(December 24, 1818 – October 11, 1889)

Through his brewing experiences and obsessions with heat energy, James Joule was able to make significant discoveries, which ensured that his name “Joule” was designated the S.I. unit of energy. By demonstrating the link between heat and mechanical work, he indirectly plotted the Law of Energy Conservation which culminated in the First Law of Thermodynamics. He then used his understanding of heat to disprove the Caloric Theory (which wrongly claimed that heat is an aggregate of self-repellent fluids). Joule studied under some of Britain’s most prominent researchers of his era, such as: John Dalton, William Henry, Eaton Hodgkinson and Peter Ewart. Having understood both the Dalton’s Law of Partial Pressures and the Henry’s Law constant, (among others); he attempted to correlate heat energy with the Kinetic Theory. He later collaborated with William Kelvin during Kelvin’s work on his absolute temperature scale. He was also interested in electricity, and how it could output heat. This saw him experimenting with batteries in 1841: evaluating how the current passed through conductors relate to the amount of heat they generated. His inference that the power of heating generated by a conductor is proportional to the product of its resistance and the square of the current eventually became known as Joule-Lenz Law (in honor of both himself and Heinrich Lenz who also discovered it independently of Joule in 1842). Again in 1842, while working with nickel, Joule discovered the magnetostriction phenomenon (i.e. the ability of ferromagnetic materials to alter their dimensions when exposed to magnetic fields).


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