For thousands of years, devices have been used to measure and keep track of time. The current sexagesimal system of time measurement dates to 2000 BC from the Sumerians; the Egyptians divided the day into two 12-hour periods, used large obelisks to track the movement of the sun. They developed water clocks, which were first used in the Precinct of Amun-Re, outside Egypt as well; the Zhou dynasty is believed to have used the outflow water clock around the same of the time, devices which were introduced from Mesopotamia as early as 2000 BC. Other ancient timekeeping devices include the candle clock, used in ancient China, ancient Japan and Mesopotamia; the sundial, another early clock, relies on shadows to provide a good estimate of the hour on a sunny day. It requires recalibration as the seasons change; the earliest known clock with a water-powered escapement mechanism, which transferred rotational energy into intermittent motions, dates back to 3rd century BC in ancient Greece. The first mechanical clocks, employing the verge escapement mechanism with a foliot or balance wheel timekeeper, were invented in Europe at around the start of the 14th century, became the standard timekeeping device until the pendulum clock was invented in 1656.
The invention of the mainspring in the early 15th century allowed portable clocks to be built, evolving into the first pocketwatches by the 17th century, but these were not accurate until the balance spring was added to the balance wheel in the mid 17th century. The pendulum clock remained the most accurate timekeeper until the 1930s, when quartz oscillators were invented, followed by atomic clocks after World War II. Although limited to laboratories, the development of microelectronics in the 1960s made quartz clocks both compact and cheap to produce, by the 1980s they became the world's dominant timekeeping technology in both clocks and wristwatches. Atomic clocks are far more accurate than any previous timekeeping device, are used to calibrate other clocks and to calculate the International Atomic Time. Many ancient civilizations observed astronomical bodies the Sun and Moon, to determine times and seasons; the first calendars may have been created during the last glacial period, by hunter-gatherers who employed tools such as sticks and bones to track the phases of the moon or the seasons.
Stone circles, such as England's Stonehenge, were built in various parts of the world in Prehistoric Europe, are thought to have been used to time and predict seasonal and annual events such as equinoxes or solstices. As those megalithic civilizations left no recorded history, little is known of their calendars or timekeeping methods. Methods of sexagesimal timekeeping, now common in both Western and Eastern societies, are first attested nearly 4,000 years ago in Mesopotamia and Egypt. Mesoamericans modified their usual vigesimal counting system when dealing with calendars to produce a 360-day year; the oldest known sundial is from Egypt. Sundials have their origin in shadow clocks, which were the first devices used for measuring the parts of a day. Ancient Egyptian obelisks, constructed about 3500 BC, are among the earliest shadow clocks. Egyptian shadow clocks divided daytime into 12 parts with each part further divided into more precise parts. One type of shadow clock consisted of a long stem with five variable marks and an elevated crossbar which cast a shadow over those marks.
It was positioned eastward in the morning so that the rising sun cast a shadow over the marks, was turned west at noon to catch the afternoon shadows. Obelisks functioned in much the same manner: the shadow cast on the markers around it allowed the Egyptians to calculate the time; the obelisk indicated whether it was morning or afternoon, as well as the summer and winter solstices. A third shadow clock, developed c. 1500 BC, was similar in shape to a bent T-square. It measured the passage of time by the shadow cast by its crossbar on a non-linear rule; the T was oriented eastward in the mornings, turned around at noon, so that it could cast its shadow in the opposite direction. Although accurate, shadow clocks relied on the sun, so were useless at night and in cloudy weather; the Egyptians therefore developed a number of alternative timekeeping instruments, including water clocks, a system for tracking star movements. The oldest description of a water clock is from the tomb inscription of the 16th-century BC Egyptian court official Amenemhet, identifying him as its inventor.
There were several types of water clocks. One type consisted of a bowl with small holes in its bottom, floated on water and allowed to fill at a near-constant rate; the oldest-known waterclock was found in the tomb of pharaoh Amenhotep I, suggesting that they were first used in ancient Egypt. Another Egyptian method of determining the time during the night was using plumb-lines calle
Dame Pratibha Laxman Gai-Boyes is a British microscopist and Professor and Chair of Electron Microscopy and former Director at The York JEOL Nanocentre, Departments of Chemistry and Physics, University of York. She created the atomic-resolution environmental transmission electron microscope and is an outspoken advocate for women with careers in science. Gai grew up in India, was fascinated by science as a child, she was influenced by Marie Curie, her education, her parents to study chemistry. However, at that time, it was not acceptance for women to have careers in the physical sciences; when she was a teenager, she was selected as a national science talent search scholar. “It would have been difficult without the scholarships because societal expectations for women at that time did not include careers in the sciences or chemistry. I would say that societal expectations today, as to what is good for women, including in the UK, do not always include scientific studies."Gai was educated at the University of Cambridge where she was awarded a PhD in 1974 for research on weak beam electron microscopy conducted in the Cavendish Laboratory.
Gai has pioneered advanced in-situ electron microscopy applications in the chemical sciences. With Edward D. Boyes, she co-invented the atomic resolution environmental transmission electron microscope, which enables the visualisation and analysis on the atomic scale of dynamic gas-catalyst reactions underpinning key chemical processes, her research has helped to understand better how catalysts function, leading to valuable new science. Her microscope and process inventions are being exploited worldwide by microscope manufacturers, chemical companies and researchers. In 2009, after years of development, who holds a chair in electron microscopy and was co-director of the York JEOL Nanocentre at the University of York, succeeded in creating a microscope capable of perceiving chemical reactions at the atomic scale; this is an advance on conventional microscopes at this scale, which can only view innate material in the "dead" conditions of a vacuum at room temperature. It is known as the atomic resolution environmental transmission electron microscope.
With the help of colleagues, she built and refined the machine over two decades, beginning with a lower-resolution prototype when she was a postdoctoral researcher at the University of Oxford. She spent 18 years in the US at chemical firm DuPont and the University of Delaware. Although her microscope is valuable to the scientific field, she made the decision to not patent it, saying, "I thought that if I patented it, no one else would be able to do work with it. I might earn some money. I was interested in applications for many researchers. So I decided not to patent it."She advocates for women's roles in science, has spoken about the challenge of having children as a woman scientist. She says, "what's needed to keep women in science. So I keep telling my female students to aim high." 2010 Gabor Medal and Prize for in-situ atomic resolution environmental transmission electron microscopy. Fellow of the Institute of Physics Fellow of the Royal Society of Chemistry 2013 L'Oréal-UNESCO For Women in Science Awards Laureate for Europe 2014 Fellow of the Royal Academy of Engineering 2016 Fellow of the Royal Society 2018 The Asian Awards for Outstanding Achievement in Science & Technology.
2018 Dame Commander of the Order of the British Empire For services to Chemical Sciences and Technology 2018 Honorary Fellow of the Royal Microscopical Society
The Gunboat Sheds is a row of 32 black-painted wooden sheds located on the east coast of Frederiksholm, part of Holmen, in Copenhagen, Denmark. Built in the first half of the 19th century for the naval base which used to occupy the grounds, they have now been adapted for other use, they were listed in 1964. The Gunboat Sheds owe their existence and name to the so-called gunboats which were built after the Danish naval fleet had been captured at the Holmen Naval Base by the Royal British Navy on 21 October 1807; the gunboats were used in the last stage of the English Wars, now known as the Gunboat War. The small gunboats were employed against the conventional Royal British Navy. Built to provide on-land protection for the gunboats when they were not in use, the sheds were built in around 1830; each shed. When the gunboats were replaced by more modern vessels, the sheds remained in use for storing motor boats and other smaller vessels, they were listed in 1964 but had fallen into a state of neglect by the time the Navy left Holmen in 1996.
They were sold in 1998 and in 1999 to Søtoftegård A/S and Keops A/S. The new owners undertook a thorough restoration and adapted the buildings for use as office space with the assistance of PLH Architects. On 18 August 2006 a fire destroyed five sheds in the middle of the row but they were subsequently rebuilt. Since the renovation, the sheds have housed small businesses in the creative sector, such as advertising agencies, media houses and architectural practises; the tenants include KHR Arkitekter and the short-lived newspaper Dagen was based there. The street Kanonbådsvej is named after the sheds. Nyholm Central Guardhouse