Skill 6 of 13
In Progress

James Prescott Joule

English (1818-1889) scientist and physicist; born in Salford, United Kingdom[1,2,3] into a rich family where he was home-schooled; died in Greater Manchester, United Kingdom.[1,3]

Photo of James P. Joule by Lady Roscoe in 1917[4]

James Joule worked as a brewer and had a laboratory for scientific experiments in his family brewery that he worked in after work-hours.[1,5] He experimented with electricity[1,2] before ever taking a physics course[5] and anecdotally knocked a servant unconscious by accident with an electric shock.[1] He eventually worked closely with physicist William Thomson (later known as Lord Kelvin),[2,3] and was as a teenager tutored by chemist John Dalton.[3]

Among many other things he tried to invent electric engines to replace steam engines,[1] which would be beneficial in the family brewery.[3]

  • James Joule discovered the now-called Joules’ Law about energy released as heat in electric systems[1,5] (so-called ‘resistive heating’),[5,3]
  • he and Lord Kelvin discovered the relation between gas expansion and freezing, eventually leading to the invention of refrigerators[1] and air conditioning,[5]
  • he was the first to calculate the speed of a gas molecule,[1] and
  • he discovered the concept of work as a type of energy transfer just like heat (‘the mechanical equivalent of heat’ as he himself called it),[5,2] a result published in 1845 in his paper ‘On the Mechanical Equivalent of Heat’.[1,2]

This latter discovery eventually lead to the formulation of the energy conservation law, now called the 1st law of thermodynamics – one of the most significant laws of physics.[1,2]

After being ignored by a sceptic scientific community for years do to his lack of credentials and official education,[5,3] he was eventually finally honoured with scientific recognition, with the SI-unit for energy, the Joule $\mathrm J$, being named after him[3] and with words such as these:[5]

He seized the lightning from the sky and the scepter from tyrants.

Benjamin Franklin[5]


  1. James Prescott Joule’ (web page), Doug Stewart, Famous Scientists, 2018, www.famousscientists.org/james-prescott-joule (accessed Jan. 14th, 2020)
  2. James Prescott Joule’ (web page), Westminster Abbey, www.westminster-abbey.org/abbey-commemorations/commemorations/james-prescott-joule (accessed Jun. 13th, 2020)
  3. James Joule’ (web page), Magnet Academy, National High Magnetic Field Laboratory, www.nationalmaglab.org/education/magnet-academy/history-of-electricity-magnetism/pioneers/james-joule (accessed Jun. 13th, 2020)
  4. James Prescott Joule’ (photo from book), Arthur Shuster & Arthur E. Shipley, Britain's Heritage of Science, 1917, photographer Lady Roscoe, www.marcdatabase.com/~lemur/lemur.com/gallery-of-antiquarian-technology/worthies (accessed Jun. 13th, 2020), page 160
  5. June 1849: James Prescott Joule and the Mechanical Equivalent of Heat’ (web page), Richard Williams, APS Physics, vol. 24, issue 6, 2015, www.aps.org/publications/apsnews/201506/physicshistory.cfm (accessed Jun. 13th, 2020)