"Of course," he was asked, "when a body is moving upon a road, the greater the velocity the greater the momentum that is generated?" "Certainly." "What would be the momentum of forty tons moving at the rate of twelve miles an hour?" "It would be very great." "Have you seen a railroad that would stand that?" "Yes." "Where?" "Any railroad that would bear going four miles an hour: I mean to say, that if it would bear the weight at four miles an hour, it would bear it at twelve." "Taking it at four miles an hour, do you mean to say that it would not require a stronger railway to carry the same weight twelve miles an hour?" "I will give an answer to that. I dare say every person has been over ice when skating, or seen persons go over, and they know that it would bear them better at a greater velocity than it would if they went slower; when they go quick, the weight in a measure ceases." "Is not than upon the hypothesis that the railroad is perfect?" "It is; and I mean to make it perfect."
It is not necessary to state that to have passed through his severe ordeal scatheless needed no small amount of courage, intelligence, and ready shrewdness on the part of the witness. Nicholas Wood, who was present on the occasion, has since stated that the point on which Stephenson was hardest pressed was that of speed. "I believe," he says, "that it would have lost the company their bill if he had gone beyond eight or nine miles an hour. If he had stated his intention of going twelve or fifteen miles an hour, not a single person would have believed it to be practicable." Mr. Alderson had, indeed, so pressed the point of "twelve miles an hour," and the promoters were so alarmed lest it should appear in evidence that they contemplated any such extravagant rate of speed, that immediately on Mr. Alderson sitting down, Mr. Joy proceeded to re-examine Stephenson, with the view of removing from the minds of the committee an impression so unfavorable, and, as they supposed, so damaging to their case. "With regard," asked Mr. Joy, "to all those hypothetical questions of my learned friend, they have been all put on the supposition of going twelve miles an hour: now that is not the rate at which, I believe, any of the engines of which you have spoken have traveled?" "No," replied Stephenson, "except as an experiment for a short distance." "But what they have gone has been three, five, or six miles an hour?" "Yes." "So that those hypothetical cases of twelve miles an hour do not fall within your general experience?" "They do not."