of iron, whether it be manufactured into rails or
locomotives; and there is a point at which both rails and tyres must
break. Every increase of speed, by increasing the strain upon the road
and the rolling stock, brings us nearer to that point. At 30 miles a
slighter road will do, and less perfect rolling stock may be run upon it
with safety. But if you increase the speed by say 10 miles, then
everything must be greatly strengthened. You must have heavier engines,
heavier and better-fastened rails, and all your working expenses will be
immediately increased. I think I know enough of mechanics to know where
to stop. I know that a pound will weigh a pound, and that no more should
be put upon an iron rail than it will bear. If you could ensure perfect
iron, perfect rails, and perfect locomotives, I grant 50 miles an hour or
more might be run with safety on a level railway. But then you must not
forget that iron, even the best, will 'tire,' and with constant use will
become more and more liable to break at the weakest point--perhaps where
there is a secret flaw that the eye cannot detect. Then look at the
rubbishy rails now manufactured on the contract system--some of them
little better than cast metal: indeed, I have seen rails break merely on
being thrown from the truck on to the ground. How is it possible for
such rails to stand a 20 or 30 ton engine dashing over them at the speed
of 50 miles an hour? No, no," he would conclude, "I am in favour of low
speeds because they are safe, and because they are economical; and you
may rely upon it that, beyond a certain point, with every increase of
speed there is an increase in the element of danger."

When railways became the subject of popular discussion, many new and
unsound theories were started with reference to them, which Stephenson
opposed as calculated, in his opinion, to bring discredit on the
locomotive system. One of these was with reference to what were called
"undulating lines." Among others, Dr. Lardner, who had originally been
somewhat sceptical about the powers of the locomotive, now promulgated
the idea that a railway constructed with rising and falling gradients
would be practically as easy to work as a line perfectly level. Mr.
Badnell went even beyond him, for he held that an undulating railway was
much better than a level one for purposes of working. For a time, this
theory found favour, and the "undulating system" was extensively adopted;
but