The next thing to be described in the Mortise, is the Bore, great Hole, or Perforation; which is best shewn in the Side of a Mortise of a Wheat-drill, being larger, as in _Fig._ 3. wherein _c e b d_ is the great Hole, and is a Section of an hollow Cylinder, that passes through the Mortise, with its Axis parallel to the Edges of the Ends of the Mortise: This Cylinder, being cut by the Side of the Mortise obliquely, and not parallel to its Base, is an Ellipse. The prick’d curve Line is a Circle parallel to the Base of the Cylinder, and the curve Line _b d c e_ is the Ellipsis; and this Curve is more or less elliptical (or oval) in proportion to the Angle of Inclination, or Bevel, of the Sides of the Mortise. Of this Ellipse the longest Diameter (or _Axis transversus_) _b c_ is at right Angles with the upper and lower Edges of the Sides of the Mortise. Its shortest Diameter (or _Axis rectus_) _d e_, is the Diameter of the Cylinder, bisecting the _Axis transversus_ at right Angles in the Centre _a_; and is in this Figure one Inch and an half. This Ellipse being concentric with the Circle, the Letter _a_ is the Centre of both. The Semi-ellipsis _c e b_ is the Part of chief Use; and therefore the Edge must of Necessity be smooth, and without Flaws, as must the Surfaces of the Sides of the Mortise betwixt the Ellipse and the Fore-end. The Tongue of the Seed-box (_Plate_ 3. _Fig._ 1.) differs from that in the Sound-board of an Organ (from which I took the Idea of it) in Shape, in Situation, and in the Manner of its being fix’d to the Mortise. The Tongue, in the Organ, is on its Surface a long Square, or rectangled Parallelogram, a little broader and longer than the Mortise (or Grove) it shuts against; but this Tongue on its upper Surface, which is here turned downwards, being a Plane, is a Trapezium, of the same Shape with the Fore-end of the Mortise just now described, except that the Tongue has a less Bevel. The Situation of that in the Organ is on the Outside of the Mortise, which it shuts by its Spring behind it, and opens immediately by the Finger of the Organist pressing down the Key to let in the compressed Air to its Pipes; but this Tongue is situate within the Mortise of the Seed-box, and placed almost, in a manner, diagonally; for, had it been placed like the other, the Seed getting betwixt it and the Edges of the Mortise, would not have given Way to its Shutting (as the Air does to the other), but have kept it always open; which would have render’d it useless for sowing of Seeds.