THE STEAAE ENGINE. 



the force of the steam may be accurately weighed. Ilia 

 a valve opening downward, to prevent the boiler being 

 crushed by atmospheric pressure, by allowing the air to 

 pass in whenever the steam happens to decline. Two 



Fis. 293. 



Boiler of iStcam-eiigine. 



tubes, with stop-cocks, c and d, one just below the water- 

 level, and the other just above it, serve to show, by open- 

 ing the cocks, whether the water is too high or too low. 



The working part of the engine is represented in the 

 figure on the following page (fig. 291). The steam enters 

 by the pipe, 5, from the boiler on the other side of the 

 brick wall, as shown in fig. 290. The steam passes through 

 what is called a four-icay-coch^ a^ first into the lower, then 

 into tlie upper end of the cylinder, C, as the piston, P^ 

 moves up and down; this is regulated by the levers, y y. 

 The piston-rod, E^ is attached to the working-beam, B 

 F, turning on the centre, A. The rod, F i?, turns the fly- 

 wheel, M IT, ciTid drives the mill, steam-boat, or machinery 

 to be set in motion. 



