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What is a Thermometer?
Thermometers measure temperature, by using materials that change in some way when they are heated or cooled. In a mercury or alcohol thermometer the liquid expands as it is heated and contracts when it is cooled, so the length of the liquid column is longer or shorter depending on the temperature. Modern thermometers are calibrated in standard temperature units such asFahrenheit or Celsius.

Early History
The first thermometers were called thermoscopes and while several inventors invented a version of the thermoscope at the same time, Italian inventor Santorio Santorio was the first inventor to put a numerical scale on the instrument. Galileo Galilei invented a rudimentary water thermometer in 1593 which, for the first time, allowed temperature variations to bemeasured. In 1714, Gabriel Fahrenheit invented the first mercury thermometer, the modern thermometer.
At the start of the seventeenth century there was no way to quantify heat.
Santorio Santorio
Santorio invented several instruments, a wind gauge, a water current meter, the "pulsilogium," and a thermoscope, a precursor to the thermometer. Santorio was the first to apply anumerical scale to his thermoscope, which later evolved into the thermometer.
Daniel Gabriel Fahrenheit
Daniel Gabriel Fahrenheit (1686-1736) was the German physicist who invented the alcohol thermometer in 1709, and the mercury thermometer in 1714. In 1724, he introduced the temperature scale that bears his name - Fahrenheit Scale.
Anders Celsius
The Celsius temperature scale is also referred to asthe "centigrade" scale. Centigrade means "consisting of or divided into 100 degrees". The Celsius scale, invented by Swedish Astronomer Anders Celsius (1701-1744), has 100 degrees between the freezing point (0 C) and boiling point (100 C) of pure water at sea level air pressure. The term "Celsius" was adopted in 1948 by an international conference on weights and measures.
Anders Celsius was bornin Uppsala, Sweden in 1701, where he succeeded his father as professor of astronomy in 1730. It was there that he built Sweden's first observatory in 1741, the Uppsala Observatory, where he was appointed director. He devised the centigrade scale or "Celsius scale" of temperature in 1742. He was also noted for his promotion of the Gregorian calendar, and his observations of the aurora borealis. In1733, his collection of 316 observations of the aurora borealis was published and in 1737 he took part in the French expedition sent to measure one degree of meridian in the polar regions. In 1741, he directed the building of Sweden's first observatory.
One of the major questions of that time was the shape of the Earth. Isaac Newton had proposed that the Earth was not completely spherical, butrather flattened at the poles. Cartographic measuring in France suggested that it was the other way around - the Earth was elongated at the poles. In 1735, one expedition sailed to Ecuador in South America, and another expedition traveled to Northern Sweden. Celsius was the only professional astronomer on that expedition. Their measurements seemed to indicate that the Earth actually was flattened atthe poles.
Celsius was not only an inventor and astronomer, but also a physicist. He and an assistant discovered that the aurora borealis had an influence on compass needles. However, the thing that made him famous is his temperature scale, which he based on the boiling and melting points of water. This scale, an inverted form of Celsius' original design, was adopted as the standard and is usedin almost all scientific work.
Anders Celsius died in 1744, at the age of 42. He had started many other research projects, but finished few of them. Among his papers was a draft of a science fiction novel, situated partly on the star Sirius.
Anders Celsius
Super scientist biography of Anders Celsius.
Lord William Thomson Kelvin
Lord Kelvin took the whole process one step further with his...
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