Benjamin Thompson

• Born: March 26, 1753
• Birthplace: Woburn, Massachusetts
• Died: August 21, 1814
• Place of death: Auteuil, France

American physicist

Thompson’s scientific studies greatly advanced understanding of heat and heat transfer. He invented the slow-roasting oven, improved oil lamps, improved double boilers and drip coffee makers, and the modern fireplace with a smoke shelf to prevent downdrafts.

Primary fields: Household products; physics

Primary inventions: Rumford stove; slow-roasting oven

Early Life

Benjamin Thompson was born to Benjamin Thompson, senior, and Ruth Simonds on March 26, 1753, in the town of Woburn, Massachusetts. His father, a farmer about whom little is known, died in November, 1754. His mother married again in March of 1756 to Josiah Pierce, Jr. Late in life, Thompson recalled his stepfather as a tyrant who virtually forced the child from the home, but this is not borne out by the historical evidence.

Schooling was hard to come by in colonial Massachusetts, but the young Thompson managed to attend three schools before the age of thirteen. Showing himself to be a bright boy deeply antagonistic to farmwork, he ended up an indentured apprentice to John Appleton, a successful retail merchant in the nearby town of Salem, in October, 1766. He continued his education on an informal, individual basis under the guidance of the Reverend Thomas Barnard, the Salem schoolmaster, with an emphasis on mathematics and astronomy.

Thompson’s apprenticeship under Appleton ended dramatically when Thompson injured himself in an explosion while attempting to manufacture homemade fireworks. His injuries were so severe that he was sent home to Woburn to be cared for by his mother. In October, 1769, as soon as his injuries permitted, he returned to work in the employment of Hopestill Capen, the owner of a dry goods shop in Boston. Thompson continued to educate himself through self-study and experimentation to the extent that Capen fired him for neglecting his duties in the shop. He returned to Woburn in 1770 and supported himself cutting firewood.

While back in Woburn, Thompson befriended Loammi Baldwin, one of the leading engineers in the colony. Baldwin and Thompson remained in correspondence for the rest of Thompson’s life, with Baldwin carefully preserving Thompson’s letters. Thompson boarded with and studied medicine under the town physician, paying his way by teaching in the nearby towns of Wilmington and Bradford. The schoolmaster in Bradford helped Thompson obtain a position as schoolmaster in Concord, New Hampshire. He took up his duties there in the summer of 1772 at the age of nineteen.

Life’s Work

Thompson’s career as an inventor and scientist was secondary to, but an integral part of, his primary career as a social climber. He began by marrying Sarah Walker Rolfe, the widow of Colonel John Rolfe, a wealthy and prominent New Hampshire politician. Thompson was nineteen; she was thirty-three. Thompson and his bride dined on their wedding day with John Wentworth, the royal governor of the colony of New Hampshire, and Thompson quickly forged a bond with him. Wentworth was interested in science and technology and possessed one of the finest libraries in the American colonies. Thompson had ready access to the governor’s books and instruments, all of which he studied assiduously.

Thompson’s climb to prominence and wealth began against the backdrop of the American Revolution. He acquired a commission as major in the Fifteenth Regiment of the New Hampshire Militia with duties of organization and recruitment. He proved to be naturally adept at both, acquiring skills there that would serve him well for many years. Thompson was particularly skilled at identifying and repatriating deserters from the British forces occupying Boston under General Thomas Gage. When this work became public knowledge in New Hampshire, Thompson became persona non grata in Concord and had to leave town precipitously. He fled to Boston to join General Gage’s staff, abandoning his wife and newborn daughter.

Over the next twenty-four years, Thompson served as a spy for the British army in revolutionary New England; aide to secretary of state for the colonies during the revolution, Lord George Germain; undersecretary of state for the colonies; commandant of the King’s American Dragoons, raised and based in South Carolina (retiring with the rank of colonel); and aide-de-camp to Carl Theodor, elector of Bavaria. Theodor eventually ennobled Thompson as Count Rumford. Along the way, Thompson raised and spent several fortunes, never hesitating to use his offices to enrich himself.

Thompson’s duties for the Bavarian military began with reform of the army but expanded into the establishment of prison workhouses to produce military materiel, and poorhouses to house Bavaria’s impoverished. Feeding all of these people in the cheapest, most efficient way possible inspired Thompson to improve the design and operation of institutional kitchens. His improved kitchen stove used many small fires with enclosed flames to keep the hot gases in contact with the cooking pans. The flue gases were used to cook additional foods before escaping up the chimney. During this time, he invented the first slow-roasting oven, a product that proved immensely popular throughout Europe and America.

While supervising the manufacture of cannons for the Bavarian army, Thompson observed that the production of heat while boring the cannons appeared to be inexhaustible. Inspired to perform detailed experiments, he showed that the heat produced was directly proportional to the length of the boring process and was quantitatively the same whether the bore was or was not cutting metal. These results were incompatible with the caloric theory of heat, which regarded heat as a material substance released from matter when it is cut, compressed, or otherwise stressed. Thompson explained the heat as a product of the work done in mechanical processes. His interpretation was later incorporated in the theory of heat as random molecular motion, and his results validated by James Prescott Joule’s measurements of the mechanical equivalent of heat.

Thompson returned to London in October, 1795, hoping to publish his scientific papers and reingratiate himself with British society. Finding this difficult to do, Thompson threw himself into developing and marketing his kitchen stoves, roasters, and fireplaces. Appalled at the dirty and inefficientfireplaces prevalent in England, he set about to improve them. Thompson’s new improved fireplaces were soon in much demand in England, Scotland, and Ireland and made him (once again) a wealthy man.

Thompson left England in September, 1802, to settle his affairs in Bavaria. On the way back to England, he passed through Paris, where he was seduced by the ladies of Parisian society and Napoleon Bonaparte, emperor of France. He consummated an ultimately unhappy marriage to the wealthy and socially prominent widow of Antoine Lavoisier, the founder of chemistry. During this period, he invented improved oil lamps and improved drip coffeemakers and experimented with new soap-making techniques. He remained in France until his death in Auteuil on August 21, 1814.

Impact

Thompson’s innovations increased the efficiency and economy of heating, cooking, and lighting at a time when the cost of fuel was a large part of domestic expense. Thompson lived during the Industrial Revolution, when the business consumption of energy began to compete with and place economic pressure on domestic consumption. When wood became scarce, it was replaced by coal. However, much like the present day, continued expansion of the industrial economy without a corresponding decrease in standards of living demanded the energy available be used with the greatest possible efficiency. Households that adopted Thompson’s improved fireplaces and ovens profited immediately from a significant drop in heating and cooking costs while also enjoying a warmer, cleaner home. Air pollution and the cost of fuel were both less than what they otherwise would have been.

Thompson is better known today as a scientist than as an inventor, remembered for his measurements of the amount of heat produced by mechanical action. His hypothesis that the heat produced is traceable to the work done during the boring process has proved to be correct. The new perspective these seminal experiments opened on the theory of heat eventually led to the recognition of heat as a form of energy, a fact not fully understood until the formulation of the law of conservation of energy and the development of the atomic theory of matter.

Bibliography

Brown, Sanborn C. Benjamin Thompson, Count Rumford. Cambridge, Mass.: MIT Press, 1979. Engaging discussion of the life and work of Thompson that does not hesitate to illuminate his less savory character traits. Illustrations, chapter notes, and index.

French, Allen. General Gages’s Informers: New Information upon Lexington and Concord—Benjamin Thompson as Loyalist and the Treachery of Benjamin Church, Jr. Cranberry, N.J.: Scholar’s Bookshelf, 2005. Reprint of a 1932 work based on General Gage’s papers. One chapter is devoted to Thompson’s service as a British spy during the American Revolution.

Lyons, John W. Fire. New York: Scientific American Library, 1985. An excellent discussion of combustion chemistry and physics that also touches on historical, economic, and safety issues of fire. Chapter 2 discusses Thompson’s role in the evolution of the scientific understanding of heat, and chapter 3 discusses his contributions to the technology of heating and cooking. Illustrations, further reading, and index.

Tyndall, John. Count Rumford, a Brief Biographical Account of this Outstanding American, Born Benjamin Thompson. Whitefish, Mont.: Kessinger, 2006. Originally published in the late nineteenth century. The author was a noted British scientist, regarded during his life as a talented popularizer of science. This small book (forty-eight pages) is one of his efforts in that direction.