Among the most promising of these first steamboats were those in which the propeller, or the paddle-wheel, was tried; but neither of these methods was looked upon favorably at first. Less promising was one in which the motive power was a jet of water pumped through a submerged tube--a principle that still periodically fascinates certain modern inventors. [Illustration: MARINE ENGINES AND AN EARLY TYPE OF STEAMBOAT. The small figure in the centre represents a very remarkable steamboat constructed in America by John Fitch. The precise date of its construction is not clearly established, but the inventor had made efforts at steam navigation as early as 1776. The upper figure shows a marine engine made in Scotland in 1788 for Patrick Miller by William Symington. It was used to equip a double-hulled pleasure boat which it is said to have propelled at the rate of five miles an hour. The motive power is supplied by two open-top Newcomen cylinders. The lower figure represents a modern side wheel steamer with oscillating engines.] But the boats that seemed to have come nearer attaining practical success for the moment were those in which several sets of oars worked by steam were placed vertically on each side of the hull, the machinery so arranged that the oars were dipped into the water and drawn sternward by one motion of the machinery, raised and carried toward the bow by the opposite motion. In some of these boats it was planned to have four sets of oars, two sets on each side, which were to work alternately, so that while one set was traveling forward through the air, its mate would be paddling through the water, thus insuring a continuous forward impulse. But the machinery for these boats proved to be too cumbersome and complicated for practical results, and this idea was finally abandoned. The jet of water did not prove any more successful, and but two other methods were available--the propeller and the paddle-wheel. Both of these methods of utilizing the power of moving water had been familiar in the form of the Archimedian screw and the commonplace overshot or undershot mill-wheel. In these examples, of course, the force of the water was used to move machinery, reversing the action of the paddle-wheel of the boat. And yet the principles were identical. Obviously if the conditions were reversed, and the undershot mill-wheel, for example, forced against the water with corresponding power, the propulsive effect might be great enough--since action and reaction are equal--to move a boat of considerable size. But curiously enough, at the time when Fulton began his experiments there was a wave of general belief that when this principle was applied to boats it would fail. The reason for this lay in the fact that several such boats had been built from time to time, and all had failed. The fault, of course, lay in some other place than in their paddle wheels; but for the time being the wheel, and not the machinery, was shouldered with the blame.