Suspension-Bridge cost four hundred thousand dollars, while a boiler-plate iron bridge upon the tubular system would cost for the same span about four million dollars, even if it were practicable to raise a tubular bridge in one piece over Niagara River at the site of the Suspension Bridge. Strength and durability, with the utmost economy, seem to have been attained by Mr. Wendel Bollman, superintendent of the road-department of the Baltimore and Ohio Railroad,—the minute details of construction being so skilfully arranged, that changes of temperature, oftentimes so fatal to bridges of metal, have no hurtful effect whatever. And here, again, is seen the distinctive American feature of adaptation or accommodation, even in the smallest detail. Mr. Bollman does not get savage and say, "Messieurs Heat and Cold, I can get iron enough out of the Alleghanies to resist all the power you can bring against me!" —but only observes, "Go on, Heat and Cold! I am not going to deal directly with you, but indirectly, by means of an agent which will render harmless your most violent efforts!"—or, in other words, he interposes a short link of iron between the principal members of his bridge, which absorbs entirely all undue strains.
It is not to be supposed from what has preceded, that the American engineer does not know how to spend money, because he gets along with so little, and accomplishes so much; when occasion requires, he is lavish of his dollars, and sees no longer expense, but only the object to be accomplished. Witness, for example, the Kingwood Tunnel, on the Baltimore and Ohio Railroad, where for a great distance the lining or protecting arching inside is of heavy ribs of cast iron, —making the cost of that mile of road embracing the tunnel about a million of dollars. Nor will the traveller who observes the construction of the New York and Erie Railroad up the Delaware Valley, of the Pennsylvania Central down the west slopes of the Alleghanies, or of the Baltimore and Ohio down the slopes of Cheat River, think for a moment that the American engineer grudges money where it is really needed.
Stone bridges so rarely occur upon the roads of America, that they hardly need remark. The Starucca Viaduct, by Mr. Adams, upon the New York and Erie Railroad, and the viaduct over the Patapsco, near the junction of the Washington branch with the main stem of the Baltimore and Ohio Railroad, show that our engineers are not at all behind those of Europe in this branch of engineering. From the civil let us pass to the mechanical department of railroad engineering. This latter embraces all the machinery, both fixed and rolling; locomotives and cars coming under the latter,—and the shop-machines, lathes, planers, and boring-machines, forging, cutting, punching, rolling, and shearing engines, pumps and pumping-engines for the water-stations, turn-tables, and the like, under the former. Of this branch, little, except the design and working of the locomotive power, needs to be mentioned as affecting the prosperity of the road. Machine-shops, engine-houses, and such apparatus, differ but slightly upon different roads; but the form and dimensions of the locomotive engines should depend upon the nature of the traffic, and upon the physical character of the road, and that most intimately, —so much, indeed, that the adjustment of the grades and curvatures must determine the power, form, and whole construction of the engine. This is a fact but little appreciated by the managers of our roads; when the engineer has completed the road-bed proper, including the bridging and masonry, he is considered as done with; and as the succeeding superintendent of machinery is not at that time generally appointed, the duty of obtaining the necessary locomotive power devolves upon the president or contractor, or some other person who knows nothing whatever of the requirements of the road; and as he generally goes to some particular friend, perhaps even an associate, he of course takes such a pattern of engine as the latter builds, —and the consequence is that not one out of fifty of our roads has steam-power in any way adapted to the duty it is called upon to perform.
There is no nicer problem connected with the establishment of a railroad, than, having given the grades, the nature of the traffic, and the fuel to be used, to obtain therefrom by pure mechanical and chemical laws the dimensions complete for the locomotives which shall effect the transport of trains in the most economical manner; and there is no problem that, until quite lately, has been more totally neglected.3
Of the whole cost of working a railroad about one third is chargeable to the locomotive department; from which it is plain that the most proper adaptation is well worth the careful attention of the engineer. Though it is generally considered that the proper person to select the locomotive power can be none other than a practical machinist, and though he would doubtless select the best workmanship, yet, if not acquainted with the general principles of locomotion, and aware of the character of the road and of the expected traffic, and able to judge, (not by so-called experience, but by real knowledge,) he may get machinery totally unfit for the work required of it. Indeed, American civil engineers ought to qualify themselves to equip the roads they build; for none others are so well acquainted with the road as those who from a thorough knowledge of the matter have established the grades and the curvatures.
The difference between adaptation and non-adaptation will plainly be seen by the comparison below. The railway from Boston to Albany may be divided into four sections, of which the several lengths and corresponding maximum grades are as tabulated.
Boston to Worcester, 44 30
Worcester to Springfield, 541/2 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
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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
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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
The most careless observer has doubtless noticed that the front part of a locomotive rests upon the centre of a track, having four small wheels; the back and middle part, he will also remember, is borne upon large spoke wheels,—which are connected with the machinery; upon the size of these last depend the power and speed of the engine. The larger the wheels, the less the power, and the higher the velocity which may be got; again, the wheel remaining of the same size, by enlarging the dimensions of the cylinders the power is increased; and the wheels and cylinders remaining the same, by enlarging the boiler we can make stronger steam and thus increase the power. There may be seen upon the road from Boston to Springfield engines with wheels nearly seven feet in diameter, used for drawing light express-trains; while upon the roads ascending the Alleghanies may be seen wheels of only three and a half feet diameter, which are employed in drawing trains up the steep grades. Increase of steepness of grades acts upon the locomotive in the same manner as increase of actual load; as upon a level the natural tendency of the engine is to stand still, while on an incline the tendency is to roll backwards down-hill.
