The drawings, model, and description of your mold-board of least resistance, which you have been pleased to submit to my inspection, and which I had not seen before, I have now examined with much attention and pleasure; and do not hesitate in giving it my approbation, if that can be thought of any consequence after the one it has already received from Mr. Rittenhouse.

The doctrine of resistance is, indeed, still but little understood; no theory having yet been established on this subject, which will perfectly agree with practice—Induction, from well conducted experiments, will in this, as in most other cases of practical science, be our surest guide.

I should suppose that a good proof of a mold-board being of the best form, would be its wearing evenly in all its parts—And I think I have frequently observed that the mold-board of a plough, however formed by the carpenter, would in time, by the wearing or friction of the sod, acquire a figure exactly resembling that of your model—

Whether a plane sided wedge (as you have taken for granted) be a solid of the best form for removing an obstacle to one side, or simply in one direction, may perhaps be doubted—Emerson, in his doctrine of fluxions, makes it a solid of a curvilineal surface—Experiment however must determine this matter.

The sod, formed by all the ploughs which I have seen is a rectangular parallelopiped; and therefore if set on edge, perpendicularly to the horizon would have no tendency to turn over, but would stand in that position—nay if its dimensions be 6 I. by 9 it must be made to decline from the perpr. upwards of 40 degrees before it will fall over.

Quere, then, whether there might not be some advantage in having the sod cut with oblique angles, the coulter, for this purpose, inclining a little towards the left hand? The transverse section of the sod would then be a rhumboid, and could not stand perpendicularly but must fall over from the plough. Indeed it would have this tendency even before it arrived at a vertical position, viz. as soon as the center of gravity came to the right hand of the left-under-acute-angle of the sod. I conceive also that the surface of the plowed land would be less uneven or corrugated when plowed in this way, as the obtuse angles of the sods would be all turned upwards—

Quere 2d. As the figure of your mold-board is exactly that which a plane board would acquire by being twisted—whether, when made of wood, which, with the generality of farmers, would most frequently be the case, mold-boards might not more easily be formed in this way, previously heating the board, either with steam or fire, as ship-builders do their planks? The friction also would be less on boards made by twisting than on those formed by the saw and adze, as it would be parallel to, and not accross the grain of the wood. Such mold-boards would moreover be much less liable to break.

Quere 3d Whether three or four rollers, with their surfaces projecting a little beyond the surface of the mold-board, might not be applied with advantage in lessening the friction from the sod?—

These crude remarks are however submitted with great diffidence, to one who is infinitely better acquainted with the subject, both in theory and practice, than I can pretend to be.

From Dr. Sir, with very great regard & esteem—Your Most obedt Servt