Opinions are divided as to whether the paddle-wheel is a development from the action of a man paddling a canoe, or the result of applying to a vessel an ordinary wheel, with blades to make it bite the water; or it may be stated thus: Did the paddle-blades grow out of the wheel, or the wheel out of a number of paddle-blades? There is no satisfactory evidence one way or the other; suffice it that the idea of revolving paddles was developed. How the power which caused the revolution of the paddles was applied at first is as unknown as the identity of the man who first thought of making navigation easier by mechanical means. It was probably human power, as the first inventor can hardly have discovered how to utilise animals for the purpose, and from what we know of primitive expedients we may conjecture what the first contrivance used to urge a boat onwards without sails or oars was like. The craft would be a small one. Perhaps the proprietor was too poor to hire rowers. Perhaps, a subtle financier, he realised that if he could bring his goods to a certain place before rival shippers he would secure the market. Hence, stimulated by poverty or cupidity or both, he reflected, experimented, and finally invented the revolving paddle. But his apparatus was probably nothing more than a smooth, straight branch or tree log, which projected over either side of the boat and carried at each end paddles fixed radially. He probably used two or four paddles, as it would be easier to attach them to the axle in pairs. The radii of the paddles consisted of two poles tied at right angles about the middle and there fastened to the axle ends, rough-hewn boards or strips of bark being attached at the extremities of the poles to form the paddle-blades. The axle was doubtless kept in place either by pins in the gunwales placed before and after it, or by bringing two of the ribs on either side above the gunwale line and disposing the axle between them. In many modern row-boats one or other of these plans is adopted for the accommodation of the oars or sculls. This much being accomplished, it only remained to apply the power. The inventor now passed a rope twice round the middle of the axle, and tied the ends together. By hauling on it he got all the power he was likely to require; to go astern he had merely to pull the rope the other way. If more power was required more men tugged at the rope.