title: Organ transplantation

text: According to former Chinese Deputy Minister of Health, Huang Jiefu, the practice of transplanting organs from executed prisoners is still occurring . World Journal reported Huang had admitted approximately 95% of all organs used for transplantation are from executed prisoners. The lack of a public organ donation program in China is used as a justification for this practice. In July 2006, the Kilgour-Matas report stated, "the source of 41,500 transplants for the six-year period 2000 to 2005 is unexplained" and "we believe that there has been and continues today to be large scale organ seizures from unwilling Falun Gong practitioners". Investigative journalist Ethan Gutmann estimates 65,000 Falun Gong practitioners were killed for their organs from 2000 to 2008. However 2016 reports updated the death toll of the 15-year period since the persecution of Falun Gong began putting the death toll at 150,000 to 1.5 million. In December 2006, after not getting assurances from the Chinese government about allegations relating to Chinese prisoners, the two major organ transplant hospitals in Queensland, Australia stopped transplantation training for Chinese surgeons and banned joint research programs into organ transplantation with China.


title: Organ transplantation

text: In May 2008, two United Nations Special Rapporteurs reiterated their requests for "the Chinese government to fully explain the allegation of taking vital organs from Falun Gong practitioners and the source of organs for the sudden increase in organ transplants that has been going on in China since the year 2000". People in other parts of the world are responding to this availability of organs, and a number of individuals (including US and Japanese citizens) have elected to travel to China or India as medical tourists to receive organ transplants which may have been sourced in what might be considered elsewhere to be unethical manner.


title: Organ transplantation

text: Some estimates of the number of transplants performed in various regions of the world have been derived from the Global Burden of Disease Study.


title: Organ transplantation

text: According to the Council of Europe, Spain through the Spanish Transplant Organization shows the highest worldwide rate of 35.1 donors per million population in 2005 and 33.8 in 2006. In 2011, it was 35.3.


title: Organ transplantation

text: In addition to the citizens waiting for organ transplants in the US and other developed nations, there are long waiting lists in the rest of the world. More than 2 million people need organ transplants in China, 50,000 waiting in Latin America (90% of whom are waiting for kidneys), as well as thousands more in the less documented continent of Africa. Donor bases vary in developing nations.


title: Organ transplantation

text: In Latin America the donor rate is 40–100 per million per year, similar to that of developed countries. However, in Uruguay, Cuba, and Chile, 90% of organ transplants came from cadaveric donors. Cadaveric donors represent 35% of donors in Saudi Arabia. There is continuous effort to increase the utilization of cadaveric donors in Asia; however, the popularity of living, single kidney donors in India yields a cadaveric donor prevalence of less than 1 per million population.


title: Organ transplantation

text: Traditionally, Muslims believe body desecration in life or death to be forbidden, and thus many reject organ transplant. However most Muslim authorities nowadays accept the practice if another life will be saved. As an example, it may be assumed in countries such as Singapore with a cosmopolitan populace that includes Muslims, a special Majlis Ugama Islam Singapura governing body is formed to look after the interests of Singapore's Muslim community over issues that includes their burial arrangements.


title: Organ transplantation

text: Organ transplantation in Singapore is generally overseen by the National Organ Transplant Unit of the Ministry of Health (Singapore). Due to a diversity in mindsets and religious viewpoints, while Muslims on this island are generally not expected to donate their organs even upon death, youth in Singapore are educated on the Human Organ Transplant Act at the age of 18, which is around the age of military conscription. The Organ Donor Registry maintains two types of information, firstly people of Singapore that donate their organs or bodies for transplantation, research or education upon their death, under the Medical (Therapy, Education and Research) Act (MTERA), and secondly people that object to the removal of kidneys, liver, heart and corneas upon death for the purpose of transplantation, under the Human Organ Transplant Act (HOTA). The Live On social awareness movement is also formed to educate Singaporeans on organ donation.


title: Organ transplantation

text: Organ transplantation in China has taken place since the 1960s, and China has one of the largest transplant programmes in the world, peaking at over 13,000 transplants a year by 2004. Organ donation, however, is against Chinese tradition and culture, and involuntary organ donation is illegal under Chinese law. China's transplant programme attracted the attention of international news media in the 1990s due to ethical concerns about the organs and tissue removed from the corpses of executed criminals being commercially traded. In 2006 it became clear that about 41,500 organs had been sourced from Falun Gong practitioners in China since 2000.


title: Organ transplantation

text: With regard to organ transplantation in Israel, there is a severe organ shortage due to religious objections by some rabbis who oppose all organ donations and others who advocate that a rabbi participate in all decision making regarding a particular donor. One-third of all heart transplants performed on Israelis are done in China; others are done in Europe. Dr. Jacob Lavee, head of the heart-transplant unit, Sheba Medical Center, Tel Aviv, believes that "transplant tourism" is unethical and Israeli insurers should not pay for it. The organization HODS (Halachic Organ Donor Society) is working to increase knowledge and participation in organ donation among Jews throughout the world.


title: Organ transplantation

text: Transplantation rates also differ based on race, sex, and income. A study done with people beginning long term dialysis showed that the sociodemographic barriers to renal transplantation present themselves even before patients are on the transplant list. For example, different groups express definite interest and complete pretransplant workup at different rates. Previous efforts to create fair transplantation policies had focused on people currently on the transplantation waiting list.


title: Organ transplantation

text: In the United States, nearly 35,000 organ transplants were done in 2017, a 3.4 percent increase over 2016. About 18 percent of these were from living donors – people who gave one kidney or a part of their liver to someone else. But 115,000 Americans remain on waiting lists for organ transplants. By September 2022, the US had reached one million organ transplants overall.


title: Organ transplantation

text: Successful human allotransplants have a relatively long history of operative skills that were present long before the necessities for post-operative survival were discovered. Rejection and the side effects of preventing rejection (especially infection and nephropathy) were, are, and may always be the key problem.


title: Organ transplantation

text: Several apocryphal accounts of transplants exist well prior to the scientific understanding and advancements that would be necessary for them to have actually occurred. The Chinese physician Pien Chi'ao reportedly exchanged hearts between a man of strong spirit but weak will with one of a man of weak spirit but strong will in an attempt to achieve balance in each man. Roman Catholic accounts report the 3rd-century saints Damian and Cosmas as replacing the gangrenous or cancerous leg of the Roman deacon Justinian with the leg of a recently deceased Ethiopian. Most accounts have the saints performing the transplant in the 4th century, many decades after their deaths; some accounts have them only instructing living surgeons who performed the procedure.


title: Organ transplantation

text: The more likely accounts of early transplants deal with skin transplantation. The first reasonable account is of the Indian surgeon Sushruta in the 2nd century BC, who used autografted skin transplantation in nose reconstruction, a rhinoplasty. Success or failure of these procedures is not well documented. Centuries later, the Italian surgeon Gasparo Tagliacozzi performed successful skin autografts; he also failed consistently with allografts, offering the first suggestion of rejection centuries before that mechanism could possibly be understood. He attributed it to the "force and power of individuality" in his 1596 work "De Curtorum Chirurgia per Insitionem".


title: Organ transplantation

text: The first successful corneal allograft transplant was performed in 1837 in a gazelle model; the first successful human corneal transplant, a keratoplastic operation, was performed by Eduard Zirm at Olomouc Eye Clinic, now in the Czech Republic, in 1905.


title: Organ transplantation

text: The first transplant in the modern sense – the implantation of organ tissue in order to replace an organ function – was a thyroid transplant in 1883. It was performed by the Swiss surgeon and later Nobel laureate Theodor Kocher. In the preceding decades Kocher had perfected the removal of excess thyroid tissue in cases of goiter to an extent that he was able to remove the whole organ without the person dying from the operation. Kocher carried out the total removal of the organ in some cases as a measure to prevent recurrent goiter. By 1883, the surgeon noticed that the complete removal of the organ leads to a complex of particular symptoms that we today have learned to associate with a lack of thyroid hormone. Kocher reversed these symptoms by implanting thyroid tissue to these people and thus performed the first organ transplant. In the following years Kocher and other surgeons used thyroid transplantation also to treat thyroid deficiency that appeared spontaneously, without a preceding organ removal.


title: Organ transplantation

text: Thyroid transplantation became the model for a whole new therapeutic strategy: organ transplantation. After the example of the thyroid, other organs were transplanted in the decades around 1900. Some of these transplants were done in animals for purposes of research, where organ removal and transplantation became a successful strategy of investigating the function of organs. Kocher was awarded his Nobel Prize in 1909 for the discovery of the function of the thyroid gland. At the same time, organs were also transplanted for treating diseases in humans. The thyroid gland became the model for transplants of adrenal and parathyroid glands, pancreas, ovary, testicles and kidney. By 1900, the idea that one can successfully treat internal diseases by replacing a failed organ through transplantation had been generally accepted. Pioneering work in the surgical technique of transplantation was made in the early 1900s by the French surgeon Alexis Carrel, with Charles Guthrie, with the transplantation of arteries or veins. Their skillful anastomosis operations and the new suturing techniques laid the groundwork for later transplant surgery and won Carrel the 1912 Nobel Prize in Physiology or Medicine. From 1902, Carrel performed transplant experiments on dogs. Surgically successful in moving kidneys, hearts, and spleens, he was one of the first to identify the problem of rejection, which remained insurmountable for decades. The discovery of transplant immunity by the German surgeon Georg Schöne, various strategies of matching donor and recipient, and the use of different agents for immune suppression did not result in substantial improvement so that organ transplantation was largely abandoned after WWI.


title: Organ transplantation

text: In 1954, the first ever successful transplant of any organ was done at the Brigham & Women's Hospital in Boston, Ma. The surgery was performed by Dr. Joseph Murray, who received the Nobel Prize in Medicine for his work. The success of this transplant was mostly due to the family relation between the recipient, a Richard Herrick of Maine, and his donor and identical twin brother Ronald. Richard Herrick was in the Navy and became severely ill with acute renal failure. His brother Ronald donated his kidney to Richard, and Richard lived on for another eight years. Prior to this case, transplant recipients did not survive for more than thirty days. Their close family relation meant there was no need for anti-rejection medications, which was not known until this time, so the case shed light on the cause of rejection and of possible anti-rejection medicine.


title: Organ transplantation

text: Major steps in skin transplantation occurred during the First World War, notably in the work of Harold Gillies at Aldershot. Among his advances was the tubed pedicle graft, which maintained a flesh connection from the donor site until the graft established its own blood flow. Gillies' assistant, Archibald McIndoe, carried on the work into the Second World War as reconstructive surgery. In 1962, the first successful replantation surgery was performed – re-attaching a severed limb and restoring (limited) function and feeling.


title: Organ transplantation

text: Transplant of a single gonad (testis) from a living donor was carried out in early July 1926 in Zaječar, Serbia, by a Russian émigré surgeon Dr. Peter Vasil'evič Kolesnikov. The donor was a convicted murderer, one Ilija Krajan, whose death sentence was commuted to 20 years imprisonment, and he was led to believe that it was done because he had donated his testis to an elderly medical doctor. Both the donor and the receiver survived, but charges were brought in a court of law by the public prosecutor against Dr. Kolesnikov, not for performing the operation, but for lying to the donor.


title: Organ transplantation

text: The first attempted human deceased-donor transplant was performed by the Ukrainian surgeon Yurii Voronoy in the 1930s; but failed due to ischemia. Joseph Murray and J. Hartwell Harrison performed the first successful transplant, a kidney transplant between identical twins, in 1954, because no immunosuppression was necessary for genetically identical individuals.


title: Organ transplantation

text: In the late 1940s Peter Medawar, working for the National Institute for Medical Research, improved the understanding of rejection. Identifying the immune reactions in 1951, Medawar suggested that immunosuppressive drugs could be used. Cortisone had been recently discovered and the more effective azathioprine was identified in 1959, but it was not until the discovery of cyclosporine in 1970 that transplant surgery found a sufficiently powerful immunosuppressive.


title: Organ transplantation

text: There was a successful deceased-donor lung transplant into an emphysema and lung cancer patient in June 1963 by James Hardy at the University of Mississippi Medical Center in Jackson, Mississippi. The patient John Russell survived for eighteen days before dying of kidney failure.


title: Organ transplantation

text: Thomas Starzl of Denver attempted a liver transplant in the same year, but he was not successful until 1967.


title: Organ transplantation

text: In the early 1960s and prior to long-term dialysis becoming available, Keith Reemtsma and his colleagues at Tulane University in New Orleans attempted transplants of chimpanzee kidneys into 13 human patients. Most of these patients only lived one to two months. However, in 1964, a 23-year-old woman lived for nine months and even returned to her job as a school teacher until she suddenly collapsed and died. It was assumed that she died from an acute electrolyte disturbance. At autopsy, the kidneys had not been rejected nor was there any other obvious cause of death. One source states this patient died from pneumonia. Tom Starzl and his team in Colorado used baboon kidneys with six human patients who lived one or two months, but with no longer term survivors. Others in the United States and France had limited experiences.


title: Organ transplantation

text: The heart was a major prize for transplant surgeons. But over and above rejection issues, the heart deteriorates within minutes of death, so any operation would have to be performed at great speed. The development of the heart-lung machine was also needed. Lung pioneer James Hardy was prepared to attempt a human heart transplant in 1964, but when a premature failure of comatose Boyd Rush's heart caught Hardy with no human donor, he used a chimpanzee heart, which beat in his patient's chest for approximately one hour and then failed. The first partial success was achieved on 3 December 1967, when Christiaan Barnard of Cape Town, South Africa, performed the world's first human-to-human heart transplant with patient Louis Washkansky as the recipient. Washkansky survived for eighteen days amid what many saw as a distasteful publicity circus. The media interest prompted a spate of heart transplants. Over a hundred were performed in 1968–1969, but almost all the people died within 60 days. Barnard's second patient, Philip Blaiberg, lived for 19 months.


title: Organ transplantation

text: It was the advent of cyclosporine that altered transplants from research surgery to life-saving treatment. In 1968 surgical pioneer Denton Cooley performed 17 transplants, including the first heart-lung transplant. Fourteen of his patients were dead within six months. By 1984 two-thirds of all heart transplant patients survived for five years or more. With organ transplants becoming commonplace, limited only by donors, surgeons moved on to riskier fields, including multiple-organ transplants on humans and whole-body transplant research on animals. On 9 March 1981, the first successful heart-lung transplant took place at Stanford University Hospital. The head surgeon, Bruce Reitz, credited the patient's recovery to cyclosporine.


title: Organ transplantation

text: As the rising success rate of transplants and modern immunosuppression make transplants more common, the need for more organs has become critical. Transplants from living donors, especially relatives, have become increasingly common. Additionally, there is substantive research into xenotransplantation, or transgenic organs; although these forms of transplant are not yet being used in humans, clinical trials involving the use of specific cell types have been conducted with promising results, such as using porcine islets of Langerhans to treat type 1 diabetes. However, there are still many problems that would need to be solved before they would be feasible options in people requiring transplants.


title: Organ transplantation

text: Recently, researchers have been looking into means of reducing the general burden of immunosuppression. Common approaches include avoidance of steroids, reduced exposure to calcineurin inhibitors, and other means of weaning drugs based on patient outcome and function. While short-term outcomes appear promising, long-term outcomes are still unknown, and in general, reduced immunosuppression increases the risk of rejection and decreases the risk of infection. The risk of early rejection is increased if corticosteroid immunosuppression are avoided or withdrawn after renal transplantation.


title: Organ transplantation

text: The emerging field of regenerative medicine promises to solve the problem of organ transplant rejection by regrowing organs in the lab, using person's own cells (stem cells or healthy cells extracted from the donor site).


title: Organ transplantation

text: Since 2000, there have been approximately 2,200 lung transplants performed each year worldwide. From 2000 to 2006, the median survival period for lung transplant patients has been 5.5 years.


title: Organ transplantation

text: In China, a kidney transplant operation runs for around $70,000, liver for $160,000, and heart for $120,000.


title: Organ transplantation

text: In the United States, tissue transplants are regulated by the US Food and Drug Administration (FDA) which sets strict regulations on the safety of the transplants, primarily aimed at the prevention of the spread of communicable disease. Regulations include criteria for donor screening and testing as well as strict regulations on the processing and distribution of tissue grafts. Organ transplants are not regulated by the FDA. It is essential that the HLA complexes of both the donor and recipient be as closely matched as possible to prevent graft rejection.


title: Organ transplantation

text: In November 2007, the CDC reported the first-ever case of HIV and Hepatitis C being simultaneously transferred through an organ transplant. The donor was a 38-year-old male, considered "high-risk" by donation organizations, and his organs transmitted HIV and Hepatitis C to four organ recipients. Experts say that the reason the diseases did not show up on screening tests is probably because they were contracted within three weeks before the donor's death, so antibodies would not have existed in high enough numbers to detect. The crisis has caused many to call for more sensitive screening tests, which could pick up antibodies sooner. Currently, the screens cannot pick up on the small number of antibodies produced in HIV infections within the last 90 days or Hepatitis C infections within the last 18–21 days before a donation is made.


title: Organ transplantation

text: Nucleic acid testing is now being done by many organ procurement organizations and is able to detect HIV and hepatitis C directly within seven to ten days of exposure to the virus.


title: Organ transplantation

text: Both developing and developed countries have forged various policies to try to increase the safety and availability of organ transplants to their citizens. However, whilst potential recipients in developing countries may mirror their more developed counterparts in desperation, potential donors in developing countries do not. The Indian government has had difficulty tracking the flourishing organ black market in their country, but in recent times it has amended its organ transplant law to make punishment more stringent for commercial dealings in organs. It has also included new clauses in the law to support deceased organ donation, such as making it mandatory to request for organ donation in case of brain death. Other countries victimized by illegal organ trade have also implemented legislative reactions. Moldova has made international adoption illegal in fear of organ traffickers. China has made selling of organs illegal as of July 2006 and claims that all prisoner organ donors have filed consent. However, doctors in other countries, such as the United Kingdom, have accused China of abusing its high capital punishment rate. Despite these efforts, illegal organ trafficking continues to thrive and can be attributed to corruption in healthcare systems, which has been traced as high up as the doctors themselves in China and Ukraine, and the blind eye economically strained governments and health care programs must sometimes turn to organ trafficking. Some organs are also shipped to Uganda and the Netherlands. This was a main product in the triangular trade in 1934.


title: Organ transplantation

text: Starting on 1 May 2007, doctors involved in commercial trade of organs will face fines and suspensions in China. Only a few certified hospitals will be allowed to perform organ transplants in order to curb illegal transplants. Harvesting organs without donor's consent was also deemed a crime.


title: Organ transplantation

text: On 27 June 2008, Indonesian, Sulaiman Damanik, 26, pleaded guilty in Singapore court for sale of his kidney to CK Tang's executive chair, Tang Wee Sung, 55, for 150 million rupiah (S$22,200). The Transplant Ethics Committee must approve living donor kidney transplants. Organ trading is banned in Singapore and in many other countries to prevent the exploitation of "poor and socially disadvantaged donors who are unable to make informed choices and suffer potential medical risks." Toni, 27, the other accused, donated a kidney to an Indonesian patient in March, alleging he was the patient's adopted son, and was paid 186 million rupiah (US$20,200). Upon sentence, both would suffer each, 12 months in jail or 10,000 Singapore dollars (US$7,600) fine.


title: Organ transplantation

text: In an article appearing in the April 2004 issue of Econ Journal Watch, economist Alex Tabarrok examined the impact of direct consent laws on transplant organ availability. Tabarrok found that social pressures resisting the use of transplant organs decreased over time as the opportunity of individual decisions increased. Tabarrok concluded his study suggesting that gradual elimination of organ donation restrictions and move to a free market in organ sales will increase supply of organs and encourage broader social acceptance of organ donation as a practice.


title: Organ transplantation

text: In the United States 24 states have no law preventing discrimination against potential organ recipients based on cognitive ability, including children. A 2008 study found that of the transplant centers surveyed in those states 85 percent considered disability when deciding transplant list and forty four percent would deny an organ transplant to a child with a neurodevelopmental disability.


title: Organ transplantation

text: The existence and distribution of organ transplantation procedures in developing countries, while almost always beneficial to those receiving them, raise many ethical concerns. Both the source and method of obtaining the organ to transplant are major ethical issues to consider, as well as the notion of distributive justice. The World Health Organization argues that transplantations promote health, but the notion of "transplantation tourism" has the potential to violate human rights or exploit the poor, to have unintended health consequences, and to provide unequal access to services, all of which ultimately may cause harm. Regardless of the "gift of life", in the context of developing countries, this might be coercive. The practice of coercion could be considered exploitative of the poor population, violating basic human rights according to Articles 3 and 4 of the Universal Declaration of Human Rights. There is also a powerful opposing view, that trade in organs, if properly and effectively regulated to ensure that the seller is fully informed of all the consequences of donation, is a mutually beneficial transaction between two consenting adults, and that prohibiting it would itself be a violation of Articles 3 and 29 of the Universal Declaration of Human Rights.


title: Organ transplantation

text: Even within developed countries there is concern that enthusiasm for increasing the supply of organs may trample on respect for the right to life. The question is made even more complicated by the fact that the "irreversibility" criterion for legal death cannot be adequately defined and can easily change with changing technology.


title: Organ transplantation

text: Surgeons, notably Paolo Macchiarini, in Sweden performed the first implantation of a synthetic trachea in July 2011, for a 36-year-old patient who had cancer. Stem cells taken from the patient's hip were treated with growth factors and incubated on a plastic replica of his natural trachea.


title: Organ transplantation

text: According to information uncovered by the Swedish documentary "Dokument Inifrån: Experimenten" (Swedish: "Documents from the Inside: The Experiments") the patient, Andemariam went on to develop an increasingly terrible and eventually bloody cough to dying, incubated, in the hospital. At that point, determined by autopsy, 90% of the synthetic windpipe had come loose. He allegedly made several trips to see Macchiarini for his complications, and at one point had surgery again to have his synthetic windpipe replaced, but Macchiarini was notoriously difficult to get an appointment with. According to the autopsy, the old synthetic windpipe did not appear to have been replaced.


title: Organ transplantation

text: Macchiarini's academic credentials have been called into question and he has recently been accused of alleged research misconduct.


title: Organ transplantation

text: Left ventricular assist devices are often used as a "bridge" to provide additional time while a patient waits for a transplant. For example, former US vice-president Dick Cheney had such a device implanted in 2010 and then 20 months later received a heart transplant in 2012. In year 2012, about 3,000 ventricular assist devices were inserted in the United States, as compared to approximately 2,500 heart transplants. The use of airbags in cars as well as greater use of helmets by bicyclists and skiers has reduced the number of persons with fatal head injuries, which is a common source of donors hearts.


title: Organ transplantation

text: An early-stage medical laboratory and research company, called Organovo, designs and develops functional, three dimensional human tissue for medical research and therapeutic applications. The company utilizes its NovoGen MMX Bioprinter for 3D bioprinting. Organovo anticipates that the bioprinting of human tissues will accelerate the preclinical drug testing and discovery process, enabling treatments to be created more quickly and at lower cost. Additionally, Organovo has long-term expectations that this technology could be suitable for surgical therapy and transplantation.


title: Organ transplantation

text: A further area of active research is concerned with improving and assessing organs during their preservation. Various techniques have emerged which show great promise, most of which involve perfusing the organ under either hypothermic (4–10 °C) or normothermic (37 °C) conditions. All of these add additional cost and logistical complexity to the organ retrieval, preservation and transplant process, but early results suggest it may well be worth it. Hypothermic perfusion is in clinical use for transplantation of kidneys and liver whilst normothermic perfusion has been used effectively in the heart, lung, liver and, less so, in the kidney.


title: Organ transplantation

text: Another area of research being explored is the use of genetically engineered animals for transplants. Similar to human organ donors, scientists have developed a genetically engineered pig with the aim of reducing rejection to pig organs by human patients. This is currently at the basic research stage, but shows great promise in alleviating the long waiting lists for organ transplants and the number of people in need of transplants outweighs the amount of organs donated. Trials are being done to prevent the pig organ transplant to enter a clinical trial phase until the potential disease transfer from pigs to humans can be safely and satisfactorily managed (Isola & Gordon, 1991).


title: Popular sovereignty

text: Popular sovereignty is the principle that the authority of a state and its government are created and sustained by the consent of its people, who are the source of all political power. Popular sovereignty, being a principle, does not imply any particular political implementation. Benjamin Franklin expressed the concept when he wrote that "In free governments, the rulers are the servants and the people their superiors and sovereigns".


title: Popular sovereignty

text: Popular sovereignty in its modern sense is an idea that dates to the social contract school represented by Thomas Hobbes (1588–1679), John Locke (1632–1704), and Jean-Jacques Rousseau (1712–1778). Rousseau authored a book titled "The Social Contract", a prominent political work that highlighted the idea of the "general will". The central tenet of popular sovereignty is that the legitimacy of a government's authority and of its laws is based on the consent of the governed. Hobbes, Locke, and Rousseau all held that individuals enter into a social contract, voluntarily giving up some of their natural freedom, so as to secure protection from the dangers inherent in the freedom of others. Whether men are seen as naturally more prone to violence and rapine (Hobbes) or to cooperation and kindness (Rousseau), the idea that a legitimate social order emerges only when liberties and duties are equal among citizens binds the social contract thinkers to the concept of popular sovereignty.


title: Popular sovereignty

text: An earlier development of the theory of popular sovereignty is found among the School of Salamanca (see e.g. Francisco de Vitoria (1483–1546) or Francisco Suarez (1548–1617)). Like the theorists of the divine right of kings and Locke, the Salamancans saw sovereignty as emanating originally from God. However, unlike the divine right theorists and in agreement with Locke, they saw it as passing from God to all people equally, not only to monarchs.


title: Popular sovereignty

text: Republics and popular monarchies are theoretically based on popular sovereignty. However, a legalistic notion of popular sovereignty does not necessarily imply an effective, functioning democracy. A party or even an individual dictator may claim to represent the will of the people and rule in its name, which would be congruent with Hobbes's view on the subject. Most modern definitions present democracy as a necessary condition of popular sovereignty.


title: Popular sovereignty

text: The application of the doctrine of popular sovereignty receives particular emphasis in American history, notes historian Christian G. Fritz's "American Sovereigns: The People and America's Constitutional Tradition Before the Civil War", a study of the early history of American constitutionalism. In describing how Americans attempted to apply this doctrine prior to the territorial struggle over slavery that led to the Civil War, political scientist Donald S. Lutz noted the variety of American applications:


title: Popular sovereignty

text: The American Revolution marked a departure in the concept of popular sovereignty as it had been discussed and employed in the European historical context. American revolutionaries aimed to substitute the sovereignty in the person of King George III, with a collective sovereign—composed of the people. Thenceforth, American revolutionaries generally agreed with and were committed to the principle that governments were legitimate only if they rested on popular sovereignty – that is, the sovereignty of the people. This was often linked with the notion of the consent of the governed—the idea of the people as a sovereign—and had clear 17th- and 18th-century intellectual roots in English history.


title: Popular sovereignty

text: In the 1850s, in the run-up to the Civil War, Northern Democrats led by Senator Lewis Cass of Michigan and Stephen A. Douglas of Illinois promoted popular sovereignty as a middle position on the slavery issue. It said that actual residents of territories should be able to decide by voting whether or not slavery would be allowed in the territory. The federal government did not have to make the decision, and by appealing to democracy, Cass and Douglas hoped they could finesse the question of support for or opposition to slavery. Douglas applied popular sovereignty to Kansas in the Kansas-Nebraska Act, which passed Congress in 1854. The Act had two unexpected results. By dropping the Missouri Compromise of 1820 (which said slavery would never be allowed in Kansas), it was a major boost for the expansion of slavery. Overnight, outrage united anti-slavery forces across the North into an "anti-Nebraska" movement that soon was institutionalized as the Republican Party, with its firm commitment to stop the expansion of slavery. Secondly, pro- and anti-slavery elements moved into Kansas with the intention of voting slavery up or down, leading to a raging state-level civil war, known as "Bleeding Kansas". Abraham Lincoln targeted popular sovereignty in the Lincoln–Douglas debates of 1858, leaving Douglas in a position that alienated Southern pro-slavery Democrats who thought he was too weak in his support of slavery. The Southern Democrats broke off and ran their own candidate against Lincoln and Douglas in 1860.


title: Allan Clarke (singer)

text: Harold Allan Clarke (born 5 April 1942) is an English rock singer, who was one of the founding members and the original lead singer of the Hollies. He achieved international hit singles with the group and is credited as co-writer on several of their best-known songs, including "On a Carousel", "Carrie Anne", "Jennifer Eccles" and "Long Cool Woman in a Black Dress". He retired from performing in 1999, but returned to the music industry in 2019. Clarke was inducted into the Rock and Roll Hall of Fame in 2010.


title: Allan Clarke (singer)

text: Harold Allan Clarke and his childhood friend Graham Nash began singing together in Manchester while still at school. They formed the Hollies in December 1962 with Vic Steele (lead guitar) and Eric Haydock (bass guitar). In April 1963, they added Tony Hicks (replacing Steele on lead guitar) and Bobby Elliott (replacing Don Rathbone on drums). In 1966, Bernie Calvert replaced Haydock as bass guitarist. Clarke was the Hollies' original lead singer, but also played occasional guitar and harmonica. In the UK they enjoyed 30 chart singles, plus two further chart entries with re-releases, 17 of which made the Top 10, with two – "I'm Alive" (1965) and "He Ain't Heavy, He's My Brother" (1988 re-issue) – reaching No. 1.


title: Allan Clarke (singer)

text: In the US charts they achieved 23 chart singles, six of which reached the Top 10. Many of the group's songs were co-written by Clarke, usually with Nash and Hicks, until Nash's departure at the end of 1968. They initially used the pseudonym "L. Ransford" for their songwriting credits, then 'Clarke-Nash-Hicks' from mid-1966 onwards. In 1966, Clarke, along with several Hollies bandmates, assisted in the Everly Brothers' recording of their album "Two Yanks in England", which featured Everly cover versions of mostly Hollies songs co-written by Clarke.


title: Allan Clarke (singer)

text: Clarke-Nash-Hicks composed the Hollies' albums "For Certain Because" (1966), "Evolution" (1967) and "Butterfly" (1967). Their UK hit singles compilation "The Hollies' Greatest Hits" topped the UK Albums Chart in August 1968.


title: Allan Clarke (singer)

text: After 1967, Clarke began writing solo songs under the team banner, notably: "Lullaby To Tim" (dedicated to his son, though sung by Nash), "Heading for a Fall", "Water on the Brain", and "Would You Believe?". Besides the full composing team, Clarke also wrote songs with Nash, such as "Try It", "Wishyouawish" (1967), "Tomorrow When it Comes", "Jennifer Eccles" and "Wings" (1968). Clarke assumed more of a figurehead profile as front man of the Hollies following Graham Nash's departure from the group in December 1968. Clarke was the sole lead singer on "Hollies Sing Dylan" (a UK No. 3 album in early 1969).


title: Allan Clarke (singer)

text: Clarke has sole credit for songs including "My Life Is Over With You", "Goodbye Tomorrow", "Not That Way at All", "Marigold" (1969), "Mad Professor Blyth", "Separated" (1970), "Row the Boat Together" and "Hold On" (1971).


title: Allan Clarke (singer)

text: Also, Clarke helped Nash's replacement, Terry Sylvester, develop as a songwriter, teaming with him to write a number of songs including "Gloria Swansong", "Look at Life" (1969), "I Wanna Shout", "Man Without a Heart" and "Perfect Lady Housewife" (1970).


title: Allan Clarke (singer)

text: Keen to launch a solo career due to Nash's success in Crosby, Stills & Nash, Clarke left the group in 1971. He was replaced by the Swedish singer Mikael Rickfors, who was formerly with Bamboo. Clarke went on to release two solo albums: "My Real Name Is " (Epic, 1972) and "Headroom" (EMI, 1973).


title: Allan Clarke (singer)

text: After Clarke left the Hollies, "Long Cool Woman in a Black Dress", a song from their 1971 album "Distant Light" which he had co-written with songwriter Roger Cook and on which Clarke sang lead and played lead guitar, became an international hit single, reaching No. 2 in the US (their most successful single ever there) and No. 32 in the UK Singles Chart. However, the Hollies toured with Nash's replacement, Sylvester, who assumed the lead vocal on performance of the single instead of Clarke. Rickfors left the group and Clarke rejoined them in July 1973. Their first single with him back in the fold was another of his songs, "The Day that Curly Billy Shot Down Crazy Sam McGee", a UK top 40 hit that autumn.


title: Allan Clarke (singer)

text: Clarke continued to record and release solo albums while remaining with the Hollies, although his solo career did not achieve much album or single chart success. He released his self-titled third album in 1974. His next album was "I've Got Time" (1976). He also performed lead vocals on "Breakdown" by The Alan Parsons Project, from their 1977 album "I Robot". He left The Hollies briefly for the second time in March 1978 and made "I Wasn't Born Yesterday" (1978), an album of original material mostly written with singer-songwriter Gary Benson. It yielded a US chart hit single in "(I Will Be Your) Shadow in the Street". He returned to the group in August. Subsequent solo albums included "Legendary Heroes" (1980), another largely original set, with its UK title and track running order changed to "The Only One". He followed with a "Best of..." compilation (Aura, 1981). His final solo album of the last century was "Reasons to Believe" (1990), issued in Germany on Polydor Records, which remains unreleased in the US and UK.


title: Allan Clarke (singer)

text: Between 1974 and 1978, Clarke composed most of the original songs the Hollies recorded on a series of studio albums with Tony Hicks and Terry Sylvester.


title: Allan Clarke (singer)

text: In 1982, Clarke issued a rare non-album single, "Someone Else Will" c/w "Castles in the Wind" on Forever Records; however, the song failed to chart. Clarke recorded cover versions of Bruce Springsteen's "Born to Run", "Blinded by the Light" and "If I Were the Priest". In this period, Clarke also used material by Lindsey Buckingham, Janis Ian, Gavin Sutherland, and Randy Newman.


title: Allan Clarke (singer)

text: 1993 saw Clarke's final chart success with the Hollies, with the Nik Kershaw-penned single "The Woman I Love", which charted in the UK at No. 42.


title: Allan Clarke (singer)

text: In 1996, Clarke, with the Hollies and Graham Nash, contributed harmony and support vocals to a new version of "Peggy Sue Got Married", featuring lead vocals by Buddy Holly, which was credited as 'Buddy Holly and The Hollies'. It appeared on the "Not Fade Away" tribute album.


title: Allan Clarke (singer)

text: Due in part to ongoing medical problems with his vocal cords, Clarke retired from the music industry in 1999 to care for his wife, who had received a second diagnosis of cancer. Clarke was replaced in the band by Carl Wayne, former lead singer of the Move. Wayne died in 2004. The Hollies continue touring and recording today with Peter Howarth as their vocalist.


title: Allan Clarke (singer)

text: On 15 March 2010, Clarke, with fellow Hollies members Graham Nash, Tony Hicks, Eric Haydock, Bobby Elliott, Terry Sylvester and Bernie Calvert, was inducted into the Rock and Roll Hall of Fame. In 2011, Clarke made a surprise appearance at a Crosby & Nash concert at the Royal Albert Hall where the two former Hollies performed "Bus Stop".


title: Allan Clarke (singer)

text: Having appeared on harmonica for Carla Olson's band The Textones in 2018, Clarke made a return to his solo career in 2019 with a new album, "Resurgence", on BMG.


title: Allan Clarke (singer)

text: Clarke married Jennifer Bowstead on 24 March 1964 in Coventry. They have three children: Tim (born 1966), Toby (b. 1969) and Piper (b. 1972). The Hollies' song title "Jennifer Eccles" was a combination of the names of Clarke's wife and Graham Nash's then-wife, Rose Eccles.


title: Man on a Ledge

text: Man on a Ledge is a 2012 American action thriller film directed by Asger Leth, starring Sam Worthington, Jamie Bell, Elizabeth Banks, Edward Burns, Anthony Mackie, Genesis Rodriguez, and Ed Harris. Filming took place in New York City on top of the Roosevelt Hotel. The film received generally negative reviews from critics and grossed $47 million against its $42 million budget.


title: Man on a Ledge

text: Joe Walker checks into The Roosevelt Hotel, enters his hotel room on the 21st floor, and climbs on the ledge, apparently ready to commit suicide. The crowd below calls the police. Dante Marcus controls the crowd, while Jack Dougherty talks with Walker. Walker will only speak to negotiator Lydia Mercer, who is on a leave of absence after failing to save a suicidal policeman. Mercer arrives at the hotel room and acquires Walker's fingerprints from a shared cigarette. Dougherty has them analyzed and discovers that "Walker" is Nick Cassidy, an ex-policeman who was jailed for stealing a diamond from businessman David Englander. Nick was given a 25-year sentence but escaped one month earlier during his father's funeral. Nick maintains his innocence and claims that Englander has framed him, as Englander lost his fortune in a bad business deal and was too proud to sell the diamond.


title: Man on a Ledge

text: Nick distracts the police while his brother, Joey, and Joey's girlfriend, Angie, break into Englander's vault across the street to recover the diamond and prove his innocence. Cassidy must use double entendres to provide instructions to Joey and Angie through an earpiece while speaking to Mercer. Dougherty informs Marcus of Nick's identity, and Marcus orders the jewelry store's security to check the vault. Joey and Angie evade them but do not find the diamond. They deliberately set off an alarm, trick Englander into retrieving the diamond, and ambush him in his office, where they steal the diamond at gunpoint. Nick's ex-partner, Mike Ackerman, arrives at the hotel with evidence that Nick is planning something and demands to be allowed into the hotel room. Mercer distrusts him, and Dougherty backs her up. Ackerman claims he has found bomb schematics in a storage unit Nick rented and is convinced that he will detonate an explosive somewhere. While the crowd is evacuated by the bomb squad, Mercer, believing in Nick's innocence, calls internal affairs and discovers that three of the cops employed by Englander were suspected of being corrupt: Ackerman, Marcus, and a deceased officer called Joe Walker.


title: Man on a Ledge

text: Joey and Angie enter the hotel and hand the bag containing the diamond to the hotel concierge. The concierge pockets the diamond while placing the bag onto the rack. Englander calls Marcus, one of the corrupt cops who helped him frame Nick, and has him capture Joey and Angie as they reach the street. Nick attempts to escape through the hotel, pursued by a tactical team. The concierge aids him by handing him a disguise containing the diamond. Marcus chases Nick to the roof, where he has Mercer arrested for obstruction to clear the roof. Englander brings Joey and Angie, threatening to kill Joey unless Nick gives him the diamond. Nick turns it over, and Englander leaves. Mercer escapes custody in an elevator and rushes back to the roof. Marcus demands Nick jump off the roof. Ackerman arrives, shoots Marcus, and is shot in return. Ackerman apologizes to Nick and says he did not know Englander would frame him. Marcus' bulletproof vest saves him. As he prepares to kill Nick, Mercer arrives and shoots him. Englander mocks Nick as he leaves the area. Nick jumps from the roof onto an airbag set up earlier by the police and catches up to Englander. With the assistance of a crowd member, Nick evades capture and pulls the diamond from Englander's jacket, publicly proving his innocence.


title: Man on a Ledge

text: Nick is cleared of all charges and released from custody. He meets Joey, Angie, and Mercer at a bar owned by Nick's father, Frank Cassidy, who had faked his death and pretended to be the hotel concierge. Mercer asks Nick to "explain everything" to her as Joey proposes to Angie with a diamond ring, presumably stolen from Englander's vault. She accepts, and they all celebrate together.


title: Man on a Ledge

text: On September 3, 2010, it was confirmed that Jamie Bell had joined the cast. Filming began on October 30 in New York City. On November 1, Ed Harris and Titus Welliver were confirmed to have joined the cast.


title: Man on a Ledge

text: The first image from the set was revealed on November 2, 2010. The first teaser poster for the film was released on November 5, 2010. The first trailer was released by Summit Entertainment on September 22, 2011. The film was distributed by Summit Entertainment and E1 Entertainment (UK).


title: Man on a Ledge

text: During development, a large, on-rails prop was used to make the Roosevelt hotel seem taller, so that the hotel would remain consistent with the shots filmed in-studio instead of on the hotel itself. During the scenes where Nick is running along the sides of the hotel, extra floors were added during post-production to save the need for a second attachment. In post-production, crowds were edited in from other shots so that the crowds would appear consistent throughout the film. The lead actor, Sam Worthington, admitted during interviews that he had a fear of heights that he had to tackle during recording of the film.


title: Man on a Ledge

text: "Man on a Ledge" grossed $18.6 million in the United States and Canada, and $29 million in other territories, for a worldwide total of $47.6 million.


title: Man on a Ledge

text: The film placed fifth in the box office with $8 million gross on its opening weekend, and made $4.4 million in its second, falling to ninth.


title: Man on a Ledge

text: On Rotten Tomatoes, the film holds an approval rating of 31% based on 162 reviews and an average score of 4.8/10. The website's critics consensus reads: "Uninspired acting and preposterous plotlines defuse "Man on a Ledge"s mildly intriguing premise." On Metacritic, it has a weighted average score of 40 out of 100 based on reviews from 32 critics, indicating "mixed or average reviews". Audiences polled by CinemaScore gave the film an average grade of "B+" on an A+ to F scale.


title: Man on a Ledge

text: Roger Ebert of the "Chicago Sun-Times" said, "The movie cuts back and forth between two preposterous plot lines and uses the man on the ledge as a device to pump up the tension." According to Ebert, too much depends on Nick securing a leave from prison, escaping from two armed guards, reaching Manhattan, checking into the correct hotel room on the correct floor and not falling off prematurely. Anna Smith felt that the film "embrace[d] its own lunacy readily enough", but criticized the "ridiculous ending". Similarly, The New Zealand Herald considered the film "a missed opportunity" that doesn't live up to its potential", pointing at the "limited" location Sam Worthington had to work with, praising how he still appeared "suitably terrified".


title: Man on a Ledge

text: The DVD and Blu-ray Disc was released in the United States on May 29, 2012 after being absorbed by Lionsgate.


title: Man on a Ledge

text: The disc contains a 20-minute featurette, which shows behind-the-scenes footage, with an explanation of how various shots or effects were achieved. For instance, producer Lorenzo explains how shots of the crowd were composited onto a green chroma keying carpet, laid down underneath the fake ledge used for shots recorded in-studio. A version of the film with voiceover is included for the visually impaired.


title: Man on a Ledge

text: The Steelbook version of the film does not have menus, so is missing the special features present in the DVD and Blu-ray releases.


title: Man on a Ledge

text: The soundtrack to "Man on a Ledge" was released on January 27, 2012. James Southall commented that while "there is occasionally some reasonably tense action music", he found most of the score "very tired-sounding". Jørn Tillnes of Soundtrackgeek.com described it as "succeed[ing] in almost every way", but that he "would prefer more variation", as he found that "as a complete listening experience, you get bored with it".


title: Overhead line

text: An overhead line or overhead wire is an electrical cable that is used to transmit electrical energy to electric locomotives, trolleybuses or trams. It is known variously as:


title: Overhead line

text: An overhead line consists of one or more wires (or rails, particularly in tunnels) situated over rail tracks, raised to a high electrical potential by connection to feeder stations at regular intervals. The feeder stations are usually fed from a high-voltage electrical grid.


title: Overhead line

text: Electric trains that collect their current from overhead lines use a device such as a pantograph, bow collector or trolley pole. It presses against the underside of the lowest overhead wire, the contact wire. Current collectors are electrically conductive and allow current to flow through to the train or tram and back to the feeder station through the steel wheels on one or both running rails. Non-electric locomotives (such as diesels) may pass along these tracks without affecting the overhead line, although there may be difficulties with overhead clearance. Alternative electrical power transmission schemes for trains include third rail, ground-level power supply, batteries and electromagnetic induction.


title: Overhead line

text: To achieve good high-speed current collection, it is necessary to keep the contact wire geometry within defined limits. This is usually achieved by supporting the contact wire from a second wire known as the "" (in the US & Canada) or "catenary" (in the UK). This wire approximates the natural path of a wire strung between two points, a catenary curve, thus the use of "catenary" to describe this wire or sometimes the whole system. This wire is attached to the contact wire at regular intervals by vertical wires known as "droppers" or "drop wires". It is supported regularly at structures, by a pulley, link or clamp. The whole system is then subjected to mechanical tension.


title: Overhead line

text: As the pantograph moves along under the contact wire, the carbon insert on top of the pantograph becomes worn with time. On straight track, the contact wire is zigzagged slightly to the left and right of the centre from each support to the next so that the insert wears evenly, thus preventing any notches. On curves, the "straight" wire between the supports causes the contact point to cross over the surface of the pantograph as the train travels around the curve. The movement of the contact wire across the head of the pantograph is called the "sweep".


title: Overhead line

text: The zigzagging of the overhead line is not required for trolley poles. For tramways, a contact wire without a messenger wire is used.


title: Overhead line

text: Depot areas tend to have only a single wire and are known as "simple equipment" or "trolley wire". When overhead line systems were first conceived, good current collection was possible only at low speeds, using a single wire. To enable higher speeds, two additional types of equipment were developed:


title: Overhead line

text: Earlier dropper wires provided physical support of the contact wire without joining the catenary and contact wires electrically. Modern systems use current-carrying droppers, eliminating the need for separate wires.


title: Overhead line

text: The present transmission system originated about 100 years ago. A simpler system was proposed in the 1970s by the Pirelli Construction Company, consisting of a single wire embedded at each support for of its length in a clipped, extruded aluminum beam with the wire contact face exposed. A somewhat higher tension than used before clipping the beam yielded a deflected profile for the wire that could be easily handled at by a pneumatic servo pantograph with only 3 g acceleration.


title: Overhead line

text: An electrical circuit requires at least two conductors. Trams and railways use the overhead line as one side of the circuit and the steel rails as the other side of the circuit. For a trolleybus or a trolleytruck, no rails are available for the return current, as the vehicles use rubber tyres on the road surface. Trolleybuses use a second parallel overhead line for the return, and two trolley poles, one contacting each overhead wire. (Pantographs are generally incompatible with parallel overhead lines.) The circuit is completed by using both wires. Parallel overhead wires are also used on the rare railways with three-phase AC railway electrification.


title: Overhead line

text: In the Soviet Union the following types of wires/cables were used. For the contact wire, cold drawn solid copper was used to ensure good conductivity. The wire is not round but has grooves at the sides to allow the hangers to attach to it. Sizes were (in cross-sectional area) 85, 100, or 150 mm. To make the wire stronger, 0.04% tin might be added. The wire must resist the heat generated by arcing and thus such wires should never be spliced by thermal means.


title: Overhead line

text: The messenger (or catenary) wire needs to be both strong and have good conductivity. They used multi-strand wires (or cables) with 19 strands in each cable (or wire). Copper, aluminum, and/or steel were used for the strands. All the 19 strands could be of the same metal or some strands could be of steel for strength with the remaining strands of aluminum or copper for conductivity. Another type looked like it had all copper wires but inside each wire was a steel core for strength. The steel strands were galvanized but for better corrosion protection they could be coated with an anti-corrosion substance.


title: Overhead line

text: In Slovenia, where 3 kV system is in use, standard sizes for contact wire are 100 and 150 mm. The catenary wire is made of copper or copper alloys of 70, 120 or 150 mm. The smaller cross sections are made of 19 strands, whereas the bigger has 37 strands.


title: Overhead line

text: Two standard configurations for main lines consist of two contact wires of 100 mm and one or two catenary wires of 120 mm, totaling 320 or 440 mm. Only one contact wire is often used for side tracks.


title: Overhead line

text: Catenary wires are kept in mechanical tension because the pantograph causes mechanical oscillations in the wire and the wave must travel faster than the train to avoid producing standing waves that would cause wire breakage. Tensioning the line makes waves travel faster, and also reduces sag from gravity.


title: Overhead line

text: For medium and high speeds, the wires are generally tensioned by weights or occasionally by hydraulic tensioners. Either method is known as "auto-tensioning" (AT) or "constant tension" and ensures that the tension is virtually independent of temperature. Tensions are typically between per wire. Where weights are used, they slide up and down on a rod or tube attached to the mast, to prevent them from swaying.


title: Overhead line

text: For low speeds and in tunnels where temperatures are constant, fixed termination (FT) equipment may be used, with the wires terminated directly on structures at each end of the overhead line. The tension is generally about . This type of equipment sags in hot conditions and is taut in cold conditions.


title: Overhead line

text: With AT, the continuous length of the overhead line is limited due to the change in the height of the weights as the overhead line expands and contracts with temperature changes. This movement is proportional to the distance between anchors. Tension length has a maximum. For most 25 kV OHL equipment in the UK, the maximum tension length is .


title: Overhead line

text: An additional issue with AT equipment is that, if balance weights are attached to both ends, the whole tension length is free to move along the track. To avoid this a midpoint anchor (MPA), close to the centre of the tension length, restricts movement of the messenger/catenary wire by anchoring it; the contact wire and its suspension hangers can move only within the constraints of the MPA. MPAs are sometimes fixed to low bridges, or otherwise anchored to vertical catenary poles or portal catenary supports. A tension length can be seen as a fixed centre point, with the two half-tension lengths expanding and contracting with temperature.


title: Overhead line

text: Most systems include a brake to stop the wires from unravelling completely if a wire breaks or tension is lost. German systems usually use a single large tensioning pulley (basically a ratchet mechanism) with a toothed rim, mounted on an arm hinged to the mast. Normally the downward pull of the weights and the reactive upward pull of the tensioned wires lift the pulley so its teeth are well clear of a stop on the mast. The pulley can turn freely while the weights move up or down as the wires contract or expand. If tension is lost the pulley falls back toward the mast, and one of its teeth jams against the stop. This stops further rotation, limits the damage, and keeps the undamaged part of the wire intact until it can be repaired. Other systems use various braking mechanisms, usually with multiple smaller pulleys in a block and tackle arrangement.


title: Overhead line

text: To allow maintenance to the overhead line without having to turn off the entire system, the line is broken into electrically separated portions known as "sections". Sections often correspond with tension lengths. The transition from section to section is known as a "section break" and is set up so that the vehicle's pantograph is in continuous contact with one wire or the other.


title: Overhead line

text: For bow collectors and pantographs, this is done by having two contact wires run side by side over the length between 2 or 4 wire supports. A new one drops down and the old one rises up, allowing the pantograph to smoothly transfer from one to the other. The two wires do not touch (although the bow collector or pantograph is briefly in contact with both wires). In normal service, the two sections are electrically connected; depending on the system this might be an isolator, fixed contact or a Booster Transformer. The isolator allows the current to the section to be interrupted for maintenance.


title: Overhead line

text: On overhead wires designed for trolley poles, this is done by having a neutral section between the wires, requiring an insulator. The driver of the tram or trolleybus must temporarily reduce the power draw before the trolley pole passes through, to prevent arc damage to the insulator.


title: Overhead line

text: Pantograph-equipped locomotives must not run through a section break when one side is de-energized. The locomotive would become trapped, but as it passes the section break the pantograph briefly shorts the two catenary lines. If the opposite line is de-energized, this voltage transient may trip supply breakers. If the line is under maintenance, an injury may occur as the catenary is suddenly energized. Even if the catenary is properly grounded to protect the personnel, the arc generated across the pantograph can damage the pantograph, the catenary insulator or both.


title: Overhead line

text: Sometimes on a larger electrified railway, tramway or trolleybus system, it is necessary to power different areas of track from different power grids, without guaranteeing synchronisation of the phases. Long lines may be connected to the country's national grid at various points and different phases. (Sometimes the sections are powered with different voltages or frequencies.) The grids may be synchronised on a normal basis, but events may interrupt synchronisation. This is not a problem for DC systems. AC systems have a particular safety implication in that the railway electrification system would act as a "Backdoor" connection between different parts, resulting in, amongst other things, a section of the grid de-energised for maintenance being re-energised from the railway substation creating danger.


title: Overhead line

text: For these reasons, Neutral sections are placed in the electrification between the sections fed from different points in a national grid, or different phases, or grids that are not synchronized. It is highly undesirable to connect synchronized grids. A simple section break is insufficient to guard against this as the pantograph briefly connects both sections.


title: Overhead line

text: In countries such as France, South Africa and the United Kingdom, a pair of permanent magnets beside the rails at either side of the neutral section operate a bogie-mounted transducer on the train which causes a large electrical circuit-breaker to open and close when the locomotive or the pantograph vehicle of a multiple unit passes over them. In the United Kingdom equipment similar to Automatic Warning System (AWS) is used, but with pairs of magnets placed the running rails (as opposed to the AWS magnets placed midway between the rails). Lineside signs on the approach to the neutral section warn the driver to shut off traction power and coast through the dead section.


title: Overhead line

text: A neutral section or phase break consists of two insulated breaks back-to-back with a short section of line that belongs to neither grid. Some systems increase the level of safety by the midpoint of the neutral section being earthed. The presence of the earthed section in the middle is to ensure that should the transducer controlled apparatus fail, and the driver also fail to shut off power, the energy in the arc struck by the pantograph as it passes to the neutral section is conducted to earth, operating substation circuit breakers, rather than the arc either bridging the insulators into a section made dead for maintenance, a section fed from a different phase, or setting up a Backdoor connection between different parts of the country's national grid.


title: Overhead line

text: On the Pennsylvania Railroad, phase breaks were indicated by a position light signal face with all eight radial positions with lenses and no center light. When the phase break was active (the catenary sections out of phase), all lights were lit. The position light signal aspect was originally devised by the Pennsylvania Railroad and was continued by Amtrak and adopted by Metro North. Metal signs were hung from the catenary supports with the letters "PB" created by a pattern of drilled holes.


title: Overhead line

text: A special category of phase break was developed in America, primarily by the Pennsylvania Railroad. Since its traction power network was centrally supplied and only segmented by abnormal conditions, normal phase breaks were generally not active. Phase breaks that were always activated were known as "Dead Sections": they were often used to separate power systems (for example, the Hell's Gate Bridge boundary between Amtrak and Metro North's electrifications) that would never be in-phase. Since a dead section is always dead, no special signal aspect was developed to warn drivers of its presence, and a metal sign with "DS" in drilled-hole letters was hung from the catenary supports.


title: Overhead line

text: Occasionally gaps may be present in the overhead lines, when switching from one voltage to another or to provide clearance for ships at moveable bridges, as a cheaper alternative for moveable overhead power rails. Electric trains coast across the gaps. To prevent arcing, power must be switched off before reaching the gap and usually the pantograph would be lowered.


title: Overhead line

text: Given limited clearance such as in tunnels, the overhead wire may be replaced by a rigid overhead rail. An early example was in the tunnels of the Baltimore Belt Line, where a Π section bar (fabricated from three strips of iron and mounted on wood) was used, with the brass contact running inside the groove. When the overhead line was raised in the Simplon Tunnel to accommodate taller rolling stock, a rail was used. A rigid overhead rail may also be used in places where tensioning the wires is impractical, for example on moveable bridges.


title: Overhead line

text: In a movable bridge that uses a rigid overhead rail, there is a need to transition from the catenary wire system into an overhead conductor rail at the bridge portal (the last post before the movable bridge). For example, the power supply can be done through a catenary wire system near a swing bridge. The catenary wire typically comprises messenger wire (also called catenary wire) and a contact wire where it meets the pantograph. The messenger wire is terminated at the portal, while the contact wire runs into the overhead conductor rail profile at the transition end section before it is terminated at the portal. There is a gap between the overhead conductor rail at the transition end section and the overhead conductor rail that runs across the entire span of the swing bridge. The gap is required for the swing bridge to be opened and closed. To connect the conductor rails together when the bridge is closed, there is another conductor rail section called "rotary overlap" that is equipped with a motor. When the bridge is fully closed, the motor of the rotary overlap is operated to turn it from a tilted position into the horizontal position, connecting the conductor rails at the transition end section and the bridge together to supply power.


title: Overhead line

text: Trams draw their power from a single overhead wire at about 500 to 750 V. Trolleybuses draw from two overhead wires at a similar voltage, and at least one of the trolleybus wires must be insulated from tram wires. This is usually done by the trolleybus wires running continuously through the crossing, with the tram conductors a few centimetres lower. Close to the junction on each side, the tram wire turns into a solid bar running parallel to the trolleybus wires for about half a metre. Another bar similarly angled at its ends is hung between the trolleybus wires, electrically connected above to the tram wire. The tram's pantograph bridges the gap between the different conductors, providing it with a continuous pickup.


title: Overhead line

text: Where the tram wire crosses, the trolleybus wires are protected by an inverted trough of insulating material extending below.


title: Overhead line

text: Until 1946, a level crossing in Stockholm, Sweden connected the railway south of Stockholm Central Station and a tramway. The tramway operated on 600-700 V DC and the railway on 15 kV AC. In the Swiss village of Oberentfelden, the Menziken–Aarau–Schöftland line operating at 750 V DC crosses the SBB line at 15 kV AC; there used to be a similar crossing between the two lines at Suhr but this was replaced by an underpass in 2010. Some crossings between tramway/light rail and railways are extant in Germany. In Zürich, Switzerland, VBZ trolleybus line 32 has a level crossing with the 1,200 V DC Uetliberg railway line; at many places, trolleybus lines cross the tramway. In some cities, trolleybuses and trams shared a positive (feed) wire. In such cases, a normal trolleybus frog can be used.


title: Overhead line

text: Alternatively, section breaks can be sited at the crossing point, so that the crossing is electrically dead.


title: Overhead line

text: Many cities had trams and trolleybuses using trolley poles. They used insulated crossovers, which required tram drivers to put the controller into neutral and coast through. Trolleybus drivers had to either lift off the accelerator or switch to auxiliary power.


title: Overhead line

text: In Melbourne, Victoria, tram drivers put the controller into neutral and coast through section insulators, indicated by insulator markings between the rails.


title: Overhead line

text: Melbourne has three level crossings between electrified suburban railways and tram lines. They have mechanical switching arrangements (changeover switch) to switch the 1500 V DC overhead of the railway and the 650 V DC of the trams, called a Tram Square. Proposals have been advanced to grade separate these crossings or divert the tram routes.


title: Overhead line

text: Athens has two crossings of tram and trolleybus wires, at Vas. Amalias Avenue and Vas. Olgas Avenue, and at Ardittou Street and Athanasiou Diakou Street. They use the above-mentioned solution.


title: Overhead line

text: In Rome, at the crossing between Viale Regina Margherita and Via Nomentana, tram and trolleybus lines cross: tram on Viale Regina Margherita and trolleybus on Via Nomentana. The crossing is orthogonal, therefore the typical arrangement was not available.


title: Overhead line

text: In Milan, most tram lines cross its circular trolleybus line once or twice. Trolleybus and tram wires run parallel in streets such as viale Stelvio, viale Umbria and viale Tibaldi.


title: Overhead line

text: Some railways used two or three overhead lines, usually to carry three-phase current. This is used only on the Gornergrat Railway and Jungfrau Railway in Switzerland, the Petit train de la Rhune in France, and the Corcovado Rack Railway in Brazil. Until 1976, it was widely used in Italy. On these railways, the two conductors are used for two different phases of the three-phase AC, while the rail was used for the third phase. The neutral was not used.


title: Overhead line

text: Some three-phase AC railways used three overhead wires. These were an experimental railway line of Siemens in Berlin-Lichtenberg in 1898 (length 1.8 kilometres), the military railway between Marienfelde and Zossen between 1901 and 1904 (length 23.4 kilometres) and an 800-metre-long section of a coal railway near Cologne between 1940 and 1949.


title: Overhead line

text: On DC systems, bipolar overhead lines were sometimes used to avoid galvanic corrosion of metallic parts near the railway, such as on the Chemin de fer de la Mure.


title: Overhead line

text: All systems with multiple overhead lines have a high risk of short circuits at switches and therefore tend to be impractical in use, especially when high voltages are used or when trains run through the points at high speed.


title: Overhead line

text: The Sihltal Zürich Uetliberg Bahn has two lines with different electrification. To be able to use different electric systems on shared tracks, the Sihltal line has its overhead wire right above the train, whilst the Uetliberg line has its overhead wire off to one side.


title: Overhead line

text: A catenary is a system of overhead wires used to supply electricity to a locomotive, tram (streetcar), or light rail vehicle that is equipped with a pantograph.


title: Overhead line

text: Unlike simple overhead wires, in which the uninsulated wire is attached by clamps to closely spaced crosswires supported by poles, catenary systems use at least two wires. The catenary or messenger wire is hung at a specific tension between line structures, and a second wire is held in tension by the messenger wire, attached to it at frequent intervals by clamps and connecting wires known as "droppers". The second wire is straight and level, parallel to the rail track, suspended over it as the roadway of a suspension bridge is over water.


title: Overhead line

text: Catenary systems are suited to high-speed operations whereas simple wire systems, which are less expensive to build and maintain, are common on light rail or tram (streetcar) lines, especially on city streets. Such vehicles can be fitted with either a pantograph or trolley pole.


title: Overhead line

text: The Northeast Corridor in the United States has catenary over the between Boston, Massachusetts and Washington, D.C. for Amtrak's inter-city trains. Commuter rail agencies including MARC, SEPTA, NJ Transit, and Metro-North Railroad utilize the catenary to provide local service.


title: Overhead line

text: In Cleveland, Ohio the interurban/light rail lines and the heavy rail line use the same overhead wires, due to a city ordinance intended to limit air pollution from the large number of steam trains that passed through Cleveland between the east coast and Chicago. Trains switched from steam to electric locomotives at the Collinwood railyards about east of Downtown and at Linndale on the west side. When Cleveland constructed its rapid transit (heavy rail) line between the airport, downtown, and beyond, it employed a similar catenary, using electrification equipment left over after railroads switched from steam to diesel. Light and heavy rail share trackage for about along the Cleveland Hopkins International Airport Red (heavy rail) line, Blue and Green interurban/light rail lines between Cleveland Union Terminal and just past East 55th Street station, where the lines separate.


title: Overhead line

text: Part of the Boston, Massachusetts Blue Line through the northeast suburbs uses overhead lines, as does the Green Line.


title: Overhead line

text: The height of the overhead line can create hazards at level crossings, where it may be struck by road vehicles. Warning signs are placed on the approaches, advising drivers of the maximum safe height.


title: Overhead line

text: The wiring in most countries is too low to allow double stack container trains. The Channel Tunnel has an extended height overhead line to accommodate double-height car and truck transporters. China and India operate lines electrified with extra height wiring and pantographs to allow for double stack container trains.


title: Overhead line

text: Overhead lines may be adversely affected by strong winds causing wires to swing. Power storms can knock the power out with lightning strikes on systems with overhead wires, stopping trains following a power surge.


title: Overhead line

text: During cold or frosty weather, ice may coat overhead lines. This can result in poor electrical contact between the collector and the overhead line, resulting in electrical arcing and power surges.


title: Overhead line

text: The installation of overhead lines may require reconstruction of bridges to provide safe electrical clearance.


title: Overhead line

text: Overhead lines, like most electrified systems, require a greater capital expenditure when building the system than an equivalent non-electric system. While a conventional rail line requires only the grade, ballast, ties and rails, an overhead system also requires a complex system of support structures, lines, insulators, power-control systems and power lines, all of which require maintenance. This makes non-electrical systems more attractive in the short term, although electrical systems can pay for themselves eventually. Also, the added construction and maintenance cost-per-mile makes overhead systems less attractive on long-distance railways, such as those found in North America, where the distances between cities are typically far greater than in Europe. Such long lines require enormous investment in overhead line equipment, and major difficulties confront energizing long portions of overhead wire on a permanent basis, especially in areas where energy demand already outstrips supply.


title: Overhead line

text: Many people consider overhead lines to be "visual pollution", due to the many support structures and complicated system of wires and cables that fill the air. Such considerations have driven the move towards replacing overhead power and communications lines with buried cables where possible. The issue came to a head in the UK with the Great Western Main Line electrification scheme, especially through the Goring Gap. A protest group with their own website has been formed.


title: Overhead line

text: The valuable copper conductor can also be subject to theft, as for example the Lahore-Khanewal line in Pakistan and the Gweru-Harare section of line in Zimbabwe.


title: Overhead line

text: The first tram with overhead lines was presented by Werner von Siemens at the 1881 International Exposition of Electricity in Paris: the installation was removed after that event. In October 1883, the first permanent tram service with overhead lines was on the Mödling and Hinterbrühl Tram in Austria. The trams had bipolar overhead lines, consisting of two U-pipes, in which the pantographs hung and ran like shuttles. From April to June 1882, Siemens had tested a similar system on his Electromote, an early precursor of the trolleybus.


title: Overhead line

text: Much simpler and more functional was an overhead wire in combination with a pantograph borne by the vehicle and pressed at the line from below. This system, for rail traffic with a unipolar line, was invented by Frank J. Sprague in 1888. From 1889 it was used at the Richmond Union Passenger Railway in Richmond, Virginia, pioneering electric traction.


title: Segmentation fault

text: In computing, a segmentation fault (often shortened to segfault) or access violation is a fault, or failure condition, raised by hardware with memory protection, notifying an operating system (OS) the software has attempted to access a restricted area of memory (a memory access violation). On standard x86 computers, this is a form of general protection fault. The operating system kernel will, in response, usually perform some corrective action, generally passing the fault on to the offending process by sending the process a signal. Processes can in some cases install a custom signal handler, allowing them to recover on their own, but otherwise the OS default signal handler is used, generally causing abnormal termination of the process (a program crash), and sometimes a core dump.


title: Segmentation fault

text: Segmentation faults are a common class of error in programs written in languages like C that provide low-level memory access and few to no safety checks. They arise primarily due to errors in use of pointers for virtual memory addressing, particularly illegal access. Another type of memory access error is a bus error, which also has various causes, but is today much rarer; these occur primarily due to incorrect "physical" memory addressing, or due to misaligned memory access – these are memory references that the hardware "cannot" address, rather than references that a process is not "allowed" to address.


title: Segmentation fault

text: Many programming languages may employ mechanisms designed to avoid segmentation faults and improve memory safety. For example, Rust employs an ownership-based model to ensure memory safety. Other languages, such as Lisp and Java, employ garbage collection, which avoids certain classes of memory errors that could lead to segmentation faults.


title: Segmentation fault

text: A segmentation fault occurs when a program attempts to access a memory location that it is not allowed to access, or attempts to access a memory location in a way that is not allowed (for example, attempting to write to a read-only location, or to overwrite part of the operating system).


title: Segmentation fault

text: The term "segmentation" has various uses in computing; in the context of "segmentation fault", a term used since the 1950s, it refers to the address space of a "program." With memory protection, only the program's own address space is readable, and of this, only the stack and the read/write portion of the data segment of a program are writable, while read-only data and the code segment are not writable. Thus attempting to read outside of the program's address space, or writing to a read-only segment of the address space, results in a segmentation fault, hence the name.


title: Segmentation fault

text: On systems using hardware memory segmentation to provide virtual memory, a segmentation fault occurs when the hardware detects an attempt to refer to a non-existent segment, or to refer to a location outside the bounds of a segment, or to refer to a location in a fashion not allowed by the permissions granted for that segment. On systems using only paging, an invalid page fault generally leads to a segmentation fault, and segmentation faults and page faults are both faults raised by the virtual memory management system. Segmentation faults can also occur independently of page faults: illegal access to a valid page is a segmentation fault, but not an invalid page fault, and segmentation faults can occur in the middle of a page (hence no page fault), for example in a buffer overflow that stays within a page but illegally overwrites memory.


title: Segmentation fault

text: At the hardware level, the fault is initially raised by the memory management unit (MMU) on illegal access (if the referenced memory exists), as part of its memory protection feature, or an invalid page fault (if the referenced memory does not exist). If the problem is not an invalid logical address but instead an invalid physical address, a bus error is raised instead, though these are not always distinguished.


title: Segmentation fault

text: At the operating system level, this fault is caught and a signal is passed on to the offending process, activating the process's handler for that signal. Different operating systems have different signal names to indicate that a segmentation fault has occurred. On Unix-like operating systems, a signal called SIGSEGV (abbreviated from "segmentation violation") is sent to the offending process. On Microsoft Windows, the offending process receives a STATUS_ACCESS_VIOLATION exception.


title: Segmentation fault

text: The conditions under which segmentation violations occur and how they manifest themselves are specific to hardware and the operating system: different hardware raises different faults for given conditions, and different operating systems convert these to different signals that are passed on to processes. The proximate cause is a memory access violation, while the underlying cause is generally a software bug of some sort. Determining the root cause – debugging the bug – can be simple in some cases, where the program will consistently cause a segmentation fault (e.g., dereferencing a null pointer), while in other cases the bug can be difficult to reproduce and depend on memory allocation on each run (e.g., dereferencing a dangling pointer).


title: Segmentation fault

text: In C code, segmentation faults most often occur because of errors in pointer use, particularly in C dynamic memory allocation. Dereferencing a null pointer, which results in undefined behavior, will usually cause a segmentation fault. This is because a null pointer cannot be a valid memory address. On the other hand, wild pointers and dangling pointers point to memory that may or may not exist, and may or may not be readable or writable, and thus can result in transient bugs. For example:


title: Segmentation fault

text: Dereferencing any of these variables could cause a segmentation fault: dereferencing the null pointer generally will cause a segfault, while reading from the wild pointer may instead result in random data but no segfault, and reading from the dangling pointer may result in valid data for a while, and then random data as it is overwritten.


title: Segmentation fault

text: The default action for a segmentation fault or bus error is abnormal termination of the process that triggered it. A core file may be generated to aid debugging, and other platform-dependent actions may also be performed. For example, Linux systems using the grsecurity patch may log SIGSEGV signals in order to monitor for possible intrusion attempts using buffer overflows.


title: Segmentation fault

text: On some systems, like Linux and Windows, it is possible for the program itself to handle a segmentation fault. Depending on the architecture and operating system, the running program can not only handle the event but may extract some information about its state like getting a stack trace, processor register values, the line of the source code when it was triggered, memory address that was invalidly accessed and whether the action was a read or a write.


title: Segmentation fault

text: Although a segmentation fault generally means that the program has a bug that needs fixing, it is also possible to intentionally cause such failure for the purposes of testing, debugging and also to emulate platforms where direct access to memory is needed. On the latter case, the system must be able to allow the program to run even after the fault occurs. In this case, when the system allows, it is possible to handle the event and increment the processor program counter to "jump" over the failing instruction to continue the execution.


title: Segmentation fault

text: Writing to read-only memory raises a segmentation fault. At the level of code errors, this occurs when the program writes to part of its own code segment or the read-only portion of the data segment, as these are loaded by the OS into read-only memory.


title: Segmentation fault

text: Here is an example of ANSI C code that will generally cause a segmentation fault on platforms with memory protection. It attempts to modify a string literal, which is undefined behavior according to the ANSI C standard. Most compilers will not catch this at compile time, and instead compile this to executable code that will crash:


title: Segmentation fault

text: When the program containing this code is compiled, the string "hello world" is placed in the rodata section of the program executable file: the read-only section of the data segment. When loaded, the operating system places it with other strings and constant data in a read-only segment of memory. When executed, a variable, "s", is set to point to the string's location, and an attempt is made to write an "H" character through the variable into the memory, causing a segmentation fault. Compiling such a program with a compiler that does not check for the assignment of read-only locations at compile time, and running it on a Unix-like operating system produces the following runtime error:


title: Segmentation fault

text: This code can be corrected by using an array instead of a character pointer, as this allocates memory on stack and initializes it to the value of the string literal:


title: Segmentation fault

text: Even though string literals should not be modified (this has undefined behavior in the C standard), in C they are of codice_1 type, so there is no implicit conversion in the original code (which points a codice_2 at that array), while in C++ they are of codice_3 type, and thus there is an implicit conversion, so compilers will generally catch this particular error.


title: Segmentation fault

text: In C and C-like languages, null pointers are used to mean "pointer to no object" and as an error indicator, and dereferencing a null pointer (a read or write through a null pointer) is a very common program error. The C standard does not say that the null pointer is the same as the pointer to memory address 0, though that may be the case in practice. Most operating systems map the null pointer's address such that accessing it causes a segmentation fault. This behavior is not guaranteed by the C standard. Dereferencing a null pointer is undefined behavior in C, and a conforming implementation is allowed to assume that any pointer that is dereferenced is not null.


title: Segmentation fault

text: This sample code creates a null pointer, and then tries to access its value (read the value). Doing so causes a segmentation fault at runtime on many operating systems.


title: Segmentation fault

text: Dereferencing a null pointer and then assigning to it (writing a value to a non-existent target) also usually causes a segmentation fault:


title: Segmentation fault

text: The following code includes a null pointer dereference, but when compiled will often not result in a segmentation fault, as the value is unused and thus the dereference will often be optimized away by dead code elimination:


title: Segmentation fault

text: The following code accesses the character array codice_4 beyond its upper boundary. Depending on the compiler and the processor, this may result in a segmentation fault.


title: Segmentation fault

text: which causes the stack to overflow which results in a segmentation fault. Infinite recursion may not necessarily result in a stack overflow depending on the language, optimizations performed by the compiler and the exact structure of a code. In this case, the behavior of unreachable code (the return statement) is undefined, so the compiler can eliminate it and use a tail call optimization that might result in no stack usage. Other optimizations could include translating the recursion into iteration, which given the structure of the example function would result in the program running forever, while probably not overflowing its stack.


title: History of the periodic table

text: The periodic table is an arrangement of the chemical elements, structured by their atomic number, electron configuration and recurring chemical properties. In the basic form, elements are presented in order of increasing atomic number, in the reading sequence. Then, rows and columns are created by starting new rows and inserting blank cells, so that rows (periods) and columns (groups) show elements with recurring properties (called periodicity). For example, all elements in group (column) 18 are noble gases that are largely—though not completely—unreactive.


title: History of the periodic table

text: The history of the periodic table reflects over two centuries of growth in the understanding of the chemical and physical properties of the elements, with major contributions made by Antoine-Laurent de Lavoisier, Johann Wolfgang Döbereiner, John Newlands, Julius Lothar Meyer, Dmitri Mendeleev, Glenn T. Seaborg, and others.


title: History of the periodic table

text: Nine chemical elements – carbon, sulfur, iron, copper, silver, tin, gold, mercury, and lead, have been known since before antiquity, as they are found in their native form and are relatively simple to mine with primitive tools. Around 330 BCE, the Greek philosopher Aristotle proposed that everything is made up of a mixture of one or more "roots", an idea originally suggested by the Sicilian philosopher Empedocles. The four roots, which the Athenian philosopher Plato called "elements", were "earth", "water", "air" and "fire". Similar ideas about these four elements existed in other ancient traditions, such as Indian philosophy.


title: History of the periodic table

text: A few extra elements were known in the age of alchemy: zinc, arsenic, antimony, and bismuth. Platinum was also known to pre-Columbian South Americans, but knowledge of it did not reach Europe until the 16th century.


title: History of the periodic table

text: The history of the periodic table is also a history of the discovery of the chemical elements. The first person in recorded history to discover a new element was Hennig Brand, a bankrupt German merchant. Brand tried to discover the philosopher's stone—a mythical object that was supposed to turn inexpensive base metals into gold. In 1669, or later, his experiments with distilled human urine resulted in the production of a glowing white substance, which he called "cold fire" ("kaltes Feuer"). He kept his discovery secret until 1680, when Anglo-Irish chemist Robert Boyle rediscovered phosphorus and published his findings. The discovery of phosphorus helped to raise the question of what it meant for a substance to be an element.


title: History of the periodic table

text: In 1661, Boyle defined an element as "those primitive and simple Bodies of which the mixt ones are said to be composed, and into which they are ultimately resolved."


title: History of the periodic table

text: In 1789, French chemist Antoine Lavoisier wrote "Traité Élémentaire de Chimie" ("Elementary Treatise of Chemistry"), which is considered to be the first modern textbook about chemistry. Lavoisier defined an element as a substance whose smallest units cannot be broken down into a simpler substance. Lavoisier's book contained a list of "simple substances" that Lavoisier believed could not be broken down further, which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc and sulfur, which formed the basis for the modern list of elements. Lavoisier's list also included 'light' and 'caloric', which at the time were believed to be material substances. He classified these substances into metals and nonmetals. While many leading chemists refused to believe Lavoisier's new revelations, the "Elementary Treatise" was written well enough to convince the younger generation. However, Lavoisier's descriptions of his elements lack completeness, as he only classified them as metals and non-metals.


title: History of the periodic table

text: In 1808–10, British natural philosopher John Dalton published a method by which to arrive at provisional atomic weights for the elements known in his day, from stoichiometric measurements and reasonable inferences. Dalton's atomic theory was adopted by many chemists during the 1810s and 1820s.


title: History of the periodic table

text: In 1815, British physician and chemist William Prout noticed that atomic weights seemed to be multiples of that of hydrogen.


title: History of the periodic table

text: In 1817, German physicist Johann Wolfgang Döbereiner began to formulate one of the earliest attempts to classify the elements. In 1829, he found that he could form some of the elements into groups of three, with the members of each group having related properties. He termed these groups "triads".


title: History of the periodic table

text: "Chemically analogous elements arranged in increasing order of their atomic weights formed well marked groups of three called Triads in which the atomic weight of the middle element was found to be generally the arithmetic mean of the atomic weight of the other two elements in the triad.


title: History of the periodic table

text: In 1860, a revised list of elements and atomic masses was presented at a conference in Karlsruhe. It helped spur creation of more extensive systems. The first such system emerged in two years.