162 THOMSON ON CARNOT'S 



it is clear that in either case the operations may 

 be performed in the reverse order, with every 

 thermal and mechanical effect reversed. Thus, in 

 the steam-engine, we may commence by placing 

 the cylinder on the impermeable stand, allow the 

 piston to rise, performing work, to the position 

 E 3 F S ; we may then place it on the body B, and 

 allow it to rise, performing work, till it reaches 

 E^F^'y after that the cylinder may be placed again 

 on the impermeable stand, and the piston may be 

 pushed down to E^F^ ; and, lastly, the cylinder 

 being removed to the body A, the piston may be 

 pushed down to its primitive position. In this 

 inverse cycle of operations a certain amount of 

 work has been spent, precisely equal, as we readily 

 see, to the amount of mechanical effect gained in 

 the direct cycle described above ; and heat has been 

 abstracted from B, and deposited in the body A, 

 at a higher temperature, to an amount precisely 

 equal to that which in the direct style was let 

 down from A to B. Hence it is impossible to 

 have an engine which will derive more mechanical 

 effect from the same thermal agency than is ob- 

 tained by the arrangement described above; since, 

 if there could be such an engine, it might be em- 

 ployed to perform, as a part of its whole work, the 

 inverse cycle of operations, upon an engine of the 



