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Sir Benjamin Thompson, Count Rumford

co-developer of the science of thermodynamics

Sir Benjamin Thompson

Benjamin Thompson was born at Woburn, Massachusetts, on March 26, 1753. He was educated mainly at the village school, and by the age of 14 was sufficiently advanced "in algebra, geometry, astronomy, and even the higher mathematics," to calculate a solar eclipse within four seconds of accuracy. In 1766 he was apprenticed to a storekeeper in Salem, Massachusetts, where he also occupied himself in chemical and mechanical experiments, and in engraving. Later he began the study of medicine under Dr. John Hayin Woburn at Cambridge, but spent most of his time in manufacturing surgical instruments. He subsequently spent a few years working in the dry goods business in Boston, attending classes in philosophy at Harvard, and teaching in Bradford, Massachusetts and Rumford, New Hampshire.

In 1772, Thompson met, charmed and married Sarah Rolfe, the wealthy widow of Colonel Benjamin Rolfe, who was also fourteen years his senior, and moved to Portsmouth, New Hampshire. Thanks to his wife's influence, Thompson became acquainted with Governor Wentworth of New Hampshire, who made him a Major in the New Hampshire Militia.

When the American Revolution broke out Thompson was a man of substantial property and standing in New England, and had important connections to the British government. He remained loyal to the British crown, and even recruited other loyalists to fight against the American patriots. These actions naturally made him unpopular with his neighbors and, in 1774, he fled his home for the British lines, leaving his wife behind. Welcomed by the British, Thompson gave valuable information about the American forces and became an advisor to General Thomas Gage. While working for the British armies in America, Thompson conducted experiments concerning the force of gunpowder, the results of which were widely acclaimed when published in the Philosophical Transactions of the Royal Society (in 1781).

When the British evacuated Boston in 1776, Thompson chose to leave with them and made his way to England. On his arrival in London Lord George Germain, Secretary of State, appointed him to a clerkship in his office. Within a few months he was advanced to the post of Secretary of the Province of Georgia, and within four years to Under-Secretary of State. Although his political occupations took up a fair amount of his time, Thompson continued his scientific pursuits, and in 1779 he was elected a Fellow of the Royal Society.

Upon resignation of Lord North's administration, of which Lord George Germain was a member, Thompson left the civil service. He was named to a cavalry command, but the American Revolution ended before he took up active duty and he left the British Army with the rank of Lieutenant-Colonel. For his services to England Thompson was honored with a knighthood by King George III.

In 1785, Thompson joined the Austrian Army, to campaign against the Turks. At Strassburg he was introduced to Prince Maximilian, Elector of Bavaria, who invited Thompson to enter the civil and military service of that state. He spent eleven years in Bavaria, reorganizing the army and establishing workhouses for the poor. In 1791, Thompson was created a Count of the Holy Roman Empire, and chose his title of Rumford from the name of the American township to which his wife's family belonged.

Thompson continued his scientific pursuits in Bavaria and contributed a number of papers to the Philosophical Transactions of the Royal Society. He invented Rumford Soup, a nutritious soup for the poor, and established the cultivation of the potato in Bavaria. He also founded the Englischer Garten in Munich, which is to this day one of the largest urban public parks in the world.

the Beer Garden in the Englischer Garten in Munich
the Beer Garden in the Englischer Garten in Munich

His scientific reputation now firmly established, Thompson returned to London in 1795 and applied himself to the discovery of methods for curing smoky chimneys and to improvements in fireplace construction. At one time it was proposed that Count Rumford should be the Bavarian ambassador to London, but the fact that he was a British subject presented an insurmountable obstacle.

Thompson lived in London until 1804, when he went to Paris. In Paris he married Marie-Anne Lavoisier, the wealthy widow of celebrated chemist Antoine Lavoisier. He eventually separated from her and took up residence at Auteuil, where he died suddenly on August 21, 1814.

Work on Heat

One of Thompson's responsibilities in Bavaria was armaments, and it was while watching the manufacture of cannon barrels that he began to formulate his theory of heat. To make the barrels, a solid block of metal was bored out with a large slow-turning drill. As the drill bit into the metal, so much heat was generated that workmen had to continually douse the block in cold water. Contemporary theory said that the motion of the drill was releasing a fluid called "caloric" from the metal, and this showed itself as heat in the atmosphere. Thompson, however, realized that heat continued to be released as the drilling went on, and felt that much more caloric was being released than could possibly have been contained in the metal. He concluded that it was the mechanical action of the drill which was being converted into heat, and therefore that heat was itself a form of motion. He presented his work to the Royal Society in 1798, in Enquiry concerning the Source of Heat which is excited by Friction.

Thompson's drawings of the apparatus for his cannon-boring experiment
Thompson's drawings of the apparatus for his cannon-boring experiment

Thompson then extended his work by trying to calculate exactly how much heat is produced by a given amount of mechanical energy. Although many of his results proved inaccurate, he succeeded in establishing the idea of what is now called a "mechanical equivalent of heat," and helped to found a branch of engineering that in later years found numerous practical applications in the interconversion of heat and mechanical energy. His theory of heat also helped to found a new branch of physics that concentrates on the nature and effects of heat, today called "thermodynamics."

Thompson next investigated the insulating properties of various materials including fur, wool, and feathers. He correctly determined that the insulating properties of these natural materials arise from the fact that they inhibit the convection of air, but then made the mistake of inferring that gases were perfect non-conductors of heat; he also extended his claim about non-conductivity to liquids. Although his claims were widely disputed by the scientific community, no instruments then existed to test and either prove or disprove them.

Establishment of the Royal Institution

In 1799, Thompson, with Sir Joseph Banks, projected the establishment of the Royal Institution of Great Britain. Chartered by King George III in 1800, Thompson and Banks chose Sir Humphry Davy as the Institution's first lecturer. Thompson endowed the Rumford Medals of the Royal Society and the American Academy of Arts and Sciences, as well as a professorship at Harvard University.


Thompson was an active inventor, developing improvements for chimneys and fireplaces and inventing the double boiler, a kitchen range, a drip coffeepot, and thermal underwear. The Rumford Stove is still considered a very thermally efficient way to heat a room.

Thompson warming himself before a Rumford Stove
Thompson warming himself before a Rumford Stove

saucepan heated by portable furnace and furnace with pot
saucepan heated by portable furnace and furnace with pot

Thompson's kettle
Thompson's kettle

Thompson's polyflame burners and spirit lamps
Thompson's polyflame burners and spirit lamps

The complete works of Benjamin Thompson, Count Rumford, with a memoir by G.E. Ellis, were published by the American Academy of Arts and Sciences in 1870-1875.

The Rumford Crater on the Moon is named in his honor.

Feldman, Anthony and Peter Ford Scientists and Inventors, The People Who Made Technology from Earliest Times to Present Day New York: Facts on File, 1979

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This page was last updated on 03/26/2017.