178 BULLETIN 173, U. S. NATIONAL MUSEUM 



This air then passes through a regenerator on the way to the furnace 

 where it is heated. The heated air returns to the cylinder and ex- 

 pands against the outer piston, producing motive power. After 

 expanding in the cylinder, the hot air is exhausted to the atmosphere 

 through the regenerator. The regenerator is a vessel containing a 

 nest of metal tubes so arranged that the cold air going to the heater 

 after compression passes through the tubes and is warmed by the 

 transfer of heat from the hot exhaust air, which passes through the 

 vessel around the tubes to the atmosphere. The two cylinders produce 

 two power impulses per revolution. 



ERICSSON HOT-AIR ENGINE, 1858 



U.S.N.M. no. 308660 ; original patent model ; transferred from the United States 

 Patent Office; not illustrated. 



This model was submitted with the application for Patent no. 

 22281, issued to John Ericsson, December 14, 1858. 



This is one of the earliest hot-air engines in which cold air is drawn 

 into, compressed, heated, and expanded within the same cylinder. 

 This and the Ericsson engine of 1855 were the basis of design for 

 most of the later commercial hot-air engines introduced in this 

 country. 



The model is of an engine having a very large horizontal cylinder, 

 one end of which is occupied by the grate and flue of a furnace. In 

 the cylinder bej^ond the furnace are two pistons, one of which is a 

 transfer or pump piston, the other the working piston. The two 

 pistons complete their outward stroke (away from the furnace) at 

 about the same time, but the transfer piston, which is nearer the 

 furnace, moves inward faster than the work piston and draws in a 

 supply of cold air through a self-acting valve in the working piston. 

 Upon the outward stroke the transfer piston closes up on the work 

 piston and compresses the charge between the two and transfers it 

 through valves to the space around the heater. The pressure pro- 

 duced by the increase of temperature during this transfer propels 

 the working piston through the outward stroke and supplies the 

 motive force. The return stroke is effected by means of a flywheel. 



ERICSSON HOT-AIR ENGINE, 1860 



U. S. N. M. no. 300822; original patent model; transferred from the United 

 States Patent Office; not illustrated. 



This model was submitted with the application for the patent issued 

 to John Ericsson, October 9, 1860, no. 30306. 



This engine employs two "equilibrium" pistons in connection with 

 two cylinders and a work piston to prevent diminution of the working 

 pressure during the stroke of the work piston. 



