

.v//i' \\-Il.LIAM SIEMENS, F.R.S. 27 



the arrangement was substantially correct. He had followed its 

 progress with considerable interest, having himself been engaged, 

 for a number of years, in maturing an engine, in which steam 

 was employed in a highly heated state. 



The pistons being on their bottom stroke, the air from the 

 reservoirs was admitted below, urging the working piston upward. 

 Being heated, in its passage through the regenerator to 400 Fahr., 

 the volume of the air was increased in the proportion of 2 to 3, 

 and hence the reservoirs were deprived of only two-thirds the 

 contents of a working cylinder of compressed air. An additional 

 means of economising the supply of compressed air was, by shutting 

 off the admission, before the upward stroke was completed, allow- 

 ing it to act expansively. 



The pumping cylinder had, in the meantime, discharged its 

 contents of fresh atmospheric air into the reservoir, to make up 

 for the supply of the working cylinder, so that the pressure of 

 10 Ibs. per square inch was always maintained. The position of 

 the slide-valve being then reversed, the air from beneath the 

 working piston was free to escape into the atmosphere, but having 

 to pass through the regenerator, the free and sensible heat con- 

 tained in it was restored to the metallic wire gauze, in the inverse 

 order to that in which it was taken up, issuing finally at a little 

 above the temperature at which it entered from the reservoir. 



The descending stroke was effected by the mere weight of the 

 pistons. When completed, the position of the slide-valve was 

 again altered, and the air from the reservoir entered and forced 

 the piston upward. In its passage through the regenerator it 

 absorbed the heat which had been deposited there, and with an 

 additional supply from the fire, its volume was again doubled, in 

 filling the working cylinder. 



Supposing the action of the regenerator could be made perfect, 

 so that the air left the regenerator at exactly the same temperature 

 at which it had entered, it might seem at first sight, that the 

 engine would work without any expenditure of heat, beyond the 

 mere losses from radiation, &c. 



This view had indeed been maintained by Captain Ericsson and 

 others ; but upon consideration it became apparent, that there 

 was a theoretical consumption of heat, which might be very accu- 

 rately calculated, from the fact that the air entered the regenerator 



