is bored, upon the Baltimore and Ohio Railroad, was surmounted
temporarily by grades of 500 feet per mile, up which each single car
was drawn by a powerful locomotive.

Another element, of which American engineers have freely availed
themselves, is curvature. More power is required to draw a train of
cars around a curved track than upon a straight line. In England the
radius of curvature is limited to half a mile, or thereabouts. The
English railway-carriage is placed on three axles, all of which are
fixed to the body of the vehicle; the passage of curves, of even a
large diameter, is thus attended by considerable wear and strain;
but in America, the cars, which are much longer than those upon
English roads, are placed upon a pintle or pin at each end, which
pin is borne upon the centre of a four-wheeled truck,--by which
arrangement the wheels may conform to the line of the rails, while
the body of the car is unaffected. This simple contrivance permits
the use of curves which would otherwise be entirely impracticable.
Thus we find curves of one thousand feet radius upon our roads, over
which the trains are run at very considerable speed; while in one
remarkable instance (on the Virginia Central Railroad, before named)
we find the extreme minimum of 234 feet. Such a track does not admit
of high speeds, and its very use implies the existence of natural
obstacles which prevent the acquirement of great velocities.

In fine, the use which the engineer makes of grades and curves, when
the physical nature of the country and the nature and amount of the
traffic expected are known, may be taken as a pretty sure index of
his real professional standing, and sometimes as an index of the
moral man; as when, for example, he steepens his grades to suit the
contractor's ideas of mechanics,--in other words, to save work.