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 W