The Atlantic Monthly, Volume 02, No. 13, November, 1858

The objectors take another step, but again put down their heavy square-toed foot, and say, "There! aren't you satisfied? you can go over grades of twenty feet per mile, but no more,—so don't try." And here English engineers stop,—twenty feet being considered a pretty stiff grade. Meanwhile, the American engineers Whistler and Latrobe, the one dealing with the Berkshire mountains in Massachusetts, the other with the Alleghanies in Virginia, find that not only are grades of ten and of twenty feet admissible, but, where Nature requires it, inclines of forty, sixty, eighty, and even one hundred feet per mile,—it being only remembered, the while, that just as the steepness of the grade is augmented, the power must be increased. This discovery, when properly used, is of immense advantage; but in the hands of those who do not understand the nice relation which exists between the mechanical and the financial elements of the question, as governed by the speed and weight of trains, and by the funds at the company's disposal, is very liable to be a great injury to the prospects of a road, or even its ruin.

It was urged at one time, that the best road would have the grades undulating from one end to the other,—so that the momentum acquired in one descent would carry the train almost over the succeeding ascent; and that very little steam-power would be needed. This idea would have place, at least to a certain extent, if the whole momentum was allowed to accumulate during the descent; but even supposing there would be no danger from acquiring so great a speed, a mechanical difficulty was brought to light at once, namely, that the resistance of the atmosphere to the motion of the train increased nearly, if not quite, as the square of the speed; so that after the train on the descent acquired a certain speed, a regular motion was obtained by the balance of momentum and resistance, —whence a fall great enough to produce this regular speed would be advantageous, but no more. On the other hand, the extra power required to draw the train up the grades much overbalances the gain by gravity in going down.

Here, then, we have the two extremes: first, spending more money than the expected traffic will warrant, to cut down hills and fill up valleys; and second, introducing grades so steep that the amount of traffic does not authorize the use of engines heavy enough to work them.

The direction of the traffic, to a certain extent, determines the rate and direction of the inclines. Thus, the Reading Railroad, from Philadelphia up the Schuylkill to Reading, and thence to Pottsville, is employed entirely in the transport of coal from the Lehigh coal-fields to tide-water in Philadelphia; and it is a very economically operated road, considering the large amount of ascent encountered, because the load goes down hill, and the weight of the train is limited only by the number of empty cars that the engine can take back.

This adoption of steep inclines may be considered as an American idea entirely, and to it many of our large roads owe their success. The Western Railroad of Massachusetts ascends from Springfield to Pittsfield, for a part of the way, at 83 feet per mile. The New York and Erie Railroad has grades of 60 feet per mile. The Baltimore and Ohio climbs the Alleghanies on inclines of 116 feet per mile. The Virginia Central Road crosses the Blue Ridge by grades of 250 and 295 feet per mile; and the ridge through which the Kingwood Tunnel is bored, upon the Baltimore and Ohio Railroad, was surmounted temporarily by grades of 500 feet per mile, up which each single car was drawn by a powerful locomotive.

Another element, of which American engineers have freely availed themselves, is curvature. More power is required to draw a train of cars around a curved track than upon a straight line. In England the radius of curvature is limited to half a mile, or thereabouts. The English railway-carriage is placed on three axles, all of which are fixed to the body of the vehicle; the passage of curves, of even a large diameter, is thus attended by considerable wear and strain; but in America, the cars, which are much longer than those upon English roads, are placed upon a pintle or pin at each end, which pin is borne upon the centre of a four-wheeled truck,—by which arrangement the wheels may conform to the line of the rails, while the body of the car is unaffected. This simple contrivance permits the use of curves which would otherwise be entirely impracticable. Thus we find curves of one thousand feet radius upon our roads, over which the trains are run at very considerable speed; while in one remarkable instance (on the Virginia Central Railroad, before named) we find the extreme minimum of 234 feet. Such a track does not admit of high speeds, and its very use implies the existence of natural obstacles which prevent the acquirement of great velocities.

In fine, the use which the engineer makes of grades and curves, when the physical nature of the country and the nature and amount of the traffic expected are known, may be taken as a pretty sure index of his real professional standing, and sometimes as an index of the moral man; as when, for example, he steepens his grades to suit the contractor's ideas of mechanics,—in other words, to save work.

Not less in the construction of bridges and viaducts, than in the preparation of the road-bed proper, does the American engineering faculty display itself. Timber, of the best quality, may be found in almost every part of the country, and nowhere in the world has the design and building of wooden bridges been carried to such perfection and such extent as in the United States. We speak here of structures built by such engineers as Haupt, Adams, and Latrobe, —and not of those works, wretched alike in design and execution, which so often become the cause of what are called terrible catastrophes and lamentable accidents, but which are, in reality, the just criticisms of natural mechanical laws upon the ignorance of pretended engineers.

Among the finest specimens of timberwork in America are the Cascade Bridge upon the New York and Erie Railroad, designed and built by Mr. Adams, consisting of one immense timber-arch, having natural abutments in the rocky shores of the creek;—the second edition of the bridges generally upon the same road, by Mr. McCallum, which replaced those originally built during the construction of the road, —these hardly needing to be taken down by other exertion than their own;—the bridges from one end to the other of the Pennsylvania Central Road, by Mr. Haupt;—the Baltimore and Ohio "arch-brace" bridges, by Mr. Latrobe;—and the Genessee "high bridge," (not a bridge, by the way, but a trestle,) near Portageville, by Mr. Seymour, which is eight hundred feet long, and carries the road two hundred and thirty feet above the river, having wooden trestles (post and brickwork) one hundred and ninety feet high, seventy-five feet wide at base, and twenty-five feet at top, and carrying above all a bridge fourteen feet high; containing the timber of two hundred and fifty acres of land, and sixty tons of iron bolts, costing only $140,000, and built in the short time of eighteen months. This structure, if replaced by an earth embankment, would cost half a million of dollars, and could not be built in less than five years by the ordinary mode of proceeding.[2 - Lest these statements should sound extravagant, the reader will please reckon up the amounts for himself. A bank twenty-five feet wide on top, eight hundred feet long, and two hundred and thirty feet high, would contain two million cubic yards of earth; which, at twenty-five cents per yard, would cost half a million of dollars, exclusive of a culvert to pass the river, of sixty, eighty, or one hundred feet span and seven hundred feet long. Twenty trains per day, of thirty cars each, one car holding two yards, would be twelve hundred yards per day; two million, divided by twelve hundred, gives 1,666 days.]

Further, the interest, for so long a time, on the large amount of money required to build the embankment, at the high rate of railroad interest, would nearly, if not quite, suffice to build the wooden structure.

Again, our wooden bridges of the average span cost about thirty-five dollars per lineal foot. Let us compare this with the cost of iron bridges, on the English tubular plan, the spans being the same, and the piers, therefore, left out of the comparison.

Suppose that a road has in all one mile in length of bridges. Making due allowance for the difference in value of labor in England and America, the cost per lineal foot of the iron tubular bridges could not be less (for the average span of 150 feet) than three hundred dollars.

5280 feet by $35 is $184,800.00

5280 feet by 300 is $1,584,000.00

The six per cent. interest on the first is $11,088.00

The six per cent. interest on the second is $95,040.00

And the difference is $83,952.00

or nearly enough to rebuild the wooden bridges once in two years; and ten years is the shortest time that a good wooden bridge should last.

The reader may wonder why such structures as the bridge over the Susquehanna at Columbia, which consists of twenty-nine arches, each two hundred feet span, the whole water-way being a mile long, and many other bridges spanning large rivers, and having an imposing appearance, are not referred to in this place. The reason is this: large bridges are by no means always great bridges; nor do they require, as some seem to think, skill proportioned to their length. There are many structures of this kind in America, of twenty, twenty-five, or thirty spans, where the same mechanical blunders are repeated over and over again in each span; so that the longer they are and the more they cost, the worse they are. It does not follow, because newspapers say, "magnificent bridge," "two million feet of timber," "eighty or one hundred tons of iron," "cost half a million," that there is any merit about either the bridge or its builder; as one span is, so is the whole; and a bridge fifty feet long, and costing only a few hundreds, may show more engineering skill than the largest and most costly viaducts in America. Few bridges require more knowledge of mechanics and of materials than Mr. Haupt's little "trussed girders" on the Pennsylvania Central Road,—consisting of a single piece of timber, trussed with a single rod, under each rail of the track.

Again, as regards American iron bridges, the same result is found to a great extent. Thus, Mr. Roebling's Niagara Railroad 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 - 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.]

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.

Length in miles. Steepest grade

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

______

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