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Rumford, Benjamin Thompson, Count

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(1753–1814) Anglo-American adventurer, social reformer, inventor and physicist: measured relation between work and heat; founded Royal Institution.

It would be hard to name a scientist who had a more extraordinary life than Rumford. He was a store apprentice, then a part-time teacher, gymnast and medical student with an interest in electrical machines. At 18 he married a rich young widow of 30 and decided to become a gentleman-soldier and farmer; he so impressed his seniors that at 19 he had become a major in the militia and squire of Concord.

However, excitement was on the way: New England was the centre of the American Revolution. His family had been there since 1630 and he had good prospects if he cast in his lot with the revolutionaries, but Thompson supported the ‘loyalist’ view and did so by acting as a secret agent for the British army. There is no good evidence that he was a double agent, but by 1776 he was prudent enough to leave America for England, where he took up his scientific interests again (on projectiles, appropriately), was elected Fellow of the Royal Society in 1779, and next year became undersecretary of state in the Colonial Office at 27. In 1782, seeking active service, he went back to America, did well as a soldier and was shocked when peace was declared the following year.

This left him with no clear future, and he had no wish to ‘vegetate in England’, but soon, through carefully nurtured contacts, he was appointed adviser to the elector of Bavaria, being knighted, rather surprisingly, by George III as a preface to his new career. He was highly effective in Bavaria, reforming the conditions of the army, setting up welfare schemes for the poor which were well ahead of their time and creating a large park in Munich still treasured as the English Garden. He became a wealthy and respected public figure, with the title of Count, and minister for war. He was there for 14 years before moving to London in 1798, where he was welcomed as a great philanthropist and an expert on new methods for heating and feeding the poor.

Scientific work was always a part of Rumford’s life and in Munich he made his greatest contribution to physics. He visited the arsenal and ‘was struck by the very considerable degree of heat which a brass cannon acquires in a short time in being bored’. At the time, heat was thought to consist of a subtle fluid, ‘caloric’, which was squeezed out of the metal on boring, but Rumford showed, by using a blunt borer, that an apparently limitless amount of heat could be got from one piece of metal and that the supposed ‘caloric’ seemed to be weightless. He concluded that caloric was non-existent and that heat was ‘the motion of the particles of a body’. He went on to measure the relation between work and heat, getting a result within 30% of the modern value. This concept was fundamental to modern physics, and the quantitative relation between heat and work was soon studied with great care .

Rumford was always an enthusiast for the application of science, himself designing improved stoves, lamps and carriages; and in London in 1800 he planned and largely created the Royal Institution, which has been so valuable in British science ever since. Rumford’s appointment in 1801 of , aged 22, to work at the Royal Institution was a happy and fruitful choice. Soon Rumford was travelling again, partly in exasperation as a result of disputes with the Royal Institution’s managers. He settled in Paris, and in 1805 married , widow of the great chemist and reformer. The marriage quickly proved unfortunate: their quarrels were dramatic, and Rumford spent much time in his laboratory, studying the heat generated in combustion and using for this an improved Lavoisier calorimeter. He separated from Marie, but he had friends, money, a resident mistress, visits from his American daughter Sally and a substantial reputation. F D Roosevelt rated him with F and Thomas Jefferson, as ‘the greatest mind America has produced’. He may well be the most colourful character in 18th-c science.

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