of input power, or about 100 microwatts, eventually converted into launched power coupled into the optical fiber.


title: Fiber-optic communication

text: LEDs have been developed that use several quantum wells to emit light at different wavelengths over a broad spectrum and are currently in use for local-area wavelength-division multiplexing (WDM) applications.


title: Fiber-optic communication

text: LEDs have been largely superseded by vertical-cavity surface-emitting laser (VCSEL) devices, which offer improved speed, power and spectral properties, at a similar cost. However, due to their relatively simple design, LEDs are very useful for very low-cost applications. Commonly used classes of semiconductor laser transmitters used in fiber optics include VCSEL, Fabry–Pérot and distributed feedback laser.


title: Fiber-optic communication

text: A semiconductor laser emits light through stimulated emission rather than spontaneous emission, which results in high output power (~100 mW) as well as other benefits related to the nature of coherent light. The output of a laser is relatively directional, allowing high coupling efficiency (~50%) into single-mode fiber. Common VCSEL devices also couple well to multimode fiber. The narrow spectral width also allows for high bit rates since it reduces the effect of chromatic dispersion. Furthermore, semiconductor lasers can be modulated directly at high frequencies because of short recombination time.


title: Fiber-optic communication

text: Laser diodes are often directly modulated, that is the light output is controlled by a current applied directly to the device. For very high data rates or very long distance links, a laser source may be operated continuous wave, and the light modulated by an external device, an optical modulator, such as an electro-absorption modulator or Mach–Zehnder interferometer. External modulation increases the achievable link distance by eliminating laser chirp, which broadens the linewidth in directly modulated lasers, increasing the chromatic dispersion in the fiber. For very high bandwidth efficiency, coherent modulation can be used to vary the phase of the light in addition to the amplitude, enabling the use of QPSK, QAM, and OFDM. "Dual-polarization quadrature phase shift keying is a modulation format that effectively sends four times as much information as traditional optical transmissions of the same speed."


title: Fiber-optic communication

text: The main component of an optical receiver is a photodetector which converts light into electricity using the photoelectric effect. The primary photodetectors for telecommunications are made from Indium gallium arsenide. The photodetector is typically a semiconductor-based photodiode. Several types of photodiodes include p-n photodiodes, p-i-n photodiodes, and avalanche photodiodes. Metal-semiconductor-metal (MSM) photodetectors are also used due to their suitability for circuit integration in regenerators and wavelength-division multiplexers.


title: Fiber-optic communication

text: Since light may be attenuated and distorted while passing through the fiber, photodetectors are typically coupled with a transimpedance amplifier and a limiting amplifier to produce a digital signal in the electrical domain recovered from the incoming optical signal. Further signal processing such as clock recovery from data performed by a phase-locked loop may also be applied before the data is passed on.


title: Fiber-optic communication

text: Coherent receivers use a local oscillator laser in combination with a pair of hybrid couplers and four photodetectors per polarization, followed by high speed ADCs and digital signal processing to recover data modulated with QPSK, QAM, or OFDM.


title: Fiber-optic communication

text: An optical communication system transmitter consists of a digital-to-analog converter (DAC), a driver amplifier and a Mach–Zehnder modulator. The deployment of higher modulation formats (>4-QAM) or higher baud Rates (>) diminishes the system performance due to linear and non-linear transmitter effects. These effects can be categorized as linear distortions due to DAC bandwidth limitation and transmitter I/Q skew as well as non-linear effects caused by gain saturation in the driver amplifier and the Mach–Zehnder modulator. Digital predistortion counteracts the degrading effects and enables Baud rates up to and modulation formats like 64-QAM and 128-QAM with the commercially available components. The transmitter digital signal processor performs digital predistortion on the input signals using the inverse transmitter model before sending the samples to the DAC.


title: Fiber-optic communication

text: Older digital predistortion methods only addressed linear effects. Recent publications also consider non-linear distortions. "Berenguer et al" models the Mach–Zehnder modulator as an independent Wiener system and the DAC and the driver amplifier are modelled by a truncated, time-invariant Volterra series. "Khanna et al" use a memory polynomial to model the transmitter components jointly. In both approaches the Volterra series or the memory polynomial coefficients are found using indirect-learning architecture. "Duthel et al" records, for each branch of the Mach-Zehnder modulator, several signals at different polarity and phases. The signals are used to calculate the optical field. Cross-correlating in-phase and quadrature fields identifies the timing skew. The frequency response and the non-linear effects are determined by the indirect-learning architecture.


title: Fiber-optic communication

text: An optical fiber cable consists of a core, cladding, and a buffer (a protective outer coating), in which the cladding guides the light along the core by using the method of total internal reflection. The core and the cladding (which has a lower-refractive-index) are usually made of high-quality silica glass, although they can both be made of plastic as well. Connecting two optical fibers is done by fusion splicing or mechanical splicing and requires special skills and interconnection technology due to the microscopic precision required to align the fiber cores.


title: Fiber-optic communication

text: Two main types of optical fiber used in optic communications include multi-mode optical fibers and single-mode optical fibers. A multi-mode optical fiber has a larger core (≥50 micrometers), allowing less precise, cheaper transmitters and receivers to connect to it as well as cheaper connectors. However, a multi-mode fiber introduces multimode distortion, which often limits the bandwidth and length of the link. Furthermore, because of its higher dopant content, multi-mode fibers are usually expensive and exhibit higher attenuation. The core of a single-mode fiber is smaller (<10 micrometers) and requires more expensive components and interconnection methods, but allows much longer and higher-performance links. Both single- and multi-mode fiber is offered in different grades.


title: Fiber-optic communication

text: In order to package fiber into a commercially viable product, it typically is protectively coated by using ultraviolet cured acrylate polymers and assembled into a cable. After that, it can be laid in the ground and then run through the walls of a building and deployed aerially in a manner similar to copper cables. These fibers require less maintenance than common twisted pair wires once they are deployed.


title: Fiber-optic communication

text: Specialized cables are used for long-distance subsea data transmission, e.g. transatlantic communications cable. New (2011–2013) cables operated by commercial enterprises (Emerald Atlantis, Hibernia Atlantic) typically have four strands of fiber and signals cross the Atlantic (NYC-London) in 60–70 ms. The cost of each such cable was about $300M in 2011.


title: Fiber-optic communication

text: Another common practice is to bundle many fiber optic strands within long-distance power transmission cable using, for instance, an optical ground wire. This exploits power transmission rights of way effectively, ensures a power company can own and control the fiber required to monitor its own devices and lines, is effectively immune to tampering, and simplifies the deployment of smart grid technology.


title: Fiber-optic communication

text: The transmission distance of a fiber-optic communication system has traditionally been limited by fiber attenuation and by fiber distortion. By using optoelectronic repeaters, these problems have been eliminated. These repeaters convert the signal into an electrical signal and then use a transmitter to send the signal again at a higher intensity than was received, thus counteracting the loss incurred in the previous segment. Because of the high complexity with modern wavelength-division multiplexed signals, including the fact that they had to be installed about once every , the cost of these repeaters is very high.


title: Fiber-optic communication

text: An alternative approach is to use optical amplifiers which amplify the optical signal directly without having to convert the signal to the electrical domain. One common type of optical amplifier is an erbium-doped fiber amplifier (EDFA). These are made by doping a length of fiber with the rare-earth mineral erbium and laser pumping it with light with a shorter wavelength than the communications signal (typically 980 nm). EDFAs provide gain in the ITU C band at 1550 nm.


title: Fiber-optic communication

text: Optical amplifiers have several significant advantages over electrical repeaters. First, an optical amplifier can amplify a very wide band at once which can include hundreds of multiplexed channels, eliminating the need to demultiplex signals at each amplifier. Second, optical amplifiers operate independently of the data rate and modulation format, enabling multiple data rates and modulation formats to co-exist and enabling upgrading of the data rate of a system without having to replace all of the repeaters. Third, optical amplifiers are much simpler than a repeater with the same capabilities and are therefore significantly more reliable. Optical amplifiers have largely replaced repeaters in new installations, although electronic repeaters are still widely used when signal conditioning beyond amplification is required.


title: Fiber-optic communication

text: Wavelength-division multiplexing (WDM) is the technique of transmitting multiple channels of information through a single optical fiber by sending multiple light beams of different wavelengths through the fiber, each modulated with a separate information channel. This allows the available capacity of optical fibers to be multiplied. This requires a wavelength division multiplexer in the transmitting equipment and a demultiplexer (essentially a spectrometer) in the receiving equipment. Arrayed waveguide gratings are commonly used for multiplexing and demultiplexing in WDM. Using WDM technology now commercially available, the bandwidth of a fiber can be divided into as many as 160 channels to support a combined bit rate in the range of .


title: Fiber-optic communication

text: Because the effect of dispersion increases with the length of the fiber, a fiber transmission system is often characterized by its "bandwidth–distance product", usually expressed in units of MHz·km. This value is a product of bandwidth and distance because there is a trade-off between the bandwidth of the signal and the distance over which it can be carried. For example, a common multi-mode fiber with bandwidth–distance product of 500 MHz·km could carry a 500 MHz signal for 1 km or a 1000 MHz signal for 0.5 km.


title: Fiber-optic communication

text: Each fiber can carry many independent channels, each using a different wavelength of light (wavelength-division multiplexing). The net data rate (data rate without overhead bytes) per fiber is the per-channel data rate reduced by the forward error correction (FEC) overhead, multiplied by the number of channels (usually up to eighty in commercial dense WDM systems ).


title: Fiber-optic communication

text: The following summarizes the current state-of-the-art research using standard telecoms-grade single-mode, single-solid-core fibre cables.


title: Fiber-optic communication

text: The 2016 Nokia/DT/TUM result is notable as it is the first result that pushes close to the Shannon theoretical limit.


title: Fiber-optic communication

text: The 2011 KIT and 2020 RMIT/Monash/Swinburne results are notable for having used a single source to drive all channels.


title: Fiber-optic communication

text: The following summaries the current state-of-the-art research using specialised cables that allow spatial multiplexing to occur, use specialised tri-mode fibre cables or similar specialised fibre optic cables.


title: Fiber-optic communication

text: The 2018 NICT result is notable for breaking the record for throughput using a single core cable, that is, not using spatial multiplexing.