Then came the introduction of the screw-propeller, which, if we are to believe some authorities, is an early invention of the Chinese. There have been many claims to its invention in modern times. In May, 1804, Mr. J. Stevens, of the United States, put to sea with a steam-boat propelled with some form of screw. Trevethick, the engineer, in 1815, patented “a worm or screw revolving in a cylinder at the head, sides, or stern of a vessel;” and the following year, Robert Kinder applied for a patent for a shaft and screw almost of exactly the form now in use. The French claim it, and only a few years since erected at Boulogne a monument to Frédéric Sauvage, as its inventor. On the front is a bronze bas-relief showing a vessel with a screw-propeller. Sauvage’s life was similar to those of many other inventors, in that he spent his days and fortune in perfecting inventions which brought him no profit. Having lost his own money, and got into great difficulties, he was thrown into a debtors’ prison, and subsequently ended his days in a madhouse. Lindsay remarks properly that “the number of claimants to every important invention is remarkable. An impartial student will, however, probably come to the conclusion that the invention of the screw and its application was, like that of the steam-engine itself, the sole property of no one man.” The time for its development and proper use had come, and many scientific students were inquiring concerning its value. There can be little doubt that the first demonstration in our country of its value on a proper scale and in convincing form, was that made by Captain John Ericsson, a Swedish engineer resident in London. After a successful experiment with a model, he had a boat built forty-five feet in length, and fitted with engine and two propellers. She was named the _Francis B. Ogden_. “The result of her first trial went far beyond his most sanguine expectations. No sooner were the engines put at full speed, than she shot ahead at the rate of more than ten miles an hour.” Afterwards she towed a schooner of 140 tons burden at seven miles an hour. The next experiment was made in the presence of the Lords of the Admiralty, and they were minute in their inspection. Ericsson felt confident that they were convinced, and would soon order the construction of a war-vessel on the new principle. In this, however, he was disappointed, though he had given them a tolerably good proof of its value by towing their barge at the rate of ten miles an hour for a considerable distance. Scientific theorists reported against it, and said that a ship thus propelled would be unsteerable. Lindsay records how Admiral Beechey, one of the old school, in 1850, stated that “he did not believe that the navy of the future—the Royal Navy—ever could consist of steamers! Nor could he endure iron ships.”