Rumford, on his return to Munich, was occupied in very important affairs. The advance of the French republican army under Moreau obliged the elector to quit the capital, leaving a council of regency, with Rumford at its head. Rumford succeeded in the arduous task of freeing Bavaria from invasion, and his conduct on this occasion increased his reputation with the elector and with the people. Among other tokens of the elector's gratitude for his services, he was permitted to settle one-half of the pension which he enjoyed on his daughter, to be paid during her lifetime. In 1798 the elector, partly with a view to gratify him with an honor which he knew he desired, and partly to afford him another opportunity of relaxation for the improvement of his health, appointed him ambassador at the court of Great Britain. On arriving in London, however, Rumford found, that in consequence of the English legal fiction, by which a born subject of the country is declared incapable of ever alienating his allegiance, he could not be received as the Bavarian ambassador. Mortified as he must have been by this circumstance, and still more deeply grieved by the loss of his friend and patron, the Elector Charles Theodore, who died in 1799, Rumford contemplated returning to spend the remainder of his life in the land of his birth. In compliance with a formal invitation which he received from the United States government, he was making preparations for his return, and had written to a friend to secure a cottage in the vicinity of Boston, as a 'quiet little retreat,' when he was led to change his design, and remain in London, in the society of which he occupied a conspicuous place. During several years, a great part of the Count Rumford's time was devoted to the interests of the Royal Institution, of which he may be considered the founder. The objects of this institution, now one of the recognized scientific establishments of the world, and one which can boast of having given employment to such men as Young, Davy, Brande, and Faraday, were 'to diffuse the knowledge and facilitate the general introduction of useful mechanical inventions and improvements, and to teach, by courses of philosophical lectures and experiments, the application of science to the useful purposes of life.' Such an institution was precisely the one which Rumford was qualified to superintend; and in its early history, the influence of his peculiar habits of thought is discernable in the choice of subjects for investigation by the members. Subsequently, the institution assumed the high scientific character which it yet holds.
In 1802, Count Rumford left England, and spent some time in travel. Revisiting Munich, he found the workhouse which he had planned, and which had been instrumental in producing so much good, abolished, and the new elector, Maximilian, friendly indeed but indisposed to follow the footsteps of his predecessor. Accordingly, after assisting in modeling a Bavarian academy of sciences, he took farewell of his adopted country, and went to reside in Paris, retaining an income of about L1200 from the Bavarian court. At the same time his daughter returned to America, her father having abandoned his intention of returning along with her. In Paris, Count Rumford appears at first to have gained the good-will and esteem which had attended him so remarkably during his previous life; and not long after he began his residence there, he contracted a second marriage with the widow of the celebrated Lavoisier, put to death during the French Revolution. From 1804 to 1814 he resided with his wife at Auteuil, a villa at a short distance from Paris, the property of Madame Lavoisier, and the scene of many of her former husband's discoveries. Here Rumford employed himself in scientific pursuits of a miscellaneous nature. The union of the American-born citizen of the world with the widow of the illustrious Frenchman does not appear to have been a happy one; and there is evidence that, towards the end of his life, Rumford had become unpopular in Parisian society. Cuvier attributes this to a certain coarseness and want of urbanity of manner; possibly, however, the fault was less in the person criticised than in the Parisian standard of criticism, for the charge seems inconsistent with the tenor of Rumford's life.
Rumford's death took place at Auteuil on the 21st of August 1814, in the sixty-second year of his age. He left some bequests for the promotion of science in America; the rest of his property, which does not appear to have been great, he left to his relatives. His only daughter inherited the title of Countess of Rumford, with the continuation of her father's Bava rian pension. She is, we believe, still alive, and has long resided in Paris.
Rumford, whose memoirs we have now detailed, was not a faultless char acter, or a person in every respect exemplary but making due allowances for circumstances in which he was at the outset unfortunately placed, and keeping in mind that every man is less or more the creature of the age in which he lives, we arrive at the conclusion, that few individuals occupying a public position have been so thoroughly deserving of esteem. The practical, calm, and comprehensive nature of his mind, his resolute and methodical habits, the benevolence and usefulness of his projects, all excite our admiration. Cuvier speaks of Rumford as 'having been the benefactor of his species without loving or esteeming them, as well as of holding the opinion that the mass of mankind ought to be treated as mere machines.' A remark this which is applicable to not a few men who have been eminent for labors of a humane description, and which naturally gives rise to this other remark - that a good intellectual method, directed to practical ends, is often of more value to mankind than what is called a good heart.