248 Mr. W. J. M. Rankiue on the Mechanical Action of Heat. 



If we make c = 0'05, as in Mr. Wicksteed's engine, then tlie 

 fraction of the stroke to be performed at fnll pressure is 



J =0-323, 



being nearly the same as in experiment F. 



The mean resistance of the useful load per square foot of 

 piston is 



R=-P,-F=1713-6 1bs. 

 s ' 



The duty of one square foot of piston per hour, 



R/«= 8,225,300 foot-lbs. 



And one horse-power being 1,980,000 foot-lbs. per hour, the 

 real horse-power of the engine is 



4- 154- per square foot of piston. 



The duty of one pound of steam is 



RViS = 97,154 foot-lbs. 



To give an example of a special case, let the duty to be per- 

 formed be 198,000,000 foot-pounds per hour, being equal to 

 100 real horse-power, for 6000 hours per annum. This being 

 called E, we find from the above data that the area of piston 

 required is 



E 

 A =:5y- = 24-072 square feet. 



The consumption of steam per hour is 



W= ,-y^= 2038 lbs., 



which requires 2038 x 0-01 6 = 32-608 tons of boilers. 

 The expenditure of steam per annum is 



2038 X 6000 = 12,228,000 lbs. 



Hence we have the following estimate : — 



Cost of engine, 24-072 square feet of piston at £250 £6018-000 

 Cost of boilers, 32-608 tons at £27 880-416 



Total capital expended £6898-416 



Interest at 5 per cent, per annum £344-921 



Cost of fuel per annum, 12,228,000 lbs. of steam 1 ^^(. rnn 

 atQ-Old J ^"-^"-^uu 



Annual cost, for interest and fuel £854-421 



I wish it to be understood that the rates I have adopted in 

 the foregoing calciilations, for interest, cost of fuel, and cost of 



