While looking up something else, I came across this statement of how New England scholars viewed Benjamin Thompson in the 1800s. It appeared as a footnote to Dr. Jacob Bigelow’s inaugural address as Rumford Professor at Harvard, as published in the North-American Review in 1817:
Count Rumford was decidedly attached to the cause of American liberty, and earnestly sought for a commission in the service of Congress. He was present at the battle of Lexington, and afterwards remained sometime with the army at Cambridge.So we can see how shocking it was in the early 1900s when Allen French studied Gen. Thomas Gage’s intelligence files and realized that Thompson had been spying for the British throughout 1775—all that time he’d supposedly been traveling around the American lines trying to help.
His expectations of promotion were disappointed, in consequence of suspicions arising from his former intercourse with Governor [John] Wentworth of New Hampshire, and some others attached to the British cause. These suspicions it was impossible to overcome, although he demanded a court of inquiry, and was honourably acquitted of all intentions inimical to the cause of his country. After remaining some time in fruitless hope with the American army, and seeing the post of his ambition filled by a rival candidate, he retired in disgust, and embarked for England in January, 1776.
While at Cambridge, he exerted himself in preserving the library and philosophical apparatus, when the Colleges were occupied as barracks by the soldiery.
Though you’d think the facts that Thompson had become secretary to the London official overseeing the war and then led a troop of dragoons on Long Island would have been a good clue about his attachments well before 1817.