Joule's paddlewheel and calorimeter

Contributed by Museum of Science and Industry

Paddlewheel and calorimeter used by James Joule between 1860 and 1880. @ Museum of Science & Industry

Joule's name is common in everyday life as the SI unit of energy found on food packaging. 1 joule = 0.24 calorie.James Prescott Joule (1818-99) was the son of a wealthy Salford brewer. He became interested in science through receiving tuition from John Dalton, famed for his atomic theory. Joule set up a laboratory in the cellar of the family home. He began a series of experiments on the nature of energy and published the findings that became known as Joule's first law in 1840.

His next experiments used a paddlewheel and calorimeter to prove that heat and mechanical work are both forms of energy. At a British Association meeting in 1843, he gave a paper that introduced the physical constant now known as 'J' or Jouleâ??s Equivalent. Previously scientists had believed that heat was a fluid known as 'caloric'. Joule's theory of the 'Mechanical Equivalent of Heat' laid the basis for the first law of thermodynamics.

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