For a short time he devoted himself to the perfection of a hot-air engine, and a sounding device by which ships might ascertain the depth of the water over which they were passing. Then he turned to a new activity. The result was revolutionary. What he had almost accomplished in the field of land-transportation with the Novelty, he now actually achieved in steam-navigation on the sea. To Ericsson should be credited the perfection and application of the screw for the propulsion of steam-driven vessels. Up to the dawn of the nineteenth century the sailing-ship had ruled the seas. And even until the middle of that century the fast clippers, with their towers of widespread canvas, had held supreme domination over the world’s waterways. But in the year 1835 Ericsson designed a rotary propeller driven by a steam-engine, which marked the beginning of the end of sailing days. The steam-engine, first placed in a ship by Robert Fulton, the American inventor, was no novelty, but it had been used only to propel vessels by means of paddle-wheels attached to each side of the vessels, huge cumbersome contrivances, which were easily damaged by heavy seas and which on ships of war afforded easy targets for the enemy. The screw of Ericsson’s was designed to operate underneath the stern of the vessel, under water and just forward of the rudder, exactly as it is placed to-day. To test this new invention Ericsson built a small vessel, the Francis B. Ogden, which was launched in the Thames River in the spring of 1837. The experiment was a great success and a speed of over ten miles an hour was attained, to the wonder of the stolid English boatmen who watched in amazement this strange ship move rapidly through the water with no visible means of propulsion. Later in the summer Ericsson invited the Lords of the British Admiralty to inspect his steamship, and even conducted them on a trial trip on the Thames; but the amazing performance of the Ogden created but little interest in the minds of the British officials, who dismissed the affair as an “interesting experiment.” But Ericsson had a friend who stood him in good stead. This friend was an American, Francis B. Ogden, our counsul at Liverpool, after whom Ericsson’s first vessel was named. Ogden was not an engineer, but he recognized in the Swedish inventor a man of sincerity and genius, and to his friendship Ericsson owed much in the way of advice and assistance. In 1838 Ericsson built and launched a larger steamship, the Robert F. Stockton which sailed from Gravesend, England, on April 13, 1839, and made a successful passage to New York City, the first screw-driven steamship ever to cross the Atlantic. As the result of this remarkable achievement Ericsson was assured that the government of the United States would try out his invention on a large scale, and persuaded him to go to America.