_Baldwin gas engine._—The cycle of this engine is somewhat similar to that of the Benz motor, one side of the piston being used for expansion and the other side for compression. Part of the bed-plate casting is arranged so as to form a reservoir for the compressed gases. The coal gas is also admitted into this vessel, so that it contains an explosive mixture. As the vessel is only made of cast-iron this arrangement is rather dangerous. There are three valves, the admission valve being regulated by the governor. The power developed is, therefore, always kept proportional to the demand, and the constancy of speed is sufficient to warrant the use of these engines for running dynamos for electric light. The ignition is by an electric spark, and is generally obtained from some extra apparatus, such as accumulators or batteries, and an induction coil. The engine is constructed by Messrs. Otis Bros. of New York.
_De Ravel motors._—The first motor constructed by M. de Ravel was exhibited in Paris in 1878, and was of the oscillating cylinder type, with a variable centre of gravity. The explosion drove up a heavy piston whose rod was directly connected to the crank-pin. The revolution of the crank-pin caused the whole cylinder to move in the same manner as that of the early oscillating steam engines. This movement was used as a means of opening and closing the ports. The efficiency of the engine was low, using some 600 to 700 litres of gas per horse-power hour; and besides the motor had, owing to faulty mechanism, the unhappy knack of suddenly stopping dead. These defects caused M. de Ravel to abandon this type and to bring out a second motor in 1885, performing one cycle per revolution. This new motor only had one cylinder, whose rear half acted as a compression chamber during the backward stroke of the piston, whilst the explosion took place in the front end of the cylinder. The consumption of gas was slightly more than an Otto engine, and the motor ran exceedingly silently and evenly, but this advantage was not of much service in the struggle against the all-conquering Otto motor.
_Midland motor (Taylor)._—Constructed in Nottingham, this engine is of the horizontal double-cylinder type. One cylinder compresses the explosive mixture and passes it on to the other, where it is ignited and does work. The cranks connected to the two pistons are placed 65° apart, and a complete cycle in the cylinders is performed every revolution. The makers of this engine claim a consumption of only 600 litres of gas per horse-power hour.