Washington, DC, 1999.
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A SUPPLEMENTARY note on the mould board described in a letter to Sir John Sinclair, of March 23, 1798, inserted in the American Philosophical transactions, vol. 4, and in Maese's Domestic Encyclopaedia voce Plough.
THE chief object in that description was to establish the true principle on which the mould board of a plough should be constructed, and to point out a mechanical method of making it's curved surfaces. The mould board there described, by way of example, was made with a square toe, to receive the sod at the hinder edge of the fin of the plough-share; but neither the principle nor the method is restrained to that single form. If it be desired for instance to give to the mould board a pointed toe, adapted to the fin of the plough-share, which may begin to raise the sod from the point, a small variation in the process effects it, and the principle of the curved surface is still the same. Having formed your block of the length, breadth, and height, suited to the nature of your soil, to the breadth and depth of your furrow, having scribed it, and taken out the pyramidal block as directed,
a. b.
across it, distant from the fore end about once and a half the breadth of the bottom; then draw the diagonal
a. f. c.
and if you wish to make the toe with the cutting edge oblique and straight, chip off the corner
d.
to the diagonal line
a. f. c.
or if you wish to make the cutting edge curved as that of the fin generally is, lay off the curvature you desire from
f.
to
e.
and either mark the curve by the eye, or with a pair of compasses, and chip off the corner
d.
to the curved line
a. e. c.
then saw in on your scribes and finish as directed, in the letter. It is hardly necessary to observe that the block being here represented bottom upwards, the cutting edge of the mould board appears on the left, though it will really be on the right when turned up.
TH: JEFFERSON.