28 THE SCIENTIFIC PAPERS OF 



in a compressed state and returned through it, after expansion to 

 atmospheric pressure had taken place. This expansion was accom- 

 panied by a diminution of temperature of some 70 or 80 Fahr., 

 which became latent and had to be replaced by the fire. 



The theoretical consumption of a perfect caloric engine, 

 amounted to only one-fourteenth part of the theoretical consump- 

 tion of a Boulton and Watt condensing engine. The practical 

 arrangement of Ericsson's engine, however, rendered the attain- 

 ment of such a result impossible, for the following reasons : 



Fully two-thirds of the power of the engine must be expended 

 in working the air pump independent of the resisting pressure of 

 the atmosphere, which was equal to three-fifths of the total 

 working pressure. The consequence was, that to produce the 

 effective displacement of the piston, for one single volume of air at 

 its full pressure, from 7 to 8 volumes had to be cooled and heated 

 alternately. 



The working piston of Ericsson's engine had, moreover, to 

 work air-tight in a heated cylinder, which Mr. Siemens had 

 practically found to be a matter of great difficulty. The lubri- 

 cating material would become rapidly carbonized, and would fill 

 up the meshes of the regenerator. 



The extent of heating surface provided, also appeared to be too 

 small for the quantity of heat required to be transmitted. It was 

 understood, from good authority, that the present working cylinders 

 of 14 feet diameter, were now being replaced by others of 16 feet, 

 which was the greatest size the breadth of beam of the vessel would 

 permit. 



Mr. Armstrong's views required correction, owing to the 

 evolution of heat in compressing the air in the pumps which 

 would produce expansion and increased resistance. A corre- 

 sponding cooling effect was, moreover, produced through its 

 expansion in the working cylinder, which would diminish the 

 power shown by him to be obtainable. These objections would, 

 he expected, mar the anticipated results of this interesting experi- 

 ment. 



