[Fig. 8.] is a Notch lying with its Ends near it, and is of the same Dimensions with those appearing in the Seed-box, [Fig. 3.]
The Cover B appears with its upper Surface rightly placed in the Mortise, in [Fig. 3. of Plate 3.] where its Breadth is shewn to be the same with that of the Mortise; but its Shape, and other Dimensions, are best seen in [Fig. 3. of Plate 2.] where s t is its Length, and reaches from the Hinder-end of the Mortise, to within the Tenth of an Inch of the upper End of the Axis transversus of the Ellipsis; its greatest Depth is from v to w, and is made so deep, that its Bottom, at w, bearing against the End of the Mortise, may prevent its Point, which is at t, from sinking down to touch the Spindle, which it neither must do, nor be so high above it as to suffer a Seed to pass between the Spindle and it, tho’ the Seed is not apt to pass that Way, because the Notches throw it forwards from the Cover. z is the Hole, thro’ which an Iron Screw-pin passes, and screws into the opposite Sides of the Mortise, to hold it firm in its Place: ’Tis made so thin betwixt x and y both for Lightness, and that the Seed may come the more freely to the Notches, without Danger of Arching at that End. The Use of the Cover is to prevent any Seed from falling down behind the Spindle.
[Fig. 10. Plate 2.] is the Fore-end of a Wheat Mortise, with its Hole A, thro’ which the Setting-screw is screw’d, and passes up to the Back of the Tongue by the Line q r in [Fig. 3.]
[Fig. 9. in Plate 3.] is the hinder End of a Wheat Mortise, which by its prick’d Lines, and the Two right-angled Triangles they make, shews the Bevel of the Mortise, and also its Depth; it also shews the Difference of the Bevel of the Mortise, and that of the Tongue, [Fig. 1.] which is placed against it: These Figures having been already demonstrated in the Description of the Turnep Mortise, and in these, I need say no more of it, but that I think these last-mention’d Figures sufficient Directions for understanding and making the Mortise of a Wheat-drill.
[Fig. 3. of Plate 3.] exhibits to View a Wheat Seed-box, with its Appurtenances, standing upon its Bottom; B the Brass Cover; C the Tongue hanging upon its Axis; c the End of the Iron Screw that holds on the Spring, coming thro’ the Tongue, and filed smooth with it; a, a, a, are Three Notches of the Spindle, with their bevel Ends; b, b, are Two Interstices betwixt the Notches.
Hitherto we have been speaking of the Parts contained in the Wheat Seed-box; let us now come to the Parts containing: As, first, d e f g is the upper Surface of the Brass Seed-box, shewing the Top of the Mortise, and what it contains; h h h, and h h h, shew the Ends of the hollow Cylinder, and its Bases coming out on each Side, farther than the Box; for if it did not project farther out than the Sides of the Box, the Surface of it would be so narrow, that it would cut the wooden Spindle by the Friction made between it and the Spindle; but the Surface, being of this Breadth, never wears into the Spindle, but makes it smooth and shining; i i i, and i i i, shew a Portion of the wooden Spindle (of an Inch and an half Diameter) coming out of the hollow Cylinder, on each Side of the Brass Box.
The Spindle is kept from moving end-ways, by Wreaths, in the same manner as the Axis of a Wheelbarrow is; which Wreaths shall be described together with the Hopper. k is the Hole by which the Fore-end of the Seed-box is held up to the Bottom of the Hopper, by a Screw and Nut. l is the Hole where the Hinder-end of the Box is held up, in the same manner as the Fore-end is. m n o p shew where the Two Halves of the Seed-box are joined together.
