In connection with this boat, Fulton invented a torpedo, or infernal machine, for the purpose of destroying vessels of war by approaching them under water and breaking up their hulls by the explosion. He offered his invention several times to the French Government, and once to the Ambassador of Holland at Paris, without being able to induce them to consider it. Somewhat later, he visited London, at the request of the British Ministry, and explained his invention to them. Although he succeeded in blowing up a vessel of two hundred tons with one hundred and seventy pounds of powder, and in extorting from Mr. Pitt the acknowledgment that, if introduced into practice, the torpedo would annihilate all navies, his invention was rejected, through the influence of Lord Melville, who feared that its adoption might injure England more than it would benefit her. At the first, when it was thought that England would purchase Fulton's invention, it was intimated to him that he would be required to pledge himself not to dispose of it to any other power. He replied promptly: "Whatever may be your award, I never will consent to let these inventions lie dormant should my country at any time have need of them. Were you to grant me an annuity of twenty thousand pounds, I would sacrifice all to the safety and independence of my country." In 1806, Mr. Fulton returned to New York, and in the same year he married Miss Harriet Livingston, a niece of Chancellor Livingston, by whom he had four children. He offered his torpedo to the General Government, but the trial to which it was subjected by the Navy Department was unsuccessful for him, and the Government declined to purchase the invention. But it was not as the inventor of engines of destruction that Robert Fulton was to achieve fame. A still nobler triumph was reserved for him--one which was to bring joy instead of sorrow to the world. From the time that Fulton had designed the paddle-wheels for his fishing-boat, he had never ceased to give his attention to the subject of propelling vessels by machinery, and after his acquaintance with Watt, he was more than ever convinced that the steam-engine could, under proper circumstances, be made to furnish the motive power. Several eminent and ingenious men, previous to this, had proposed to propel vessels by steam power, among whom were Dr. Papin, of France, Savery, the Marquis of Worcester, and Dr. John Allen, of London, in 1726. In 1786, Oliver Evans, of Philadelphia, and about the same time Dr. Franklin, proposed to accomplish this result by forcing a quantity of water, by means of steam power, through an opening made for that purpose in the stern of the hull of the boat.