114 MOTIVE POWER OF HEAT. 



caloric is 100 or 1000 when the difference of 

 temperature between the bodies A and B is 100 

 or 1000. 



In a steam-engine which works under a pressure 

 of six atmospheres the temperature of the boiler is 

 160. This is the body A. It is kept, by contact 

 with the furnace, at the constant temperature of 

 160, and continually furnishes the heat necessary 

 for the formation of steam. The condenser is the 

 body B. By means of a current of cold water it 

 is kept at a nearly constant temperature of 40. It 

 absorbs continually the caloric brought from the 

 body A by the steam. The difference of tempera- 

 ture between these two bodies is 160 - 40, or 120. 

 Hence we say that the fall of caloric is here 120. 



Coal being capable of producing, by its combus- 

 tion, a temperature higher than 1000, and the 

 cold water, which is generally used in our climate, 

 being at about 10, we can easily procure a fall of 

 caloric of 1000, and of this only 120 are utilized 

 by steam-engines. Even these 120 are not wholly 

 utilized. There is always considerable loss due 

 to useless re-establishments of equilibrium in the 

 caloric. 



It is easy to see the advantages possessed by 

 high-pressure machines over those of lower pres- 

 sure. This superiority lies essentially in the power 



