of the way along which the engine traveled. 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."

All railways were at that time laid in a careless and loose manner, and great inequalities of level were allowed to occur without much attention being paid to repairs. The consequence was a great loss of power, as well as much wear and tear of the machinery, by the frequent jolts and blows of the wheels against the rails. Stephenson's first object, therefore, was to remove the inequalities produced by the imperfect junction between rail and rail.

At that time (1816) the rails were made of cast iron, each rail being about three feet long; and sufficient care was not taken to maintain the points of junction on the same level. The chairs, or cast-iron pedestals into which the rails were inserted, were flat at the bottom, so that whenever any disturbance took place in the stone blocks or sleepers supporting them, the flat base of the chair upon which the rails rested being tilted by unequal subsidence, the end of one rail became depressed, while that of the other was elevated. Hence constant jolts and shocks, the reaction of which very often caused the fracture of the rails, and occasionally threw the engine off the road.

To remedy this imperfection, Mr. Stephenson devised a new chair, with an entirely new mode of fixing the rails therein. Instead of adopting the butt-joint which had hitherto been used in all cast-iron rails, he adopted the half-lap joint, by which means

HALF-LAP JOINT.

the rails extended a certain distance over each other at the ends like a scarf-joint. These ends, instead of resting on the flat chair, were made to rest upon the apex of a The supports were also

curve forming the bottom of the chair. extended from three feet to three feet nine inches or four feet apart. These rails were accordingly substituted for the old castiron plates on the Killingworth Colliery Railway, and they were found to be a very great improvement on the previous system,

CHAP. VII.] STEPHENSON'S IMPROVED LOCOMOTIVE.

201

adding both to the efficiency of the horse-power (still used on the railway) and to the smooth action of the locomotive engine, but more particularly increasing the efficiency of the latter.

This improved form of the rail and chair was embodied in a patent taken out in the joint names of Mr. Losh, of Newcastle, iron founder, and of Mr. Stephenson, bearing date the 30th of September, 1816. Mr. Losh being a wealthy, enterprising ironmanufacturer, and having confidence in George Stephenson and his improvements, found the money for the purpose of taking out the patent, which in those days was a very costly as well as troublesome affair. At the same time, Mr. Losh guaranteed Stephenson a salary of £100 per annum, with a share in the profits arising from his inventions, conditional on his attending at the Walker Iron-works two days a week-an arrangement to which the owners of the Killingworth Colliery cheerfully gave their

sanction.

The specification of 1816 included various important improvements in the locomotive itself. The wheels of the engine were improved, being altered from cast to malleable iron, in whole or in part, by which they were made lighter as well as more durable and safe. The patent also included the ingenious and original

contrivance by which the steam generated in the boiler was made to serve as a substitute for springs-an expedient already explained in a preceding chapter.

The result of the actual working of the new locomotive on the improved road amply justified the promises held forth in the specification. The traffic was conducted with greater regularity and economy, and the superiority of the engine, as compared with horse traction, became still more marked. And it is a fact worthy of notice, that the identical engines constructed by Stephenson in 1816 are to this day in regular useful work upon the Killingworth Railway, conveying heavy coal-trains at the speed of between five and six miles an hour, probably as economically as any of the more perfect locomotives now in use.

George Stephenson's endeavors having been attended with such marked success in the adaptation of locomotive power to railways, his attention was called by many of his friends, about the year 1818, to the application of steam to traveling on common roads. It was from this point, indeed, that the locomotive had started, Trevithick's first engine having been constructed with this special object. Stephenson's friends having observed how far behind he had left the original projector of the locomotive in its application to railroads, perhaps naturally inferred that he would be equally successful in applying it to the purpose for which Trevithick and Vivian had intended their first engine. But the accuracy with which he estimated the resistance to which loads were exposed on railways, arising from friction and gravity, led him at a very early stage to reject the idea of ever applying steam-power economically to common road traveling. In October, 1818, he made a series of careful experiments, in conjunction with Mr. Nicholas Wood, on the resistance to which carriages were exposed on railways, testing the results by means of a dynamometer of his own contrivance. The series of practical observations made by means of this instrument were interesting, as the first systematic attempt to determine the precise amount of resistance to carriages moving along railways. It was then for the first time ascertained by experiment that the friction was a constant quantity at all velocities. Although this theory had long before been developed by Vince and Coulomb, and was well known to scientific men as an established truth, yet, at the time when Stephenson made his

ROBERT STEPHENSON'S NARRATIVE.

203

CHAP. VII.] experiments, the deductions of philosophers on the subject were neither believed in nor acted upon by practical engineers. To quote again from the MS. account supplied to the author by Robert Stephenson for the purposes of his father's "Life;"

“It was maintained by many that the results of the experiments led to the greatest possible mechanical absurdities. For instance, it was maintained that, if friction were 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, that same small excess of power would be able to convey the carriage along a level railway at all conceivable velocities. When this position was put by those who opposed the conclusions at which my father had arrived, he felt great hesitation in maintaining his own views; for it appeared to him at first sight really to be as it was put by his opponents-an absurdity. Frequent repetition, however, of the experiments to which I have alluded, left no doubt upon his mind that his conclusion that friction was uniform at all velocities was a fact which must be received as positively established; and he soon afterward boldly maintained that that which was an apparent absurdity was, instead, a necessary consequence. I well remember the ridicule that was thrown upon this view by many of those persons with whom he was associated at the time. Nevertheless, it is undoubted, that, could you practically be always applying a power in excess of the resistance, a constant increase of velocity would of necessity follow without any limit. This is so obvious to most professional men of the present day, and is now so axiomatic, that I only allude to the discussion which took place when these experiments of my father were announced for the purpose of showing how small was the amount of science at that time blended with engineering practice. A few years afterward, an excellent pamphlet was published by Mr. Silvester on this question; he took up the whole subject, and demonstrated in a very simple and beautiful manner the correctness of all the views at which my father had arrived by his course of experi

ments.

"The other resistances to which carriages were exposed were also investigated experimentally by my father. He perceived that these resistances were mainly three-the first being upon the axles of the carriage; 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 he accurately ascertained; but the rolling resistance was a matter of greater difficulty, for it was subject to great variation. He, however, satisfied himself that it was so great, when the surface presented to the wheel was of a rough character, that the idea of working steam-carriages economically on common roads was out of the question. Even so early as the period alluded to he brought his theoretical calculations to a practical test; he scattered sand upon the rails when an engine was running, and found that a small quantity was quite sufficient to retard and even stop the most powerful locomotive engine that he had at that time made. And he never failed to urge this conclusive experiment upon the attention of those who were wasting their money and time upon the vain attempt to apply steam to common roads.

"The following were the principal arguments which influenced his mind to work out the use of the locomotive in a directly opposite course to that pursued by a number of ingenious inventors, who, between 1820 and 1836, were engaged in attempting to apply steam-power to turnpike roads. Having ascertained that resistance might be taken as represented by 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 upward of fifty per cent. This fact called my father's attention to the question of gradients in future locomotive lines. He then became convinced of the vital importance, in an economical point of view, of reducing the country through which a railway was intended to pass to as near a level as possible. This originated in his mind the distinctive character of railway works as contradistinguished 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 low ground with the excess cut down from the adjacent high ground. In proportion as these views fixed themselves upon his mind, and were corroborated by his daily experience, he became more and more convinced of the hopelessness of applying steam locomotion to common roads; for every argument in favor of a level railway was an argument against the rough and hilly course of a common road. He never ceased to urge upon the patrons of road steam-carriages that if, by any amount of ingenuity, an engine could be made which could by possibility traverse a turnpike road at a speed at least equal to that obtainable by horsepower, and at a less cost, such an engine, if applied to the more perfect surface of a railway, would have its efficiency enormously