It is described, together with some of its Appurtenances, in [Plates 2] and [3].
The Mortise.
As the Seed-box is the principal Part of a Drill, so is the Mortise the principal Part of the Seed-box.
The following Descriptions shew how this Mortise differs from a common Mortise.
[Fig. 1. Plate 2.] shews both the upper and lower Edges of a Turnep-Seed-box, and the Manner how they are posited one over another, a b c d is a rectangled Parallelogram, and shews the upper Edges (or Top) of the Mortise. e f g h, being a Figure of the same Denomination with the former, is the lower Edges (or Bottom) of the Mortise. The Line e h is the Length of the lower Edge of the Hinder-end of the Mortise. a d is the upper Edge of the Hinder-end of the Mortise, and posited just over the lower Edge of the same End. The Space between the Line a b, and the Line e f, shews half the Excess whereby the Bottom of the Mortise exceeds the Top in Breadth; as the Space on the opposite Side, betwixt the Line c d, and the Line g h, shews the other Half of that Excess, both which Halves, taken together, shew the whole Bevel (or Angle of Inclination) described in [Fig. 2.] That Part of the Line a b, from the Angle at b to the Line f g, which intersects it, shews the Excess whereby the Top of the Mortise exceeds the Bottom in Length.
[Fig. 2.] Is the Mortise cut down by its Four Corners, and laid open. a b c d is a Trapezium, with Two parallel Sides, and mark’d A, the right Side of the Mortise; its opposite Side e f g h, mark’d B, the left Side of the Mortise; the Areas of both being true Planes[261].
[261]Take care that these opposite Sides be sure to be true Planes, especially all that Part of their Areas, that is before the transverse Axes of their Ellipses herein after described; for should they be otherwise, the Bevel of the Mortise would be spoiled, and so would the Ellipses, and the acute Triangles, on the Sides of the Tongue; which how necessary they are to be true, is shewn in the proper Place. Workmen are very apt to fail in this when they file by Hand, and make these Sides of the Mortise convex instead of plane. Therefore this might be done with less Difficulty, and more Exactness, with a File placed in a Frame, whereby it might move upon a true Level without rising or sinking of either End.
d i k h Shew the Fore-end of the Mortise, mark’d C. a l m e shew the Hinder-end of the Mortise, mark’d D. a d h e shew the Bottom of the Mortise already described in [Fig. 1.] If these opposite Sides and Ends were all raised up, until the Angle at b join the Angle at l, and that at m join f, and that at g join k, and that i join c, the Top of the Mortise would be formed, and the same with the Parallelogram a b c d, in [Fig. 1.] and then the intire Mortise of the Turnep Seed-box would appear in its true Form, standing upon its Bottom.
This differs from a common Mortise, in that it is impossible to fit it with a Tenon; because it is narrower above, and shorter below, as in [Fig. 1.]