CHAPTER XXVI 

 THE STEAM ENGINE 



367. History of the Steam Engine. The steam engine 

 is one of the most important mechanical contrivances used 

 in trade and industry. With its discovery came the great 

 industrial development of the world. The first steam engine 

 was invented by James Watt in 1781. For a long time he 

 seems to have been practically the only engine-builder doing 

 business and his patents probably prevented others from 

 entering this field until about the beginning of the nineteenth 

 century. The steam engine of today is the controlling feature 

 of our industrial civilization. It furnishes the motive power 

 for all our factories, and without it scarcely one of the articles 

 we use in every-day life could be produced in sufficient quan- 

 tity to satisfy human needs. 



The steam pressure of the first engines was very low. Watt 

 ran his engines with a pressure of only seven or eight pounds 

 more than atmospheric pressure. The boiler pressures in 

 current use have steadily risen during the past century as 

 better materials and better workmanship made higher pres- 

 sures safe and advisable. Today 125 Ibs. per square inch is 

 a very common pressure for ordinary stationary engines; 

 150 to 175 Ibs. pressure is frequently met with in large power 

 plants; and in special cases 200 Ibs. pressure is employed. 

 This increased pressure, of course, enables the steam engine 

 to yield a much larger output of power per ton of total weight 

 and the limit is not yet reached. As it has been possible to 



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