INTERNAL COMBUSTION ENGINES. An internal combustion engine is one in which energy is directly translated into mechanical power by causing an explosion to take place be hind a piston. Professor Andrade has epigrammatically described this as "putting the furnace into the cylinder." An explosion is an event of so sudden and violent a character that it might well seem impossible for man effectively to bring under his complete control so destructive and apparently unruly an agent; yet many billions of perfectly regulated gaseous ex plosions now minister daily to our needs in internal combustion engines of all kinds throughout the world.
Genghis Khan, in China, is recorded as having first used gun powder in cannon about A.D. 1234 and King Edward III. in west ern Europe about A.D. 13 2 7 ; the earliest proposal to utilize explo sions (of gunpowder) to obtain continuous motive power was probably made by Christian Huygens in 168o, and Papin and the Abbe Hautefeuille later endeavoured to develop his proposal, but without success; it has now long been agreed that gunpowder is an entirely unsuitable substance for employment in any internal combustion engine.
R. Street, in 1794, proposed an engine driven by a flame-ignited explosive mixture of vapourized spirits of turpentine and air, and Sir Dugald Clerk regards this as the first real gas engine described in Britain. In 182o W. Cecil at Cambridge described to the Cam bridge Philosophical Society his engine operated by the explosions of a hydrogen-air mixture used to create a partial vacuum be low a piston, the atmospheric pressure then producing the working stroke, much as in the earliest steam engines ; he describes such an engine and states that at 6o revolutions per minute the explosions were perfectly regular ; this is considered to have been the first actually working gas engine in the world.
With this brief introduction, we pass to the consideration of the various forms in which the internal combustion engine is used. These may be divided as follows :