Arriving in England, as he did, the bearer of gloomy despatches, and sustaining the equivocal character of a deserter from the American cause, Thompson soon proved that he was a man who could command his fortune anywhere. The capacity in which he had come over introduced him to various public men, who could not fail to be struck by his abilities, as well as charmed by his manner; and the consequence was, that in a short time after his arrival he was offered a post in the colonial office. Probably the minister was of opinion that none of all the American refugees, who then swarmed in London, was able to render Rich assistance as Thomp son in conducting the department over which he presided.
Of whatever nature were the services which Thompson rendered to the public business, they must have been of considerable value; for in 1780, four years after his arrival in England, he was raised by his patron, Lord Germain, to the post of under-secretary of state for the colonies; an instance of promotion which, considering the circumstances in which the subject of it stood, is almost unexampled. The usual accompaniment of such a situation was, and is, a seat in parliament; and according to the practice of those days, when noblemen had seats in the House of Commons at their disposal, Lord Germain, if he had so chosen, might have conferred a seat on his American protégé; but it was probably imagined that the admission into parliament of a man so unpopular in America would be attended with disadvantages, and that, at all events, Thompson's talents were better fitted for the desk than the senate. The income and conse quence, however, which he derived from his office, gave him admission to the highest metropolitan circles; and he had thus opportunities not only of becoming known, but also of exercising his inventive mind in many pursuits not immediately connected with his official duties. Fertility - a disposition to propose improvements in all departments - seems to have been his most striking characteristic; and it was probably this ready genius for practical reforms in everything which came under his notice, that recommended him so much to public men. A man who, in his general intercourse with society, can drop valuable suggestions, allowing others to grasp at them, and enjoy the credit of carrying them into effect, is likely to be a favorite. Thomp son appears to have been such a man a person who, holding no ostensible post but that of under-secretary for the colonies, could yet, out of the richness of an ever-inventive mind, scatter hints which would be thankfully received by men of all professions.
While concerning himself generally, however, in a variety of matters, Thompson was at the same time following out certain specific lines of sci entific investigation. 'As early as 1777,' says his biographer, 'he made some curious and interesting experiments on the strength of solid bodies. These were never published, and would probably have been superseded by more full investigations made by subsequent experiments. In 1778, he employed himself in experiments on the strength of gunpowder, and the velocity of military projectiles, and these were followed by a cruise of some months in the channel fleet, where he proposed to repeat his investi gations on a larger scale.' On this subject Thompson communicated sev eral papers to the 'Philosophical Transactions' of the Royal Society, of which he had become a member. Passing over these scientific lucubrations, we hasten to reach that period of Rumford's life at which he found himself in a situation to give full scope to his genius for improvements.
As the war between great Britain and the colonies proceeded, it became evident that the latter must triumph. The anti-American party in Great Britain lost ground; and on the news of the capitulation of Lord Cornwal lis reaching England, a division took place in the cabinet, and Lord George Germain found it necessary to resign office. As his policy, however, in American affairs, had been agreeable to the wishes of George III, he retired with the honors of a peerage, and was able still to for ward the interests of his friends. Not the least distinguished of these was Under-Secretary Thompson, who, whether he had cooperated with his principal in all his measures and views, or whether, according to his own statement afterwards to Cuvier, he was disgusted at Lord Germain's want of judgment,' had at least done a sufficient amount of work to deserve a parting token of regard. Accordingly, by the influence of the fallen min ister, Thompson was sent out to New York, in the year 1781, with the royal commission of major, which was afterwards changed for that of lieutenant-colonel, charged with the task of organizing an efficient regiment of dra g oons out of the broken and disjointed native cavalry regiments which had been fighting on the royalist side. What were to be the specific uses of this force are now uncertain. The regiment, fortunately, was of no avail.
Peace having been concluded between the United States 'and Great Britain, Colonel Thompson, shortly after his return obtained leave of absence in order that he might travel on the continent.