_Koerting-Lieckfeld motor._—The first of these motors was constructed in 1877, and was based on the Dugald-Clerk cycle. The original type has, however, been abandoned, and the firm of Brûlé et Cie. of Paris now construct these engines on the Otto system. All the moving parts are attached to a vertical frame of cast-iron (Fig. 10), the lower half containing the cylinder. The admission and exhaust valves are situated in front and near the base. The governor is of the centrifugal type and acts directly on the levers of the valves. The flame ignition makes it necessary to occasionally clean out the valves, but otherwise the motor has few drawbacks, and is very neat and compact. The consumption of coal gas for engines of 8 horse-power and upwards is about 800 litres per horse-power hour. The crank-shaft is placed horizontally across the top of the frame, and the cams acting upon the valves are rotated by a bevel gear enclosed in a case, driving a thin supplementary shaft on which they are placed. The motor is self-lubricating, and is also constructed as a horizontal gas engine. [Illustration: FIG. 10.—Koerting-Boulet Motor.] _Andrews’ motor._—The governing apparatus in this engine is exceedingly simple and ingenious, consisting of a weight fixed to an oscillating lever which controls the admission valve. The position which the weight takes up depends upon the rapidity with which the lever oscillates, and consequently upon the speed of the engine. If, therefore, the engine is running too fast or too slow the weight takes up a new position, and the effect upon the admission valve is to either slow down or quicken the speed. The gases are ignited by means of a tube kept red-hot by a gas flame. This engine possesses the special advantage of being self-starting, that is to say, it is not necessary, as in many other motors, to start the engine by giving the fly-wheel a few rapid turns by hand. The motor is stopped with the crank in a position slightly in advance of the point corresponding to ignition. The gas is allowed to enter by a small auxiliary valve, which closes after the first explosion. This volume of gas entering the cylinder mixes with the air already in it, forming an explosive mixture. This explosive mixture then begins to escape by similar automatic self-closing valves situated at the top of the red-hot ignition tube. Ignition takes place, and is communicated to the rest of the gas in the cylinder, closing the two small valves by the force of the explosion. The piston is therefore driven forward, and the energy of this combustion is sufficient to start the engine. It must be understood that this operation is only performed once at starting, for immediately afterwards the engine falls into its normal cycle of operations. Two fly-wheels are as a rule provided to ensure constancy of speed. The consumption of gas is as low as 580 litres per horse-power hour in the large units of 100 horse-power.