_Niel motor._—As will be seen from Fig. 11, the valves are actuated by cams rotating on a supplementary shaft placed parallel to the cylinder. A pair of toothed wheels transmit the rotation of the crank to this valve-shaft, and it is arranged so as to give one rotation to every two of the crank. The cycle of operations is somewhat similar to the Otto cycle; gas is only admitted to the cylinder for two-thirds of the forward stroke, so that the compression on the back stroke is somewhat lessened. It is doubtful whether there is much advantage in this method, but the Niel motors have had a large sale, which is a sufficient proof of their good qualities. [Illustration: FIG. 11.—Niel Gas Engine (elevation and sectional plan).] _Lombart, Martini_ (Fig. 12), _Adam, Le Parisien, and Le Kientzy motors._—All these motors, each of which is constructed by a different maker, are based in principle on the Otto engine, and except for slight modifications of the working parts, they do not call for any particular notice. The small amount of space at our disposal only admits of our mentioning them. [Illustration: FIG. 12.—Martini Motor.] _Lablin motor_ (Fig. 13).—M. Lablin of Nantes set himself to produce a motor which should correspond with the Brotherood and Westinghouse steam engine, that is to say, a motor developing the maximum of power for the minimum of space and weight. This might be termed the dynamic density of the motor, which M. Lablin sought to increase. He has succeeded in constructing gas motors of ½ horse-power weighing about 90 lbs., and of 8 horse-power weighing 7 cwt. Unfortunately they consume a rather large quantity of fuel—about 1000 litres of coal gas, or 500 grammes of gasoline per horse-power hour. There are three cylinders grouped at equal distances round the same shaft, and all attached to one single crank. By this arrangement a more constant torque or twisting movement on the shaft is obtained, and consequently the weight of the fly-wheel can be considerably reduced. Three explosions are produced during every revolution, that is to say, each cylinder performs a complete cycle of operations during every revolution, a fact which accounts for the low efficiency. Ignition is obtained by a platinum tube heated to incandescence when using coal gas, and by an electric spark when carburetted air is used. The governor is centrifugal, and controls the admission of gas. [Illustration: FIG. 13.—Lablin Three-cylinder Motor.] _Crossley Bros. gas engine_ (Figs. 14, 15).—This engine is from the cycle point of view purely and simply an Otto gas engine. A light shaft runs parallel to the cylinder, being driven by a worm-gear of the crank-shaft. On it are situated the cams which force open the four spring-valves, controlling respectively the admission of air gas and the ignition and exhaust. [Illustration: FIG. 14.—Crossley Gas Engine (X type).] [Illustration: FIG. 15.—Crossley Gas Engine.]