An American officer serving in the English Army during the American War of Independence, Thompson then moved to Europe, where for several years he was in the service of the Bavarian Government. In 1781, he was elected Fellow of the Royal Society of London. In 1791, the King of England made him Count for his work in Bavaria. In 1799, Rumford returned to England, where he founded the Royal Institution with Joseph Banks (1743-1820). In the early 1800s, he settled in France, where he married Lavoisier's widow. His most important research was on heat: Rumford helped to demolish the phlogiston theory, and was the first to demonstrate that heat was not a fluid but a form of "movement." He also studied the transmission of heat in fluids and their expansion. His name is linked to several instruments - such as the differential thermometer and the photometer - and inventions: he improved the construction of domestic chimneys and kitchen stoves. Rumford was an advocate of the introduction of the potato in Europe. The medal bearing his name, which he established in 1796, remains one of the world's most prestigious scientific honors.