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.

In 1820 Mr. Cecil, of Cambridge, proposed the employment of a mixture of air and hydrogen as a source of motive power; he gave a detailed account of his invention in the Transactions of the Cambridge Philosophical Society, together with some interesting theoretical considerations. The author observes here that an explosion may be safely opposed by an elastic resistance--that of compressed air, for example--if such resistance possesses little or no inertia to be brought into play; contrariwise, the smallest inertia opposed to the explosion of a mixture subjected to instantaneous combustion is equivalent to an insurmountable obstacle. Thus a small quantity of gunpowder, or a detonating mixture of air and hydrogen, may without danger be ignited in a large closed vessel full of air, because the pressure against the sides of the vessel exerted by the explosion is not more than the pressure of the air compressed by the explosion. If a piece of card board, or even of paper, is placed in the middle of the bore of a cannon charged with powder, the cannon will almost certainly burst, because the powder in detonating acts upon a body in repose which can only be put in motion in a period of time infinitely little by the intervention of a force infinitely great.

The piece of paper is therefore equivalent to an insurmountable obstacle. Of all detonating mixtures, or explosive materials, the most dangerous for equal expansions, and the least fitted for use as motive power, are those which inflame the most rapidly. Thus, a mixture of oxygen and hydrogen, in which the inflammation is produced instantaneously, is less convenient for this particular usage than a mixture of air and hydrogen, which inflames more slowly. From this point of view, ordinary gunpowder would make a good source of motive power, because, notwithstanding its great power of dilatation, it is comparatively slow of ignition; only it would be necessary to take particular precautions to place the moving body in close contact with the powder. Cecil pointed out that while a small steam engine could not be started in work in less than half an hour, or probably more, a gas engine such as he proposed would have the advantage of being always ready for immediate use. Cecil's engine was the first in which the explosive mixture was ignited by a simple flame of gas drawn into the cylinder at the right moment.

In the first model, which was that of a vertical beam engine with a long cylinder of comparatively small diameter, the motive power was simply derived from the descent of the piston by atmospheric pressure; but Mr. Cecil is careful to state that power may also be obtained directly from the force of the explosion. The engine was worked with a cylinder pressure of about 12 atmospheres, and the inventor seems to have recognized that the noise of the explosions might be an objection to the machine, for he suggests putting the end of the cylinder down in a well, or inclosing it in a tight vessel for the purpose of deadening the shock.

It is interesting to rescue for a moment the account of Mr. Cecil's invention from the obscurity into which it has fallen--obscurity which the ingenuity of the ideas embodied in this machine does not merit. It is probable that in addition to the imperfections of his machinery, Mr. Cecil suffered from the difficulty of obtaining hydrogen at a sufficiently low price for use in large quantities. It does not transpire that the inventor ever seriously turned his attention to the advantages of coal gas, which even at that time, although very dear, must have been much cheaper than hydrogen. Knowing what we do at present, however, of the consumption of gas by a good engine of the latest pattern, it may be assumed that a great deal of the trouble of the gas engine builders of 60 years ago arose from the simple fact of their being altogether before their age. Of course, the steam engine of 1820 was a much more wasteful machine, as well as more costly to build than the steam engine of to-day; but the difference cannot have been so great as to create an advantage in favor of an appliance which required even greater nicety of construction.

The best gas-engine at present made would have been an expensive thing to supply with gas at the prices current in 1820, even if the resources of mechanical science at that date had been equal to its construction; which we know was not the case. Still, this consideration was not known, or was little valued, by Mr. Cecil and his contemporaries. It was not long, however, before Mr. Cecil had to give way before a formidable rival; for in 1823 Samuel Brown brought out his engine, which was in many respects an improvement upon the one already described. It will probably be right, however, to regard the Rev. Mr. Cecil, of Cambridge, as the first to make a practicable model of a gas-engine in the United Kingdom.--Journal of Gas Lighting.

Alabama has 2,118 factories, working 8,248 hands, with a capital invested of $5,714,032, paying annually in wages $2,227,968, and yielding annually in products $13,040,644.