“It is true,” he observed on other occasions, “I have said the locomotive engine _might_ be made to travel 100 miles an hour; but I always put a qualification on this, namely, as to what speed would best suit the public. The public may, however, be unreasonable; and 50 or 60 miles an hour is an unreasonable speed. Long before railway travelling became general, I said to my friends that there was no limit to the speed of the locomotive, _provided the works could be made to stand_. But there are limits to the strength 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.”