336 Of the Drill-Boxes. Chap XX, 



Tongue, which have each its vertical Angle extremely 

 acute at the Axis of the Tongue, and have their 

 Bafes at the Bottom of the Mortife, and of the 

 Tongue : Thefe Triangles are alfo Bevels, which con- 

 fill of the Difference, or Complement, of the Bevel 

 of the Tongue, and that of the Mortife, the latter 

 being about One-third greater than the former ; i. e. 

 One-third of the whole Bevel of the Mortife is di- 

 vided between thefe Two Triangles, to each a Sixth 

 Part; fo that if the Angle of Inclination of the Sides 

 of the Mortife were Nine Degrees, then the vertical 

 Angle of each of thefe empty Triangles would be of 

 One Degree and Thirty Minutes, and Six Degrees, 

 would be left for the Bevel of the Tongue. And 

 thefe triangular Spaces help to fecure the free Motion 

 of the Tongue, and free Defcent of the Seed down 

 its Surface ; becaufe they permit no Impediment to 

 lodge in them, they being, by means of the Bevel 

 of the Mortife, wider downwards* both obliquely 

 arid perpendicularly, fo that no Duft, nor whatever 

 elfe happens to get in betwixt the Tongue and the 

 Side of the Mortife, can re it there ; for it will be 

 immediately removed thence by the Motion of the 

 Tongue, and its own Gravity, and either thrown 

 perpendicularly down, or elfe obliquely to the 

 Notches, and the firft Notch that takes it will carry 

 it out at the Seed-pailage. 



The Fourth Ufe of the Bevel is, that thereby the 

 Sections of the hollow Cylinder (before defcribed) do 

 form Eilipfes inftead of Circles ; which they muft 

 have been, if cut parallel to the Bafes of that Cylin- 

 der ; and the Sections muft have been thus parallel, 

 had the Mortife been without any Bevel. 



Now the Two Semi-eliipfes, which are on the 

 Fore-fides of their longed. Axes or Diameters, and 

 next to the Tongue, are oppofite to, and do ftiil 

 uniformly depart from each other, even from the 

 upper End of their faid longed Axis, until they 



arrive 



