Chap. XX. Of the Drill-Boxes. . 311 



Cylinder, being cut by the Side of the Mortife ob~ 

 -liquely, and not parallel to its Bale, is an Ellipfe. 



The prick'd curve Line is a Circle parallel to the 

 Bafe of the Cylinder., and the curve Line b d c e is 

 •the Ellipfis; and this Curve is more or lefs elliptical 

 (or oval) in proportion to the Angle of Inclination, 

 •or Bevel, of the Sides of the Mortife. 



Of this Ellipfe the Jongeft Diameter (or Axis tranf- 

 lerjus) b c is at right Angles with the upper and 

 lower Edges of the Sides of the Mortife. 



Its fhorteft Diameter (or Axis remits) d £, is the 

 Diameter of the Cylinder, bifecling the Axis iranj- 

 verjus at right Angles in. the Centre a j and is in this 

 Figure one Inch and an half. 



This Ellipfe being concentric with the Circle, the 

 Letters is the Centre of both. 



The Semi-ellipfis c e b is the Part of chief Ufe *, 

 and therefore the Edge muil of Necefiity be fmooth, 

 and without Flaws, as muft the Surfaces of the Sides 

 of the Mortife betwixt the Ellipfe and the Fore-end. 



The Tongue of the Seed- box (Plate 3. Fig. 1,) 

 differs from that in the Sound-board of an Organ 

 X from which I took the Idea of it) in Shape, in Si- 

 tuation, and in the Manner of its being fix'd to the 

 Mortife. 



The Tongue, in the Organ, is on its Surface a 

 long Square, or reclangied Parallelogram, a little 

 'broader and longer than the Mortife (or Grove) ir 

 fhuts againft ; but this Tongue on its upper Surface, 

 which is here turned downwards, being a Plane, is a 

 Trapezium, of the fame Shape with the Fore-end of 

 the Mortife juft now defcribed, except that the Tongue 

 has a lefs Bevel. 



The Situation of that in the Organ 4s on the Out- 

 fide of the Mortife, which it fruits by its Spring 

 behind it, and opens immediately by the Finger of 

 the Organift prefling down the Key to let in the com- 

 breffed Air to its Pipes; but this Tongue is fituate 



X 4 with id 



