Submarine communications cable
A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean and sea. The first submarine communications cables laid beginning in the 1850s carried telegraphy traffic, establishing the first instant telecommunications links between continents, such as the first transatlantic telegraph cable which became operational on 16 August 1858. Subsequent generations of cables carried telephone traffic data communications traffic. Modern cables use optical fiber technology to carry digital data, which includes telephone and private data traffic. Modern cables are about 1 inch in diameter and weigh around 2.5 tons per mile for the deep-sea sections which comprise the majority of the run, although larger and heavier cables are used for shallow-water sections near shore. Submarine cables first connected all the world's continents when Java was connected to Darwin, Northern Territory, Australia in 1871 in anticipation of the completion of the Australian Overland Telegraph Line in 1872 connecting to Adelaide, South Australia and thence to the rest of Australia.
After William Cooke and Charles Wheatstone had introduced their working telegraph in 1839, the idea of a submarine line across the Atlantic Ocean began to be thought of as a possible triumph of the future. Samuel Morse proclaimed his faith in it as early as 1840, in 1842, he submerged a wire, insulated with tarred hemp and India rubber, in the water of New York Harbor, telegraphed through it; the following autumn, Wheatstone performed a similar experiment in Swansea Bay. A good insulator to cover the wire and prevent the electric current from leaking into the water was necessary for the success of a long submarine line. India rubber had been tried by Moritz von Jacobi, the Prussian electrical engineer, as far back as the early 19th century. Another insulating gum which could be melted by heat and applied to wire made its appearance in 1842. Gutta-percha, the adhesive juice of the Palaquium gutta tree, was introduced to Europe by William Montgomerie, a Scottish surgeon in the service of the British East India Company.
Twenty years earlier, Montgomerie had seen whips made of gutta-percha in Singapore, he believed that it would be useful in the fabrication of surgical apparatus. Michael Faraday and Wheatstone soon discovered the merits of gutta-percha as an insulator, in 1845, the latter suggested that it should be employed to cover the wire, proposed to be laid from Dover to Calais, it was tried on a wire laid across the Rhine between Cologne. In 1849, C. V. Walker, electrician to the South Eastern Railway, submerged a two-mile wire coated with gutta-percha off the coast from Folkestone, tested successfully. Having earlier obtained a concession from the French government, in August 1850 John Watkins Brett's English Channel Submarine Telegraph Company laid the first line across the English Channel, using the converted tug Goliath, it was a copper wire coated with gutta-percha, without any other protection, was not successful. The experiment served to secure renewal of the concession, in September 1851, a protected core, or true, cable was laid by the reconstituted Submarine Telegraph Company from a government hulk, the Blazer, towed across the Channel.
In 1853 further successful cables were laid, linking Great Britain with Ireland and the Netherlands, crossing The Belts in Denmark. The British & Irish Magnetic Telegraph Company completed the first successful Irish link on May 23 between Portpatrick and Donaghadee using the collier William Hutt; the same ship was used for the link from Dover to Ostend in Belgium, by the Submarine Telegraph Company. Meanwhile, the Electric & International Telegraph Company completed two cables across the North Sea, from Orford Ness to Scheveningen, The Netherlands; these cables were laid by the Monarch, a paddle steamer which became the first vessel with permanent cable-laying equipment. In 1858 the steamship Elba was used to lay a telegraph cable from Jersey to Guernsey, on to Alderney and to Weymouth, the cable being completed in September of that year. Problems soon developed with eleven breaks occurring by 1860 due to storms and sand movements and wear on rocks. A report to the Institution of Civil Engineers in 1860 set out the problems to assist in future cable laying operations.
The first attempt at laying a transatlantic telegraph cable was promoted by Cyrus West Field, who persuaded British industrialists to fund and lay one in 1858. However, the technology of the day was not capable of supporting the project. Subsequent attempts in 1865 and 1866 with the world's largest steamship, the SS Great Eastern, used a more advanced technology and produced the first successful transatlantic cable. Great Eastern went on to lay the first cable reaching to India from Aden, Yemen, in 1870. From the 1850s until 1911, British submarine cable systems dominated the most important market, the North Atlantic Ocean; the British had demand side advantages. In terms of supply, Britain had entrepreneurs willing to put forth enormous amounts of capital necessary to build and maintain these cables. In terms of demand, Britain's vast colonial empire led to business for the cable companies from news agencies and shipping companies, the British government. Many of Britain's colonies had significant populations of European settlers, making news about them of interest to the general public in the home country.
British officials believed that depending on telegraph lines that passed through non-British territory posed a security
Crimes against humanity
Crimes against humanity are certain acts that are deliberately committed as part of a widespread or systematic attack directed against any civilian or an identifiable part of a civilian population. The first prosecution for crimes against humanity took place at the Nuremberg trials. Crimes against humanity have since been prosecuted by other international courts as well as in domestic prosecutions; the law of crimes against humanity has developed through the evolution of customary international law. Crimes against humanity are not codified in an international convention, although there is an international effort to establish such a treaty, led by the Crimes Against Humanity Initiative. Unlike war crimes, crimes against humanity can be committed during war, they are not isolated or sporadic events, but are part either of a government policy or of a wide practice of atrocities tolerated or condoned by a government or a de facto authority. War crimes, massacres, genocide, ethnic cleansing, unethical human experimentation, extrajudicial punishments including summary executions, use of WMDs, state terrorism or state sponsoring of terrorism, death squads and forced disappearances, military use of children, unjust imprisonment, cannibalism, rape, political repression, racial discrimination, religious persecution and other human rights abuses may reach the threshold of crimes against humanity if they are part of a widespread or systematic practice.
The term "crimes against humanity" is ambiguous because of the ambiguity of the word "humanity", which can mean humankind or the value of humanness. The history of the term shows. There were several bilateral treaties in 1814 that foreshadowed the multilateral treaty of Final Act of the Congress of Vienna that used wording expressing condemnation of the slave trade using moral language. For example, the Treaty of Paris between Britain and France included the wording "principles of natural justice"; the multilateral Declaration of the Powers, on the Abolition of the Slave Trade, of 8 February 1815 included in its first sentence the concept of the "principles of humanity and universal morality" as justification for ending a trade, "odious in its continuance". The term "crimes against humanity" was used by George Washington Williams in a pamphlet published in 1890 to describe the practices of Leopold II of Belgium's administration of the Congo Free State. In treaty law, the term originated in the Second Hague Convention of 1899 preamble and was expanded in the Fourth Hague Convention of 1907 preamble and their respective regulations, which were concerned with the codification of new rules of international humanitarian law.
The preamble of the two Conventions referenced the "laws of humanity" as an expression of underlying inarticulated humanistic values. The term is part of. On May 24, 1915, the Allied Powers, Britain and Russia, jointly issued a statement explicitly charging for the first time another government of committing "a crime against humanity". An excerpt from this joint statement reads: In view of these new crimes of Ottoman Empire against humanity and civilization, the Allied Governments announce publicly to the Sublime Porte that they will hold responsible for these crimes all members of the Ottoman Government, as well as those of their agents who are implicated in such massacres. At the conclusion of the war, an international war crimes commission recommended the creation of a tribunal to try "violations of the laws of humanity". However, the US representative objected to references to "law of humanity" as being imprecise and insufficiently developed at that time and the concept was not pursued.
After the Second World War, the London Charter of the International Military Tribunal set down the laws and procedures by which the Nuremberg trials were to be conducted. The drafters of this document were faced with the problem of how to respond to the Holocaust and the grave crimes committed by the Nazi regime. A traditional understanding of war crimes gave no provision for crimes committed by a power on its own citizens. Therefore, Article 6 of the Charter was drafted to include not only traditional war crimes and crimes against peace, but crimes against humanity, defined as Murder, enslavement and other inhumane acts committed against any civilian population, before or during the war, or persecutions on political, racial or religious grounds in execution of or in connection with any crime within the jurisdiction of the Tribunal, whether or not in violation of the domestic law of the country where perpetrated. Under this definition, crimes against humanity could only be punished insofar as they could be connected somehow to war crimes or crimes against peace.
The jurisdictional limitation was explained by the American chief representative to the London Conference, Robert H. Jackson, who pointed out that it "has been a general principle from time immemorial that the internal affairs of another government are not ordinarily our business". Thus, "it is justifiable that we interfere or attempt to bring retribution to individuals or to states only because the concentration camps and the deport
Central Intelligence Agency
The Central Intelligence Agency is a civilian foreign intelligence service of the federal government of the United States, tasked with gathering and analyzing national security information from around the world through the use of human intelligence. As one of the principal members of the United States Intelligence Community, the CIA reports to the Director of National Intelligence and is focused on providing intelligence for the President and Cabinet of the United States. Unlike the Federal Bureau of Investigation, a domestic security service, the CIA has no law enforcement function and is focused on overseas intelligence gathering, with only limited domestic intelligence collection. Though it is not the only agency of the Federal government of the United States specializing in HUMINT, the CIA serves as the national manager for coordination of HUMINT activities across the U. S. intelligence community. Moreover, the CIA is the only agency authorized by law to carry out and oversee covert action at the behest of the President.
It exerts foreign political influence through its tactical divisions, such as the Special Activities Division. Before the Intelligence Reform and Terrorism Prevention Act of 2004, the CIA Director concurrently served as the head of the Intelligence Community. Despite transferring some of its powers to the DNI, the CIA has grown in size as a result of the September 11 attacks. In 2013, The Washington Post reported that in fiscal year 2010, the CIA had the largest budget of all IC agencies, exceeding previous estimates; the CIA has expanded its role, including covert paramilitary operations. One of its largest divisions, the Information Operations Center, has shifted focus from counter-terrorism to offensive cyber-operations; when the CIA was created, its purpose was to create a clearinghouse for foreign policy intelligence and analysis. Today its primary purpose is to collect, analyze and disseminate foreign intelligence, to perform covert actions. According to its fiscal 2013 budget, the CIA has five priorities: Counterterrorism, the top priority Nonproliferation of nuclear and other weapons of mass destruction.
Warning/informing American leaders of important overseas events. Counterintelligence Cyber intelligence; the CIA has an executive office and five major directorates: The Directorate of Digital Innovation The Directorate of Analysis The Directorate of Operations The Directorate of Support The Directorate of Science and Technology The Director of the Central Intelligence Agency is appointed by the President with Senate confirmation and reports directly to the Director of National Intelligence. The Deputy Director is formally appointed by the Director without Senate confirmation, but as the President's opinion plays a great role in the decision, the Deputy Director is considered a political position, making the Chief Operating Officer the most senior non-political position for CIA career officers; the Executive Office supports the U. S. military by providing it with information it gathers, receiving information from military intelligence organizations, cooperates on field activities. The Executive Director is in charge of the day-to-day operation of the CIA.
Each branch of the military service has its own Director. The Associate Director of military affairs, a senior military officer, manages the relationship between the CIA and the Unified Combatant Commands, who produce and deliver to the CIA regional/operational intelligence and consume national intelligence produced by the CIA; the Directorate of Analysis, through much of its history known as the Directorate of Intelligence, is tasked with helping "the President and other policymakers make informed decisions about our country's national security" by looking "at all the available information on an issue and organiz it for policymakers". The Directorate has four regional analytic groups, six groups for transnational issues, three that focus on policy and staff support. There is an office dedicated to Iraq; the Directorate of Operations is responsible for collecting foreign intelligence, for covert action. The name reflects its role as the coordinator of human intelligence activities between other elements of the wider U.
S. intelligence community with their own HUMINT operations. This Directorate was created in an attempt to end years of rivalry over influence and budget between the United States Department of Defense and the CIA. In spite of this, the Department of Defense organized its own global clandestine intelligence service, the Defense Clandestine Service, under the Defense Intelligence Agency; this Directorate is known to be organized by geographic regions and issues, but its precise organization is classified. The Directorate of Science & Technology was established to research and manage technical collection disciplines and equipment. Many of its innovations were transferred to other intelligence organizations, or, as they became more overt, to the military services. For example, the development of the U-2 high-altitude reconnaissance aircraft was done in cooperation with the United States Air
Radio is the technology of signalling or communicating using radio waves. Radio waves are electromagnetic waves of frequency between 300 gigahertz, they are generated by an electronic device called a transmitter connected to an antenna which radiates the waves, received by a radio receiver connected to another antenna. Radio is widely used in modern technology, in radio communication, radio navigation, remote control, remote sensing and other applications. In radio communication, used in radio and television broadcasting, cell phones, two-way radios, wireless networking and satellite communication among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal in the transmitter. In radar, used to locate and track objects like aircraft, ships and missiles, a beam of radio waves emitted by a radar transmitter reflects off the target object, the reflected waves reveal the object's location. In radio navigation systems such as GPS and VOR, a mobile receiver receives radio signals from navigational radio beacons whose position is known, by measuring the arrival time of the radio waves the receiver can calculate its position on Earth.
In wireless remote control devices like drones, garage door openers, keyless entry systems, radio signals transmitted from a controller device control the actions of a remote device. Applications of radio waves which do not involve transmitting the waves significant distances, such as RF heating used in industrial processes and microwave ovens, medical uses such as diathermy and MRI machines, are not called radio; the noun radio is used to mean a broadcast radio receiver. Radio waves were first identified and studied by German physicist Heinrich Hertz in 1886; the first practical radio transmitters and receivers were developed around 1895-6 by Italian Guglielmo Marconi, radio began to be used commercially around 1900. To prevent interference between users, the emission of radio waves is regulated by law, coordinated by an international body called the International Telecommunications Union, which allocates frequency bands in the radio spectrum for different uses. Radio waves are radiated by electric charges undergoing acceleration.
They are generated artificially by time varying electric currents, consisting of electrons flowing back and forth in a metal conductor called an antenna. In transmission, a transmitter generates an alternating current of radio frequency, applied to an antenna; the antenna radiates the power in the current as radio waves. When the waves strike the antenna of a radio receiver, they push the electrons in the metal back and forth, inducing a tiny alternating current; the radio receiver connected to the receiving antenna detects this oscillating current and amplifies it. As they travel further from the transmitting antenna, radio waves spread out so their signal strength decreases, so radio transmissions can only be received within a limited range of the transmitter, the distance depending on the transmitter power, antenna radiation pattern, receiver sensitivity, noise level, presence of obstructions between transmitter and receiver. An omnidirectional antenna transmits or receives radio waves in all directions, while a directional antenna or high gain antenna transmits radio waves in a beam in a particular direction, or receives waves from only one direction.
Radio waves travel through a vacuum at the speed of light, in air at close to the speed of light, so the wavelength of a radio wave, the distance in meters between adjacent crests of the wave, is inversely proportional to its frequency. In radio communication systems, information is carried across space using radio waves. At the sending end, the information to be sent is converted by some type of transducer to a time-varying electrical signal called the modulation signal; the modulation signal may be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal consisting of a sequence of bits representing binary data from a computer. The modulation signal is applied to a radio transmitter. In the transmitter, an electronic oscillator generates an alternating current oscillating at a radio frequency, called the carrier wave because it serves to "carry" the information through the air; the information signal is used to modulate the carrier, varying some aspect of the carrier wave, impressing the information on the carrier.
Different radio systems use different modulation methods: AM - in an AM transmitter, the amplitude of the radio carrier wave is varied by the modulation signal. FM - in an FM transmitter, the frequency of the radio carrier wave is varied by the modulation signal. FSK - used in wireless digital devices to transmit digital signals, the frequency of the carrier wave is shifted periodically between two frequencies that represent the two binary digits, 0 and 1, to transmit a sequence of bits. OFDM - a family of complicated digital modulation methods widely used in high bandwidth systems such as WiFi networks, digital television broadcasting, digital audio broadcasting to transmit digital data using a minimum of radio spectrum bandwidth. OFDM has higher spectral efficiency and more resistance to fading than AM or FM. Multiple radio carrier waves spaced in frequency are transmitted within the radio channel, with each carrier modulated with bits from the incoming bitstream
Freedom of speech
Freedom of speech is a principle that supports the freedom of an individual or a community to articulate their opinions and ideas without fear of retaliation, censorship, or legal sanction. The term "freedom of expression" is sometimes used synonymously but includes any act of seeking and imparting information or ideas, regardless of the medium used. Freedom of expression is recognized as a human right under article 19 of the Universal Declaration of Human Rights and recognized in international human rights law in the International Covenant on Civil and Political Rights. Article 19 of the UDHR states that "everyone shall have the right to hold opinions without interference" and "everyone shall have the right to freedom of expression; the version of Article 19 in the ICCPR amends this by stating that the exercise of these rights carries "special duties and responsibilities" and may "therefore be subject to certain restrictions" when necessary "or respect of the rights or reputation of others" or "or the protection of national security or of public order, or of public health or morals".
Freedom of speech and expression, may not be recognized as being absolute, common limitations or boundaries to freedom of speech relate to libel, obscenity, sedition, fighting words, classified information, copyright violation, trade secrets, food labeling, non-disclosure agreements, the right to privacy, the right to be forgotten, public security, perjury. Justifications for such include the harm principle, proposed by John Stuart Mill in On Liberty, which suggests that: "the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others."The idea of the "offense principle" is used in the justification of speech limitations, describing the restriction on forms of expression deemed offensive to society, considering factors such as extent, motives of the speaker, ease with which it could be avoided. With the evolution of the digital age, application of the freedom of speech becomes more controversial as new means of communication and restrictions arise, for example the Golden Shield Project, an initiative by Chinese government's Ministry of Public Security that filters unfavorable data from foreign countries.
Freedom of speech and expression has a long history that predates modern international human rights instruments. It is thought that ancient Athenian democratic principle of free speech may have emerged in the late 6th or early 5th century BC; the values of the Roman Republic included freedom of freedom of religion. Concepts of freedom of speech can be found in early human rights documents; the Declaration of the Rights of Man and of the Citizen, adopted during the French Revolution in 1789 affirmed freedom of speech as an inalienable right. The Declaration provides for freedom of expression in Article 11, which states that: The free communication of ideas and opinions is one of the most precious of the rights of man; every citizen may, speak and print with freedom, but shall be responsible for such abuses of this freedom as shall be defined by law. Article 19 of the Universal Declaration of Human Rights, adopted in 1948, states that: Everyone has the right to freedom of opinion and expression.
Today, freedom of speech, or the freedom of expression, is recognized in international and regional human rights law. The right is enshrined in Article 19 of the International Covenant on Civil and Political Rights, Article 10 of the European Convention on Human Rights, Article 13 of the American Convention on Human Rights and Article 9 of the African Charter on Human and Peoples' Rights. Based on John Milton's arguments, freedom of speech is understood as a multi-faceted right that includes not only the right to express, or disseminate and ideas, but three further distinct aspects: the right to seek information and ideas; this means that the protection of freedom of speech as a right includes not only the content, but the means of expression. The right to freedom of speech and expression is related to other rights, may be limited when conflicting with other rights; the right to freedom of expression is related to the right to a fair trial and court proceeding which may limit access to the search for information, or determine the opportunity and means in which freedom of expression is manifested within court proceedings.
As a general principle freedom of expression may not limit the right to privacy, as well as the honor and reputation of others. However greater latitude is given; the right to freedom of expression is important for media, which plays a special role as the bearer of the general right to freedom of expression for all. However, freedom of the press does not enable freedom of speech. Judith Lichtenberg has outlined conditions in which freedom of the press may constrain freedom of speech, for example where the med
Cathedral Square, Vilnius
The Cathedral Square in Vilnius is the main square of the Vilnius Old Town, right in front of the neo-classical Vilnius Cathedral. It is a key location in city's public life, situated as it is at the crossing of the city's main streets and reflecting the city's diversity. Held at this site are fairs and gatherings of townspeople, military parades and official public events and large concerts, New Year’s salutes and exhibitions, it is not the most lively and important location in the city, but is one of the most significant and known symbols of Lithuania. The cathedral square was founded as late as 19th century, during the reconstruction and refurbishment of the cathedral; the area was densely populated and built up with medieval and renaissance houses. Parts of the area were occupied by the Lower Castle. Following the creation of a new square it became the main open space of the city's centre, it was there that the Russian military parades were held and where the annual St. Casimir's Fair was held.
In 1905 a monument to Catherine the Great was erected. After the city was occupied by Germany in 1915 and the local Polish administration was allowed to govern the city, the monument was destroyed and the St. Casimir's Fair was moved to the Łukiszki Square. In modern times and festivities are held at the site, it is there that the tallest Christmas tree in the city is erected, as well as a number of other Christmas decorations, including outdoor nativity scenes. It is there that the yearly public celebrations of New Year's Eve are held. One of the most distinctive features of the square is the Cathedral's bell tower, situated several yards from the cathedral itself, a thing uncommon outside of Italy. According to many scholars, the tower was in fact one of the towers of the ancient city walls of the mediaeval Lower Castle that once stood near the modern square. According to another version, not supported by modern historians, the base of the tower was in fact a small pagan temple and turned into the bell tower.
Regardless of its origins, the lower parts of the tower are mediaeval, with several small loop-holes preserved. Its oldest underground square section was built in the 13th century on the bottom of the old riverbed. Upper parts of the tower were added in the 18th century while the neo-classical finish was added in the 19th century, during the reconstruction of the cathedral. Other notable feature of the square is the monument to Gediminas, one of the first rulers of Lithuania, by Vytautas Kašuba, uncovered in 1996; the bronze used for the monument was donated by Lithuanian border guards who confiscated it on the border. The marble sockle was a gift of the government of Ukraine, while the sculpture itself was cast free of charge in Tallinn. Nearby is a magical place, a small stone marking the place where, according to a local urban legend, the human chain of Baltic Way was started linking Vilnius with Riga and Tallinn, an event that marked the beginning of national liberation of the Baltic States.
It is said that if a person steps on this stone and turns around three times, his or her wish will be granted. The paving of the square has been extensively renovated in 2000; the new tiles were made of light granite. Excavated remains of former fortifications of the Lower Castle have been highlighted in the paving by using red-couloured granite
A telephone, or phone, is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be heard directly. A telephone converts sound and most efficiently the human voice, into electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user. In 1876, Scottish emigrant Alexander Graham Bell was the first to be granted a United States patent for a device that produced intelligible replication of the human voice; this instrument was further developed by many others. The telephone was the first device in history that enabled people to talk directly with each other across large distances. Telephones became indispensable to businesses and households and are today some of the most used small appliances; the essential elements of a telephone are a microphone to speak into and an earphone which reproduces the voice in a distant location. In addition, most telephones contain a ringer to announce an incoming telephone call, a dial or keypad to enter a telephone number when initiating a call to another telephone.
The receiver and transmitter are built into a handset, held up to the ear and mouth during conversation. The dial may be located either on a base unit to which the handset is connected; the transmitter converts the sound waves to electrical signals which are sent through a telephone network to the receiving telephone, which converts the signals into audible sound in the receiver or sometimes a loudspeaker. Telephones are duplex devices; the first telephones were directly connected to each other from one customer's office or residence to another customer's location. Being impractical beyond just a few customers, these systems were replaced by manually operated centrally located switchboards; these exchanges were soon connected together forming an automated, worldwide public switched telephone network. For greater mobility, various radio systems were developed for transmission between mobile stations on ships and automobiles in the mid-20th century. Hand-held mobile phones were introduced for personal service starting in 1973.
In decades their analog cellular system evolved into digital networks with greater capability and lower cost. Convergence has given most modern cell phones capabilities far beyond simple voice conversation, they may be able to record spoken messages and receive text messages and display photographs or video, play music or games, surf the Internet, do road navigation or immerse the user in virtual reality. Since 1999, the trend for mobile phones is smartphones that integrate all mobile communication and computing needs. A traditional landline telephone system known as plain old telephone service carries both control and audio signals on the same twisted pair of insulated wires, the telephone line; the control and signaling equipment consists of three components, the ringer, the hookswitch, a dial. The ringer, or beeper, light or other device, alerts the user to incoming calls; the hookswitch signals to the central office that the user has picked up the handset to either answer a call or initiate a call.
A dial, if present, is used by the subscriber to transmit a telephone number to the central office when initiating a call. Until the 1960s dials used exclusively the rotary technology, replaced by dual-tone multi-frequency signaling with pushbutton telephones. A major expense of wire-line telephone service is the outside wire plant. Telephones transmit both the outgoing speech signals on a single pair of wires. A twisted pair line rejects electromagnetic interference and crosstalk better than a single wire or an untwisted pair; the strong outgoing speech signal from the microphone does not overpower the weaker incoming speaker signal with sidetone because a hybrid coil and other components compensate the imbalance. The junction box arrests lightning and adjusts the line's resistance to maximize the signal power for the line length. Telephones have similar adjustments for inside line lengths; the line voltages are negative compared to earth. Negative voltage attracts positive metal ions toward the wires.
The landline telephone contains a switchhook and an alerting device a ringer, that remains connected to the phone line whenever the phone is "on hook", other components which are connected when the phone is "off hook". The off-hook components include a transmitter, a receiver, other circuits for dialing and amplification. A calling party wishing to speak to another party will pick up the telephone's handset, thereby operating a lever which closes the switchhook, which powers the telephone by connecting the transmitter and related audio components to the line; the off-hook circuitry has a low resistance which causes a direct current, which comes down the line from the telephone exchange. The exchange detects this current, attaches a digit receiver circuit to the line, sends a dial tone to indicate readiness. On a modern push-button telephone, the caller presses the number keys to send the telephone number of the called party; the keys control a tone generator circuit. A rotary-dial telephone uses pulse