Lebon, in the certificate dated 1801, in addition to his first patent, described and illustrated a three-cylinder gas-engine in which an explosive mixture of gas and air was to have been ignited by an electric spark. This is a curious anticipation of the Lenior system, not brought out until more than fifty years later; but there is no evidence that Lebon ever constructed an engine after the design referred to. It is an instructive lesson to would-be patentees, who frequently expect to reap immediate fame and fortune from their property in some crude ideas which they fondly deem to be an "invention," to observe the very wide interval that separates Lebon from Otto. The idea is the same in both cases; but it has required long years of patient work, and many failures, to embody the idea in a suitable form. It is almost surprising, to any one who has not specially studied the matter, to discover the number of devices that have been tried with the object of making an explosion engine, as distinguished from one deriving its motive power from the expansion of gaseous fluids. A narrative of some of these attempts has been presented to the Societe des Ingenieurs Civils; mostly taken in the first place from Stuart's work upon the origin of the steam engine, published in 1820, and now somewhat scarce. It appears from this statement that so long ago as 1794, Robert Street described and patented an engine in winch the piston was to be driven by the explosion of a gaseous mixture whereof the combustible element was furnished by the vaporization of _terebenthine_ (turpentine) thrown upon red hot iron. In 1807 De Rivaz applied the same idea in a different manner. He employed a cylinder 12 centimeters in diameter fitted with a piston. At the bottom of the cylinder there was another smaller one, also provided with a piston. This was the aspirating cylinder, which drew hydrogen from an inflated bag, and mixed it with twice its bulk of air by means of a two-way cock. The ignition of the detonating mixture was effected by an electric spark. It is said that the inventor applied his apparatus to a small locomotive.