But even in those days when slaves could be made to work to the limits of their endurance, it is fairly evident that man believed that there was a future for the mechanical propulsion of ships, and the usual form which this took was of applying paddle-wheels to the side of the ship, and revolving these by means of a capstan turned either by slaves or by oxen. The Chinese, it is scarcely to be wondered at, adopted this means, and so also did the Romans. In 264 B.C., when Appius Claudius Caudex one dark night crossed the Straits of Messina to Sicily, he transported the troops in boats propelled by paddle-wheels through the medium of capstans revolved by oxen, and there is in existence an ancient bas-relief which shows a galley with three wheels on either side to be used for this purpose. Over and over again this same idea was exploited, and even as recently as 1829 Charles Napier, a British naval officer, when he was in command of the frigate _Galatea_, was by special permission of the Admiralty allowed to fit her with paddles, which were worked by winches on the main deck. He found that in a calm he could thus get his ship along at three knots an hour, and tow a line-o’-battle ship at one and a half knots. But it was noticed then, what experimenters of this nature always found in every age, that, firstly, this method of capstan-plus-paddle-wheels was good only for a short distance; and, secondly, that so great an expenditure of physical force could be more advantageously applied by using the old-fashioned method of rowing.