The Dowson gas generator does not differ essentially from the numerous generators devised during recent years for the manufacture of gaseous combustibles, the use of which is so often convenient. The motor that it supplies is the most powerful single cylinder one that has hitherto been constructed. It is of 100 indicated h.p., and its normal angular velocity is 100 revolutions per minute. On trial it has yielded 112 indicated h.p., and 76.8 effective h.p., corresponding to an organic rendering of 69 per cent. This motor, elaborated by Messrs. Delamare-Bouteville & Malandin, of Rouen, operates by compression and in four periods, according to the Beau de Rochas cycle. We give the aspect of it in Fig. 3. In the first period the mixture of air and gas is sucked in, in the second it is compressed, in the third it is ignited, and in the fourth the products of combustion are expelled. [Illustration: FIG. 2.--SIMPLEX MOTOR, DOWSON GENERATOR OF 100 INDICATED H.P.--ELEVATION AND PLAN. A, cylinder; B, gas conduit; C, rubber pockets; D. gasometer; E, purifier; F, scrubber; G, hydraulic main; H, cooling pipe; I steam injector; K, steam boiler and superheater; L, gas generator; M, charger; N, discharge of the motor.] Ignition is effected electrically by a series of sparks playing between two platinum points in the slide valve, and this permits of regulating the instant of ignition through the edges of the orifices. The angular velocity is regulated by a Watt's governor, which secures an isochronism of the motion independently of the charge. The setting in motion of so powerful an engine is effected very easily by means of an arrangement that permits of introducing into the cylinder, while the piston is in the center of the stroke, a mixture of air and gas whose pressure is sufficient at the arrival to expel the inert products. After this the ignition takes place, and the explosion is sufficient to set the motor in motion. The trials made by Mr. Witz with the motor represented in Fig. 3 gave the following results, deduced from an experiment of 68 hours. The figures relate to one effective horse power, measured with the brake upon the shaft of the motor. Consumption of anthracite. 516 grammes. " " coke. 96 " Consumption of water for the injection of steam. 0.487 liters. Consumption of water for cooling the cylinder. 50.0 " Consumption of oil for lubricating the cylinder. 3.74 grammes. Consumption of grease. 0.45 " Consumption of gas reduced to 0° C. and to 760 mm. 2,370 liters.