The American-born British physicist Benjamin Thompson, Count Rumford (1753-1814), is best known for his attacks on the caloric theory of heat.

Benjamin Thompson was born on March 26, 1753, in Woburn, Mass. He received only 2 years of formal education and at 13 was apprenticed to a local merchant. At the age of 19, while teaching in Concord, N.H., he married a wealthy widow, 14 years his senior. He thus acquired not only an extensive estate but social and political influence as well.

Thompson's open support of the British crown, however, made his position increasingly precarious as political tensions mounted in the Colonies. As a result of his loyalist activities, he was forced in December 1774 to flee to Boston, abandoning his wife and infant daughter. He spent the next 15 months actively spying for the British government, supplying them with detailed reports on the condition and activities of the assembling colonial forces. When the British abandoned Boston in March 1776, Thompson departed for London.

Thompson arrived in London a confident, aggressive young man with a very useful knowledge of the colonial military situation; within 4 years he had risen to the position of undersecretary of state for colonial affairs. He also found time to pursue his scientific interests, and he soon gained a reputation as a productive natural philosopher as well. He undertook a series of studies on the explosive force of gunpowder, and his published report of these experiments was influential in his election as a fellow of the Royal Society in 1781. In that year he suddenly left London and returned to the Colonies, where he spent an undistinguished 2 years as a commanding officer in the British forces. He then returned to London and from there set out for the Continent.

Social Reform

In 1784 Thompson settled down in Munich as an aide-de-camp and confidential adviser to Elector Karl Theodor of Bavaria. Thompson did much to advance the stature of the Bavarian court by promoting scientific and technological advances and by instituting reform in the military, educational, and economic structure of the country. His standing was such as to guarantee him both the financial and technical support necessary for his varied, and often grandiose, projects, and in return for his activities he was in 1793 made a count of the Holy Roman Empire. He chose as his title Count Rumford, Rumford being the original name of Concord, N.H.

While in Munich one of Rumford's chief responsibilities was reorganizing the Bavarian army. In an effort to find more efficient and economical means of feeding and clothing the troops, he undertook an extensive study of the thermal conductivity of various types of cloth, in the process discovering the principle of heat transfer through what are today known as convection currents. Unable to persuade any commercial manufacturer to adopt the results of this research, Rumford set up what he called a "military workhouse" for producing the new military uniforms and in so doing became actively involved in social reform. Munich at the time was noted for its swarms of beggars, and on New Year's Day, 1790, Rumford had the Bavarian army arrest and jail every beggar in the city. These were then trained in his workhouse to manufacture the desired uniforms and in return for their labor received shelter, food, and education. The operation of this workhouse also involved Rumford in the associated practical problems of nutrition, heating, and lighting.

Theory of Heat

Rumford is best known today, however, for his contributions to the theory of heat. At the end of the 18th century the predominant theory of heat was the so-called caloric theory, according to which heat was a fluid substance that flowed into bodies when they were heated and flowed out of them as they cooled. The success of this theory in explaining then known phenomena is reflected in many terms, such as "heat flow" and "calorie," still used by physicists today. During his earlier gunpowder studies, however, Rumford had observed certain anomalies which the caloric theory seemed unable to explain, and for the remainder of his life he was constantly on the lookout for additional experimental evidence which might refute this theory.

Rumford's famous cannon-boring experiments present perhaps the most graphic evidence. One of his positions in Munich was inspector general of artillery for the Bavarian army, and, in the course of supervising work in the Munich arsenal, he was struck by the large amount of heat produced in boring a brass cannon. He devised an experiment in which, by utilizing a blunt borer to maximize the heat produced, he was able to boil large quantities of water with the resultant heat. The important aspect of this experiment, as Rumford himself noted, was the seemingly endless supply of heat that could be thus produced. According to the caloric theory, the boring tool produced heat by squeezing the caloric fluid out of the bodies rubbed together, but, as Rumford pointed out, anything which could be produced without limitation could not be a material substance such as caloric fluid. It should be emphasized, however, that although Rumford also produced numerous other experiments to refute the caloric theory, these experiments did not alone disprove the caloric theory, and not until much later in the 19th century was the concept of heat as a mode of motion generally adopted.

Royal Institution and Later Life

Rumford's position in Munich had always been somewhat precarious. His privileged status, the rapidity and success of his numerous innovations, and his ruthless disdain for his political opponents did nothing to silence the clamor of his enemies, and in 1798 the elector found it expedient to appoint him minister plenipotentiary to England, a position of honor which nonetheless effectively removed him from Munich politics. Arriving in London, he discovered that George III refused to accept a British subject (which Rumford still was) as minister from a foreign country.

Finding himself without a job, Rumford settled down in London to the task of establishing the Royal Institution. Justly renowned today for its research and popular lectures, the institution at its founding was part science museum and part technical school, reflecting Rumford's concern for the practical application of his researches. In 1801, after financial and personality difficulties, Rumford dissociated himself from the institution.

In 1804 Rumford moved to Paris and there, the following year, married Madame Lavoisier, the widow of the famous French chemist. A fashionable, though discordant, marriage, it lasted but 2 years, and in 1807 Rumford retired to the village of Auteuil near Paris. He became a member of the National Institute of France, as the Academy of Sciences was then called, and was a frequent contributor to its sessions and debates, as well as actively working to adapt his theoretical researches to practical applications. He died at Auteuil on Aug. 21, 1814.

Further Reading

• A new edition of Rumford's works is being edited by Sanborn C. Brown, Collected Works of Count Rumford, of which volume 1 is The Nature of Heat (1968). Of the full-length biographies the reader may most profitably consult W. J. Sparrow, Knight of the White Eagle: A Biography of Sir Benjamin Thompson, Count Rumford (1964). Sanborn C. Brown, Count Rumford: Physicist Extraordinary (1962), is an excellent, brief account. Other studies are James A. Thompson, Count Rumford of Massachusetts (1935), and Egon Larsen, An American in Europe (1953).
• Brown, Sanborn Conner, Benjamin Thompson, Count Rumford, Cambridge, Mass.: MIT Press, 1979.
• Brown, Sanborn Conner, Count Rumford, physicist extraordinary, Westport, Conn.: Greenwood Press, 1979, 1962.
• Dabney, Betty Page, The silver sextant: four men of the Enlightenment, Norfolk, Va.: B.P. Dabney, 1993.
• Jones, Bence, The Royal Institution, its founder and its first professors, New York: Arno Press, 1975.