The specification of the same patent also described 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. But the most ingenious and original contrivance embodied in this patent was the substitute for springs which Mr. Stephenson invented. He contrived that the steam generated in the boiler should perform this important office. The method by which this was effected displayed such genuine mechanical genius, that we would particularly call attention to the device, which was the more remarkable, as it was contrived long before the possibility of steam locomotion had become an object of general inquiry or of public interest. It has already been observed that up to, and indeed after, the period of which we speak, there was no such class of skilled mechanics, nor were there any such machines and tools in use, as are now available to inventors and manufacturers. Although skilled workmen were in course of gradual training in a few of the larger 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 locomotive engines of ten tons weight. In order to avoid the dangers arising from the inequalities of the road, Stephenson 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 the 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 bear the weight of locomotive engines. [Picture: Old Killingworth Locomotive, still in use]