from 332 FORMS OF ENERGY occurring at the proper time and for the right duration of time. schedule on wliich \ Fig. 124. The the engine runs to do this is called the four-stroke A stroke is one movement of the piston cycle. from one end of the cylinder to the other; top to bottom, or from bottom to top. I ^5^H-—If— ^"*^'
THE INTERNAL-COMBUSTION ENGINE 333 cannon the movable part is the ball which is forced out of the mouth of the cannon by the burning of the powder.