Transportation on Land 



331 



nate forward strokes of the piston. The other three strokes 

 must be made with energy transmitted from the working stroke 

 through the flywheel, or from additional cylinders. Because 

 of the fact that one stroke only of four is the working stroke, 

 this type is called the four-cycle motor. The crank shaft makes 

 two complete cycles or revo- 

 lutions with energy applied 

 to one half cycle. In a 

 motor consisting of four cyl- 

 inders the working energy is 

 delivered upon the crank 

 shaft for each half revolu- 

 tion. With six, eight, or 

 twelve cylinders the im- 

 pulses are made more and 

 more nearly continuous. 



The two-cycle motor is much 

 lighter per horse power, with- 

 out poppet valves, but less 

 economic of fuel than the 

 four-cycle. Its principle of 

 operation is identical. The 

 chief difference is that every 

 alternate stroke is a working stroke, or energy is delivered at 

 each revolution of the crank shaft. 



147. Dependence upon other mechanisms. The develop- 

 ment of any machine seems generally to be dependent upon the 

 perfecting of something else. The gasoline motor depends for 

 its usefulness upon several other mechanisms. One of these is 

 the carburetor, in which gasoline or other hydrocarbon is 

 vaporized and mixed with the right proportion of air. Another 

 is the means by which the gas mixture in the cylinder is ignited. 

 This may be effected in the stationary engine by a torch ; but 

 it is to-day generally effected by an electric spark, the electric 

 current for which is derived from a battery of dry or other cells, 



FIG. 109. The operation of the one- 

 working-stroke-in-four or four cycle gas 

 engine. 



