To Robert Patterson
Philadelphia Mar. 31. 98.
I return you Emerson with thanks. it has suggested a qualification of the expression in my letter, which had supposed the [wedge] the form offering least resistance to the rising sod.—I did at f[irst], as you do now, consider this mould board as a twisted plane. but a little reflection convinced me, as it will you, that it is not, and that it would be impossible to twist a board into that form. a second view of the mould board would shew you that the breadth of it’s face varies much, and that parallel lines drawn on it horizontally would not be strait ones. I have sometimes thought however of making a mouldboard on that principle: that is to say take a block formed into a wedge 2. f. long, 12. I. high (the breadth of the wedge) & 13½ I. wide at the thick end, as in the margin. Fig. 1. saw in, at a.b.c.d.e.f.g Fig. 2 in lines parallel to the ground, and at increasing depths from top to bottom, so that the saw shall enter 4½ I in the bottom line at the but end of the wedge, & not at all at the point. then [dish] out the sawed stuff, and a face would be presented offering strait lines both longitudinally & transversely. such a surface would be generated by laying a stick h. k. (Fig. 3.) on the floor,1 & another h.i. 12. I. above it parallel with the plane of the floor, the point h. of each2 perpendicularly over or under the other & the end i. of the upper one3 4½ I. to the right of the end k. of the under one. then move a strait line back from h. parallel with itself, keeping the lower end on h.k. & the upper on h.i. & the surface would be formed. this would be perfect for turning over the sod, but not at all for raising it. I am with great esteem Dear Sir
Your friend & servt
PrC (DLC); faint; at foot of text: “Mr. Patterson.”
1. Word interlined in place of “ground.”
2. TJ here canceled “[parallel?].”
3. Preceding four words interlined by TJ.