The life of George Stephenson, railway engineer - Lighthouse ...

CHAP, xn.] EOLLING EESISTANCE. I39
The other resistances to which carriages are exposed, were at
the same time investigated by Mr. Stephenson. He perceived
that these resistances were mainly three ; the first being upon
the axles of the carriage, the second (which may be called the
rolling resistance) being between the circumference of the wheel
and the surface of the rail, and the third being the resistance of
gravity. The amount of friction and gravity was accurately
ascertained ; but the rolling resistance was a matter of greater
difficulty, being subject to great variation. He however satisfied
himself that it was so great when the surface presented to the
wheel was of a rough character, that the idea of working steam
carriages upon common roads was dismissed by him as entirely
out of the question. Even so early as the period alluded to
(1818) he brought his theoretical calculations to a practical test
he scattered sand upon the rails when an engine was running,
and found that a small quantity was quite sufficient to retard and
even to stop the most powerful locomotive that he had at that
time made. And he never failed to urge this conclusive experiment
upon the attention of those who were at that time wasting
their money and ingenuity upon the vain attempt to apply steam
power to the purposes of travelling on common roads.
Having ascertained that resistance might be taken as represented
by 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 effiDrt of a locomotive by upwards of 50 per cent.
This was demonstrated by repeated experiments, and the impor-
tant fact, thus rooted deeply 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 thus
early became convinced of the vital importance, in an economi-
cal 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 col-
liery 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 an easy matter for it
to haul the empty wagons back to the colliery up even a pretty
: