ON THE DISSIPATION OF ENERGY. 467 



into the engine from A, and causing heat to leave 

 the engine and pass into B, except by falls of 

 temperature from the temperature of A to the 

 highest effective temperature of the engine, and 

 from the lowest effective temperature in the engine 

 to the temperature of B, violate the condition of 

 perfect reversal and involve essentially irreversible 

 actions in the cycle of the engine, whether working 

 forwards or worked backwards. In the condensing 

 steam-engine, A is the burning coal of the furnace. 

 The highest effective temperature in the engine is 

 the temperature of the steam entering the cylinder 

 from the boiler. The lowest effective temperature 

 is the temperature of the " exhaust steam," that 

 is to say, of the steam coming out of the cylinder 

 in a single cylinder engine, or out of the lowest- 

 pressure cylinder in a triple or quadruple expan- 

 sion engine. In a condensing engine, B is the 

 condensing water: in the non-condensing engine 

 B is the air into which the waste steam is blown. 

 The superiority of the double, triple, and quadruple 

 expansion engines, over a single cylinder engine, 

 is due to their diminishing the ineffective 



H H 2 



