James Joule became a world-renowned physicist, initially by seeking scientific advances to help his family brewery. He is best remembered for his discovery that different forms of energy – electrical, mechanical, heat – are interchangeable, and for establishing that energy can neither be created nor destroyed. The International unit of energy, the joule, is named in his honour.

James Joule (1818 – 1889) was born in Salford, Manchester into a fairly wealthy family. He and his brothers were taught chemistry, physics and maths by John Dalton who inspired James to conduct his own research. James and his brothers were fascinated by electricity and carried out experiments together, giving themselves and one of their servants electric shocks in the process.

As James grew older, he managed the family’s brewing business, but in the 1840s began to publish scientific papers in areas that related to his industry and interests. In his now famous ‘paddlewheel’ experiment, he established the relationship between heat and energy that formed the basis of his Mechanical Equivalent of Heat paper, in 1845. He found that when gravitational mechanical energy (falling weights on a pulley) was used to rotate metal plates in a container of water, the temperature of the water rose. He became the first to put forward the idea that heat is a form of energy.

Many of Joule’s ideas took time to be accepted by the scientific world. Eventually, however, he was rewarded by being elected to the Royal Society of London in 1850. The unit of energy, the joule, is named after him.

Did you know..?

In 1852, Joule and William Thomson (later Lord Kelvin) described the Joule-Thomson Effect, which stated that when gas expands without the production of work, its temperature falls – a concept that led to the development of refrigeration.

Sources & acknowledgements

This object description and its related educational resources were researched and written by our team of historians and education specialists. For further information see the item’s home museum, gallery or archive, listed above.