James Prescott Joule 

James Prescott Joule (b. Salford, England, 24th Dec. 1818, d. Salford, England, 11th October 1889) was the second son of a prosperous brewer. The SI Unit of energy or work was named after him as the Joule. James was not a strong child. He had a spinal injury which left a slight deformity. Because of this, his education was limited. To a large extent he was self taught. He even read relatively little and had no pretence of being a great scientist. When he was 16, he and his brother, Benjamin, studied under Dalton for about two years. His chief contact with the world was with the members of the Manchester Literary and Philosophical Society. He began his quantitative electrical work when he was 19, using a standard resistance of copper wire.
He was a simple, earnest and modest man. He was the first to give an expression for the heat generated in a resistor by current flow, in 1840, and to observe magnetostriction. He spent a major part of his life working on the mechanical equivalence of heat. In 1845, he investigated the relationship between the temperature and the internal energy of gas. In April 1847, he gave a popular lecture in Manchester in which he stated the concept of the conservation of energy. But, it went unnoticed. At a meeting at Oxford in June 1847, he was advised by the chairman to restrict himself to a brief oral report on his experiments, rather than a paper, and not to invite discussion. Fortunately, his idea was grasped by William Thomson, Faraday and Stokes. Recognition to Joule came from Faraday who introduced Joule's 1849 paper to the Society. This paper won for him the 1852 Royal Medal. His last remarkable contribution was work in 1860 which resulted in a significant improvement of steam-engine efficiency. In the same year, he made one of the first accurate galvanometers and calibrated it by use of a voltmeter. He received many awards and medals including the 1870 Copley Medal and a pension from the queen in 1878.
His mother died in 1836. His father retired in 1883 due to illness. James and Benjamin took over the family brewing. James married in 1847 and had a daughter and a son. After the death of his wife in 1854, the brewery was sold. Joule's health became worse as time passed. He suffered from frequent nose-bleeding, presumably haemophilia. But, he kept on working as much as he could until his death.