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Portrait of Lord Kelvin (1824-1907), born William Thomson, Scottish physicist and mathematician. Thomson was among the first to support Joule's work on the "mechanical equivalent of heat". Together, in 1852, they discovered that when a gas is allowed to expand freely, its temperature drops slightly, an important phenomenon known as the Joule-Thomson effect. In 1848, after studying Charles's work on gases, Thomson proposed the existance of absolute zero and suggested the use of the absolute temperature scale, which was later named after him. In 1866 he was knighted for his work as director of the first Trans-Atlantic cable-laying project.
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