Joule's contribution: the conservation energy

The principle of energy conservation that Joule began writing about in his work, led to the development of thermodynamics. Although he was not the first scientist to suggest this principle, he was the first to investigate its legitimacy. Joule is therefore regarded as the chief founder of thermodynamics. He showed that "work" can be converted into heat with a fixed ratio of one to the other, and that heat can be converted into work. Joule's first law of thermodynamics states that energy can neither be created or destroyed. Energy can only be changed from one form into another. Joule's insight is one of the outstanding achievements in the history of science. Joule was very much a product of his times, steeped in the tenants of protestant Christianity and the teachings of the Church of England. He realized that his work was controversial but he stuck with his faith. He believed that his 'law' was evidence that the universe did not create itself! He could not be budged in his convictions, and based his work around his beliefs.

In 1848 Joule became the first person to estimate the speed of gas molecules. Other scientists armed with this information soon furthered his work on the kinetic theory. Joule was one of the first scientists to recognize the need for standard units of electricity, and he strongly advocated their establishment. This standardization was later done by the British Association for the Advancement of Science under the direction of Maxwell. He became president of the British Association in 1872 and again in 1887. In recognition of Joule's contribution in relating heat and mechanical motion, the unit of energy (or work) in physics was later named the 'Joule'."

In 1852, Joule began working with Thomson who later became Lord Kelvin. Thompson, seven years his junior, had earlier supported him in his faltering efforts for recognition by the scientific establishment, in the form of the Royal Society. Joule and Thompson were perfect partners, and just when everything seemed to be improving in his life, Joule's wife died after only six years of marriage. He was forced to sell the brewery and raise young children. He now led a more secluded life but he dedicated himself to his scientific work. For the next eight years he worked with Thomson on a number of important experiments to confirm some of the predictions being made in the new discipline of thermodynamics. The most famous of these experiments involved the decrease in temperature associated with the expansion of a gas without the performance of external work. This cooling of gases as they expand is known as the 'Joule-Thomson effect'. This principle provided the basis for the development of the refrigeration industry.

Summary: Catherine Melendez

References:
http://www.sciencetrek.net/graphics/joule.jpg
http://jdb.psu.edu/ohm-joule.gif
http://users.sisna.com/jmgreen/joule-1.gif
http://www.answersingenesis.org/docs/3277.asp