3 46 Of the Wheat-Drill Chap. XXL 



the right, as the other is from the left End of the 

 Plank. 



This Plough makes its Chanels by Three Sheats, 

 and their Shares and Trunks ; the Firft or Foremoft 

 of which Sheats (lands under the Middle of the 

 Plank, with Part of it appearing at b\ and is fully 

 defcrib'd in Fig. 2, where A is the Tenon, of a con- 

 venient Size, Two Inches broad between Shoulder 

 and Shoulder, Three quarters of an Inch thick : It 

 is driven into the Plank thro' a Mortife, and pinn'd 

 up by its Hole : It (lands thus obliquely, and point- 

 ing forwards, that it may (land the more out of the 

 Way of the Funnel. The Shoulder at a is a quarter 

 of an Inch. The hinder Shoulder, from the Tenon 

 to the Angle at £, is Three quarters of an Inch. The 

 Depth of the Back of the Sheat, and Thicknefs of the 

 Share, when it is on, from b to c, is Nine Inches and 

 a quarter ; and the Angle at c mull be a right Angle, 

 contrary to the Opinion of fome, who fanly it ought 

 to be acute, fuppofing that when this Angle is right, 

 whilfl the Seed is defcending by the Back of the Sheat, 

 the Plough, as it moves forwards, would get before 

 the Seed, and fo it might fall to the Ground behind 

 the Trunk •, but this Miftake is for want of confider- 

 ino- the vaft Difproportion between the Celerity of the 

 Seed's defcending near the Earth, and the (low Pro- 

 grefs of the Plough ; the Seed defcending at the Rate 

 of Sixteen Feet in a Second of Time, and the Plough 

 proceeding but about Three Miles an Hour, does not 

 advance the Thicknefs of a Seed, whilft it is falling 

 to the Gtound by the whole Depth of the Sheat. 



The Thicknefs of the Sheat is an Inch, at its upper 

 Part. The reft of it is to be no thicker than the 

 Breadth of the Share. 



Fig. 3. "is the Share, lying Bottom upwards. ah 

 its Point, b the Socket, Three Inches long, Seven 

 Sixteenths of an Inch broad, c is the Hole, by which 

 it is faftened up ta the Sheat. d is another Hole, 

 which is never made uk of, except when the Share^ 



beine 



