OF ARTS AND SCIENCES. 



31 



Eustis, was in the printer's hands, and would probably be 

 finished in a few weeks. 



Mr. Charles Jackson, Jr., in reference to the discussion at 

 the last meeting on the Ericsson engine, said that the calcula- 

 tion showed that the efficient pressure was three fourths of a 

 pound per inch in the up stroke, and nothing in the down 

 stroke, or three eighths of a pound average. He did not be- 

 lieve this was enough to overcome the mere friction of the 

 engine, and thought there must be an error in the facts on 

 which the calculation that gave the result was based. He be- 

 lieved the air-engine, working at about 500°, and cutting off 

 at one half or two thirds of the stroke, would give the same 

 result as a non-condensing expansive steam-engine working 

 with fifteen pounds of steam. 



Steam at that pressure having about the same weight as 

 common air, but the latent heat of the steam being twice the 

 500° the air required, and the capacity of water for heat being 

 nearly four times that of air, the steam-engine required eight 

 times as much fuel as the air-engine did. Half the power of 

 the air-engine would be used in working the supply-pump, 

 leaving the air-engine still four times better than the steam- 

 engine even without any regenerator. The amount of heat- 

 ing surface required would be a great deal less with air than 

 with water. In hot-blast iron smelting-furnaces which he 

 has observed, there was five times as much air heated to 600° 

 as there was water boiled off for the engine, and yet the hot- 

 air ovens did not occupy one tenth of the room the boilers 

 required. 



Professor Treadwell remarked, that it was a matter of every 

 day's observation, that in regard to the heat-cond acting sur- 

 face of iron necessary with air and with water, the advantage 

 was very much in favor of water, even twenty to one. 



Professor Peirce reaffirmed his statements at the preceding 

 meeting, with a few modifications, not changing his general 

 results. He said that accurate measurements by the Coast 

 Survey showed that the actual speed of the Ericsson was only 



