When the _Letters of a Pennsylvanian Farmer_ became known in Europe, Diderot said that it was madness to allow Frenchmen to read such things, as they could not do it without becoming intoxicated and changed into different men. But France was impressed by the event more than by the literature that accompanied it. America had made herself independent under less provocation than had ever been a motive of revolt, and the French Government had acknowledged that her cause was righteous and had gone to war for it. If the king was right in America, he was utterly wrong at home, and if the Americans acted rightly, the argument was stronger, the cause was a hundredfold better, in France itself. All that justified their independence condemned the Government of their French allies. By the principle that taxation without representation is robbery, there was no authority so illegitimate as that of Lewis XVI. The force of that demonstration was irresistible, and it produced its effect where the example of England failed. The English doctrine was repelled at the very earliest stage of the Revolution, and the American was adopted. What the French took from the Americans was their theory of revolution, not their theory of government--their cutting, not their sewing. Many French nobles served in the war, and came home republicans and even democrats by conviction. It was America that converted the aristocracy to the reforming policy, and gave leaders to the Revolution. "The American Revolution," says Washington, "or the peculiar light of the age, seems to have opened the eyes of almost every nation in Europe, and a spirit of equal liberty appears fast to be gaining ground everywhere." When the French officers were leaving, Cooper, of Boston, addressed them in the language of warning: "Do not let your hopes be inflamed by our triumphs on this virgin soil. You will carry our sentiments with you, but if you try to plant them in a country that has been corrupt for centuries, you will encounter obstacles more formidable than ours. Our liberty has been won with blood; you will have to shed it in torrents before liberty can take root in the old world." Adams, after he had been President of the United States, bitterly regretted the Revolution which made them independent, because it had given the example to the French; although he also believed that they had not a single principle in common.