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 | |||
| From summit to Pittsburg, 106 miles | { | 47 | 172.4 | 103.4 | 0.266 | 3.76 | |
| 50 | 50 | 163.7 | 98.2 | 0.252 | 3.95 | ||
| 52.8 | 52.8 | 156.2 | 93.7 | 0.241 | 4.14 | ||
It will be perceived from the foregoing table that three locomotives are fully sufficient to transport the same load up the 80 feet gradient that two will carry on the gradient of the western division, and one on the eastern; hence the practical working of the road on the two methods of ascent would be to run two locomotives with the load brought from below from Logan's Narrows to the summit, say 31¾ miles, up the 50 feet gradient; while, on the other, the same engine that brought the load from Harrisburg would continue with it to Robinson's (15 miles), where it would accompany the two destined for Pittsburg to the summit of the mountain and return.
In the first case the engines together will have traveled 63½ miles, and, in the other, the three 51¾, leaving a difference in distance to be traveled by the moving power due to each full train, from the east, 11¾ miles in favor of the 80 feet gradient.
In practice it will therefore be seen—chiefly on account of the actual distance saved—that transportation can be afforded cheaper, in this case, on the 80 feet gradient than on the 50, without bringing into the estimate the interest on $841,000 that the latter would cost to obtain it more than the former. Under these circumstances we did not hesitate when the choice of routes was reduced to a selection between these two methods of overcoming the mountain, to decide in favor of the line by Robinson's, which has the additional advantage of bringing us within 6-1/3 miles of Hollidaysburg, where a connection may be made with the Allegheny Portage by a branch line, passing over favorable ground.
The distance from Harrisburg to Robinson's summit is 132-2/3 miles; upon the whole of this line, the only extraordinary impediments to the easy graduation of the road bed are the bridge over the Susquehanna, a deep and long cut near Newton Hamilton, and a tunnel 1,200 feet in length through a point of Tussey's mountain, and in this distance the maximum ascending gradient to Lewistown is 16 feet per mile, and descending 8 feet. Thence, to Robinson's summit, they are increased to 21 feet ascending, and 10-1/8 feet descending.
The descending gradients are generally so short that they will not be found, in practice, to decrease the load going east much below what is due to a fair working load for a locomotive on a level.