MOTIVE POWER OF HEAT. 153 



(2) The cylinder is placed on the impermeable 

 stand K, so that its contents can neither gain nor 

 lose heat, and the piston is allowed to rise farther, 

 still performing work, till the temperature of the 

 air sinks to T. 



(3) The cylinder is placed on B, so that the air 

 is retained at the temperature T, and the piston is 

 pushed down till the air gives out to the body B 

 as much heat as it had taken in from A, during the 

 first operation. 



[Note of Nov. 5, 1881. To eliminate the assumption of 

 the materiality of heat, make Professor James Thomson's 

 correction here also ; as above in 15; or take Maxwell's 

 rearrangement of the cycle described in the foot-note to 

 15, p. 144.] 



(4) The cylinder is placed on K 9 so that no more 

 heat can be taken in or given out, and the piston 

 is pushed down to its primitive position. 



23. At the end of the fourth operation the tem- 

 perature must have reached its primitive value S, 

 in virtue of CARNOT'S axiom. 



24. Here, again, as in the former case, we observe 

 that work is performed by the piston during the 

 first two operations ; and during the third and 

 fourth work is spent upon it, but to a less amount, 

 since the pressure is on the whole less during the 

 third and fourth operations than during the first 



