Stephenson’s experiments on fire-damp, and his labours in connexion with the invention of the safety-lamp, occupied but a small portion of his time, which was necessarily devoted for the most part to the ordinary business of the colliery. From the day of his appointment as engine-wright, one of the subjects which particularly occupied his attention was the best practical method of winning and raising the coal. He was one of the first to introduce steam machinery underground with the latter object. Indeed, the Killingworth mines came to be regarded as the models of the district; the working arrangements generally being conducted in a skilful and efficient manner, reflecting the highest credit on the colliery engineer. Besides attending to the underground arrangements, the improved transit of the coals above-ground from the pithead to the shipping-place, demanded an increasing share of his attention. Every day’s experience convinced him that the locomotive constructed by him after his patent of the year 1815, was far from perfect; though he continued to entertain confident hopes of its eventual success. He even went so far as to say that the locomotive would yet supersede every other traction-power for drawing heavy loads. Many still regarded his travelling engine as little better than a curious toy; and some, shaking their heads, predicted for it “a terrible blow-up some day.” Nevertheless, it was daily performing its work with regularity, dragging the coal-waggons between the colliery and the staiths, and saving the labour of many men and horses. There was not, however, so marked a saving in haulage as to induce the colliery masters to adopt locomotive power generally as a substitute for horses. How it could be improved and rendered more efficient as well as economical, was constantly present to Stephenson’s mind. At an early period of his labours, or about the time when he had completed his second locomotive, he began to direct his particular attention to the state of the Road; as he perceived that the extended use of the locomotive must necessarily depend in a great measure upon the perfection, solidity, continuity, and smoothness of the way along which the engine travelled. Even at that early period, he was in the habit of regarding the road and the locomotive as one machine, speaking of the rail and the wheel as “man and wife.”