20 EVIDENCE OF THE STEAM ENGINE. 



years converting heat into mechanical effect, but, so far from 

 suggesting such a conversion, it seemed to indicate the con- 

 trary. For not only did all experience show that the power 

 which was developed by the agency of heat was ultimately 

 annihilated in overcoming friction, but the condenser, by 

 which the heat was removed from the engine, was as 

 essential to its action as the furnace in which the heat was 

 produced. And although, as we now know, the heat 

 removed by the condenser is less than the heat received 

 from the boiler by the equivalent of the work done, this 

 latter quantity is so small compared with either of the 

 former that it can only be detected by most difficult tests, 

 which not only had not been made at that time but were 

 not made for 20 years after its existence was known as the 

 result of the discovery of the law of the conservation of 

 energy. 



Nor was this all the apparently contrary evidence afforded 

 by the steam engine. It rendered it evident that a principal 

 function of the heat received was that of imparting elas- 

 ticity to the steam, which elasticity having been expended 

 in doing work, apparently left the steam possessed of its 

 heat but useless. The amount of work that could be 

 obtained from a given amount of heat was thus found to 

 depend on the degree of elasticity or pressure at which the 

 water was boiled, and this depended on the temperature ;. 

 so that the steam engine, so far from showing that heat was 

 converted into work, showed that the amount of work pro- 

 duced by the agency of heat depended on the temperature. 

 This experience was generalized by Carnot, 1824, in his 

 well-known Theorem, which, though perfectly true and 

 consistent with the conversion of heat, was for some time, 

 an apparent stumbling block. 



