operations requiring powers of from 1 to 50 horse-power, and large vertical engines have been constructed for marine purposes up to 100 horse-power, and have always given complete satisfaction to persons using them. A few minutes are required for the apparatus to become sufficiently heated to be able to start, after which the consumption of fuel is about 380 to 500 grammes of petroleum per horse-power hour, or about ·85 lb. The six-horse size weighs about 1½ tons. Ignition can be had either electric or by a flame, according to the wishes of the purchaser. _Campbell gas engine._—Fig. 29 shows a very compact engine, built by the Campbell Gas Engine Co. There are only three valves; the admission valve is regulated by a centrifugal governor. The petroleum is gasified in a vaporizer heated by a lamp. The speed is very constant and the motor easily started. [Illustration: FIG. 29.—Campbell Oil Engine.] _Grob motor._—This engine is constructed in Leipzig and uses the Otto cycle, and, like the motors already described, works well with ordinary petroleum. The arrangement (Fig. 30) is vertical; the cylinder and valve gear are supported on a hollow cast-iron column, which in turn is bolted to a circular bed-plate. The shaft has on one side a fly-wheel and on the other a pulley. The working valve parts are all situated on the outside so as to be easily got at. The oil-pump marked in the figure drives, the petroleum into a vaporizer, where it is broken up into very minute drops. This oil spray becomes mixed with air, and passes through a vaporizing tube heated by a flame. In the state of vapour the explosive mixture passes into the cylinder, where it is ignited at the right moment by a red-hot tube. In consequence of the compression during a quarter of the cycle, the combustion is very rapid, the power of these engines being very great for their size. Ignition, and therefore the explosion, only takes place when the speed falls below the normal. This regulation is obtained by a pendulum governor, and ensures a very constant speed. The cylinder walls are warm enough to make sure of ignition happening. [Illustration: FIG. 30.—Section of a Grob Motor.]