MR. ROGERS says: "The problem is naturally divided into two parts: ( a ) The mechanical operation of moving the plate to be ruled over given and equal spaces ; (b) The operation of producing on glass, lines of varying degrees of fineness." Mr. Rogers then gives an elaborate description of his meritorious efforts to supply the exigencies of the first division " ( a ) ", and modestly gives the results as " the outgrowth of his own experience." * Page 74, ante.