MOTIVE PO WEE OF HEAT. 197 



pounds of work that & per feet engine with its boiler 

 at 140 and its condenser at 30 would produce for 

 each unit of heat transmitted. Hence the Fowey 

 Consols engine, during the experiments reported 

 on, performed f JJ of its theoretical duty, or 57J- 

 per cent. 



(2) The best duty on record, as performed by an 

 engine at work (not for merely experimental pur- 

 poses), is that of Taylor's engine, at the United 

 Mines, which in 1840 worked regularly for sev- 

 eral months at the rate of 98,000,000 foot-pounds 

 for each bushel of coals burned. This is ^/j, or 

 .784 of the experimental duty reported in the case 

 of the Fowey Consols engine. Hence the best 

 useful work on record is at the rate of 198.3 foot- 

 pounds for each unit of heat transmitted, and is 

 -Y^ 3 , or 45 per cent of the theoretical duty, on 

 the supposition that the boiler is at 140 and the 

 condenser at 30. 



(3) French engineers contract (in Lille, in 1847, 

 for example) to make engines for mill-power which 

 will produce 30,000 metre-pounds or 98,427 foot- 

 pounds of work for each pound of steam used. If 



corresponding to the fall from 100 to 0, given in Table 

 II. Hence, tlie fall from 140 to 30 of the scale of the 

 air-thermometer is equivalent, with reference to motive 

 power, to the fall from 100 to 0. 



