36 BULLETIN 119, U. S. NATIONAL MUSEUM. 



from the heater. The outward movement of the pistons of cylinder 

 No. 2 causes the pistons of cylinder No. 1 to start their instroke. The 

 " working " piston moves slowly but the " supplj^ " piston, through 

 its mechanical connections to the crank shaft, moves rapidly and in 

 so doing draws cold air after it through an open valve in the " work- 

 ing" piston, and drives expanded hot air ahead of it through the 

 exhaust valve and into the " regenerator." When it reaches the end 

 of its stroke the exhaust valve closes and the " working " piston con- 

 tinuing inward compresses the cold air ahead of it. 



As the " working " piston approaches the " supply " piston and 

 about reaches the end of its stroke an intake valve opens, admitting 

 hot air from the heater. The expansion of this air in the cylinder 

 head acting against the " supply " piston starts it on its outstroke to 

 meet the "working" piston, thus assisting in the further compres- 

 sion of the cold air for an instant, after which the opening of a valve 

 allows the compressed air to pass out of the cylinder and into the 

 " regenerator " tubes. At the same time a valve opens in the " supply " 

 piston, admitting hot air to the area between the two pistons, whose 

 expansive force moves the " working " piston outward — the " supply " 

 piston following by the action of the levers to which it is attached. 



Cat. No. 251,279 U.S.N.M. 



Model of John Ericsson Air Engine. IT. S. Patent, No. 266052, March 30, 

 1880. Transferred from United States Patent Office. 



The cylinder of the engine is open at the upper end and contains 

 two pistons designated as the " working " piston and the " exchange " 

 piston. The lower part of the cylinder is closed and is intended to be 

 heated by any suitable type of burner or fireplace. The " working " 

 piston, which is in the upper part of the cylinder, is packed so as to 

 work air-tight. The "exchange" piston, which is of considerable 

 length in an axial direction, is so much smaller than the cylinder 

 that an annular space for the free passage of air is left between its 

 exterior and the interior wall of the cylinder. This piston is hollow, 

 the upper half being filled with cotton or other fibrous material, 

 which in turn is separated from the lower end of the piston by a 

 layer of charcoal or other nonconducting material so as to protect 

 the cotton from the heat to which the bottom part of the piston is 

 subjected. The "working" piston is connected by a hollow rod and 

 short side links with a beam above the cylinder, the connection being 

 at a short distance from the fixed center of oscillation of the beam. 



The beam is connected at a much greater distance from the other 

 side of the center by a connecting rod with a short crank on the main 

 shaft of the engine. This short crank is also connected by a rod with 

 one arm of a "bell" crank lever which has a fixed center of oscilla- 



