366 



THE PHILOSOPHY OF BIOLOGY 



THE CARNOT POSITIVE CYCLE 



We have therefore a substance which can be heated 

 by contact with a hot body, and which can then 

 expand, doing mechanical work by raising a piston, 

 and perhaps turning a flywheel, and on which work 

 is then done so that it returns to its original condition. 

 This is a cycle of operations. If we consider only the 

 changes which occur in the working substance we can 

 represent these changes by a diagram. 



i 



v 



V. 



Q s units of 

 N^ / heat enter 



Q, units V- 

 of heat lea.ve 



]ncrea-S i n g uotume 

 Fig. 32. 



Y 



First operation, (1^2). We suppose that the valve 

 is turned so that the non-conducting plug closes the 

 cylinder. The piston is in the position II (Fig. 31). 

 Heat cannot then enter or leave the gas. But the 

 latter already contains heat : it is at a temperature 

 of T 2 °, so that it can expand doing work. Let it 

 expand, forcing up the piston. During this operation 

 the pressure of the gas will fall from a point on the 

 vertical axis opposite 1 to a point opposite 2, and its 

 volume will increase from a point on the horizontal 

 axis beneath 1 to a point beneath 2. It will cool 

 because it has expanded, and no heat is allowed to 



