Benjamin Thompson Rumford, count, an American natural philosopher, born in Woburn, Mass., March 26, 1753, died at Auteuil, near Paris, Aug. 21, 1814. He was educated at the common school in his native place, afterward at Medford, and at the age of 13 entered the counting house of a Salem merchant. In 1770 he taught an academy in Rumford (now Concord), N. H., and in 1772 married Mrs. Rolfe of that place, a wealthy widow considerably his senior, and was made major in the militia of New Hampshire by the royal governor. This excited the jealousy of older officers, and he was charged with disaffection to the cause of the colonies, driven from his home, and finally took refuge in Boston, where he became an associate of Gen. Gage and the other British officers. He was subsequently tried at Woburn, and, though not condemned, was refused a full acquittal, and afterward made an unsuccessful effort to obtain a commission in the continental army. When Boston fell into the hands of the patriots he carried to England the despatches announcing that event. There he was employed by Lord George Germain, secretary of state for the department of the colonies, and in 1780 became under secretary of state.

After the retirement of Lord Germain in 1781 Mr. Thompson returned to America, and there formed a regiment of dragoons, of which he received the command with the rank of lieutenant colonel. Returning to England at the close of hostilities, he obtained leave of absence to visit the continent of Europe, and by permission of the English government entered the service of the elector of Bavaria, who knighted him. Toward the end of 1784 he settled in Munich with the appointment of aide-de-camp and chamberlain to the elector. Here he reorganized the entire military establishment of Bavaria. In the beginning of 1790 he undertook to suppress beggary in Bavaria, which had become a profession, and inculcated habits of industry and order in the people of the lower class. In this he was successful, and was also wholly or partially so in the establishment of a military school, the improvement of the breed of horses and of horned cattle, and the conversion of an old hunting ground near Munich into a park, where after his departure the inhabitants erected a monument in his honor.

He had been successively raised to the rank of a major general in the army, member of the council of state, lieutenant general, commander-in-chief of the general staff, minister of war, and count of the holy Roman empire, on which occasion he chose as a title the name of the place in America in which he had resided. His health failing under his arduous labors, he made a tour in Italy; but not finding himself recovered, he visited England, reaching that country in September, 1795, and on his arrival in London was robbed of a trunk containing all his private papers and original notes and observations on philosophical subjects. Returning to Bavaria when that country was threatened by the war in 1796 between France and Germany, he was appointed head of the council of regency during the absence of the elector, and maintained the neutrality of Munich; for this service many honors were conferred upon him, one of which was an appointment to the su-perintendency of the general police of the electorate. As the climate did not agree with him, after spending two years in public duties and private studies, he determined to fix his residence in England, and was named minister to the court of St. James; but the English government, acting on the rule of inalienable allegiance, refused to recognize him in this capacity.

While in England he was largely concerned in the affairs of the royal institution, of which he was the real founder. After the death of Charles Theodore, elector of Bavaria (1799), Rumford gave up his citizenship in the electorate, and finally settled at Paris. He married in 1804 for his second wife the widow of Lavoisier, and with her retired to the villa of Auteuil, the residence of her former husband, where he spent the remainder of his life. He contributed a large number of papers to various scientific journals. The subject to which he devoted his philosophical investigations more than any other was that of heat, and what has been done to demonstrate experimentally the doctrine of "correlation of forces" was begun by him in a series of experiments suggested by the heat evolved in boring cannon at the arsenal in Munich. (See Correlation of Forces.) For Count Rum-ford's claim to having very nearly established the "mechanical equivalent of heat," see a paper by Prof. Robert H. Thurston in the "Transactions of the American Society of Civil Engineers," vol. ii., p. 289; also Tyndall's "Heat as a Mode of Motion." Rumford also devoted a good deal of attention to the construction of chimneys, with principal reference to remedies for their smoking, and wrote popular essays on the subject.

His investigations into the strength of materials and the force of gunpowder resulted in great improvements in artillery; and on the subjects of light and illumination he also made many experiments and discoveries. Some years before his death he instituted prizes for discoveries in light and heat, to be awarded by the royal society of London and the American academy of sciences, of which he himself received the first on the former subject from the royal society; and he bequeathed to Harvard university the funds by which was founded the Rumford professorship of the physical and mathematical sciences as applied to the useful arts, which was established in October, 1816. - The results of his investigations were published in pamphlets and essays, in French, English, or German. A complete edition of his writings has been published in 4 vols., with his life by the Rev. G. E. Ellis (Philadelphia, 1871). See also his life by Prof. Renwick, in Sparks's "American Biography," 2d series, vol. v.