The Simplex was invented in 1884 by MM. Edouard Delamare-Deboutteville and Léon Malandin. In appearance it is of the usual four-cycle type. A lateral shaft transmits the rotation of the crank-shaft to a small crank which actuates the sliding valve. This sliding valve forms one of the principal features of the engine, and consists of a sliding iron plate pierced with two holes, one oblique regulating the ignition, and the other straight forming the admission valve. The piston having completed its first forward stroke comes back to compress the explosive mixture, and the sliding valve having advanced puts it in communication with a chamber containing two metallic points, between which a continuous stream of electric sparks is made to flow. After the explosion this cavity and the passage leading to it are filled with burnt gas, which must be driven out to prevent a miss-fire at the next stroke. This is effected by a small purging hole, through which they are driven by a fresh charge entering the cylinder. In earlier patterns of this engine an ingenious air governor was used, but it has now been replaced by a fresh arrangement of a different pattern. This governor (Figs. 46 and 47) consists of a double pendulum, which takes up a vertical position because of the lower ball, seen in the illustration, being the heaviest. The whole pendulum is pivoted on a fixed bearing. The variation in the speed is obtained by a weighted knife blade acting on the gas-valve. The sliding valve is provided with a knife blade square at one end and pointed at the other, which catches in a notch on the pendulum, and is held by it in position so that the square end hits the end of the gas-valve and admits gas. If, however, the speed of the engine be too great the sliding valve carries its knife blade forward too soon and it does not catch in the notch, with the result that no gas is admitted as the square end is too low. The speed of the engine, therefore, tends to remain adjusted to the rate of vibration of the pendulum, which is a fixed quantity. A self-starting arrangement is provided by stopping the engine half-way back along the compression stroke, so that it is only necessary to pass an electric spark across for an explosion to occur and give it the necessary starting impetus. [Illustration: FIG. 45.—Simplex Gas Engine (Delamare-Deboutteville).] [Illustration: FIGS. 46, 47.—Governor of the Simplex Engine.] MM. Delamare-Deboutteville and Malandin were the first to construct units of very great power. At the Havre Exhibition in 1889 they exhibited a Simplex engine using Dowson gas, and in 1889 they exhibited at the Paris Exhibition a 100 horse-power single-cylinder motor.