102 NEW RAIL AND CHAIR. CHAP. VII. 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, whilst 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 the rails extended a certain distance over each other at the ends, somewhat like a scarf joint. These ends, instead of resting upon the flat chair, were made to rest upon the apex of a curve forming the bottom of the chair. The supports were extended from three feet to three feet nine inches or four feet apart. These rails were accordingly substituted for the old cast-iron plates on the Killingworth Colliery Railway, and they were found to be a very great improvement upon the previous system, 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 iron-manufacturer, and having con CHAP. VII. SCARCITY OF SKILLED WORKMEN. 103 fidence 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. The specification of the same patent also described various important improvements on all locomotives previously constructed. 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. Thus the road was rendered smoother, and the wheels of the locomotive were made stronger. But the most ingenious and original contrivance embodied in this patent was the substitute for springs which was devised by Mr. Stephenson. He contrived an arrangement by which the steam generated in the boiler was made to perform this important office! The means by which this was effected were so strikingly characteristic of true mechanical genius, that we would particularly call the reader's attention to this ingenious device, which was the more remarkable, as it was contrived long before the possibility of steam locomotion had become an object of parliamentary inquiry or even of public interest. It has already been observed that up to, and indeed for some time after the period of which we speak, there was no such class of skilled mechanics, nor were there any such machinery and tools in use, as are now at the disposal of inventors and manufacturers. The same difficulty had been experienced by Watt many years before, in the course of his improvements in the steam-engine; and on the occasion of the construction of his first condensing engine at Soho, Mr. Smeaton, although satisfied of its great superiority to Newcomen's, expressed strong doubts as to the practicability of getting the different parts executed with the requisite precision; and he consequently argued that, in its improved form, this powerful machine would never be generally introduced. Such was the low state of the mechanical arts in those days. Although skilled workmen were in course of gradual training in a few of the larger 104 STEAM SPRINGS. CHAP. VII. manufacturing towns, they did not, at the date of Stephenson's patent, exist in any considerable numbers, nor was there then any class of mechanics capable of constructing springs of sufficient strength and elasticity to support a locomotive engine ten tons in weight. The rails then used being extremely light, the road soon. became worn down by the traffic, and, from the inequalities of the way, the whole weight of the engine, instead of being uniformly distributed over the four wheels, was occasionally thrown almost diagonally upon two. Hence frequent jerks of the locomotive, and increased stress upon the slender road, which occasioned numerous breakages of the rails and chairs, and consequent interruptions to the safe working of the railway. In order to avoid the dangers arising from this cause, Mr. Stephenson contrived his Steam Springs. He so arranged the boiler of his new patent locomotive that it was supported upon the frame of the engine by four cylinders, which opened into the interior of the boiler. These cylinders were occupied by pistons with rods, which passed downwards and pressed upon the upper side of the axles. The cylinders opening into the interior of the boiler, allowed the pressure of steam to be applied to the upper side of the piston; and that pressure being nearly equivalent to one-fourth of the weight of the engine, each axle, whatever might be its position, had at all times nearly the same amount of weight to bear, and consequently the entire weight was pretty equally distributed amongst the four wheels of the locomotive. Thus the four floating pistons were ingeniously made to serve the purpose of springs in equalising the weight, and in softening the jerks of the machine; the weight of which, it must also be observed, had been increased, on a road originally calculated to bear a considerably lighter description of carriage. This mode of supporting the engine remained in use until the progress of spring-making had so far advanced that steel springs could be manufactured of sufficient strength to be used in locomotives. CHAP. VII. HIS ENGINES STILL IN USE. 105 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 locomotive engine, as compared with horse traction, became more apparent. And it is a fact worthy of notice, that the identical engines constructed by Mr. Stephenson in 1816 are to this day to be seen in regular useful work upon the Killingworth railway, conveying heavy coal trains at the speed of between five or six miles an hour, probably as economically as any of the more perfect locomotives now in use. Mr. Stephenson's endeavours having been attended with such marked success in the adaptation of locomotive power 106 CONSTRUCTS A DYNAMOMETER. CHAP. VII. to railways, his attention was called, by many of his friends, about the year 1818, to the application of steam to travelling on common roads. It was from this point, indeed, that the locomotive had been 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 originally intended it. 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 successfully applying steam power to common road travelling. 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 construction. His readiness at all times with a contrivance to enable him to overcome a difficulty, and his fertility in expedients, were in no respect more strikingly displayed than in the invention of this dynamometer. Though it was found efficient for the purpose for which it was contrived, it will not of course bear a comparison with other instruments for a similar purpose that have since been invented. 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 thus 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 Mr. Stephenson made his experiments, the deductions of philosophers on the subject were neither believed in nor acted upon by practical engineers. And notwithstanding that the carefully conducted experiments in question went |