The Manner of fastening the Organ-tongue to its Mortise is by Parchment and Leather glu’d to its Surface, and also to the Sound-board, at its End which is opposite to that pressed open by the Key, and shut by the Spring; but this our Tongue is held within the Mortise, and moves on an Axis, which passes thro’ its upper and narrower End, which Axis is the Pin A (which must be exactly parallel to the Edge of the End of the Mortise), and also thro’ the Hole f in [Fig. 3. in Plate 2.] which is seen in its Place at A in [Fig. 3.] [Plate 3.] and likewise through both Sides of the Mortise near their upper Edges, and as near the Fore-end of the Mortise as may be, without the Tongue’s rubbing against the said Fore-end.
The Breadth of the Tongue must be conformed to the Breadth and Bevel of the Mortise, and when it is on its Axis, it being raised tight up as far as the short prick’d Line l m in [Fig. 3. Plate 2.] being One-eighth Part of the great Hole, and being there, you see its upper Edges touch both Sides of the Mortise by their whole Length: Then it is rightly made: and by this touching both Sides of the Mortise tightly and closely, when raised up to that Degree, it appears, that the Two upper Edges of the Sides of the Tongue are inclined to each other in an Angle that is more acute, by about One-third, than is the Angle of Inclination of the Sides of the Mortise.
Hence, when the Tongue is let down to its Place, there will be on each Side of it an empty Space, betwixt it and the Mortise, of the Form of a very acute Triangle, whose vertical Angle is more or less acute, according as the Tongue approaches nearer to, or recedes farther from the Spindle.
This [Fig. 1. Plate 3.] is the brass Tongue with its Back-side upwards. The Two outer Lines a b and c d are the Edges of the upper Surface (tho’ turned downwards in this Figure), which are inclined to each other, as afore-mentioned; but the Two inner Lines e f and g h are nearer to each other, whereby this under Surface is narrower than the upper: Both must be plain Surfaces, but the upper and its Two Edges very free from Flaws, and smooth, or polished.
The Reason why the under Surface is narrower than the upper, is to preserve the Bevel of the empty Triangle: For though the Bevel of the Sides of the Mortise would be sufficient for this, if both Sides of the Tongue were sure to keep equally distant from the Spindle; yet as the Tongue never is so tight on its Axis, but that sometimes one Corner of it may be nearer to the Spindle than the other, in this Case, that Side which is nearest to the Spindle would reverse that Bevel, so as to make the small empty Space that is betwixt the Mortise and the Tongue, wider above than underneath.
C C are the Two little Knobs that prevent the Spring from slipping to either Side, and are at the Distance from one another of the Breadth of the Spring.
[Fig. 2.] shews one Side, and the Thickness of the Tongue the other Side, being the same. a b shews the polished Surface (being a true Plane), whereon the Seed runs down to the Spindle. c d the Back-side, which lies turned uppermost in [Fig. 1.] b e d shews one End of the hollow Cylinder of the Tongue, thro’ which its Axis passes.
The Length of the Tongue must be such, as will reach lower than just to touch the Bottom of the great Hole as a Tangent: for, if it be not longer than that, it might happen, that when the Mortise is empty of Seed, and the Tongue set up close, a Wheel might, in Turning, or otherwise, go a little backwards, and cause a Notch of the Spindle to take hold of the End of the Tongue, and tear it out of the Mortise: Therefore let the Tongue reach a little below the Spindle, as the pricked Line g h, in [Fig. 3. of Plate 2.] doth.
As for the Posture in which the Tongue ought to stand in the Mortise, it is shewn by the Three pricked Lines in [Fig. 3. Plate 2.] where the pricked Line g h makes an Angle of Forty-five Degrees, being the nearest that it can stand to the Spindle; the pricked Line i h makes a somewhat greater Angle, and it is a mean (or middle) Distance from the Spindle; and the pricked Line k h is supposed to be its greatest Distance, where the Tongue makes its greatest Angle with the Top and Bottom of the Mortise. If the Tongue stood so obliquely as to make an Angle much less than Forty-Five, the Tongue would rise too much against the Bevel of the Mortise, and the Spring would have the greater Difficulty in returning it to its Place, when driven back by the Force of the Notches.
And beside, when the Tongue stood wide from the Spindle, there might be so much Room betwixt it and the Sides of the Mortise, that some Seeds might fall thro’ there.