PROCEEDINGS OF THE POLYTECHNIC ASSOCUTION. 503 



use a certain quantity of air, alternately heated and cooled during 

 the stroke. In this class are the Stirling, Hazletine, and others. 



Fourth class includes those engines in which fresh air is taken 

 from the atmosphere at each stroke, expand in the engine, and 

 again discharged. In this class are the Ericsson ship engines, 

 his small engines, and the Wilcox. The fourth class only are 

 now in practical operation. 



The Chairman. — Why are not the other classes in practical 

 operation ? 



Mr. Babcock. — I know of no practical reason why the first and 

 third are not in use. The power lost in the condensation of the 

 air might be one reason why the first are not successful. Of all 

 the experiments that have been made three only have been in 

 successful operation — the Stirling, the Wilcox, and the Ericsson. 

 At the present time the Ericsson and the Wilcox are the only 

 ones I know of in daily operation, which are regularly used and 

 performing useful work. 



The Chairman. — How small a power is used ? 



Mr. Babcock. — It would be easier to tell how large a horse 

 power is used. The Wheeler & Wilson sewing machines require 

 about one-sixtieth part of a horse power. The smallest air 

 engine would drive several of these. The Ericsson engines are 

 running in some cases up to two-horse power. The Ericsson is 

 probably familiar to all present, several hundred of them being 

 in use in various parts of the country. The Wilcox engine 

 being more recent is probably familiar to few. One 18-inch is 

 driving a cracker bakery in Pawtucket, Rhode Island; another 

 smaller one has pumped the water for sprinkling the streets of 

 New London during the past season. A 12-inch engine is now 

 driving a large double medium printing press in Westerly, Rhode 

 Island. Another of the same size has been running in the base- 

 ment of this building pumping water for supplying the upper 

 stories. Mr. Cooper has consented to have it in operation this 

 evening, so that the association can witness its action after the 

 adjournment. 



The Chairman inquired what the cost for fuel per day would be. 



Mr. Babcock could not say. He was informed the engine at 

 Pawtucket used sixty pounds of coal during twelve hours. He 

 had prepared drawings and diagrams, showing the construction 

 and operation of this engine. This engine consists, principally, 

 in two upright cylinders. One is the working cylinder, and is 



