APPENDIX. THE KILLINGWORTH LOCOMOTIVE. 487 



practicable. Hence it became necessary to form a joint at the 

 top of the piston-rod where it united with the cross-head, so as 

 to permit the cross-head always to preserve complete parallelism 

 with the axle of the wheels with which it was in communi- 

 cation. 



" In order to obtain the flexibility combined with direct action 

 which was essential for ensuring power and avoiding needless 

 friction and jars from irregularities in the rail, my father em- 

 ployed the " ball and socket " joint for effecting a union between 

 the ends of the cross-heads where they united with the con 

 necting-rods, and between the end of the connecting-rods where 

 they were united with the crank-pins attached to each driving- 

 wheel. By this arrangement the parallelism between the cross- 

 head and the axle was at all times maintained, it being per- 

 mitted to take place without producing jar or friction upon any 

 part of the machine. 



" The next important point was to combine each pair of wheels 

 by some simple mechanism, instead of the cog-wheels which 

 had formerly been used. My father began by inserting each 

 axle into two cranks at right angles to each other, with rods 

 communicating horizontally between them. An engine was 

 made on this plan, and answered extremely well. But at that 

 period (1815) the mechanical skill of the country was not equal 

 to the task of forging cranked axles of the soundness and 

 strength necessary to stand the jars incident to locomotive work ; 

 so my father was compelled to fall back upon a substitute 

 which, though less simple and less efficient, was within the me- 

 chanical capabilities of the workmen of that day, either for 

 construction or repair. He adopted a chain which rolled over 

 indented wheels placed on the centre of each axle, and so 

 arranged that the two pairs of wheels were effectually coupled 

 and made to keep pace with each other. But these chains 

 after a few years' use, became stretched, and then the engines 

 were liable to irregularity in their working, especially in 

 changing from working back to forward again. Nevertheless, 

 these engines continued in profitable use upon the Killingworth 

 Colliery Kail way for some years. Eventually the chain was 

 laid aside, and the front and hind-wheels were united by rods 

 on the outside, instead of by rods and crank-ankles inside, as 

 specified in the original patent ; and this expedient completely 

 answered the purpose required, without involving any expensive 

 or difficult workmanship. 



