Congress not only declined to receive his resignation, but with its refusal sent him a commission, jointly with John Adams and John Jay, who had been the agent of the congress in Spain, to negotiate a peace. Cornwallis had surrendered at Yorktown on the 17th of October of that year, the anniversary of Burgoyne's disastrous surrender at Saratoga just four years before, and a farther prosecution of the war beyond what might be necessary to secure the most favourable terms of peace was no longer advocated by any party in England. Active negotiations with Franklin and his associates were opened, and on the 30th of November a preliminary treaty was signed by the English and American commissioners; a definitive treaty was signed on the 30th of September 1783, and ratified by congress January 14, 1784, and by the English Government on the 9th of April following. At the conclusion of the preliminary treaty Franklin renewed his application to congress to be relieved, to which he received no answer. A few weeks after signing the definitive treaty, he renewed it again, but it was not until the 7th of March 1785 that congress adopted the resolution which permitted "The Honourable Benjamin Franklin to return to America as soon as convenient," and three days later it appointed Thomas Jefferson to succeed him. During his stay in Paris Franklin gave by no means all his time to political problems. He wrote a paper for the Royal Society on the subject of balloons, a topic which, under the auspices of the Montgolfiers, attracted a great deal of attention at that time in France. Sir Joseph Banks commended it for its completeness. To some one who asked the use of the new invention Franklin replied by asking, "What is the use of a new-born baby?" In 1784 he was appointed by the French Academy one of a commission ordered by the king to investigate the phenomena of "mesmerism"; and to a large extent he directed the investigation which resulted in the disgrace and flight of Mesmer and his final disappearance from the public eye. Franklin's _Information to those who would Remove to America_, his _New Treatise on Privateering_, his _Essay on Raising the Wages in Europe by the American Revolution_, his _Letter to Vaughan on Luxury_, his _Story of the Whistle_, together with his private as well as official correspondence, kept the world constantly talking about him and wondering at the inexhaustible variety and unconventional novelty of his resources. "You replace Dr Franklin," I hear, said the Count de Vergennes to Jefferson when they first met. "I succeed, no one can replace him," was Jefferson's reply.