to reach the height found most suitable for passing the mountain, which is attained by a continuous gradient of 80 feet per mile, encountering no very formidable difficulties.
A resort to a gradient of 80 or more feet per mile is by no means an unusual expedient on leading railroads.
Upon the Western Railroad, in Massachusetts, their maximum gradient is 83½ feet per mile. On the Baltimore & Ohio Railroad they now have, between the waters of the Patapsco and Potomac, on each side of Parr's ridge, gradients of 82 feet per mile, and from the greater elevation of the Allegheny mountains at the place they must cross, it is to be presumed that their gradients at that point will still be increased to a higher rate.
Many other instances might be cited, some running up to 120 feet per mile, but it seems unnecessary to extend the list. Theoretically, the power necessary to overcome a given height is the same at all inclinations of the plane of ascent, but in practice, it is to some extent dependent upon the kind of power to be applied.
In the case under consideration, the locomotive steam engine will be the medium used, where the power is carried with the train, and forms part of the load to be moved, consequently, the cost of power on a plane ascending 80 feet per mile is greater than upon one of a more moderate inclination of equal height, by the difference between the gravity of the engines required to carry the same load on both planes.
As a general principle this would be true when the lengths of the roads to overcome the same height are equal, and it is necessary to carry the locomotives, required for the high gradient, over the same distance that they must run upon the low gradient.
But in one of these cases the maximum gradient due to the line below Logan's Narrows is carried to within 12¼ miles of the summit of the mountain—requiring extra power for that distance only—and in the other it ends 32 miles from it.
To explain more fully the relative value of the maximum gradients used on the different divisions of our Road, I have prepared the following table:
Table headings:
Col A: Division of Road.
Col B: Maximum Gradient, ascending westwardly, per mile.
Col C: Maximum Gradient, ascending eastwardly, per mile.
Col D: Gross load of a 20 ton freight locomotive,
exclusive of engine, and a tender of 10 tons. Friction
8½ lbs. per T. Adhesion ½.
Col E: Load of merchandise for a 20 ton freight engine,
the cars being estimated at 4/10ths of their
weight and load.
Col F: Relative load of locomotive on each gradient,
level being unit.
Col G: Number of locomotives of equal power necessary to carry
the same load up each gradient.
| A | B | C | D | E | F | G | |
| From Harrisburg to Lewistown, 60–7/10 miles | { | 16 | 346.6 | 207.9 | 0.534 | 1.87 | |
| 8 | 454.3 | 272.6 | 0.697 | 1.42 | |||
| From Lewistown to foot of Allegheny Mts., 72 miles | { | 21 | 300.7 | 180.4 | 0.464 | 2.15 | |
| 10½ | 414.6 | 248.8 | 0.640 | 1.56 | |||
| From foot to summit of Allegheny Mountains, 12–3/10 miles | { | 80 | 105.6 | 63.4 | 0.163 | 6.13 | |
| Level | 648.0 | 388.8 | 1.000 | 1.00 | |||
