A manual of the principles and practice of road-making: comprising the location, construction, and improvement of roads, (common, macadam, paved, plank, etc.) and rail-roads. By W. M. Gillespie ...

L-DVANTAGES OF CURVING. 27
nounced to be a bad road; for the straightness must have
been obtained either by submitting to steep slopes in ascending the hills and descending into the valleys, or these
natural obstacles must have been overcome by incurring
a great and unnecessary expense in making deep cuttings
and fillings.
A good road should wind around these hills instead of
running over them, and this it may often do without at all
increasing its length. For if a hemisphere (such as half
a btillet) be placed so as to rest upon its plane base, the
halves of great circles which join two opposite points of
this base are all equal, whether they pass horizontally or
vertically. Or let an egg be laid upon a table, and it will
be seen that if a level line be traced upon it from one end
to the other, it will be no longer than the line traced between the same points, but passing over the top. Precisely so may the curving road around a hill be often no
longer than the straight one over it; for the latter road is
straight only with reference to the vertical plane which
passes through it, and is curved with reference to a horizontal plane; while the former level road, though curved
as to the vertical plane, is straight as to a horizontal one.
Both lines thus curve, and we call the latter one straight
in preference, only because its vertical curvature is less
apparent to our eyes.
The difference in length between a straight road and
one which is slightly curved is very small. If a road between two places ten miles apart were made to curve so
that the eye could nowhere see farther than a quarter of
a mile of it at once, its length would exceed that of a
perfectly straight road between the same points by only
about one hundred and fifty yards.*
* Sganzin, p. 89.