178 RAILROAD remarked, the old system of occasional inclined planes is almost wholly abandoned for roads of general travel, and the construction and capacity of locomotives and carriages are so much better understood, that a much greater range in curvatures and grades is now found practicable than was formerly ever thought of. As regards curves, it was at first recommend- ed in England to fix the minimum radius that should be allowed at one mile, and in 1846 it was one of the "standing orders" of parlia- ment that no curve should be made with a ra- dius of less than half a mile (2,640 ft.) without special permission of parliament. In France a minimum was established by " the administra- tion of roads and bridges" of 2,700 ft., or about 2. On the Hudson River railroad the minimum curve has a radius of 2,062 ft. =2'75. But the Baltimore and Ohio road was built with several curves of 400 ft. radius (14-25), and with one of 318 ft. (18), and no difficulty was experienced in running over them at 15 m. an hour. The narrow-gauge railroads now coming into favor for light traffic, in thinly settled or mountainous districts, are built with curves of very much shorter radius, in some instances not exceeding 50 ft. in length. The objectionable features of the curves are avoided by making the wheels conical, of greater diam- eter within than at their outer edge ; the effect of this in running on a curve, when the wheels on the outer side are pushed by the centrifugal force outwardly, is to make them roll on their larger diameter, and at the same time the wheels on the other side, drawn in toward the centre of the track, roll on their smaller diameter. On each side they are thus accommodated to the different lengths they have to traverse, without straining the axles and without great- ly increased friction or slipping of the inner wheel upon the rail. The friction against the outer rail due to the centrifugal force is par- tially prevented by elevating the outer rail. The object of attaching the wheels to their axles, instead of letting them turn upon these, is to secure greater steadiness at high speed. The requiring of minimum degrees of curva- ture has been abandoned upon the English and French roads. In France, upon the Paris and Orsay and Paris and Sceaux railroads, there are curves of 82 ft. radius, and trains, the engines and carriages of which are provided with loose wheels and guide rollers, run through complete semicircles at 20 m. an hour. Upon the earlier roads in Great Britain and in the United States grades of 30 or 40 ft. to the mile were con- sidered heavy, at the last figure nearly tripling the power that was required to draw the load upon a level. Grades of 70 to 80 ft. were re- garded as almost impracticable, as they would compel the carrying of light loads over the whole line, and therefore, when such grades could not be otherwise avoided, inclined planes worked by stationary engines were adopted. The Hudson and Mohawk railroad, in a length of 16 m., was built with one such plane at Albany, and another at Schenectady. The Philadelphia and Columbia railroad was also built with two planes, one at Columbia and the other near P.'.Jadelphia, and there were ten on the Allegheny Portage road over the Allegheny mountains, all of which have been displaced by the substitution of heavier grades on more extended lines. But as experience was acquired in the working of railroads, it was found that locomotives rarely carried max- imum loads for the moderate grades, and that a temporary slackening of the speed upon the steep grades rendered a further portion of the power of the locomotive available for over- coming the increased resistance. Thus, when the doubtful point as to the adhesion of the driving wheels to the rails was satisfactorily determined, and the common law of mechanics, that power can be gained at the expense of mo- tion, was found to be applicable to ascending grades of a railroad, these were increased much beyond thejr former limits. High grades were sooner introduced in this country than in Eu- rope, but they have since been adopted there also. On the Mount Savage and George's Creek railroads in Maryland grades of 140 ft. to the mile have long been used ; and on the Balti- more and Ohio road, through the Allegheny mountains, of 114 ft. In England those of 100 ft. to the mile are not uncommon, and there are several from 180 to 150 ft. At Sheffield is a grade of 196 ft. to the mile, and the same is seen at Oldham on the Lancashire and York- shire road, extending for 1$ m. In France on the St. Germain railroad is a grade of 123 ft. to the mile for about 1 J in. ; and it is now assert- ed by engineers that grades of 870 ft. to the mile can bo worked by locomotives, but that on heavy grades the locomotive should take no more cars in descending than in ascend- ing. The proper preparation of the road bed should be an object of the most particular care. Being the foundation and support of the whole superstructure, it should as a mat- ter of economy be made as firm and dura- ble as possible. But it is in this that the American roads are most defective. The least width of embankments for double tracks ought not to be less than the width of the two tracks, with 6 ft. between them, and 6 ft. outside of each. In excavations the width of ditches on each side should be added. A common width of embankments in England is 83 ft., while on the principal American roads it varies with the height of the embankment. The transverse slopes of the English roads are much flatter than ours, and are commonly well protected with a good grass sod. But the most essential difference is in the drainage, upon which more than anything else depends the durability of the earthwork and of the sleep- ers and rails. Upon some American roads the sleepers are laid directly upon the natural soil, or upon this thrown up in a bank. Where the ground freezes, any superstructure on such a basis is certain to be more or less displaced in
