That year the French sculptor Jean-Antoine Houdon, who had immortalized Voltaire in marble, did his bust of Franklin, catching his likeness better than any other had done. And that Baron Turgot, the French Minister of Finance, made his most famous epigram about Franklin: “He snatched the lightning from the sky and the sceptre from the tyrants.” Vainly Franklin protested that other Americans, “able and brave men,” deserved credit for the Revolution. On September 14, 1778, Congress revoked the commission of three and elected Franklin sole plenipotentiary to France—America’s first official ambassador to a foreign land. With only Temple and a clerk to help him with detail work, he was in actual fact consul-general, consultant on American affairs, propagandist for America, and, the part which pleased Franklin least but which he performed expertly, official beggar to the Court of Versailles for the ever increasing sums of money which Congress instructed him to procure for their costly war. With his other duties, he was director of naval affairs, Judge of the Admiralty, and in effect if not in name, overseas Secretary of the Navy. In this capacity in March of 1779 he wrote a “passport” for the Pacific explorer Captain James Cook, instructing commanders of American ships that Cook and his crew should be treated as “common friends to mankind” and allowed to go on their way. The sad news had not reached Europe; a month before Franklin’s instructions, Cook had been killed by natives on the Hawaiian Islands. Ever since his arrival in France, he had been concerned with the plight of captured American seamen, whom the English kept in foul prisons and treated not as prisoners-of-war but as traitors, charged with high treason and subject to execution. To Lord Stormont, the British ambassador, he had sent a formal plea requesting the exchange of American prisoners for English ones, man for man. It was ignored. A second came back unopened with a note: “The King’s Ambassador receives no Letters from Rebels but when they come to implore his Majesty’s Mercy.” Through an English friend, David Hartley, Franklin sent money for the relief of the American prisoners, and generous Englishmen added to the fund. That was all that could be done until some nine months after the signing of the treaty with France, when he received reluctant consent from the London ministry for prisoner exchange. There was still the problem of getting sufficient English prisoners for the exchange. Before the treaty, British seamen on the “prizes” which American ships brought into French ports had to be set free by maritime law. With France now officially at war with England, the ban no longer applied, but there were still far fewer English prisoners in France than American ones in England.