APPENDIX. . STEAM-SPRINGS. 489 



" Engines constructed by my father in the year 1818 upon the 

 principles just described are in use on the Killingworth Colliery 

 Railway to this very day (1857), conveying, at the speed of 

 perhaps five or six miles an hour, heavy coal-trains, probably as 

 economically as any of the more perfect engines now in use. 



" There was another remarkable piece of ingenuity in this ma- 

 chine, which was completed so many years before the possibility 

 of steam-locomotion became an object of general commercial 

 interest and parliamentary inquiry. I have before observed 

 that up to and after the year 1818 there was no such class of 

 skilled mechanics, nor were there such machinery and tools for 

 working in metals, as are now at the disposal of inventors and 

 manufacturers. Among other difficulties of a similar character, 

 it was not possible at that time to construct springs of sufficient 

 strength to support the improved engines. The rails then used 

 being extremely light, the roads became worn down by the 

 traffic, and occasionally the whole weight of the engine, instead 

 of being uniformly distributed over four wheels, was thrown 

 almost diagonally upon two. In order to avoid the danger 

 arising from such irregularities in the road, my father arranged 

 the boiler so 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 equal to the support of one- 

 fourth of the weight of the engine, each axle, whatever might 

 be its position, had the same amount of weight to bear, and 

 consequently the entire weight was at all times nearly equally 

 distributed amongst the wheels. This expedient was more neces- 

 sary in this case, as the weight of the new locomotive engines 

 far exceeded that of the carriages which had hitherto been used 

 upon colliery railways, and therefore subjected the rails to much 

 greater risk from breakage. And this mode of supporting the 

 engine remained in use until the progress of spring-making had 

 considerably advanced, when steel springs of sufficient strength 

 superseded this highly ingenious mode of distributing the weight 

 of the engine uniformly among the wheels. 



"Having advanced the locomotive engine to this stage of 

 improvement, my father next turned his attention to the state 

 of the road ; as he perceived, and said, that the extended use 



