44 THE SCIENTIFIC PAPERS OF 



Therefore 



The total heat supplied to the air = 77 + 25 = 102 Fahr. 

 The sensible heat carried off = 136 60 = 76 



There remains the heat absorbed by being con- 

 verted into effect 26 Fahr. 



26 

 Or the Ericsson engine produces the effect of y^~- 770= 196 Ibs. 



lifted 1 foot high, for every (water) unit of heat expended. 



This proves, that the Ericsson engine realises, theoretically, 

 nearly one-fourth the effect of a perfect engine, and would possess 

 a considerable advantage over any of those before considered, but 

 for the following serious imperfections : 



1st. Its gross working pressure has been demonstrated to be 

 3 Ibs. per square inch, but the engine being single-acting, the true 

 average pressure is only \\ Ib. per inch, and supposing the engine 

 will move with \ Ib. pressure per inch upon the working piston, 

 its mere friction will absorb one-third of the whole power. 



2nd. The working piston has to move air-tight in a heated 

 cylinder, which by former attempts has been proved to be 

 attended with great practical difficulties. These are no doubt 

 reduced, by the air being heated in a smaller degree than had been 

 'attempted before ; but the temperature still remains sufficient to 

 carbonise the lubricating material, and by affecting the shape of 

 the cylinder, to cause leakage. 



3rd. The available heating surface of the engine is confined to 

 the bottom surface of the working cylinder, and to the passage 

 leading to the regenerator. 



Taking into account the intermittent action and slow heat- 

 absorbing power of the air, the heating surface of an air-engine 

 should, in the opinion of the author, not be less than 6 superficial 

 feet for 1 Ib. of coal consumed per hour, or about seven times 

 larger than in the engines of the " Ericsson." 



4th. The weight, bulk, and first cost of Ericsson's engine are 

 inversely proportionate to its low working pressure and slow 

 speed. 



5th. Incidental losses of heat, by radiation from the large 

 exposed surface of the heated cylinder, necessitate a very con- 

 siderable addition to the expenditure of fuel. 



