James Prescott - Joul
English physicist Joul was born in Salford, Lancashire on 24 December, 1818. Joul was the second son of a rich brewer. As a kid he was not very healthy and so he had a lot of time for books and learning. His father supported him in his studies and he even built him his own laboratory. Joul was known because everything he knew, he tried to prove it by measuring it. In his teenage years he published an article about his measures of heat by electric motors. In 1833 his father had to retire because he was sick. So Joul had to take some responsability in his father's brewery, but even then, he found some time for his measures. In 1840 he developed a formula for the heat that goes out from the electric current in a conductor. For several decades he tried to define the heat which goes off from many different processes that he could think off. From mixing water and mercury he calculated the work which the system got and he calculated the heat. He also pushed water through little pipes and he compressed gases and let them expand. From this he concluded that an specific amount of work always gets an specific amount of heat: 41,000.000 ergs of work always gave one calory of heat. This transformation is called the mechanic equivalent of heat. Joul announced the results from his measurements in 1847. Scientists were not very impressed by his report and it was rejected by many scientific journals and so he had to let his work be known on a public lecture in Manchester. He could finally have his work published in a Manchester journal where his brother wrote music critics. A few months later he got a chance to speak before a scientific public. Now his work found some interest by the scientific audience, because among the public there was 23 year-old William Thomson, later known as lord Kelvin. He supported Joul's work and so Joul got his first glory and became famous. He was even better known after 1849, when he read his work in front of the Royal Society. Joul was not the first one who tried to define the mechanic equivalent of heat. Rumford tried to define it 50 years before, but the values he got were too high. Joul's calculations were the most precise and they were backed up with many measures. So this discovery and all the glory goes to Joul, and the unit for work was named after him. Today we take one kilocalory as equivalent to 4180 jouls of work.
In the last years of his life he was broke, but the
Queen of England supported him because he was a famous scientist
and he was known in royal society. He died on 11 October, 1889
in Saleuv, Cheshire. Author: Matej Kucan, 3.C |
