_Early Lenoir engine_ (1860).—The motor (Fig. 1) resembled in external appearance a horizontal double-acting steam engine. This design was in great favour at that time, being copied from the steam engine, and was to a certain extent suitable for use with an explosive gas instead of steam. The valve chest is cylindrical and the valves themselves flat, and work off two eccentrics; ignition is effected by an electric spark from a Ruhmkorff coil, which passes through the gas in the cylinder when the piston is commencing the second half of the forward stroke. The exploded gases having done their work are driven out through the exhaust in the return stroke, during which work is being done by a similar explosion on the other side of the piston. A water jacket prevents the cylinder walls from becoming overheated. This arrangement is therefore double-acting, but a compression of the explosive gas is not possible without the use of a second cylinder. It has been abandoned because regularity of working is only obtained at the expense of economy, and by using both sides of the piston as explosive chambers it is found that the quantity of gas used is quite out of proportion to the power developed. [Illustration: FIG. 1.—Early Lenoir Motor (1860).] _The Bisschop gas engine._—This motor (Fig. 2), based on a mixed principle, uses the explosion to do work during the forward stroke, and in the return the atmosphere exerts an excess of pressure on the other side of the piston, as in the Otto and Langen atmospheric engine which we have previously mentioned. In its time the Bisschop gas engine obtained a great measure of success, but it has now almost completely disappeared. It was, however, well thought out and constructed; the cylinder was vertical, and relied on longitudinal corrugations, and the air to keep it cool. Above the cylinder was placed a cylindrical guide; a connecting rod and cross-head formed the attachment between the piston rod and crank. The machine was principally constructed for small workshops requiring small powers of from a quarter to one horse-power, the cost of fuel for the half horse-power size being about one penny per hour. The inventor received a prize of 1000 francs from the Société d’Encouragement for the best small motor applicable to home industries. [Illustration: FIG. 2.—Bisschop Motor.] _François motor._—This type, which is now quite obsolete, was somewhat similar in character to the last, but rather more complicated and perfect. The crank shaft was not in a line with the cylinder, and was connected by two connecting rods to the cross-head. Two fly-wheels were placed one on each side of the cylinder and connected by toothed wheels. The machine was on the whole too complicated, and although its consumption of fuel was comparatively small and its speed constant, it did not succeed in ousting the Bisschop motor from its position.