_Trusty oil engine._—This motor was devised by Mr. Knight, and is constructed by Messrs. Weyman and Hitchcock. There is no spray-maker, the liquid oil being directly converted into vapour. The vaporizer is heated by the waste gas from the cylinder, and the oil falls drop by drop on to the hot metal walls and becomes vaporized. The engine is of the ordinary four-cycle type, the most noticeable feature being the governing arrangement; a governor of the inertia pattern regulating the admission valve and the oil-pump. If the speed becomes too great the action of the governor on the valves ceases, and oil is no longer supplied to the vaporizer from the pump and the admission valve remains closed. Ignition is obtained by a red-hot tube heated by an oil lamp; a layer of asbestos on the outside prevents the tube from cooling, and keeps the tube at a high temperature. It takes twenty minutes before the vaporizer becomes sufficiently heated to enable a start to be made, and the cylinder is very liable to become fouled by tarry products from the oil. These serious disadvantages are scarcely neutralized by the variety and small quantity of oils which the engine will burn. An engine of this type with two cylinders consumed in certain trials only half-a-pint of oil, which speaks for itself. _Griffin oil engine_ (Figs. 41, 42).—Yet another Otto cycle engine provided with a pump reservoir and vaporizer. The latter is hidden in the bed-plate, and is heated by the gases from the exhaust. The pump is driven by an eccentric on the main shaft, and compresses the air to about 8 lbs. on the square inch in a reservoir also situated in the bed-plate. The compressed air passes from this chamber into a needle pulverizer, along with a quantity of oil which it has gathered in a small ante-chamber. This pulverized oil arrives in the vaporizer at the same moment as the air for the explosive mixture. A portion of the vaporized oil and air is used for the lamp, which red-heats the ignition tube. At starting, a small quantity of air is compressed in a hand pump, and in ten minutes the vaporizer is hot enough to gasify the oil. The Griffin engine is very economical, and only uses about a pint of petroleum per horse-power hour. [Illustration: FIGS. 41, 42.—Griffin Oil Engine.]