These conclusions, which tend to nothing less than to limit the reign of the steam engine, are confirmed on the one hand by an experiment carried on for the last two years in the Barataud flour mill of Marseilles, where a 50 h.p.  “Simplex” motor has been running day and night for several months without stopping, and consuming but about 500 grammes of English anthracite per effective horse hour, and, on another hand, by some personal experiments of Mr. Witz’s, to which we shall shortly advert, and whence there results a sensibly equivalent production for a motor of 100 indicated h.p., corresponding to a power of 75 effective horses.

Before establishing, with Mr. Witz, a comparison of the two systems in pressure, steam or gas, let us state in a few words in what the latter consists, the steam engine and the boiler that supplies it being so well known that no description is necessary.

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.