Within a few months of arriving in Concord, Thompson married the Reverend's daughter, Sarah Walker Rolfe, whose deceased first husband left her a large estate. Through his wife, Thompson met the colonial governor, John Wentworth, who commissioned him in the New Hampshire militia. This appointment apparently caused resentment among his neighbors who felt there were veterans of the French and Indian War better qualified for the commission. Also, Thompson did not participate in the growing fervor in the 1770s against British rule. His unpopularity in Concord forced him to leave his wife and infant daughter to return to Massachusetts.

In May 1775 Thompson was arrested on the charge of "being inimical to the liberties of this country." He was released but never received a public hearing. He also may have been the author of a secret letter to British General Gage which conveyed military information about colonial troops during the siege of Boston. In late 1775 Thompson sent General Howe, Gage's successor, a lengthy report on the numbers, disposition, and equipment of American forces surrounding Boston. When Howe evacuated Boston in March, 1776, Thompson sailed to England.

Thompson entered the British Colonial Office, becoming an advisor to the Secretary of State for North America, Lord George Germain, at whose estate in 1778 he performed a series of experiments in the interior ballistics of small arms. In 1779 he was made a fellow of the Royal Society. He also continued his ballistic experiments, switching to studying cannons in the Royal Navy. He contributed an original design for an armed frigate to a treatise on naval architecture published in 1781.

In 1780 Thompson became Secretary of State for the Northern Department, which comprised New York, New England, and sections of Canada. The following year he received a commission in the British Army as a lieutenant colonel and left for America, shortly before Germain was drummed out of the colonial service by critics who accused him of incompetence in prosecuting the war with the rebellious colonies. He returned to England in 1783, but soon left for travel on the continent. It appears that Thompson envisioned a brighter future outside England since the influence of his friends and patrons had waned.

After several months wandering Europe, Thompson entered the service of the Elector of Bavaria, in whose employ he remained for fifteen years, achieving prominence as a public servant. He cleaned the streets of Munich of beggars, giving them clean quarters and putting them to work. He reformed the organization of the military, which raised morale, lessened the paper-work required of officers, and improved the pay, provisions, and leisure time of enlisted men. He planned and developed the English Garden, which still exists. At the age of 36 the King of England knighted Thompson; at 38 the Elector made him a Count of the Holy Roman Empire. Thompson was allowed to choose his own title; he selected Count Rumford, after the name by which Concord, New Hampshire, had been known before 1765.

In the early nineteenth century Rumford raised money for the Royal Institution of Great Britain, founded in 1800 for "teaching the application of scientific discoveries to the improvement of arts and manufactures in this country and to the increase of domestic comfort and convenience." The Institution consisted of a museum to exhibit useful machines, a scientific library, and a research laboratory. Rumford played a major role in the early success of the Institution, which was founded at a time when there were no institutional laboratories, and scientists conducted experiments in their homes. The first educational establishment to provide laboratories for students was Rensselaer Polytechnic Institute, founded in 1824 in the United States. It was not until the 1870s that the famous Cavendish Laboratory opened in Cambridge, England.

No doubt, Rumford's interest in public facilities for scientific research stemmed from his own scientific inquiries. In addition to his interest in gunpowder, Rumford did research on light, some chemical studies, and wrote at least one paper on mechanics. His inventions include a photometer and a calorimeter, and, given his interest in the "useful arts," he devised a stove, a roaster, and a lamp with multiple wicks. But his major scientific focus was on heat and his most important discoveries centered on the contention that heat is a form of motion.

Rumford spent the last dozen years of his life in Paris. In 1805 — his first wife having died in 1792 — he married the widow of the famous French chemist, Antoine Lavoisier. It was not a happy marriage; the couple separated in 1809, and Rumford moved to Auteuil, where he died in 1814. In his will he left Harvard University an annuity of $1,000, plus some additional funds, to establish a professorship "to teach… the utility of the physical and mathematical sciences for the improvement of the useful arts, and for the extension of industry, prosperity, happiness, and well-being of Society." The professorship was created in 1816 and the third Rumford Professor was Eben Horsford.

¹ In Thompson's day physical science would have been called natural philosophy.

² On the colorful and controversial life of Benjamin Thompson, see the following: Sanborn C, Brown, Benjamin Thompson, Count Rumford, (Cambridge, Mass: MIT Press, 1981); C. Raymond Adams, "Benjamin Thompson, Count Rumford," The Scientific Monthly 71, No. 6 (December 1950): 380-86.