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THREE:It is strange, considering the simplicity of construction and the very important office filled by machines for cutting on plane surfaces, that they were not sooner invented and applied in metal work. Many men yet working at finishing, can remember when all flat surfaces were chipped and filed, and that long after engine lathes had reached a state of efficiency and were generally employed, planing machines were not known. This is no doubt to be accounted for in the fact that reciprocal movement, except that produced by cranks or eccentrics, was unknown or regarded as impracticable for useful purposes until late years, and when finally applied it was thought impracticable to have such movements operate automatically. This may seem quite absurd to even an apprentice of the present time, yet such reciprocating movement, as a mechanical problem, is by no means so simple as it may at first appear.