PROCKEDINGS OF THE POLYTECHNIC ASSOCIATION. 501 



run for a year and a half. A heater having to be replaced in six 

 months the expense would be small, $25 for an engine. The 

 economy of air over steam due to the engine may not be much, 

 but the saving lies in the little attention required. An Ericsson 

 engine of one horse power will cost $700, while a steam engine 

 of the same power will cost only $200, but the cost of running 

 will be in favor of the Ericsson engine. Mr. Simpson told me 

 that the power which kept his engine running was the different 

 temperature above and below, which was due to the economizer. 

 Ericsson undertook to get 1500 horse power from his engines, and 

 succeeded in getting only 300. One of Wilcox's improvements is 

 that he uses the air hot. Mr. Sterling using a double acting 

 engine uses the air cold, while Wilcox uses two single acting 

 engines. Any one who may wish to see Mr. Wilcox's engine, 

 Mr. Simpson will show it to him in the basement of the Institute. 



Mr. Garvey stated that he had studied the mode of economiz- 

 ing caloric sixteen years ago, also, that he had obtained a patent 

 for that purpose, but that as it was connected with a series of 

 patents of the same nature he did not wish to say much on the 

 subject. 



Mr. Seely thought Mr. Garvey had given up the idea of using 

 the products of combustion too soon. 



Mr. Dibben said that he had made experiments on this subject 

 as far back as 1850. He felt disposed to question the actual 

 facts as presented by Mr. Babcock. He did not believe the Ster- 

 ling engine ever did what the gentleman said it did. Its only good 

 feature is that it requires very little attention. He had seen an 

 engine called a four horse power worked by a good engineer, 

 which only gave one and a half horse power. Ericsson's engine 

 works on the medium principle. It takes air and compresses it. 

 He tried compressing air at a high temperature and found that 

 he could not obtain as good an engine. Why not super-heat your 

 steam a little ? The fatal mistake against the caloric engine be- 

 gins with the deterioration of its machinery ; if it is not that, it 

 is the loss by friction. Steam engineers wont admit that they 

 lose more than two and a half pounds on the piston. I think the 

 loss will be twelve per cent. A two horse engine, with the ex- 

 ception of the fire, requires more attention, or as much at least, 

 as a forty horse power. 



Mr. Babcock stated that Mr. Ericsson was using air at the 

 initial pressure of 15 pounds. 



