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 Mr. Stephenson never ceased to inveigh against it; and experience has amply proved that his judgment was correct. His practice, from the beginning of his career until the end of it, was to secure a road as nearly as possible on a level, following the course of the valleys and the natural line of the country: preferring to go round a hill rather than to tunnel under it or carry his railway over it, and often making a considerable circuit to secure good, workable gradients. He studied to lay out his lines so that long trains of minerals and merchandise, as well as passengers, might be hauled along them at the least possible expenditure of locomotive power. He had long before ascertained, by careful experiments at Killingworth, that the engine expends half of its power in overcoming a rising gradient of 1 in 260, which is about 20 feet in the mile; and that when the gradient is so steep as 1 in 100, not less than three-fourths of its power is sacrificed in ascending the acclivity. He never forgot the valuable practical lesson taught him by the early trials which he had made and registered long before the advantages of railways had been recognised. He saw clearly that the longer flat line must eventually prove superior to the shorter line of steep gradients as respected its paying qualities. He urged that, after all, the power of the locomotive was but limited; and, although he and his son had done more than any other men to increase its working capacity, it provoked him to find that every improvement made in it was neutralised by the steep gradients which the new school of engineers were setting it to overcome. On one occasion, when Robert Stephenson stated before a Parliamentary Committee that every successive improvement in the locomotive was being rendered virtually nugatory by the difficult and almost impracticable gradients proposed on many of the new lines, his father, on his leaving the witness-box, went up to him, and said, “Robert, you never spoke truer words than those in all your life.”