Operant conditioning
Operant conditioning is a learning process through which the strength of a behavior is modified by reinforcement or punishment. It is a procedure, used to bring about such learning. Although operant and classical conditioning both involve behaviors controlled by environmental stimuli, they differ in nature. In operant conditioning, stimuli present when a behavior is rewarded or punished come to control that behavior. For example, a child may learn to open a box to get the sweets inside, or learn to avoid touching a hot stove. Operant behavior is said to be "voluntary": for example, the child may face a choice between opening the box and petting a puppy. In contrast, classical conditioning involves involuntary behavior based on the pairing of stimuli with biologically significant events. For example, sight of sweets may cause a child to salivate, or the sound of a door slam may signal an angry parent, causing a child to tremble. Salivation and trembling are not operants; the study of animal learning in the 20th century was dominated by the analysis of these two sorts of learning, they are still at the core of behavior analysis.
Operant conditioning, sometimes called instrumental learning, was first extensively studied by Edward L. Thorndike, who observed the behavior of cats trying to escape from home-made puzzle boxes. A cat could escape from the box by a simple response such as pulling a cord or pushing a pole, but when first constrained, the cats took a long time to get out. With repeated trials ineffective responses occurred less and successful responses occurred more so the cats escaped more and more quickly. Thorndike generalized this finding in his law of effect, which states that behaviors followed by satisfying consequences tend to be repeated and those that produce unpleasant consequences are less to be repeated. In short, some consequences strengthen some consequences weaken behavior. By plotting escape time against trial number Thorndike produced the first known animal learning curves through this procedure. Humans appear to learn many simple behaviors through the sort of process studied by Thorndike, now called operant conditioning.
That is, responses are retained when they lead to a successful outcome and discarded when they do not, or when they produce aversive effects. This happens without being planned by any "teacher", but operant conditioning has been used by parents in teaching their children for thousands of years. B. F. Skinner is referred to as the father of operant conditioning, his work is cited in connection with this topic, his 1938 book "The Behavior of Organisms: An Experimental Analysis", initiated his lifelong study of operant conditioning and its application to human and animal behavior. Following the ideas of Ernst Mach, Skinner rejected Thorndike's reference to unobservable mental states such as satisfaction, building his analysis on observable behavior and its observable consequences. Skinner believed that classical conditioning was too simplistic to be used to describe something as complex as human behavior. Operant conditioning, in his opinion, better described human behavior as it examined causes and effects of intentional behavior.
To implement his empirical approach, Skinner invented the operant conditioning chamber, or "Skinner Box", in which subjects such as pigeons and rats were isolated and could be exposed to controlled stimuli. Unlike Thorndike's puzzle box, this arrangement allowed the subject to make one or two simple, repeatable responses, the rate of such responses became Skinner's primary behavioral measure. Another invention, the cumulative recorder, produced a graphical record from which these response rates could be estimated; these records were the primary data that Skinner and his colleagues used to explore the effects on response rate of various reinforcement schedules. A reinforcement schedule may be defined as "any procedure that delivers reinforcement to an organism according to some well-defined rule"; the effects of schedules became, in turn, the basic findings from which Skinner developed his account of operant conditioning. He drew on many less formal observations of human and animal behavior. Many of Skinner's writings are devoted to the application of operant conditioning to human behavior.
In 1948 he published Walden Two, a fictional account of a peaceful, productive community organized around his conditioning principles. In 1957, Skinner published Verbal Behavior, which extended the principles of operant conditioning to language, a form of human behavior, analyzed quite differently by linguists and others. Skinner defined new functional relationships such as "mands" and "tacts" to capture some essentials of language, but he introduced no new principles, treating verbal behavior like any other behavior controlled by its consequences, which included the reactions of the speaker's audience. Operant behavior is said to be "emitted", thus one may ask. The answer to this question is like Darwin's answer to the question of the origin of a "new" bodily structure, namely and selection; the behavior of an individual varies from moment to moment, in such aspects as the specific motions involved, the amount of force applied, or the timing of the response. Variations that lead to reinforcement are strengthened, if reinforcement is consistent, the behavior tends to remain stable.
However, behavioral variability can itself be altered through the manipulation
Harvard University
Harvard University is a private Ivy League research university in Cambridge, with about 6,700 undergraduate students and about 15,250 postgraduate students. Established in 1636 and named for its first benefactor, clergyman John Harvard, Harvard is the United States' oldest institution of higher learning, its history and wealth have made it one of the world's most prestigious universities; the Harvard Corporation is its first chartered corporation. Although never formally affiliated with any denomination, the early College trained Congregational and Unitarian clergy, its curriculum and student body were secularized during the 18th century, by the 19th century, Harvard had emerged as the central cultural establishment among Boston elites. Following the American Civil War, President Charles W. Eliot's long tenure transformed the college and affiliated professional schools into a modern research university. A. Lawrence Lowell, who followed Eliot, further reformed the undergraduate curriculum and undertook aggressive expansion of Harvard's land holdings and physical plant.
James Bryant Conant led the university through the Great Depression and World War II and began to reform the curriculum and liberalize admissions after the war. The undergraduate college became coeducational after its 1977 merger with Radcliffe College; the university is organized into eleven separate academic units—ten faculties and the Radcliffe Institute for Advanced Study—with campuses throughout the Boston metropolitan area: its 209-acre main campus is centered on Harvard Yard in Cambridge 3 miles northwest of Boston. Harvard's endowment is worth $39.2 billion, making it the largest of any academic institution. Harvard is a large residential research university; the nominal cost of attendance is high, but the university's large endowment allows it to offer generous financial aid packages. The Harvard Library is the world's largest academic and private library system, comprising 79 individual libraries holding over 18 million items; the University is cited as one of the world's top tertiary institutions by various organizations.
Harvard's alumni include eight U. S. presidents, more than thirty foreign heads of state, 62 living billionaires, 359 Rhodes Scholars, 242 Marshall Scholars. As of October 2018, 158 Nobel laureates, 18 Fields Medalists, 14 Turing Award winners have been affiliated as students, faculty, or researchers. In addition, Harvard students and alumni have won 10 Academy Awards, 48 Pulitzer Prizes and 108 Olympic medals, have founded a large number of companies worldwide. Harvard was established in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. In 1638, it acquired British North America's first known printing press. In 1639, it was named Harvard College after deceased clergyman John Harvard, an alumnus of the University of Cambridge, who had left the school £779 and his scholar's library of some 400 volumes; the charter creating the Harvard Corporation was granted in 1650. A 1643 publication gave the school's purpose as "to advance learning and perpetuate it to posterity, dreading to leave an illiterate ministry to the churches when our present ministers shall lie in the dust".
It offered a classic curriculum on the English university model—many leaders in the colony had attended the University of Cambridge—but conformed to the tenets of Puritanism. It was never affiliated with any particular denomination, but many of its earliest graduates went on to become clergymen in Congregational and Unitarian churches; the leading Boston divine Increase Mather served as president from 1685 to 1701. In 1708, John Leverett became the first president, not a clergyman, marking a turning of the college from Puritanism and toward intellectual independence. Throughout the 18th century, Enlightenment ideas of the power of reason and free will became widespread among Congregational ministers, putting those ministers and their congregations in tension with more traditionalist, Calvinist parties; when the Hollis Professor of Divinity David Tappan died in 1803 and the president of Harvard Joseph Willard died a year in 1804, a struggle broke out over their replacements. Henry Ware was elected to the chair in 1805, the liberal Samuel Webber was appointed to the presidency of Harvard two years which signaled the changing of the tide from the dominance of traditional ideas at Harvard to the dominance of liberal, Arminian ideas.
In 1846, the natural history lectures of Louis Agassiz were acclaimed both in New York and on the campus at Harvard College. Agassiz's approach was distinctly idealist and posited Americans' "participation in the Divine Nature" and the possibility of understanding "intellectual existences". Agassiz's perspective on science combined observation with intuition and the assumption that a person can grasp the "divine plan" in all phenomena; when it came to explaining life-forms, Agassiz resorted to matters of shape based on a presumed archetype for his evidence. This dual view of knowledge was in concert with the teachings of Common Sense Realism derived from Scottish philosophers Thomas Reid and Dugald Stewart, whose works were part of the Harvard curriculum at the time; the popularity of Agassiz's efforts to "soar with Plato" also derived from other writings to which Harvard students
YouTube
YouTube is an American video-sharing website headquartered in San Bruno, California. Three former PayPal employees—Chad Hurley, Steve Chen, Jawed Karim—created the service in February 2005. Google bought the site in November 2006 for US$1.65 billion. YouTube allows users to upload, rate, add to playlists, comment on videos, subscribe to other users, it offers a wide variety of corporate media videos. Available content includes video clips, TV show clips, music videos and documentary films, audio recordings, movie trailers, live streams, other content such as video blogging, short original videos, educational videos. Most of the content on YouTube is uploaded by individuals, but media corporations including CBS, the BBC, Hulu offer some of their material via YouTube as part of the YouTube partnership program. Unregistered users can only watch videos on the site, while registered users are permitted to upload an unlimited number of videos and add comments to videos. Videos deemed inappropriate are available only to registered users affirming themselves to be at least 18 years old.
YouTube and its creators earn advertising revenue from Google AdSense, a program which targets ads according to site content and audience. The vast majority of its videos are free to view, but there are exceptions, including subscription-based premium channels, film rentals, as well as YouTube Music and YouTube Premium, subscription services offering premium and ad-free music streaming, ad-free access to all content, including exclusive content commissioned from notable personalities; as of February 2017, there were more than 400 hours of content uploaded to YouTube each minute, one billion hours of content being watched on YouTube every day. As of August 2018, the website is ranked as the second-most popular site in the world, according to Alexa Internet. YouTube has faced criticism over aspects of its operations, including its handling of copyrighted content contained within uploaded videos, its recommendation algorithms perpetuating videos that promote conspiracy theories and falsehoods, hosting videos ostensibly targeting children but containing violent and/or sexually suggestive content involving popular characters, videos of minors attracting pedophilic activities in their comment sections, fluctuating policies on the types of content, eligible to be monetized with advertising.
YouTube was founded by Chad Hurley, Steve Chen, Jawed Karim, who were all early employees of PayPal. Hurley had studied design at Indiana University of Pennsylvania, Chen and Karim studied computer science together at the University of Illinois at Urbana–Champaign. According to a story, repeated in the media and Chen developed the idea for YouTube during the early months of 2005, after they had experienced difficulty sharing videos, shot at a dinner party at Chen's apartment in San Francisco. Karim did not attend the party and denied that it had occurred, but Chen commented that the idea that YouTube was founded after a dinner party "was very strengthened by marketing ideas around creating a story, digestible". Karim said the inspiration for YouTube first came from Janet Jackson's role in the 2004 Super Bowl incident, when her breast was exposed during her performance, from the 2004 Indian Ocean tsunami. Karim could not find video clips of either event online, which led to the idea of a video sharing site.
Hurley and Chen said that the original idea for YouTube was a video version of an online dating service, had been influenced by the website Hot or Not. Difficulty in finding enough dating videos led to a change of plans, with the site's founders deciding to accept uploads of any type of video. YouTube began as a venture capital-funded technology startup from an $11.5 million investment by Sequoia Capital and an $8 million investment from Artis Capital Management between November 2005 and April 2006. YouTube's early headquarters were situated above a pizzeria and Japanese restaurant in San Mateo, California; the domain name www.youtube.com was activated on February 14, 2005, the website was developed over the subsequent months. The first YouTube video, titled Me at the zoo, shows co-founder Jawed Karim at the San Diego Zoo; the video was uploaded on April 23, 2005, can still be viewed on the site. YouTube offered the public a beta test of the site in May 2005; the first video to reach one million views was a Nike advertisement featuring Ronaldinho in November 2005.
Following a $3.5 million investment from Sequoia Capital in November, the site launched on December 15, 2005, by which time the site was receiving 8 million views a day. The site grew and, in July 2006, the company announced that more than 65,000 new videos were being uploaded every day, that the site was receiving 100 million video views per day. According to data published by market research company comScore, YouTube is the dominant provider of online video in the United States, with a market share of around 43% and more than 14 billion views of videos in May 2010. In May 2011, 48 hours of new videos were uploaded to the site every minute, which increased to 60 hours every minute in January 2012, 100 hours every minute in May 2013, 300 hours every minute in November 2014, 400 hours every minute in February 2017; as of January 2012, the site had 800 million unique users a month. It is estimated that in 2007 YouTube consumed as much bandwidth as the entire Internet in 2000. According to third-party web analytics providers and SimilarWeb, YouTube is the second-most visited website in the world, as of December 2016.
Bern
Bern or Berne is the de facto capital of Switzerland, referred to by the Swiss as their "federal city", in German Bundesstadt, French Ville Fédérale, Italian Città Federale. With a population of 142,493, Bern is the fifth-most populous city in Switzerland; the Bern agglomeration, which includes 36 municipalities, had a population of 406,900 in 2014. The metropolitan area had a population of 660,000 in 2000. Bern is the capital of the canton of Bern, the second-most populous of Switzerland's cantons; the official language in Bern is German, but the most-spoken language is an Alemannic Swiss German dialect, Bernese German. In 1983, the historic old town in the centre of Bern became a UNESCO World Heritage Site; the etymology of the name "Bern" is uncertain. According to the local legend, based on folk etymology, Berchtold V, Duke of Zähringen, the founder of the city of Bern, vowed to name the city after the first animal he met on the hunt, this turned out to be a bear, it has long been considered that the city was named after the Italian city of Verona, which at the time was known as Bern in Middle High German.
As a result of the finding of the Bern zinc tablet in the 1980s, it is now more common to assume that the city was named after a pre-existing toponym of Celtic origin *berna "cleft". The bear was the heraldic animal of the coat of arms of Bern from at least the 1220s; the earliest reference to the keeping of live bears in the Bärengraben dates to the 1440s. No archaeological evidence that indicates a settlement on the site of today′s city centre prior to the 12th century has been found so far. In antiquity, a Celtic oppidum stood on the Engehalbinsel north of Bern, fortified since the second century BC, thought to be one of the 12 oppida of the Helvetii mentioned by Caesar. During the Roman era, a Gallo-Roman vicus was on the same site; the Bern zinc tablet has the name Brenodor. In the Early Middle Ages, a settlement in Bümpliz, now a city district of Bern, was some 4 km from the medieval city; the medieval city is a foundation of the Zähringer ruling family, which rose to power in Upper Burgundy in the 12th century.
According to 14th-century historiography, Bern was founded in 1191 by Duke of Zähringen. In 1218, after Berthold died without an heir, Bern was made a free imperial city by the Goldene Handfeste of Holy Roman Emperor Frederick II. In 1353, Bern joined the Swiss Confederacy, becoming one of the eight cantons of the formative period of 1353 to 1481. Bern invaded and conquered Aargau in 1415 and Vaud in 1536, as well as other smaller territories, thereby becoming the largest city-state north of the Alps; the city grew out towards the west of the boundaries of the peninsula formed by the river Aare. The Zytglogge tower marked the western boundary of the city from 1191 until 1256, when the Käfigturm took over this role until 1345, it was, in turn, succeeded by the Christoffelturm until 1622. During the time of the Thirty Years' War, two new fortifications – the so-called big and small Schanze – were built to protect the whole area of the peninsula. After a major blaze in 1405, the city's original wooden buildings were replaced by half-timbered houses and subsequently the sandstone buildings which came to be characteristic for the Old Town.
Despite the waves of pestilence that hit Europe in the 14th century, the city continued to grow due to immigration from the surrounding countryside. Bern was occupied by French troops in 1798 during the French Revolutionary Wars, when it was stripped of parts of its territories, it regained control of the Bernese Oberland in 1802, following the Congress of Vienna of 1814, it newly acquired the Bernese Jura. At this time, it once again became the largest canton of the Confederacy as it stood during the Restoration and until the secession of the canton of Jura in 1979. Bern was made the Federal City within the new Swiss federal state in 1848. A number of congresses of the socialist First and Second Internationals were held in Bern during World War I when Switzerland was neutral; the city's population rose from about 5,000 in the 15th century to about 12,000 by 1800 and to above 60,000 by 1900, passing the 100,000 mark during the 1920s. Population peaked during the 1960s at 165,000 and has since decreased to below 130,000 by 2000.
As of September 2017, the resident population stood at 142,349, of which 100,000 were Swiss citizens and 42,349 resident foreigners. A further estimated 350,000 people live in the immediate urban agglomeration. Bern lies on the Swiss plateau in the canton of Bern west of the centre of Switzerland and 20 km north of the Bernese Alps; the countryside around Bern was formed by glaciers during the most recent ice age. The two mountains closest to Bern are Gurten with a height of 864 m and Bantiger with a height of 947 m; the site of the old observatory in Bern is the point of origin of the CH1903 coordinate system at 46°57′08.66″N 7°26′22.50″E. The city was built on a hilly peninsula surrounded by the river Aare, but outgrew natural boundaries by the 19th century. A number of bridges have been built to allow the city to expand beyond the Aare. Bern is built on uneven ground. An elevation difference of several metres exists betwe
Electrical telegraph
An electrical telegraph is a telegraph that uses coded electrical signals to convey information via dedicated electrical wiring. Electrical telegraphy dates from the early 1800s, is distinct from the electrical telephony, which uses the analogue magnitude of electrical signals to convey information; the electrical telegraph, or more just telegraph, superseded optical semaphore telegraph systems, thus becoming the first form of electrical telecommunications. In a matter of decades after their creation in the 1830s, electrical telegraph networks permitted people and commerce to transmit messages across both continents and oceans instantly, with widespread social and economic impacts. From early studies of electricity, electrical phenomena were known to travel with great speed, many experimenters worked on the application of electricity to communications at a distance. All the known effects of electricity - such as sparks, electrostatic attraction, chemical changes, electric shocks, electromagnetism - were applied to the problems of detecting controlled transmissions of electricity at various distances.
In 1753, an anonymous writer in the Scots Magazine suggested an electrostatic telegraph. Using one wire for each letter of the alphabet, a message could be transmitted by connecting the wire terminals in turn to an electrostatic machine, observing the deflection of pith balls at the far end. Telegraphs employing electrostatic attraction were the basis of early experiments in electrical telegraphy in Europe, but were abandoned as being impractical and were never developed into a useful communication system. In 1774, Georges-Louis Le Sage realised an early electric telegraph; the telegraph had a separate wire for each of the 26 letters of the alphabet and its range was only between two rooms of his home. In 1800, Alessandro Volta invented the voltaic pile, allowing for a continuous current of electricity for experimentation; this became a source of a low-voltage current that could be used to produce more distinct effects, and, far less limited than the momentary discharge of an electrostatic machine, which with Leyden jars were the only known man-made sources of electricity.
Another early experiment in electrical telegraphy was an'electrochemical telegraph' created by the German physician and inventor Samuel Thomas von Sömmering in 1809, based on an earlier, less robust design of 1804 by Spanish polymath and scientist Francisco Salva Campillo. Both their designs employed multiple wires to represent all Latin letters and numerals. Thus, messages could be conveyed electrically up to a few kilometers, with each of the telegraph receiver's wires immersed in a separate glass tube of acid. An electric current was sequentially applied by the sender through the various wires representing each digit of a message; the telegraph receiver's operator would watch the bubbles and could record the transmitted message. This is in contrast to telegraphs that used a single wire. Hans Christian Ørsted discovered in 1820 that an electric current produces a magnetic field that will deflect a compass needle. In the same year Johann Schweigger invented the galvanometer, with a coil of wire around a compass, which could be used as a sensitive indicator for an electric current.
In 1821, André-Marie Ampère suggested that telegraphy could be done by a system of galvanometers, with one wire per galvanometer to indicate each letter, said he had experimented with such a system. In 1824, Peter Barlow said that such a system only worked to a distance of about 200 feet, so was impractical. In 1825, William Sturgeon invented the electromagnet, with a single winding of uninsulated wire on a piece of varnished iron, which increased the magnetic force produced by electric current. Joseph Henry improved it in 1828 by placing several windings of insulated wire around the bar, creating a much more powerful electromagnet which could operate a telegraph through the high resistance of long telegraph wires. During his tenure at The Albany Academy from 1826 to 1832, Henry first demonstrated the theory of the'magnetic telegraph' by ringing a bell through a mile of wire strung around the room. In 1835, Joseph Henry and Edward Davy invented the critical electrical relay. Davy's relay used a magnetic needle which dipped into a mercury contact when an electric current passed through the surrounding coil.
Davy demonstrated his telegraph system in Regent's Park in 1837 and was granted a patent on 4 July 1838. Davy invented a printing telegraph which used the electric current from the telegraph signal to mark a ribbon of calico impregnated with potassium iodide and calcium hypochlorite; the first working telegraph was built by the English inventor Francis Ronalds in 1816 and used static electricity. At the family home on Hammersmith Mall, he set up a complete subterranean system in a 175 yard long trench as well as an eight mile long overhead telegraph; the lines were connected at both ends to revolving dials marked with the letters of the alphabet and electrical impulses sent along the wire were used to transmit messages. Offering his invention to the Admiralty in July 1816, it was rejected as "wholly unnecessary", his account of the scheme and the possibilities of rapid global communication in Descriptions of an Electrical Telegraph and of some other Electrical Apparatus was the first published work on electric telegraphy and described the risk of signal retardation due to induction.
Elements of Ronalds’ design were utilised in the subsequent commercialisation of the telegraph over 2
Wireless telegraphy
Wireless telegraphy means transmission of telegraph signals by radio waves. Before about 1910 when radio became dominant, the term wireless telegraphy was used for various other experimental technologies for transmitting telegraph signals without wires, such as electromagnetic induction, ground conduction telegraph systems. Radiotelegraphy was the first means of radio communication, it continued to be the only type of radio transmission during the first three decades of radio, called the "wireless telegraphy era" up until World War I, when the development of amplitude modulation radiotelephony allowed sound to be transmitted by radio. In radiotelegraphy, information is transmitted by pulses of radio waves of two different lengths called "dots" and "dashes", which spell out text messages in Morse code. In a manual system, the sending operator taps on a switch called a telegraph key which turns the transmitter on and off, producing the pulses of radio waves. At the receiver the pulses are audible in the receiver's speaker as beeps, which are translated back to text by an operator who knows Morse code.
Radiotelegraphy was used for long distance person-to-person commercial and military text communication throughout the first half of the 20th century. It became a strategically important capability during the two world wars, since a nation without long distance radiotelegraph stations could be isolated from the rest of the world by an enemy cutting its submarine telegraph cables. Beginning about 1908, powerful transoceanic radiotelegraphy stations transmitted commercial telegram traffic between countries at rates up to 200 words per minute. Radiotelegraphy was transmitted by several different modulation methods during its history; the primitive spark gap transmitters used until 1920 transmitted damped waves, which had large bandwidth and tended to interfere with other transmissions. This type of emission was banned by 1930; the vacuum tube transmitters which came into use after 1920 transmitted code by pulses of unmodulated sinusoidal carrier wave called continuous waves, still used today. To make CW transmissions audible, the receiver requires a circuit called a beat frequency oscillator.
A third type of modulation, frequency shift keying was used by radioteletypes. Morse code radiotelegraphy was replaced by radioteletype networks in most high volume applications by World War 2. Today it is nearly obsolete, the only remaining users are the radio amateur community and some limited training by the military for emergency use. Wireless telegraphy or radiotelegraphy called CW, ICW transmission, or on-off keying, designated by the International Telecommunication Union as emission type A1A, is a radio communication method in which the sending operator taps on a switch called a telegraph key, which turns the radio transmitter on and off, producing pulses of unmodulated carrier wave of different lengths called "dots" and "dashes", which encode characters of text in Morse code. At the receiving location the code is audible in the radio receiver's earphone or speaker as a sequence of buzzes or beeps, translated back to text by an operator who knows Morse code. Although this type of communication has been replaced since its introduction over 100 years ago by other means of communication it is still used by amateur radio operators as well as some military services.
A CW coastal station, KSM, still exists in California, run as a museum by volunteers, occasional contacts with ships are made. Radio beacons in the aviation service, but as "placeholders" for commercial ship-to-shore systems transmit Morse but at slow speeds; the US Federal Communications Commission issues a lifetime commercial Radiotelegraph Operator License. This requires passing a simple written test on regulations, a more complex written exam on technology, demonstrating Morse reception at 20 words per minute plain language and 16 wpm code groups. Wireless telegraphy is still used today by amateur radio hobbyists where it is referred to as radio telegraphy, continuous wave, or just CW. However, its knowledge is not required to obtain any class of amateur license. Continuous wave radiotelegraphy is regulated by the International Telecommunication Union as emission type A1A. Efforts to find a way to transmit telegraph signals without wires grew out of the success of electric telegraph networks, the first instant telecommunication systems.
Developed beginning in the 1830s, a telegraph line was a person-to-person text message system consisting of multiple telegraph offices linked by an overhead wire supported on telegraph poles. To send a message, an operator at one office would tap on a switch called a telegraph key, creating pulses of electric current which spelled out a message in Morse code; when the key was pressed, it would connect a battery to the telegraph line, sending current down the wire. At the receiving office the current pulses would operate a telegraph sounder, a device which would make a "click" sound when it received each pulse of current; the operator at the receiving station who knew Morse code would translate the clicking sounds to text and write down the message. The ground was used as the return path for current in the telegraph circuit, to avoid having to use a second overhead wire. By the 1860s, telegraph was the standard way to send most urgent commercial and milita
