CATALOGUE OF THE MECHANICAL ENGINEERING COLLECTION. 37 



tion The other arm is connected by arched side rods on opposite sides 

 of the cylinder by an arched yoke. The piston rod of the " exchange " 

 piston passes through the arched rods before mentioned. 



The movement of the pistons is as follows: During the upward 

 movement of the " exchange " piston the cool air from the upper part 

 of the cylinder will be transferred by this piston through the annular 

 space between it and the cylinder wall to the bottom and lower part 

 of the cylinder. The air so transferred, becoming heated, expands 



FIG. 13. ERICSSON AIR ENGINE, 1880. 



in the lower part of the cylinder, and its expansion causes it to force 

 the "working" piston upward— the movement of the exchange ^^ 

 piston being about three-fourths completed before the " working ^^ 

 piston commences its upward movement-and when the working 

 piston has nearly completed the working stroke the " exchange pis- 

 ton begins to descend and forces the hot air back from the lower to 

 the upper or cooler part of the cylinder, completing its stroke by 

 the time the " working " piston has made about one-third of its return 

 stroke The " working " piston is actuated by the air which is con- 

 fined in the cylinder and which is caused to be heated and co^ed 

 alternately by the peculiar motion of the "exchange" piston. Ihe 



