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 as Fahrenheit or Celsius.

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 a numerical 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 as the "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 born in 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. In 1733, 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, but rather 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 at the 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 used in 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 invention of the Kelvin Scale in 1848. The Kelvin Scale measures the ultimate extremes of hot and cold. Kelvin developed the idea of absolute temperature, what is called the "Second Law of Thermodynamics", and developed the dynamical theory of heat.

Sir William Thomson, Baron Kelvin of Largs, Lord Kelvin of Scotland (1824 - 1907) studied at Cambridge University, was a champion rower, and later became a Professor of Natural Philosophy at the University of Glasgow. Among his other achievements was the 1852 discovery of the "Joule-Thomson Effect" of gases and his work on the first transatlantic telegraph cable (for which he was knighted), and his inventing of the mirror galvanometer used in cable signaling, the siphon recorder, the mechanical tide predictor, an improved ship's compass.

Kelvin, William Thomson, 1st Baron
Mathematician and physicist, one of the leading physical scientists and greatest teachers of his time.
Lord William Thomson Kelvin
The Kelvin Scale and the work of Lord Kelvin.
Biography of Lord Kelvin
It was from his father that William learn mathematics and at a very young age he became an accomplished mathematician with knowledge of the latest developments in the subject.
Who Is This Man Called Kelvin?
A whimsical site that promotes an admiration for Lord Kelvin and his ideas.

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