CHAP. VII. ROLLING RESISTANCE. 107 directly to corroborate the philosophical theories on the subject, it was a considerable time (so great were the prejudices then existing) before the conclusions which they established received the sanction of practical men. It was maintained by many that the results of these experiments led to the greatest possible mechanical absurdities. For example, it was insisted that, if friction was constant at all velocities upon a level railway, when once a power was applied to a carriage, which exceeded the friction of that carriage by the smallest possible amount, such excess of power, however small, would be able to convey the carriage along a level railway at all conceivable velocities. When this position was taken by those who opposed the conclusions to which Mr. Stephenson had arrived, he felt the greatest hesitation in maintaining his own views; for it appeared to him at first sight really the absurdity which his opponents asserted it to be. Frequent and careful repetition of his experiments, however, left no doubt upon his mind as to the soundness of his conclusion-that friction was uniform at all velocities. Notwithstanding the ridicule that was thrown upon his views by many persons with whom he associated at the time, he continued to hold to this conclusion as a fact positively established; and he soon afterwards boldly maintained, that that which was an apparent absurdity was indeed an inevitable consequence, and that every increase of speed involved a necessary expenditure of power almost in a direct ratio. The other resistances to which carriages are exposed, were at the same time investigated by Mr. Stephenson. He perceived that these resistances were mainly three; the first being upon the axles of the carriages, the second (which may be called the rolling resistance) being between the circumference of the wheel and the surface of the rail, and the third being the resistance of gravity. The amount of friction and gravity was accurately ascertained; but the rolling resistance was a matter of greater difficulty, being subject to much variation. He however satisfied himself that it was so great when the surface presented to the 108 ROLLING RESISTANCE. CHAP. VII. wheel was of a rough character, that the idea of working steam carriages upon common roads was dismissed by him as entirely out of the question. Taking it as 10 lbs. to a ton weight on a level railway, it became obvious to him that so small a rise as 1 in 100 would diminish the useful effort of a locomotive by upwards of 50 per cent. This was demonstrated by repeated experiments, and the important fact, thus rooted deeply in his mind, was never lost sight of in the course of his future railway career. It was owing in a great measure to these painstaking experiments that he thus early became convinced of the vital importance, in an economical point of view, of reducing the country through which a railway was intended to pass as nearly as possible to a level. Where, as in the first coal railways of Northumberland and Durham, the load was nearly all one way,—that is, from the colliery to the shipping-place,-it was an advantage to have an inclination in that direction. The strain on the powers of the locomotive was thus diminished, and it was an easy matter for it to haul the empty waggons back to the colliery up even a pretty steep incline. But when the loads were both ways, it appeared obvious to him that the railroad must be constructed as nearly as possible on a level. The strong and sagacious mind of Stephenson early recognised this broad principle; and he had so carefully worked out the important facts as to the resistance offered by adverse gradients, that he never afterwards swerved from it, invariably insisting upon the importance of flat railroads. It is true, great and important additions were made to the powers of the locomotive; but no sooner were these effected, than lines of steeper and still steeper gradients were devised, until, as he used to declare, engineers were constantly neutralising the increased powers of the engine, and in precisely the same degree diminishing the comparative advantages of railways over common roads. These views, thus early entertained, originated, in Mr. Stephenson's mind, the peculiar character of railroad works CHAP. VII. LOCOMOTION ON COMMON ROADS. 109 as distinguished from all other roads; for, in railroads, he early contended that large sums would be wisely expended in perforating barriers of hills with long tunnels, and in raising the lower levels with the excess cut down from the adjacent high ground. In proportion as these views forced themselves upon his mind and were corroborated by his daily experience, ne became more and more convinced of the hopelessness of applying steam locomotion to common roads; for every argument in favour of a level railway was, in his view, an argument against the rough and hilly course of a common road. Nor did he cease to urge upon the numerous patrons of road steam-carriages, that if, by any amount of ingenuity, an engine could be made, which could by possibility travel on a turnpike road at a speed equal to that obtainable by horse power, and at a less cost, such an engine, if applied to the more perfect surface of a railway, would have its efficiency enormously enhanced. For instance, he calculated that, if an engine had been constructed, and had been found to travel uniformly between London and Birmingham at an average speed of 10 miles an hour, conveying say 20 or 30 passengers, at a cost of 1s. per mile, it was clear that the same engine, if applied to a railway, instead of conveying 20 or 30 persons, would easily convey 200 or 300; and, instead of travelling at a speed of 10 or 12 miles an hour, a speed of at least 30 or 40 miles an hour might be attained. All this seems trite and commonplace enough, now that the thing has been done; but it was not so in those days, before it had been attempted or even thought of, excepting by one man, whom his contemporaries spoke of as a dreamer and enthusiast on the subject of railways. Then, the socalled "practical" men were bent upon a really impracticable thing-the economical application of steam power to turnpike roads; while the "enthusiast" was pursuing the only safe road to practical success. At this day it is difficult to understand how the sagacious and strong commonsense views of Stephenson on this subject failed to force themselves sooner upon the minds of those who were per 110 INDIFFERENCE OF THE PUBLIC CHAP. VII. sisting in their vain though ingenious attempts to apply locomotive power to ordinary roads. For a long time they continued to hold with obstinate perseverance to the belief that for steam purposes a soft road was better than a hard one-a road easily crushed better than one incapable of being crushed; and they held to this after it had been demonstrated in all parts of the mining districts, that iron tramways were better than paved roads. But the fallacy that iron was incapable of adhesion upon iron continued to prevail, and the projectors of steam-travelling on common roads only shared. in the common belief. They still considered that roughness of surface was essential to produce "bite," especially in surmounting acclivities; the truth being, that they confounded roughness of surface with tenacity of surface and contact of parts; not perceiving that a yielding surface which would adapt itself to the tread of the wheel, could never become an unyielding surface to form a fulcrum for its progression. It is somewhat remarkable that, although George Stephenson's locomotive engines were in daily use for many years on the Killingworth railway, they excited comparatively little interest. Yet by them he had already solved the great problem of the employment of steam power for the purposes of railway traction. In his hands the locomotive was no longer an experiment, for he had ascertained and proved by the experience of years, that it worked more steadily, drew heavier loads, and was, on the whole, a more economical power to employ on railways, than horses. Nevertheless eight years passed before another locomotive railway was constructed and opened for the purposes of coal traffic. It is difficult to account for this early indifference on the part of the public to the merits of the greatest mechanical invention of the age. Steam carriages were exciting great interest, and numerous and repeated experiments were made with them. The improvements effected by M'Adam in the mode of constructing turnpike-roads were the subject of frequent discussions in the legislature, on the grants of CHAP. VII. TO THE NEW INVENTION. 111 public money being proposed, which were from time to time made to him. Yet here at Killingworth, without the aid of a farthing of government money, a system of road locomotion had been in existence since 1814, which was destined, before many years, to revolutionise the internal communications of England and of the world, but of which the English public and the English government as yet knew nothing. Mr. Stephenson had no means of bringing his important invention prominently under the notice of the public. He himself knew well its importance, and he already anticipated its eventual general adoption; but being an unlettered man, he could not give utterance to the thoughts which brooded within him on the subject. Killingworth Colliery lay far from London, the centre of scientific life in England. It was visited by no savans nor literary men, who might have succeeded in introducing to notice the wonderful machine of Stephenson. Even the local chroniclers seem to have taken no notice of the Killingworth railway. The "Puffing Billy" was doing its daily quota of hard work, and had long ceased to be a curiosity in the neighbourhood. Blenkinsop's clumsier and less successful engine-which has long since been disused, while Stephenson's Killingworth engines continue working to this day-excited far more interest; partly, perhaps, because it was close to the large town of Leeds, and used to be visited by strangers as one of the few objects of interest in that place. Blenkinsop was also an educated man, and was in communication with some of the most distinguished personages of his day upon the subject of his locomotive, which thus obtained considerable notoriety. The first locomotive constructed after the Killingworth model and tried upon any other railway, was made to the order of the Duke of Portland in 1817, for use upon his tramroad, about ten miles long, extending from Kilmarnoch to Troon, in Ayrshire. The engine was employed for the purpose o hauling the coals from the Duke's collieries along the line to Troon harbour. Its use was however discontinued in consequence of the frequent breakages of the cast-iron rails, |