PROCEEDINGS OP THE POLYTECHNIC ASSOCIATION. 501 



on to explain the composition of coal oils, and argued therefrom 

 that .by burning them within the engine a great amount of saving 

 in fuel might be realized. 



Mr. Dibben thought that the practical air engineers might have 

 shown better proofs of economy. 



The Chairman inquired if the great advantage claimed for the 

 air engine was not due to its safety. 



Mr. Dibben did not think so. He failed to understand the dif- 

 ference in action between Mr. Wilcox's engine and the engines of 

 the caloric ship Ericsson. 



T. D. Stetson explained one of the great points in which the 

 Wilcox engine differed from those in the Ericsson. In that ship 

 the supply of air was forced in by pumping it through large force 

 pumps against the pressure which obtained within. In the Wil- 

 cox engine there is a period while the working piston is descend- 

 ing, when the whole interior of the engine is in free communica- 

 tion with the external atmosphere. During that period the 

 changing piston descends and inhales a full charge of cold air 

 above it, precisely as the air enters an accordeon when it is ex- 

 panded. That is the way the air is received. It occasions no 

 resistance, because there is no pressure against the under side of 

 the changing piston. The moment it is thus inhaled the induc- 

 tion port closes, and the dense-cold air is subsequently transferred 

 by the rising of the changing piston into the hot part of the 

 engine, when, by its expansion the working piston is driven up 

 and power is developed. The rising of the changing piston occa- 

 sions no resistance, because, while it rises the same pressure ob- 

 tains on its under as on its upper side, whatever that may be. 

 The two sides are in free communication through the openings in 

 the economizer. As the changing piston rises and compels the 

 air above it to pass down through the economizer into the hot 

 part of the engine, the pressure rises in consequence of the heat 

 received by the air ; but it is felt equally on the upper and under 

 side of the changing piston, and is only sensible on the working- 

 piston, which latter receives the pl-essure on the under side. The 

 upper end of the working cylinder is always open to the atmos- 

 phere. 



The question of most interest, Mr. Stetson believed, was not 

 the difference between this and the variety of air engines, but 

 whether either or any had practically solved the problem pre- 

 sented, and was a really successful and important machine. He 



