_Fig._ 1. in _Plate_ 4. is the Drill-plough, which makes the Chanels for a treble Row of Wheat, at Seven-inch Partitions, and covers the Seed by the Harrow which moves on its Beams. A, is the Plank, Three Feet and an half long, Eight Inches and an half broad, one Inch and a quarter thick; its upper and under Surfaces are true Planes. B, B, the Two Beams, each Two Feet Four Inches long, Two Inches Three quarters broad, and Two Inches and a quarter deep, standing under the Plank at right Angles with it, and held up to it by the Four Screws and Nuts _a_₂ _a_₂ _a_₂ _a_₂ the one being at the same Distance from 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 First or Foremost of which Sheats stands under the Middle of the Plank, with Part of it appearing at _b_; and is fully describ’d in _Fig._ 2, where A is the Tenon, of a convenient Size, Two Inches broad between Shoulder and Shoulder, Three quarters of an Inch thick: It is driven into the Plank thro’ a Mortise, and pinn’d up by its Hole: It stands thus obliquely, and pointing forwards, that it may stand 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 _b_, is Three quarters of an Inch. The Depth of the Back of the Sheat, and Thickness of the Share, when it is on, from _b_ to _c_, is Nine Inches and a quarter; and the Angle at _c_ must be a right Angle, contrary to the Opinion of some, who fansy it ought to be acute, supposing that when this Angle is right, whilst the Seed is descending by the Back of the Sheat, the Plough, as it moves forwards, would get before the Seed, and so it might fall to the Ground behind the Trunk; but this Mistake is for want of considering the vast Disproportion between the Celerity of the Seed’s descending near the Earth, and the slow Progress of the Plough; the Seed descending 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 Thickness of a Seed, whilst it is falling to the Ground by the whole Depth of the Sheat. The Thickness of the Sheat is an Inch, at its upper Part. The rest of it is to be no thicker than the Breadth of the Share.