THE CONQUEST OF NATURE 



about four explosions per minute are necessary, and 

 at full power 30 to 35 are made, so that about 28 ex- 

 plosions per minute are available for useful work under 

 the control of the governor." 



The definitive improvement in this gas engine was 

 introduced in 1876 by Dr. N. A. Otto, when he com- 

 pressed the explosive mixture in the working cylinder 

 before igniting it. This expedient so all-important 

 in its results had been suggested by William Barnett 

 in 1838, but at that time gas engines were not sufficiently 

 developed to make use of the idea. Now, however, Dr. 

 Otto demonstrated that by compressing the gas before 

 exploding it a much more diluted mixture can be fired, 

 and that this gives a quieter explosion, and a more sus- 

 tained pressure during the working stroke, while as the 

 engine runs at a high speed the fly-wheel action is gener- 

 ally sufficient to correct the fluctuations arising from 

 there being but one explosion for four strokes of the 

 piston. 



In this perfected engine, then, the method of opera- 

 tion is as follows: 



The piston is pulled forward with the application of 

 some outside force, which in practice is supplied by the 

 inertia of the fly-wheel, or in starting the engine by the 

 action of a crank with which every user of an automobile 

 is familiar. In being pulled forward, the piston draws 

 gas into the cylinder; as the piston returns, this gas is 

 compressed; the compressed gas, constituting an 

 explosive mixture, is then ignited by a piece of in- 

 candescent metal or by an electric spark ; the exploding 

 gas expands, pushing the piston forward, this being the 



