He regularized the temperature of kitchens and other rooms; his fireplace remains unexcelled.

His first marriage was contracted well above his station: to the wealthiest widow in Concord, New Hampshire, where he went as a tutor at nineteen. (The town of Concord had been called Rumford, Massachusetts, when first settled. Once the border dispute was resolved, with the banks of the Merrimack River serving as boundary between the colonies, the town was renamed Concord in honor of that treaty. When he became a count of the Holy Roman Empire, Thompson signaled his nobility by taking his wife’s town’s name.) She was in her thirties and, by his account, rapacious: “She married me, not I her.”

Of their brief union, before he had to flee America as a British spy, came Thompson’s single legitimate child. Daughter Sarah did not marry, although she wanted to; he sent for her in Europe to serve as his companion. Their relationship proved uneasy, often strained; after his death she returned to Concord and hung portraits of his mistresses on the parlor walls. She burned her father’s “scolding letters” and the treatise with which he had occupied himself during his retirement. An essay on “The Nature and Effects of Order,” it was to have been Rumford’s magnum opus, or so he in his correspondence claimed.

His second marriage—to the widow of the great French chemist Lavoisier—was a very public failure, and it made society laugh. Madame Marie Paulze Lavoisier lost both her father and her first husband to the guillotine; in middle age she enjoyed entertaining and maintained a salon. But Count Rumford wanted to pursue his scientific work in peace. They had bedroom disagreements and drawing-room harangues. She poured boiling water on his flowers; he locked the gate on her guests.

Not surprisingly, perhaps, given Baron Delessert’s assertion (“what service he has rendered to humanity by introducing the general use of the soups which go by his own name”), Count Rumford had become the butt of jokes. He was a firm believer in the value of proper nutrition; he wrote about the virtue of potatoes and dry bread in soup. But when the French ate poorly, they called it dining à la Rumford . He invented the photometer and improved the Argand lamp, yet a cartoon showed a man so blinded by the count’s hand lantern that he wandered all night in the Bois de Boulogne and fell down in a ditch.

At last, and fearing for his health, he withdrew from the center of Paris to the suburb of Auteuil. There he inhabited the house where another distinguished American Benjamin, Franklin, had come calling years before, paying flirtatious attention to its owner, Madame Helvétius. Unlike the sociable Franklin, however, Count Rumford as he aged grew more and more reclusive: jealous of his reputation, quick to pick a quarrel when his honor was impugned. He busied himself playing billiards and chess—solo, complaining of a “fire in his head.” His final consort and housekeeper was Victoire LefÀvre, with whom he had his final illegitimate child. His will provided for them also, but the boy, registered as born to un père absent , grew up to be a soldier and was killed in the Crimea.

His one acknowledged child, the Dowager Sarah, Countess Rumford, died on December 2, 1852, when she was seventy-nine years old. She left her large house and land in Concord, and her considerable fortune, to charity. She had two favorite causes and endowed them by bequest: a home for parentless children and the New Hampshire Asylum for the indigent insane.

“To make vicious and abandoned people happy,” Thompson wrote, “it has been generally supposed necessary first to make them virtuous. But why not reverse this order? Why not make them first happy, and then virtuous? If happiness and virtue be inseparable , the end will be as certainly obtained by one method as by the other; and it is most undoubtedly much easier to contribute to the happiness and comfort of persons in a state of poverty and misery, than, by admonitions and punishments, to reform their morals.”