to much
variation. He satisfied himself, however, that it was so great when the
surface presented to the wheel was of a rough character, that the idea of
working steam carriages economically on common roads was dismissed by him
as entirely impracticable. Taking it as 10 lbs to a ton weight on a
level railway, it became obvious to him that so small a rise as 1 in 100
would diminish the useful effort of a locomotive by upwards of 50 per
cent. This was demonstrated by repeated experiments, and the important
fact, thus rooted in his mind, was never lost sight of in the course of
his future railway career.

It was owing in a great measure to these painstaking experiments that he
early became convinced of the vital importance, in an economical point of
view, of reducing the country through which a railway was intended to
pass as nearly as possible to a level. Where, as in the first coal
railways of Northumberland and Durham, the load was nearly all one
way,--that is, from the colliery to the shipping-place,--it was an
advantage to have an inclination in that direction. The strain on the
powers of the locomotive was thus diminished, and it was easy for it to
haul the empty waggons back to the colliery up even a pretty steep
incline. But when the loads were both ways, he deemed it of great
importance that the railroad should be constructed as nearly as possible
on a level.

These views, thus early entertained, originated in Stephenson's mind the
peculiar character of railroad works as distinguished from other roads;
for, in railways, he early contended that large sums would be wisely
expended in perforating barriers of hills with long tunnels, and in
raising the lower levels with the excess cut down from the adjacent high
ground. In proportion as these views forced themselves upon his mind and
were corroborated by his daily experience, he became more and more
convinced of the hopelessness of applying steam locomotion to common
roads; for every argument in favour of a level railway was, in his view,
an argument against the rough and hilly course of a common road.

Although Stephenson's locomotive engines were in daily use for many years
on the Killingworth Railway, they excited comparatively little interest.
They were no longer experimental, but had become an established tractive
power. The experience of years had proved that they worked more
steadily, drew heavier loads, and were, on the whole, considerably more
eco