SOME COMMON MECHANICAL MOTORS 



567 



a boiler, the steam soon develops great pressure and it is this 

 pressure which is utilized in the steam engine. 



677. The Newcomen Air-steam Engine. Although several 

 devices using steam had earlier been invented, the first really 

 useful engine was invented by an Englishman named New- 

 comen in 1705. The NEWCOMEN ENGINE, however, was an 

 air-steam engine; in fact, it was not steam pressure but air 

 pressure which actually did the work. For about three- 

 quarters of a century, or until about 1874, this air-steam 

 engine was the only type known and used. 



FIG. 354. The Newcomen air-steam engine, 1705. 



678. Principle of the Newcomen Engine. The principle 

 of this engine is shown in Fig. 354. The only use to which 

 this engine was put was pumping water. The pump-rod 

 and piston were balanced at the two ends of a beam, 7, 

 which was free to rotate on its axis, V. The piston moved up 



