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