CATALOGUE OF THE MECHANICAL ENGINEERING COLLECTION, 25 



the remainder. At the end of the stroke a slide valve opens and the 

 steam passes the top of the larger cylinder where it acts expansively 

 on the piston, pushing it downward. The size of this second cylin- 

 der is such that the steam is able to exert as great a force for the 

 full stroke as it exerted in the first cylinder. At the same time that 

 the steam is passing to the second cylinder a portion is directed 

 through a suitable passage to the underside of the piston of the 

 first cylinder, so that while the piston of the second cylinder is mov- 



FIG. 5. ERICSSON STEAM ENGINE, 1849. 



ing downward by the expansive force of the steam the piston of the 

 first cylinder is balanced during its return motion by the pressure 

 of steam on both sides of it, thus making available the full pressure 

 of the steam on the piston of the larger cylinder. 



The lower end of the second cylinder beneath the piston is in 

 constant communication with the condenser. The upper end also 

 communicates with the condenser by means of a valve-controlled 

 passage which is opened when the piston reaches the end of its 

 stroke and permits the exhaust of steam from the cylinder so that 

 a vacuum is created above as well as below the piston, permitting 



