194 THOMSON ON CARNOT'S 



place we remark, that out of the entire "fall" 

 from the temperature of the coals to that of the 

 atmosphere it is only part that from the tem- 

 perature of the boiler to the temperature of the 

 condenser that is made available; while the very 

 great fall from the temperature of the burning 

 coals to that of the boiler, and the comparatively 

 small fall from the temperature of the condenser 

 to that of the atmosphere, are entirely lost as 

 far as regards the mechanical effect which it is 

 desired to obtain. We infer from this, that the 

 temperature of the boiler ought to be kept as 

 high as, according to the strength, is consistent 

 with safety, while that of the condenser ought 

 to be kept as nearly down at the atmospheric 

 temperature as possible. To take the entire ben- 

 efit of the actual fall, Carnot showed that the 

 " principle of expansion" must be pushed to the 

 utmost.* 



* From this point of view, we see very clearly how im- 

 perfect is the steam-engine, even after all Watt's improve- 

 ments. For to " push the principle of expansion to the 

 utmost, " we must allow the steam, before leaving the cyl- 

 inder, to expand until its pressure is the same as that of 

 the vapor in the condenser. According to "Watt's law/ 5 

 its temperature would then be the same as (actually a little 

 above, as Regnault has shown) that of the condenser, and 



