{"content": "The trend in question involves inscriptions, a novel way of etching data in the form of code, image, audio, and text files to the Bitcoin blockchain. Each inscription is tied to a so-called ordinal, representing an individual, unique satoshi (sat)—the smallest unit of Bitcoin. The term ordinal comes from what its inventor Casey Rodamor dubbed \"Ordinals Theory,\" a proposed methodology for the off-chain tracking and labeling of individual sats based on the order in which they're mined and transferred.", "id": "bitcoin/25785deb_4434.txt"}
{"content": "This change effectively increased the block size limit from 1MB (or megabyte) to 4MB. The original block size limit was kept at 1MB, but the new witness field doesn’t count toward that limit. Not only can more information be packed into transactions and blocks, but the data put into the witness field gets an effective discount when it comes to fees since this data isn’t taking up the more valuable 1MB transaction space.\n\nTaproot was another soft-fork upgrade activated in late 2021. The main Taproot upgrade removed the data limit per transaction. ", "id": "bitcoin/f8d55502_4435.txt"}
{"content": "Glassnode data shows that Bitcoin’s mean block size upper range has increased significantly since the launch of Ordinals, rising from 1.5-2.0 MB to 3.0-3.5 MB within a few weeks. The increase correlates with not only images but larger files such as audio and video starting to be stored as Ordinals.", "id": "bitcoin/0246b9bf_4436.txt"}
{"content": "Ordinals, a method for creating unique digital assets on the Bitcoin blockchain, has significantly impacted the blockchain over the past year, yet there is a notable lack of research on it. This study is the first to demonstrate that Bitcoin Ordinals-related data is a crucial feature for predicting Bitcoin transaction fee rates and prices. Our main contributions are as follows: Dataset Construction: We construct a dataset that includes Bitcoin chain data, Ordinals index data, and Ordinals market data, as well as a dataset excluding Ordinals-related data. Our findings reveal that the fluctuation in the number of Ordinals inscriptions tends to correlate with market activity. When the Ordinals market is active, the share of Ordinals inscribed fees and the average Bitcoin transaction fee rate remain high. We argue that the upgrades of SegWit and Taproot drove the creation and development of Bitcoin Ordinals. Combined with users’ interest in Ordinals, this in turn affected the Bitcoin blockchain and its price. Prediction: Using three metrics (MAE, RMSE, and MAPE) and the TemporalFusionTransformer model as a baseline, our comparative experiments show that Bitcoin Ordinals-related data is essential for predicting Bitcoin transaction fee rates and prices. This finding aids investors and participants in the Bitcoin Ordinals market in avoiding losses and leveraging congestion-related arbitrage opportunities, thus enabling more accurate decision-making in the cryptocurrency market. ", "id": "bitcoin/938bf04f_4437.txt"}
{"content": "Bitcoin uses the UTXO (Unspent Transaction Output) model to track ownership, transactions, and prevent double-spending.\n\n\n\nWhen you receive Bitcoin, you're essentially getting a new UTXO added to your collection. If you want to spend BTC, you need to use one or more of your existing UTXOs.", "id": "bitcoin/9ec36c9a_4438.txt"}
{"content": "According to the European Commission, the EU’s economic growth model rests on four pillars: (a) sustainable competitiveness; (b) economic security; (c) open strategic autonomy; and (d) fair competition. The concept of competitiveness is used very frequently in economics, business and even daily conversation, and the idea that the EU no longer ranks as a competitive location, especially in comparison with the US, has gradually become an accepted notion. But defining competitiveness itself, and thus comparing the EU with other jurisdictions, is far from straightforward. Notwithstanding this, the European Commission has identified the following nine drivers of the EU’s competitiveness:\n\nThe single market\nAccess to private capital and investments\nPublic investment and infrastructure\nResearch and innovation\nEnergy\nCircularity\nDigitalisation\nEducation and skills\nTrade and open strategic autonomy\nThis paper will use concrete indicators to explore whether there is any foundation for the pessimism regarding the EU’s competitiveness compared with that of the US, and what the main areas for improvement might be. To do this, it uses the European Commission’s key performance indicators (KPIs), in addition to other indicators.\n\nThe need to study this phenomenon stems from a progressive divergence in per capita GDP between the EU and the US (which emerged from the last financial crisis earlier and better), and comes in addition to the relative loss of worldwide GDP share that both have suffered compared with other powers, such as China.", "id": "economics/005e4d61_1984.txt"}
{"content": "The slowdown in European economic growth began before these shocks, indicating longer-standing structural factors. GDP per capita in the eurozone, expressed in constant dollars and purchasing power parity, grew by an average of 0.9% a year over the period studied, a rate lower than in the United States. The GDP per capita in the eurozone represented 77% of the one in the US in 2000, compared with 72% in 2019 (and 70.6% in 2022). It should be noted that the differential with the US has remained stable at 68% in the 27-member European Union (EU) (growth of 1.2% per year). China’s GDP per capita has increased fivefold over this period, but in 2019 will be only 40% of that of the EU. At national level, the picture is mixed. Germany’s GDP per capita relative to that of the United States rose slightly to a peak of almost 85% in the early 2010s, before falling to 82% in 2019. Italy has seen a steady decline from over 80% to 65%. France’s trajectory is similar to that of the eurozone.\n\n\n\n\nThe economic and financial crisis of 2008 marked a turning point, with European economies unable to rebound as quickly and strongly as their American counterparts, facing a depression exacerbated by the sovereign debt crisis. So in their paper, the authors ask is it “ex ante fragility (institutional and/or economic) that is preventing the rebound, an inability to fully embrace the digital economy that has driven growth over the past 10 years, or […] greater vulnerability to emerging players, notably China, that is hampering the European export engine that had previously been its strength?”. To shed light on this question, they analyse\n\n", "id": "economics/c4fe2ca4_1985.txt"}
{"content": "By 2022, investment in new technologies will represent 5% of GDP in the United States and 2.8% of GDP in the eurozone. Research and development spending in 2022 will amount to 3.5% of GDP in the United States and 2.3% of GDP in the eurozone. What’s more, from 2016–2017 onwards, the investment and R&D effort in the United States increased significantly compared to that of the eurozone. At the same time, productivity began to grow much faster in the United States than in Europe. It is therefore the lag in technological investment and R&D that explains a large part of Europe’s lag behind the United States in terms of labour productivity and GDP.\n\nHow can Europe hope to catch up with the United States in terms of productivity and growth? The first step would be to change the nature of business investment. The rate of business investment is virtually the same at the start of 2024 in the United States and the eurozone (13.5% of GDP), but the proportion of this investment in technology is much higher in the United States (5% of GDP compared with 2.8% in the eurozone). We therefore need to correct the fact that business investment in the eurozone is too mundane and not sufficiently high-end.\n\nThe second measure is to increase R&D spending and university budgets in the eurozone. The resources available for university and corporate research are much higher in the United States. And, as mentioned earlier, these resources are an important and significant determinant of productivity gains.\n\nIt is to be feared that Europe will be drawn into a vicious circle of low investment in new technologies and research and development, and hence low productivity gains and growth. Firstly, these declines could have a negative impact on Europe’s attractiveness to foreign investors. Secondly, they could reduce tax revenues and the ability of European governments to pursue policies to support innovation and boost Europe’s attractiveness.", "id": "economics/643a6683_1986.txt"}
{"content": "Immigration has been the major driving force behind U.S. labor force growth over the past 20 years, according to data from the U.S. Census Bureau. Between 2000 and 2022, the foreign born accounted for nearly three-quarters of all growth in the civilian, prime-age (age 25 to 54) labor force. As the U.S. population ages and more U.S.-born residents enter retirement, immigration will become increasingly important for driving labor force growth. Due to population aging, the number of U.S.-born people of prime working age (age 25-54) hardly changed between 2000 and 2022. In contrast, the number of foreign-born people of prime working age grew by almost 7 million over this period. And the U.S.-born senior population (age 65 and older) grew by almost 18 million over the same timeframe.\n\n\n\nThis trend will only accelerate in the future. By one estimate, all U.S. population growth will come from international migration starting in 2040.\n\nEfforts to boost fertility, as an alternative to immigration, are unlikely to be sufficient. Around the world, government efforts to raise fertility through economic incentives or family-friendly policies have a mixed record of success.", "id": "economics/159b52d4_1987.txt"}
{"content": "Population and per capita incomes\nIt is also important to relate GDP to the population sizes and dynamics. Per-capita GDP at PPP is the most frequently used metric for cross-country development comparisons. The US population has grown faster than the EU population over the past decades and is expected to continue to grow faster. The EU has, in fact, come closer to the US in terms of GDP per capita, from 67 percent in 1995 (the first year for which EU27 data is available) to 72 percent in 2022 (Figure 2, Panel A). China’s convergence has been impressive, from a mere 2 percent of the US GDP per capita in 1980, to 28 percent of the US in 2022. The IMF expects that China will reach 33 percent of the US level by 2028.  \n\nThe EU is composed of countries at diverse levels of economic development. Western EU countries diverged from the US from 1980 to 2004 (from 88 percent to 80 percent in terms of GDP per capita), but since then, per-capita income has fluctuated at about the same level (Panel B of Figure 2). The gap between Northern EU countries and the US has more or less been the same since 1980. Eastern EU countries have converged impressively, from 32 percent of US GDP per capita in 1995 to 55 percent in 2022; IMF projections suggest continued convergence to 60 percent by 2028, nearing the development level of Southern EU countries. Only the southern part of the EU is lagging. Per-capita GDP in the south was 73 percent of the US level in the early 2000s, but had fallen to 61 percent by the pandemic, though at least the IMF does not foresee continued relative declines in the years to come.\n\n\nMade with Flourish • Create a chart\nWorking habits  \nA further twist to the EU/US comparison is an adjustment to working time. In Europe, employees tend to work fewer hours than in the US, partly because there are more paid holidays, the typical working week of a full-time employee is shorter and there is a larger share of part-time workers than in the US. At the same time, the employment rate (the share of working-age people employed) is higher in the EU than in the US. Thus, it is useful to compare output per number of workers and output per hours worked (Figure 3).  ", "id": "economics/d984113a_1988.txt"}
{"content": "The 1931 census for England and Wales was destroyed by fire on 19 December 1942, during the Second World War, while in storage, along with a large amount of furniture, at the Office of Works in Hayes, Middlesex. W. A. Derrick of the General Register Office, who visited the scene of the aftermath, commented in a letter to the Central National Registration Office that \"The fire was not occasioned by enemy action and how it achieved such dimensions in a store in which special hydrants had been fitted and said to have been in charge of a fire guard of 6 paid watchers, is a mystery which will need investigation\".[4][5][6] A report the following year mentioned a theory that the fire may have been started by a fire-watch employee's discarded cigarette; no action was taken.[4] The entire census – schedules, enumeration books and plans – was destroyed, and it was recommended that in future census records be stored separately to prevent a similar complete loss. Fortunately the 1931 census for Scotland was not affected as it was stored in Edinburgh.[7][8]\n\nThere was no census taken in 1941 due to the Second World War; however, the register taken as a result of the National Registration Act 1939 captures many of the same details as the census, with the added advantage of having each subject's date of birth, and has assumed greater significance following the destruction of the 1931 census. The 1939 register was released into the public domain on a subscription basis in 2015 with some redactions, including details of those still alive being blanked out.[9]", "id": "genealogy/a98b7dcc_8730.txt"}
{"content": "Many of you will know that the English and Welsh 1931 census returns were destroyed during WW11. What many people do not realise, however, is that this was not as a result of enemy action but caused by a ferocious fire which mysteriously broke out in a store room at the Office of Works one night in December 1942. The devastation was so great that, in the words of W. A. Derrick, the member of staff who reported the loss, it left behind ‘’nothing more than shapeless mounds of paper” making any attempt at salvage “useless”. The hearts of all family historians reading this will no doubt just have shuddered in horror!\nMr Derrick worryingly also stated in his report (written to a colleague at the Central National Registration Office at Southport) “Will you also let us know where the enumeration books and plans of division relating to the 1921 census are stored. The schedules, as you are aware, were damaged by water at Leonard Street and have since been dried out and are scattered over various parts of Somerset House; but no plans or enumeration books were brought from Leonard Street and it is assumed that they were stored elsewhere.”\nThankfully archival storage arrangements are now far superior to the arrangements of the 1940s and, putting it into some historical perspective, few people today would consider a documentary source of a mere twenty year’s age to be that important! However I still can’t help casting a swift backwards curse in time at the fate of these records and the fact that no-one thought to separate the census books from the householders’ schedules when they were stored away. At least the Scottish returns were housed safely in Edinburgh!", "id": "genealogy/fa7e0311_8731.txt"}
{"content": "The entire 1931 census including schedules, enumeration books and plans were destroyed in a fire at the Office of Works store at Hayes, Middlesex on Saturday 19 December 1942.  The fire was not due to enemy bombing in the Second World War but was due to an unexplained incident.\n\nThere is an interesting letter published on the National Archives website from a W A Derrick of the General Register Office to F C Stobart of the Central National Registration Office.  He is mystified as to the cause and extent of the fire, particularly as there were 6 paid ‘watchers’ from the fire service on hand.  He states:\n\n‘The fire was not occasioned by enemy action and how it achieved such dimensions in a store in which special hydrants had been fitted and said to have been in charge of a fire guard of 6 paid watchers, is a mystery which will need investigation’.\n\nNational Archives.\n\nThe subsequent investigation the following year mentions a police report and a suggestion that the fire may have actually been started by a lighted cigarette thrown down by one of the fire watchers.  No action was taken. ", "id": "genealogy/8aec496b_8732.txt"}
{"content": "As family history enthusiasts, we get one of our best pictures of each family as the censuses are released for public use. We are still celebrating the release of the 1911 census and rejoicing in the information we are gleaning from its pages. At the same time, we are anxiously awaiting the release of the 1921 census around 2021.\n\nJust beyond 2021, we are looking at a drought-filled 20 years without an England and Wales census as we know them. The 1931 census returns, including schedules, enumeration books and plans, were completely destroyed in a fire in Hayes, Middlesex, where the census was being stored. Many precautions had been taken to protect the census, which all failed. To read more about the 1931 census, see http://www.1911census.org.uk/1931.htm.\n\nThe 1941 UK census was not taken due to World War II. However, The National Registration Act, 1939, established a National Register “for the issue of identity cards.” This population count took place on 29 September 1939, and provided information for “all persons in the United Kingdom at the appointed time” and “all persons entering or born in the United Kingdom after that time.” The United Kingdom included England, Wales, Scotland, Northern Ireland, and the Isle of Man. Forty million people were registered in some 7,000 transcript books. (See the sample page below.) These provide a viable census substitute for the 1941 census. The schedule requested the following information: Name; Sex; Age (not year of birth); Occupation, Profession, trade or employment; Residence; Condition as to marriage; Membership of Naval, Military or Air Force Reserves or Auxiliary Forces or of Civil Defence Services or Reserves.\n\n\nSo, in answer to the title question, there are no censuses for 1931 or 1941, but all is not lost. There is a census substitute for 1941 that we will all learn to use and rely upon. For more information, see \"Identity cards in Britain: past experience and policy implications,\" by John Agar.", "id": "genealogy/8e2575e3_8733.txt"}
{"content": "Unfortunately during the night on Saturday, 19 December 1942, an extensive fire broke out at an Office of Works store in Hayes, Middlesex.  It destroyed all the 1931 census records (apart from the Scottish census that was safely stored in Edinburgh). \n\nThe circumstances of the 1942 fire are most mysterious. Although the fire broke out during the Second World War, it was not caused by bombing. The Office of Works store housed the entire census schedules, enumeration books and plans. All reasonable precautions had been taken to ensure the safekeeping of these documents. Special hydrants had been fitted to the store and they were being guarded by 6 paid fire watchers. Yet the ferocious fire destroyed everything. A report into the fire the next year suggested that a lighted cigarette from one of the fire watchers might be an explanation. But there was no proof and no action was taken.\n\n\nThe National Archives has archived a letter from W A Derrick of the General Register Office dated 22 December 1942 to F T Stobart of the Central National Registration Office which gives information about the fire. It can be found at this link: \n\nwebarchive.nationalarchives.gov.uk\n\n", "id": "genealogy/dcc1fbc0_8734.txt"}
{"content": "If you’ve been building your family tree using census records, you might have noticed a glaring gap. After the detailed 1921 Census of England and Wales, the next available enumeration jumps forward to 1951 – this is because the 1931 Census was destroyed in a fire.  \n\nWhat happened to the 1931 Census?\nOn 19 December 1942, in the shadow of the Second World War, disaster struck not from bombs or enemy fire, but from an unexpected spark in a quiet storeroom at the Office of Works in Hayes, Middlesex. There, the 1931 Census schedules for England and Wales lay stacked like the collective memory of a nation - millions of sheets holding the voices, occupations, and family stories of an entire generation. \n\nBut flames swept through the paper like an unrelenting tide, turning decades of history to ash. The brave fire crews battled the blaze, but the damage was done. Recorded by every household on 26 April 1931, these schedules had captured a vivid portrait of Britain between the wars. In a single night, that portrait was lost to the smoke. \n\nDid any traces of the records survive? \nTragically, there was no backup copy of the 1931 Census; no summaries survived either. The Scottish census returns were stored separately in Edinburgh, so remained unharmed. Due to Scotland’s 100-year privacy rule, they are due to be released in 2031. \n\nWhat does it mean for family history?\nThe loss of the 1931 Census leaves a 30-year gap in census coverage for England and Wales. Due to the pressures of war, the 1941 Census was never taken. A special Register was recorded in 1939, however, to organise identity cards and rationing, and we can use this as a stand-in for those missing two decades of census data. \n\nBetween the 1921 Census and the 1939 Register, family historians miss out on a valuable mid-century snapshot of households. The 1931 Census would have shed light on families living through the Great Depression, in a transitional interwar period and on the eve of huge social changes.  \n\nSources you can use instead\nWhile we can’t replace the 1931 Census, there are other resources that can help bridge the gap: \n\nThe 1939 Register. Available to search on websites like Findmypast, this important collection lists names, addresses, dates of birth, occupations, and later notes on marriages or deaths. \nElectoral rolls, which show eligible voters at a given address and can help trace movement over time. \nHistorical newspapers. Millions of digitised pages contain everything from local scandals to community photographs, and can offer a detailed glimpse into the lives of your ancestors. \nThe destruction of the 1931 Census is one of British genealogy’s great losses, but it also reminds us to use a variety of sources to delve deeper into our ancestors’ stories. Even without those missing pages, there are still many ways to uncover who they were and how they lived. ", "id": "genealogy/a9888245_8735.txt"}
{"content": "Tax assessments (known in the later Empire as the indiction) were made in Britain in Roman times, but detailed records have not survived.[5] In the 7th century AD, Dál Riata (parts of what is now Scotland and Northern Ireland) conducted a census, called the \"Tradition of the Men of Alba\" (Scottish Gaelic: Senchus fer n-Alban). The first census in England was the Domesday Book, compiled in 1086 under William the Conqueror for tax purposes.\n\nDistinct from earlier, less inclusive censuses (e.g. for religious purposes), national decennial censuses of the general population started in 1801, championed by the statistician John Rickman. The censuses were initially conducted partly to ascertain the number of men able to fight in the Napoleonic Wars, and partly over population concerns stemming from the 1798 work An Essay on the Principle of Population by Reverend Thomas Robert Malthus. Rickman's twelve reasons – set out in 1798 and repeated in parliamentary debates – for conducting a census of Great Britain included the following justifications:[citation needed]\n\n\"the intimate knowledge of any country must form the rational basis of legislation and diplomacy\"\n\"an industrious population is the basic power and resource of any nation, and therefore its size needs to be known\"\n\"the number of men who were required for conscription to the militia in different areas should reflect the area's population\"\n\"there were defence reasons for wanting to know the number of seamen\"\n\"the need to plan the production of corn and thus to know the number of people who had to be fed\"\n\"a census would indicate the Government's intention to promote the public good\", and\n\"the life insurance industry would be stimulated by the results\".\nRegular national censuses have taken place every ten years since 1801, most recently in 2021; other partial censuses have been made on some of the intervening fifth anniversaries. The first four censuses (1801–1831) were mainly statistical: that is, mainly headcounts, with virtually no personal information. A small number of older records exist in local record offices as by-products of the notes made by enumerators in the production of those earlier censuses; these might list all persons or just the heads of households. The 1841 Census was the first to intentionally record names of all individuals in a household or institution.[6][7]\n\nThe first simultaneous census of the British Empire, covering the United Kingdom, India and the Crown Settlements, took place in 1881.[8]\n\nThe Census Act 1920 provides the legal framework for conducting all censuses in Great Britain (Scotland,[9] England, and Wales). The primary legislation for Northern Ireland was introduced in 1969. Before this legislation, it was necessary to have a separate act of parliament for each census.[10] Britain was also responsible for initiating and co-ordinating censuses in many of its overseas colonies.\n\nBecause of the disruption caused by the Second World War, there was no census in 1941. However, following the passage into law on 5 September 1939 of the National Registration Act 1939, a population count was carried out on 29 September 1939. The resulting National Register was later used to develop the National Health Service Central Register. Censuses were taken on 26 April 1931 in Great Britain, but the returns for England and Wales were destroyed in an accidental fire during the Second World War.[11]\n\nOn 24 April 1966, the UK trialled an alternative method of enumeration – long form/short form. Every household was given a short form to complete, while a sample of the population was given a long form to collect more detailed information. The short form was used for the population count and to collect basic information such as usual address, sex, age and relationships to other household members. This was the first and only time that a five-yearly census was carried out in the UK.[12][13][14]\n\nThe 1971 and 1981 census in Northern Ireland were boycotted by some Irish Republicans, with the 1981 census happening at the same time as the 1981 hunger strike.[15]", "id": "genealogy/f8148e11_8736.txt"}
{"content": "The Superfest story\nBack in the 1980s, East Germany faced a glass shortage. Their solution? A product called Superfest. This wasn’t your ordinary glassware – it was made using a special process that resulted in nearly indestructible drinking vessels.\n\nSuperfest glasses underwent a chemical treatment called ion exchange. Without getting too technical, this process essentially created a compressed outer layer on the glass, making it incredibly resistant to breaking. These glasses were a hit in East Germany, with around 120 million sold by 1990.\n\nInterestingly, while Superfest was seen as a potential export star, it never really took off internationally. Some speculate that foreign companies weren’t keen on the idea of glassware that rarely needed replacing – after all, broken glasses mean more sales.\n\nModern Ion Exchange glassware\nWhile Superfest itself is no more, the technology behind it lives on. Today, ion exchange is primarily used to create durable smartphone screens as it’s the basis behind the famous Gorilla Glass. However, there are still a few companies making glassware using similar techniques:\n\nAderia: This Japanese brand produces a range of durable glasses, including beer glasses and other drinkware.", "id": "history/b3cbb00d_1361.txt"}
{"content": "Due to temperature and time effects, the smaller sodium ions are exchanged for larger potassium ions in the glass surface. Their size puts the glass surface under compressive stress and thus leads to higher fracture resistance. The outcome by far exceeded expectations: the so solidified glasses exhibited as much as a 15-fold increase longevity, were heat-resistant, stackable, and even lighter than conventional drinking glasses!\n\nWith this patent, the GDR glass researchers defined the state of the art for mass production of solidified drinking glasses. Under the brand CEVERIT (composed of CE for chemical, VER for solidified and IT, the usual ending for mineral substances), production started in 1980 at VEB Sachsenglas Schwepnitz, manufacturing beer glasses. Soon the selection was extended by juice and shot glasses, while the name was changed to \"Superfest\". In total, more than 110 million glasses were made until 1990. The products received awards for their design at the \"Leipzig Spring Fair\" in 1980 and 1983.\n\nUnfortunately, the invention did not catch on in the capitalist system, as the glass market had no interest in unbreakable glass, so an all-German success failed to come about.\n\nThe Patent & Standards Centre would like to wish unbreakable confidence to your ideas!!\n\n“From idea to product\" – We provide practical services for researchers, entrepreneurs, craftsmen, founders and independent inventors to protect your ideas.\nAll our services are now online available!", "id": "history/a2e8dd5e_1362.txt"}
{"content": "Before anything could be done to potentially decrease Superfest’s extreme durability, the brand’s parent company, VEB Sachsenglas Schwepnitz, went bankrupt after the fall of the Berlin Wall in 1989. Since then, Superfest glasses were exiled to live on in vintage shops, personal collections, and Ebay listings—which may sound familiar to those who know the story of Depression glass. The Superfest brand still maintains a loyal following, with some listings for vintage Superfest glasses reaching hundreds of U.S. dollars.\n\nNow, the demand for an extremely durable drinking glass may be on the rise again with soulbottles, a Berlin startup that aims to bring back the legacy of Superfest with a focus on sustainability.\n\nThe company creates engraved, customizable glass water bottles that encourage users to drink more tap water while also donating to the charity Viva con Agua’s drinking water projects—one euro donated for each soulbottle purchased.\n\nAccording to The Guardian article, soulbottles has crowdfunded €251,139 (US$275,948) to open a production facility reminiscent of the Superfest production process, decades after the economy forced Superfest to lose its grip on consumers.", "id": "history/4915d46c_1363.txt"}
{"content": "Superfest – a design icon\nAt the same time, the Generalkollektiv under Paul Bittner, Fritz Keuchel and Tilo Poitz set out to design a universally versatile glass. It needed to be as light as possible, take up as little space as possible and be as durable as could be. \n\nBy 1978, the Generalkollektiv came up with a glass that essentially ushered in a new standard of “catering” glass in the GDR. They had come up with a newly patented way to reduce the weight and increase the durability of the glass by introducing a special salt in the production process. The design and practicality of the glasses, especially their stackability (earning them the nickname stapelglas) was even recognized by the GDR, earning itself the “Good Design” award in 1980. \n\ngestapelt ddr glas superfest ceverit bierglas logo ost deutschland\nSo, with the design and the chemical process in place, the Ministry for Glass and Ceramic Industries gave the order to expand the glass production plant in Schewpnitz with a new production hall. A total of one million marks was made available, and Ceverit glass production began in April 1980.", "id": "history/7422ee6e_1364.txt"}
{"content": "The problem with the original Superfest glass is that its manufacturers worked with modified alumino or borosilicate glass, which is not as easy to recycle as the more common soda-lime glass. So Soulbottles’ challenge is to produce glass that is both durable and recyclable. Initial tests were promising, and delivery of the first bottles is expected next year. How strong are they? Well the prototypes were dropped from a height of two metres – and didn’t smash.", "id": "history/36ee7e8e_1365.txt"}
{"content": "Historically the second was considered a 60th of a minute, which was one 60th of an hour. A second based on the Earth’s variable rotation was impractical for modern timekeeping requirements. With the introduction of Ephemeris Time, the ephemeris second was defined in 1954 and revised in 1956 as 1/31 556 925.9747 of the length of the tropical year for 1900.0. The availability of atomic clocks made a more accurate and available second possible. So in 1968, the Système International (SI) second was defined as the duration of 9 192 631 770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the Caesium 133 atom. With such an accurate measure of the second, the meter was defined as the length of path traveled by light in vacuum during a time interval of 1/299 792 458 of a second. Other SI units are defined in terms of the second and meter. With improved accuracies of timekeeping based on optical frequency standards, a redefinition of the second is under consideration.", "id": "hsm/3a821edf_0216.txt"}
{"content": "This new definition was termed the “ephemeris second.” Much more precise than the previous definition, it was also extremely unwieldy: The second would now be defined as 1/31,556,925.9747 of a tropical year (the time between two summer solstices) for 1900. Just a few years later, the CGPM would declare the ephemeris second to be “inadequate for the present needs of metrology.”\n\nAround this time, a new clock burst onto the scene and revolutionized timekeeping and the second itself. It finally promised to realize Maxwell’s vision of a clock based on an unvarying natural vibration.\n\nThe new clock’s genesis began in 1947 in the Washington, D.C., laboratory of NIST’s Harold Lyons. Lyons’ group bombarded a cloud of ammonia molecules trapped in a 30-foot-long cell with microwaves. As the researchers tried different microwave frequencies — the number of wave peaks per second — they hit upon one that caused the molecules to absorb and re-emit a maximum amount of microwaves. The team then used a device that counted the microwave frequency and manually transferred it to a quartz crystal oscillator. This process is akin to how you might tune a guitar: You hear a reference pitch and tighten or loosen the string you want to tune until it plays that pitch. With this method, the team was able to define the second as the time it took the ammonia to emit roughly 23.9 billion cycles of radiation.\n\n \n\nCondon and Lyons with Atomic Clock and Ammonia Molecule Model\nNIST Director Edward Condon (left) and clock inventor Harold Lyons contemplate the ammonia molecule upon which the clock was based.\nLyons’ team had the clock working by August 1948; the researchers first demonstrated it publicly in 1949. The ammonia clock was crude by modern standards and ultimately proved no more accurate or precise than keeping time by measuring the Earth’s rotation. Still, it proved the concept of an atomic clock.  \n\nIn 1955, Louis Essen at the National Physical Laboratory in the U.K. built upon an idea proposed by Nobel Prize-winning physicist Isidor Rabi to use a beam of cesium atoms rather than a diffuse cloud of ammonia molecules. Cesium, as Rabi and others had discovered, has several properties that made it easy for physicists to work with. Essen constructed the first atomic clock stable enough to be used as a time interval standard. \n\nNIST had also started building cesium atomic clocks in the early 1950s, and by 1959, the institute had finished two high-performance cesium atomic beam frequency standards that could be precisely compared. NBS-1 became the U.S. national standard of frequency in 1959, quickly followed by NBS-2 in 1960.\n\n \n\nMan standing behind a big horizontal cylinder of metal and a lot of wires\nAtomic clock NBS-1\nCredit: NIST\nWhat is a “standard of frequency” and how is it related to timekeeping? The first thing to note is that atoms don’t actually tell time. Instead, they absorb and release radiation such as microwaves or visible light. This radiation has a well-defined frequency — the number of wave cycles per second. In an atomic clock, a particular frequency of radiation absorbed and released by cesium or another atom is converted into a time interval. In other words, scientists define a second as the time it takes to count a certain number of radiation cycles. \n\nAnd despite what headlines seem to suggest, atomic clocks don’t run forever once they are turned on. They run very accurately for limited periods of time, then need to be recalibrated or adjusted. But to get a sense of how accurate these clocks are, it’s often helpful to imagine how long it would take one to gain or lose a second if it ran continuously.\n\nBoth NBS-1 and NBS-2 had accuracies of 10 parts per trillion or better, meaning neither clock would gain or lose a second if it ran continuously for 3,000 years. By 1966, their successor NBS-3 had achieved an accuracy 10 times better and wouldn’t have gained or lost a second in 30,000 years. \n\nWith the advent of super-accurate atomic clocks, the definition of the second was ripe for change. In 1967, the CGPM redefined the second in the International System of Units (SI) to be the duration of 9,192,631,770 cycles of microwave radiation, corresponding to what’s known as the “hyperfine energy transition” in the cesium atom. \n\nLet’s break down this phrase a bit. An “energy transition” refers to little up-and-down jumps in energy made by the outermost electron orbiting the cesium atom’s core, or nucleus, when the atom absorbs or emits radiation at specific energies determined by quantum mechanics. “Hyperfine” refers to a splitting of the atom’s energy levels when the electron interacts magnetically with the atom’s nucleus. Microwaves with a frequency of 9,192,631,770 cycles per second carry exactly the amount of energy the electron needs to go between the two hyperfine energy levels of the cesium atom in its lowest-energy configuration. When these microwaves hit a cesium atom, it makes the hyperfine energy transition: The outermost electron flips its “spin,” which can be imagined as a tiny bar magnet inherent to the electron flipping upside down, and the atom attains a higher energy level. When the atom then reflips its spin and drops to the lower energy level, it releases microwaves with the same frequency of 9,192,631,770 cycles per second. The frequency of the absorbed and emitted microwave radiation is used as a timekeeping standard.\n\n(The value of 9,192,631,770 cycles per second to which the second was fixed emerged when astronomers at the U.S. Naval Observatory calculated the duration of a 1950s-era ephemeris second based on measurements of the Moon’s motion, and Essen and a colleague at the National Physical Laboratory then counted the cycles of radiation absorbed and emitted by cesium atoms during one of those seconds. The measurement, published in 1958, had an error of a few parts per billion, which suddenly enabled timekeeping with significantly lower uncertainty than with a second based on astronomical observations.)\n\nThe new cesium clocks, while better than any that had come before, were still far from perfect. Scientists continued to root out and minimize sources of error such as temperature variations and unwanted energy transitions. By 1975, NIST’s NBS-6 atomic clock was accurate and stable enough to neither gain nor lose a second in 400,000 years.\n\n \n\nLong metal cylinder on a table with a man standing at the far end.\nPhysicist David Glaze with atomic clock NBS-6\nCredit: NIST\nLaunched nearly two decades later, in 1993, NIST’s NIST-7 atomic clock was significantly more accurate and wouldn’t gain or lose a second in 6 million years. \n\n \n\nThree men stand behind a glass tube with equipment inside\nAtomic frequency standard NIST-7 and its creators (left to right) John P. Lowe, project leader Robert E. Drullinger, and David J. Glaze\nCredit: NIST\nYou don’t need this kind of precision for your wristwatch. But being able to measure such tiny fractions of a second opened up technological applications that would have been impossible just decades earlier. Atomic clocks have led to advances in timekeeping, communication, metrology, geodesy and advanced positioning and navigation systems. \n\nMost famously, atomic clocks make possible the GPS satellite network that many of us rely on every day. Each of the 31 satellites in the GPS network has multiple atomic clocks that are synchronized daily with atomic clocks on the ground and with each other. GPS satellites continually broadcast information about their positions along with the time they broadcast that position. When a GPS unit in a car or a phone receives signals from four of these satellites, it can use the time and position signals to determine where it — and thus you — are on the globe with a high degree of accuracy. ", "id": "hsm/fe179b08_0217.txt"}
{"content": "Following several years of work, two astronomers at the U.S. Naval Observatory (USNO) and two astronomers at the National Physical Laboratory (Teddington, England) determined the relationship between the frequency of the cesium atom (the standard of time) and the ephemeris second. They determined the orbital motion of the Moon about the Earth, from which the apparent motion of the Sun could be inferred, in terms of time as measured by an atomic clock.  As a result, in 1967 the Thirteenth General Conference on Weights and Measures defined the second of atomic time in the International System of Units (SI) as:\n \nthe duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.\nThe ground state is defined at zero magnetic field.  The second thus defined is equivalent to the ephemeris second.\n \nThe Sub-bureau for Rapid Service and Predictions of Earth Orientation Parameters of the International Earth Rotation Service (IERS), located at the USNO, monitors the Earth's rotation. Part of its mission involves the determination of a time scale based on the current rate of the rotation of the Earth. UT1 is the non-uniform time based on the Earth's rotation.\n \nThe Earth is constantly undergoing a deceleration caused by the braking action of the tides. Through the use of ancient observations of eclipses, it is possible to determine the average deceleration of the Earth to be roughly 1.4 milliseconds per day per century. This deceleration causes the Earth's rotational time to slow with respect to the atomic clock time. Thus, the definition of the ephemeris second embodied in Newcomb's motion of the Sun was implicitly equal to the average mean solar second over the eighteenth and nineteenth centuries.  Modern studies have indicated that the epoch at which the mean solar day was exactly 86,400 SI seconds was approximately 1820.  This is also the approximate mean epoch of the observations analyzed by Newcomb, ranging in date from 1750 to 1892, that resulted in the definition of the mean solar day on the scale of Ephemeris Time.  Before then, the mean solar day was shorter than 86,400 seconds and since then it has been longer than 86,400 seconds.\n \nThe length of the mean solar day has increased by roughly 2 milliseconds since it was exactly 86,400 seconds of atomic time about 1.88 centuries ago (i.e. the 188 year difference between 2008 and 1820).   That is, the length of the mean solar day is at present about 86,400.002 seconds instead of exactly 86,400 seconds.  Over the course of one year, the difference accumulates to almost one second, which is compensated by the insertion of a leap second into the scale of UTC with a current regularity of a little less than once per year.  Other factors also affect the Earth, some in unpredictable ways, so that it is necessary to monitor the Earth's rotation continuously.\n \nIn order to keep the cumulative difference in UT1-UTC less than 0.9 seconds, a leap second is added to the atomic time to decrease the difference between the two. This leap second can be either positive or negative depending on the Earth's rotation. Since the first leap second in 1972, all leap seconds have been positive, and there have been 28 leap seconds in the 48 years to January, 2020.\n \nConfusion sometimes arises over the misconception that the regular insertion of leap seconds every few years indicates that the Earth should stop rotating within a few millennia. The confusion arises because some mistake leap seconds for a measure of the rate at which the Earth is slowing. The 1 second increments are, however, indications of the accumulated difference in time between the two systems.  (Also, it is important to note that the current difference in the length of day from 86,400 seconds is the accumulation over nearly two centuries, not just the previous year.)  As an example, the situation is similar to what would happen if a person owned a watch that lost 2 seconds per day. If it were set to a perfect clock today, the watch would be found to be slow by 2 seconds tomorrow. At the end of a month, the watch will be roughly a minute in error (30 days of 2 second error accumulated each day). The person would then find it convenient to reset the watch by one minute to have the correct time again.\n \nThis scenario is analogous to that encountered with the leap second. The difference is that instead of setting the clock that is running slow, we choose to set the clock that is keeping a uniform, precise time. The reason for this is that we can change the time on an atomic clock, while it is not possible to alter the Earth's rotational speed to match the atomic clocks! Currently the Earth runs slow at roughly 2 milliseconds per day. After 500 days, the difference between the Earth rotation time and the atomic time would be 1 second. Instead of allowing this to happen, a leap second is inserted to bring the two times closer together.\n \nInternational Atomic Time (TAI)  is a statistical atomic time scale based on a large number of clocks operating at standards laboratories around the world that is maintained by the Bureau International des Poids et Mesures; its unit interval is exactly one SI second at sea level. The origin of TAI is such that UT1-TAI is approximately 0 (zero) on January 1, 1958. TAI is not adjusted for leap seconds.  It is recommended by the BIPM that systems which cannot handle leap seconds use TAI instead.\n \nCoordinated Universal Time (UTC) is defined by the CCIR Recommendation 460-4 (1986). It differs from TAI by the total number of leap seconds, so that UT1-UTC stays smaller than 0.9s in absolute value.  The decision to introduce a leap second in UTC is the responsibility of the International Earth Rotation Service (IERS). According to the CCIR Recommendation, first preference is given to the opportunities at the end of December and June, and second preference to those at the end of March and September. Since the system was introduced in 1972, only dates in June and December have been used.  TAI is expressed in terms of UTC by the relation TAI = UTC + dAT, where  dAT is the total algebraic sum of leap seconds.\n \nThe first leap second was introduced on June 30, 1972. The historical list of leap seconds can be found here.\n \nThe Global Positioning System (GPS) epoch is January 6, 1980 and is synchronized to UTC. GPS is NOT adjusted for leap seconds.\n \nAs of 1 January 2017,\n        TAI is ahead of UTC   by 37 seconds.\n        TAI is ahead of GPS   by 19 seconds.\n        GPS is ahead of UTC   by 18 seconds.\n \nUntil 1960, Universal Time (UT) was taken as the independent variable of astronomical ephemerides.  UT was then replaced by Ephemeris Time (ET),  based on the motion of the sun.  However, ET did not include relativistic effects, such as corrections for the gravitational potential and velocity, as required by advances in the accuracy of time comparisons.  Thus ET was superseded in 1981 by Terrestrial Dynamical Time (TDT) and Barycentric Dynamical Time (TDB), which distinguish coordinate systems with origins at the center of the Earth and the center of the solar system, respectively, and are consistent with the general theory of relativity.  In the language of general relativity, TDT is a proper time while TDB is a coordinate time.  In 1991, TDT was renamed simply Terrestrial Time (TT) and two additional relativistic time scales, Geocentric Coordinate Time (TCG) and Barycentric Coordinate Time (TCB) were adopted.  Definitions of these time scales are given in Systems of Time.\n \nTerrestrial Time (TT) is a uniform atomic time scale, whose unit is the SI second, that replaces Ephemeris Time and maintains continuity with it.  TT may be regarded as the time that would be kept by an ideal atomic clock on the geoid.  To convert a TT value to a prediction of UT1, it is necessary to know the difference dT = TT - UT1.  Values of dT are tabulated in the Astronomical Almanac.  For example, mathematical predictions of lunar and solar eclipses in the distant past and future depend sensitively on estimates of dT.  The computed path of a solar eclipse that occurred 2000 years ago would be in error by about 3 hours, or some 45 degrees in longitude to the west, on the assumption that the rate of rotation of the earth were uniform.  Conversely, records of well documented ancient eclipses, together with modern telescopic observations of occultations, Very Long Baseline Interferometry, satellite laser ranging,  lunar laser ranging, and other measurements correlated to atomic time scales since 1955, have provided the data on which long term trends and short term fluctuations have been derived.  Since dT was approximately 32.184 seconds at the origin of TAI in 1958, a practical realization of TT is TT = TAI + 32.184 seconds. Although this expression gives TT in terms of TAI, in practice TT is obtained from the relation TT = UTC + dAT + 32.184 seconds for a known value of UTC and a given number of leap seconds.", "id": "hsm/52da71e8_0218.txt"}
{"content": "This current definition was adopted in 1967 when it became feasible to define the second based on fundamental properties of nature with caesium clocks.[2] As the speed of Earth's rotation varies and is slowing ever so slightly, a leap second is added at irregular intervals to civil time[nb 1] to keep clocks in sync with Earth's rotation.\n\nThe definition that is based on 1⁄86400 of a rotation of the earth is still used by the Universal Time 1 (UT1) system.\n\nEtymology\n\"Minute\" comes from the Latin pars minuta prima, meaning \"first small part\" i.e. first division of the hour – dividing into sixty, and \"second\" comes from the pars minuta secunda, \"second small part\", dividing again into sixty.[3]\n\nUses\nAnalog clocks and watches often have sixty tick marks on their faces, representing seconds (and minutes), and a \"second hand\" to mark the passage of time in seconds. Digital clocks and watches often have a two-digit seconds counter.\n\nSI prefixes are frequently combined with the word second to denote subdivisions of the second: milliseconds (thousandths), microseconds (millionths), nanoseconds (billionths), and sometimes smaller units of a second. Multiples of seconds are usually counted in hours and minutes. Though SI prefixes may also be used to form multiples of the second such as kiloseconds (thousands of seconds), such units are rarely used in practice. An everyday experience with small fractions of a second is a 1-gigahertz microprocessor that has a cycle time of 1 nanosecond. Camera shutter speeds are often expressed in fractions of a second, such as 1⁄30 second or 1⁄1000 second.\n\nSexagesimal divisions of the day from a calendar based on astronomical observation have existed since the third millennium BC, though they were not seconds as we know them today.[4] Small divisions of time could not be measured back then, so such divisions were mathematically derived. The first timekeepers that could count seconds accurately were pendulum clocks invented in the 17th century. Starting in the 1950s, atomic clocks became better timekeepers than Earth's rotation, and they continue to set the standard today.\n\nClocks and solar time\nA mechanical clock, which does not depend on measuring the relative rotational position of the Earth, keeps uniform time called mean time, within whatever accuracy is intrinsic to it. That means that every second, minute and every other division of time counted by the clock has the same duration as any other identical division of time. A sundial, which measures the relative position of the Sun in the sky called apparent time, does not keep uniform time. The time kept by a sundial varies by time of year, meaning that seconds, minutes and every other division of time is a different duration at different times of the year. The time of day measured with mean time versus apparent time may differ by as much as 15 minutes, but a single day differs from the next by only a small amount; 15 minutes is a cumulative difference over a part of the year. The effect is due chiefly to the obliqueness of Earth's axis with respect to its orbit around the Sun.\n\nThe difference between apparent solar time and mean time was recognized by astronomers since antiquity, but prior to the invention of accurate mechanical clocks in the mid-17th century, sundials were the only reliable timepieces, and apparent solar time was the only generally accepted standard.\n\nEvents and units of time in seconds\nFractions of a second are usually denoted in decimal notation, for example 2.01 seconds, or two and one hundredth seconds. Multiples of seconds are usually expressed as minutes and seconds, or hours, minutes and seconds of clock time, separated by colons, such as 11:23:24, or 45:23 (the latter notation can give rise to ambiguity, because the same notation is used to denote hours and minutes). It rarely makes sense to express longer periods of time like hours or days in seconds, because they are awkwardly large numbers. For the metric unit of second, there are decimal prefixes representing 10−30 to 1030 seconds.\n\nSome common units of time in seconds are: a minute is 60 seconds; an hour is 3,600 seconds; a day is 86,400 seconds; a week is 604,800 seconds; a year (other than leap years) is 31,536,000 seconds; and a (Gregorian) century averages 3,155,695,200 seconds; with all of the above excluding any possible leap seconds. In astronomy, a Julian year is precisely 31,557,600 seconds.\n\nSome common events in seconds are: a stone falls about 4.9 meters from rest in one second; a pendulum of length about one meter has a swing of one second, so pendulum clocks have pendulums about a meter long; the fastest human sprinters run 10 meters in a second; an ocean wave in deep water travels about 23 meters in one second; sound travels about 343 meters in one second in air; light takes 1.3 seconds to reach Earth from the surface of the Moon, a distance of 384,400 kilometers.\n\nOther units incorporating seconds\nA second is directly part of other units, such as frequency measured in hertz (inverse seconds or s−1), speed in meters per second, and acceleration in meters per second squared. The metric system unit becquerel, a measure of radioactive decay, is measured in inverse seconds and higher powers of second are involved in derivatives of acceleration such as jerk. Though many derivative units for everyday things are reported in terms of larger units of time, not seconds, they are ultimately defined in terms of the SI second; this includes time expressed in hours and minutes, velocity of a car in kilometers per hour or miles per hour, kilowatt hours of electricity usage, and speed of a turntable in rotations per minute.\n\nMoreover, most other SI base units are defined by their relationship to the second: the meter is defined by setting the speed of light (in vacuum) to be 299 792 458 m/s, exactly; definitions of the SI base units kilogram, ampere, kelvin, and candela also depend on the second. The only base unit whose definition does not depend on the second is the mole, and only two of the 22 named derived units, radian and steradian, do not depend on the second either.\n\nTimekeeping standards\nMain article: Time standard\nA set of atomic clocks throughout the world keeps time by consensus: the clocks \"vote\" on the correct time, and all voting clocks are steered to agree with the consensus, which is called International Atomic Time (TAI). TAI \"ticks\" atomic seconds.[5]: 207–218 \n\nCivil time is defined to agree with the rotation of the Earth. The international standard for timekeeping is Coordinated Universal Time (UTC). This time scale \"ticks\" the same atomic seconds as TAI, but inserts or omits leap seconds as necessary to correct for variations in the rate of rotation of the Earth.[5]: 16–17, 207 \n\nA time scale in which the seconds are not exactly equal to atomic seconds is UT1, a form of universal time. UT1 is defined by the rotation of the Earth with respect to the Sun, and does not contain any leap seconds.[5]: 68, 232  UT1 always differs from UTC by less than a second.\n\nOptical lattice clock\nMain article: Optical lattice clock\nWhile they are not yet part of any timekeeping standard, optical lattice clocks with frequencies in the visible light spectrum now exist and are the most accurate timekeepers of all. A strontium clock with frequency 430 THz, in the red range of visible light, during the 2010s held the accuracy record: it gains or loses less than a second in 15 billion years, which is longer than the estimated age of the universe. Such a clock can measure a change in its elevation of as little as 2 cm by the change in its rate due to gravitational time dilation.[6]\n\nHistory of definition\nSee also: History of timekeeping devices\nThere have only ever been three definitions of the second: as a fraction of the day, as a fraction of an extrapolated year, and as the microwave frequency of a caesium atomic clock, which have each realized a sexagesimal division of the day from ancient astronomical calendars.\n\nSexagesimal divisions of calendar time and day\nCivilizations in the classic period and earlier created divisions of the calendar as well as arcs using a sexagesimal system of counting, so at that time the second was a sexagesimal subdivision of the day (ancient second = ⁠\nday\n/\n60×60\n⁠), not of the hour like the modern second (= ⁠\nhour\n/\n60×60\n⁠).[citation needed] Sundials and water clocks were among the earliest timekeeping devices, and units of time were measured in degrees of arc. Conceptual units of time smaller than realisable on sundials were also used.\n\nThere are references to \"second\" as part of a lunar month in the writings of natural philosophers of the Middle Ages, which were mathematical subdivisions that could not be measured mechanically.[nb 2][nb 3]\n\nFraction of solar day\nSee also: Seconds pendulum § Defining the second\nThe earliest mechanical clocks, which appeared starting in the 14th century, had displays that divided the hour into halves, thirds, quarters and sometimes even 12 parts, but never by 60. In fact, the hour was not commonly divided in 60 minutes as it was not uniform in duration. It was not practical for timekeepers to consider minutes until the first mechanical clocks that displayed minutes appeared near the end of the 16th century. Mechanical clocks kept the mean time, as opposed to the apparent time displayed by sundials. By that time, sexagesimal divisions of time were well established in Europe.[nb 4]\n\nThe earliest clocks to display seconds appeared during the last half of the 16th century. The second became accurately measurable with the development of mechanical clocks. The earliest spring-driven timepiece with a second hand that marked seconds is an unsigned clock depicting Orpheus in the Fremersdorf collection, dated between 1560 and 1570.[9]: 417–418 [10] During the third quarter of the 16th century, Taqi al-Din built a clock with marks every 1⁄5 minute.[11] In 1579, Jost Bürgi built a clock for William of Hesse that marked seconds.[9]: 105  In 1581, Tycho Brahe redesigned clocks that had displayed only minutes at his observatory so they also displayed seconds, even though those seconds were not accurate. In 1587, Tycho complained that his four clocks disagreed by plus or minus four seconds.[9]: 104 \n\nIn 1656, Dutch scientist Christiaan Huygens invented the first pendulum clock. It had a pendulum length of just under a meter, giving it a swing of one second, and an escapement that ticked every second. It was the first clock that could accurately keep time in seconds. By the 1730s, 80 years later, John Harrison's maritime chronometers could keep time accurate to within one second in 100 days.\n\nIn 1832, Gauss proposed using the second as the base unit of time in his millimeter–milligram–second system of units. The British Association for the Advancement of Science (BAAS) in 1862 stated that \"All men of science are agreed to use the second of mean solar time as the unit of time.\"[12] BAAS formally proposed the CGS system in 1874, although this system was gradually replaced over the next 70 years by MKS units. Both the CGS and MKS systems used the same second as their base unit of time. MKS was adopted internationally during the 1940s, defining the second as 1⁄86,400 of a mean solar day.\n\nFraction of an ephemeris year\nSee also: Ephemeris time\nSometime in the late 1940s, quartz crystal oscillator clocks with an operating frequency of ~100 kHz advanced to keep time with accuracy better than 1 part in 108 over an operating period of a day. It became apparent that a consensus of such clocks kept better time than the rotation of the Earth. Metrologists also knew that Earth's orbit around the Sun (a year) was much more stable than Earth's rotation. This led to proposals as early as 1950 to define the second as a fraction of a year.\n\nThe Earth's motion was described in Newcomb's Tables of the Sun (1895), which provided a formula for estimating the motion of the Sun relative to the epoch 1900 based on astronomical observations made between 1750 and 1892.[13] This resulted in adoption of an ephemeris time scale expressed in units of the sidereal year at that epoch by the IAU in 1952.[14] This extrapolated timescale brings the observed positions of the celestial bodies into accord with Newtonian dynamical theories of their motion.[13] In 1955, the tropical year, considered more fundamental than the sidereal year, was chosen by the IAU as the unit of time. The tropical year in the definition was not measured but calculated from a formula describing a mean tropical year that decreased linearly over time.\n\nIn 1956, the second was redefined in terms of a year relative to that epoch. The second was thus defined as \"the fraction 1⁄31,556,925.9747 of the tropical year for 1900 January 0 at 12 hours ephemeris time\".[13] This definition was adopted as part of the International System of Units in 1960.[15]\n\nAtomic definition\nEven the best mechanical, electric motorized and quartz crystal-based clocks develop discrepancies from environmental conditions; far better for timekeeping is the natural and exact \"vibration\" in an energized atom. The frequency of vibration (i.e., radiation) is very specific depending on the type of atom and how it is excited.[16] Since 1967, the second has been defined as exactly \"the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom\". This length of a second was selected to correspond exactly to the length of the ephemeris second previously defined. Atomic clocks use such a frequency to measure seconds by counting cycles per second at that frequency. Radiation of this kind is one of the most stable and reproducible phenomena of nature. The current generation of atomic clocks is accurate to within one second in a few hundred million years. Since 1967, atomic clocks based on atoms other than caesium-133 have been developed with increased precision by a factor of 100. Therefore a new definition of the second is planned.[17]\n\nAtomic clocks now set the length of a second and the time standard for the world.[5]: 231–232 \n\nTable\nEvolution of the Second\nDecisions of the CIPM\tResolution of the CGPM\tInformation\nThat according to the decisions of the 8th General Assembly of the International Astronomical Union (Rome, 1952), the second of ephemeris time (ET) is the fraction\n12960276813\n408986496\n×\n10\n−\n9\n{\\displaystyle {\\frac {12960276813}{408986496}}\\times 10^{-9}} of the tropical year for 1900 January 0 at 12 h ET.\n\nThe second is the fraction \n1\n31556925.9747\n{\\displaystyle {\\frac {1}{31556925.9747}}} of the tropical year for 1900 January 0 at 12 hours ephemeris time.\t1956 CIPM\n11th CGPM 1960 Resolution 9\n\nThe standard to be employed is the transition between the hyperfine levels F=4, M=0 and F=3, M=0 of the ground state \n2\nS\n1\n/\n2\n{\\displaystyle ^{2}S_{1/2}} of the caesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9192631770 hertz.\tThe second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom\t13th CGPM Resolution 1\nCIPM 1967\n\nThis definition implies that the caesium atom is at rest and unperturbed. In consequence, in its practical realization, measurements must be corrected for velocity of the atoms with respect to the clock reference frame, for magnetic and electric fields including ambient black-body radiation, for spin-exchange effects and for other possible perturbations.\tAt its 1997 meeting, the CIPM affirmed that: This definition refers to a caesium atom at rest at a temperature of 0 K. This note was intended to make it clear that the definition of the SI second is based on a Cs atom unperturbed by black-body radiation, that is, in an environment whose temperature is 0 K, and that the frequencies of primary frequency standards should therefore be corrected for the shift due to ambient radiation, as stated at the meeting of the CCTF in 1999.\tfootnote added by the 14th meeting of the Consultative Committee for Time and Frequency in 1999\nthe footnote was added at the 86th (1997) meeting of the CIPM GCPM 1998 7th Edition SI Brochure\n\nThe definition of a unit refers to an idealized situation that can be reached in the practical realization with some uncertainty only. In this spirit, the definition of the second has to be understood as referring to atoms free of any perturbation, at rest and in the absence of electric and magnetic fields.\nA future re-definition of the second would be justified if these idealized conditions can be achieved much easier than with the current definition.\n\nThe definition of the second should be understood as the definition of the unit of proper time: it applies in a small spatial domain that shares the motion of the caesium atom used to realize the definition.\n\nIn a laboratory sufficiently small to allow the effects of the non-uniformity of the gravitational field to be neglected when compared to the uncertainties of the realization of the second, the proper second is obtained after application of the special relativistic correction for the velocity of the atom in the laboratory. It is wrong to correct for the local gravitational field.\n\nThe second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s−1.\nThe reference to an unperturbed atom is intended to make it clear that the definition of the SI second is based on an isolated caesium atom that is unperturbed by any external field, such as ambient black-body radiation.\n\nThe second, so defined, is the unit of proper time in the sense of the general theory of relativity. To allow the provision of a coordinated time scale, the signals of different primary clocks in different locations are combined, which have to be corrected for relativistic caesium frequency shifts (see section 2.3.6).\n\nThe CIPM has adopted various secondary representations of the second, based on a selected number of spectral lines of atoms, ions or molecules. The unperturbed frequencies of these lines can be determined with a relative uncertainty not lower than that of the realization of the second based on the 133Cs hyperfine transition frequency, but some can be reproduced with superior stability.\n\nCurrent Definition resolved in 2018 effective after the 26th GCPM approved the redefinition May 20, 2019.\nSI Brochure 9\n\nFuture redefinition\nIn 2022, the best realisation of the second is done with caesium primary standard clocks such as IT-CsF2, NIST-F2, NPL-CsF2, PTB-CSF2, SU–CsFO2 or SYRTE-FO2. These clocks work by laser-cooling a cloud of Cs atoms to a microkelvin in a magneto-optic trap. These cold atoms are then launched vertically by laser light. The atoms then undergo Ramsey excitation in a microwave cavity. The fraction of excited atoms is then detected by laser beams. These clocks have 5×10−16 systematic uncertainty, which is equivalent to 50 picoseconds per day. A system of several fountains worldwide contribute to International Atomic Time. These caesium clocks also underpin optical frequency measurements.\n\nOptical clocks are based on forbidden optical transitions in ions or atoms. They have frequencies around 1015 Hz, with a natural linewidth \nΔ\nf\n{\\displaystyle \\Delta f} of typically 1 Hz, so the Q-factor is about 1015, or even higher. They have better stabilities than microwave clocks, which means that they can facilitate evaluation of lower uncertainties. They also have better time resolution, which means the clock \"ticks\" faster.[18] Optical clocks use either a single ion, or an optical lattice with 104–106 atoms.\n\nRydberg constant\nA definition based on the Rydberg constant would involve fixing the value to a certain value: \nR\n∞\n=\nm\ne\ne\n4\n8\nε\n0\n2\nh\n3\nc\n=\nm\ne\nc\nα\n2\n2\nh\n{\\displaystyle R_{\\infty }={\\frac {m_{\\text{e}}e^{4}}{8\\varepsilon _{0}^{2}h^{3}c}}={\\frac {m_{\\text{e}}c\\alpha ^{2}}{2h}}}. The Rydberg constant describes the energy levels in a hydrogen atom with the nonrelativistic approximation \nE\nn\n≈\n−\nR\n∞\nc\nh\nn\n2\n{\\displaystyle E_{n}\\approx -{\\frac {R_{\\infty }ch}{n^{2}}}}.\n\nThe only viable way to fix the Rydberg constant involves trapping and cooling hydrogen. This is difficult because it is very light and the atoms move very fast, causing Doppler shifts. The radiation needed to cool the hydrogen – 121.5 nm – is also difficult. Another hurdle involves improving the uncertainty in QED calculations, specifically the Lamb shift in the 1s-2s transition of the hydrogen atom.[19]\n\nRequirements\nA redefinition must include improved optical clock reliability. TAI must be contributed to by optical clocks before the BIPM affirms a redefinition. A consistent method of sending signals must be developed before the second is redefined, such as fiber-optics.[19]", "id": "hsm/8292b7d6_0219.txt"}