Page:The Atlantic Monthly Volume 2.djvu/658

 50 Springfield to Pittsfield,          52                83 Pittsfield to Albany,              431/2               45 A load of five hundred tons upon a grade of thirty feet per mile requires of the locomotive a drawing-power of 11,500 lbs. Upon a 50 feet grade 15,500 lbs. Upon an 83 feet grade 22,500 lbs. Upon a 45 feet grade 14,500 lbs. Now, if the engines are all alike, (as they are very nearly,) and each is able to exert a drawing-power of five thousand pounds to move a load of five hundred tons from Boston to Albany, we need as follows: B. to W.—11500/5000 or 2 engines. W. to S.—15500/5000 or 3 engines. S. to P.—22500/5000 or 5 engines. P. to A.—14500/5000 or 3 engines. From which the whole number of miles run by engines for one whole trip would be,— B. to W. 44  miles by 2 engines, or  88 W. to S. 541/2 miles by 3 engines, or 1631/2 S. to P. 52  miles by 5 engines, or 260 P. to A. 491/2 miles by 3 engines, or 1481/2 ______                         And the sum, 660 Now suppose, that, by making the engines for the several divisions strong in proportion to the resistance encountered upon these divisions, one engine only is employed upon each; our mileage becomes, B. to W. 44  by 1 or 44 W. to S. 541/2 by 1 or 541/2 S. to P. 52  by 1 or 52 P. to A. 49  by 1 or 491/2 ______         And the sum, 200 miles.

And the saving of miles run is therefore 660 less 200, or 460; and if 500 tons pass over the road daily, the annual saving of mileage becomes 460 by 313, or 143,980, or 70 per cent. of the whole. The actual cost for freight-locomotives per ton, per mile run, during the year ending Sept. 30, 1855, was 384/1000 of a cent; and the above 143,980 miles saved, multiplied by this fraction, amounts to $55,288 per annum. The actual expense of working the power will not of course show the whole 70 per cent. of saving, as heavy and strong engines cost more at first, and cost more to operate, than lighter ones; but the figures show the effect of correct adaptation. If we call the saving 50 per cent. only of the mileage, we have then (as the locomotive power consumes 30/100 of the whole cost of operating) 50/100 of 30/100, or 15/100, of the whole cost of working the road, and this by simply knowing how to adapt the machinery to the requirement.

So very slight are the points of difference between a good and a bad engine, that they often escape the eye of those whose business it is to deal with such works. It is not the brass and steel and bright metal and elaborate painting that make the really good and serviceable engine,—but the length, breadth, and depth of its furnace, the knowledge of proportion shown in its design, and the mechanical skill exhibited in the fitting of its parts. The apparently complex portions are really very simple in action, while the apparently simple parts are those where the greatest knowledge is required. Any man of ordinary mechanical acquirements can design and arrange the general form,—the whole mass of cranks, pistons, connecting-rods, pumps, and the various levers for working the engine; but to find the correct dimensions of the inner parts of the boiler, and of the valve-gearing, by which the movements of the steam are governed, require