_Merlin motor._—This motor is of the vertical type, and resembles the Capitaine motor in some respects. The oil is stored in a reservoir in the bed-plate; this receptacle is in communication with an air-pump driven by the motor, and also with an oil-pump. The pressure of air generated by the former forces the petroleum up into the oil-pump, which in its turn passes it drop by drop through a pulverizer, after which the spray of oil enters a vaporizer and becomes gasified. The vaporizer is heated by a special petroleum lamp. Ignition takes place when the explosive mixture comes into contact with the heated walls of the vaporizer, their temperature being always high enough to ensure ignition taking place. The consumption of fuel is regulated by a governor acting on the oil-pump, preventing it from supplying more oil than is absolutely necessary to keep up the speed. The governor regulates the exhaust valve as well, so that the speed, which is pretty high, is kept quite constant. _Hornsby-Akroyd oil engine_ (Figs. 35, 36).—This interesting machine was invented by Messrs. Akroyd, Stuart and Binney; it works with ordinary petroleum, and without the help of a carburator uses oils varying greatly in specific gravity. The reservoir of fuel is situated in the bed-plate. The ignition is automatic, and an electric spark is unnecessary, in fact, the whole engine is of the simplest construction, in order that there may be no inconvenience due to breakdowns. Referring to Fig. 35, L is a special petroleum lamp situated at the back of the cylinder A. When starting this lamp is supplied with air from a rotary fan turned by hand; in a short space of time, by the help of this stream of high-pressure air, the cartridge C becomes sufficiently heated to ensure the ignition of the explosive mixture. This cartridge C is provided on its interior with radiating ribs, which greatly increase the surface. During the back-stroke of the piston it becomes filled with compressed air from the cylinder, and towards the end of this stroke a quantity of petroleum, exactly sufficient for the explosion, is squirted into it. To do this a small pump is provided, which is actuated by a cam driving the oil into the cartridge and brought back by a spring. The centrifugal governor G acts on the admission valve from this pump. The sudden injection of the oil into the middle of the heated chamber completely vaporizes it, forming with the air already present the necessary explosive charge, which immediately ignites in contact with the heated walls. [Illustration: FIG. 35.—Hornsby-Akroyd Oil Engine (section).]