As before remarked, the whole problem of steam propulsion waited upon the development of the steam engine. In the meantime the application of convenient forms of man power received considerable study, especially in France. In Bouguer’s _Traité du Navire_ the problem was investigated of propulsion by blades or panels, hinged, and folding when not in use against the vessel’s sides; and in 1753 the prize offered by the Academy of Sciences for an essay on the subject was won by Daniel Bernouilli, for a plan on those lines. Euler proposed paddlewheels on a transverse shaft geared like Savery’s, by mortice wheels to a multiple capstan. Variations of this method were proposed by other writers and inventors, and some of the best intellects in France attacked the problem. But nothing definite resulted. The most valuable result of the discussion was the conclusion drawn by M. Gautier, a professor of mathematics at Nancy, that the strength of the crew was not sufficient to give any great velocity to a ship. He proposed, therefore, as the only means of attaining that object, the employment of a steam engine, and pointed out several ways in which it might be applied to produce a rotary motion.[136] In the course of time the problem marched forward to a solution. The first great improvement in the steam engine which rendered it adaptable to marine use was the invention by Watt of the “double impulse”; the second, Pickard’s invention of the crank and connecting-rod. By virtue of these two developments the steam engine was made capable of imparting to a shaft a continuous rotary motion without the medium of noisy, brittle or inefficient gearing. As soon as engines having this power were placed on the public market attempts were made to mount them in boats and larger vessels; steam navigation was discerned as a possibility. § Of the many efforts which were made at the end of the eighteenth century to apply steam power to the propulsion of ships a striking feature is their complete independence from each other and from the results of prior experience and research. Little information is available as to the results of various experiments which were known to be carried on in France at this time, and, with all respect, it is improbable that they contributed in any way to the subsequent evolution of the steam vessel. The Abbé Darnal in 1781, M. de Jouffroi in 1782, and M. Desblancs in 1802 and 1803, proposed or constructed steamboats. M. de Jouffroi is said to have made several successful attempts on the Saone at Lyons; but the intervention of the Revolution put an end to his undertakings.