The great advantage of railways over ordinary roads is the diminished
friction, which is produced by the wheels passing over the smooth
iron instead of rough stones. It was found when iron rails were first
used, before the introduction of locomotives, that the horse-power
requisite was diminished to one-fortieth; for instance, ten horses
on a railway could do the work of four hundred on a common road, this
being the case, and the great power of the locomotive engine being
superadded, there can be no wonder that the difference of the rate
of speed between the train and the wagon should be so great. When
it has been settled what general direction the railway shall take,
it is then to be determined whether or to what extent the elevations
or depressions that may occur can be conveniently overcome, so that
the line may take a straight course, or whether the road shall go
out of the straight line, and how far to avoid them. The route it
should therefore take ought to exactly balance the objections to
each extreme, that is the expense, &c., of going straight on through
hills and over valleys on the one side, and the increased distance
and consequent loss of time which a winding track would cause to the
transit on the other.