204 MR W. J. M. RANKINE ON EXPANSIVE STEAM-ENGINES. 
The expenditure of steam per annum is 
2088 x 6000 =12,228,000 lb. 
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 five per cent. per annum, : : £344-921 
Cost of fuel per annum, 12,228,000 Ib. of steam ai 0-01d., 509°500 
Annual cost for interest and fuel, £854-421 
I wish it to be understood that the rates I have adopted in the foregoing 
calculations, for interest, cost of fuel, and cost of construction, are not intended 
as estimates of their average amount, nor of their amount in any particular case, 
but are merely assumed in order to illustrate, by a numerical example, the rules 
laid down in the preceding article. It is of course the business of the engineer 
to ascertain those data with reference to the special situation and circumstances 
of the proposed work; and having done so, the method explained in this paper 
will enable him to determine the dimensions and ratio of expansion which ought 
to be adopted for the engine, in order that it may effect its duty with the greatest 
possible economy. : 

