In placing of the Share rightly upon the Sheat, consists the well going of a Plough, and is the most difficult Part of a Plough-wright’s Trade, and is very difficult to be shewn. Supposing the Axis of the strait Beam, and the left Side of the Share, to be both horizontal, they must never be parallel to each other; for if they were, the Tail of the Share, bearing against the Side of the Trench, as much as the Point, would cause the Point to incline to the right Hand, and go out of the Ground into the Furrow. If the Point of the Share should be set, so that its Side should make an Angle on the right Side of the Axis of the Beam, this Inconvenience would be much greater; and if its Point should incline much to the Left, and make too large an Angle on that Side with the Axis of the Beam, the Plough would run quite to the left Hand; and if the Holder, to prevent its running out of the Ground, turns the upper Part of his Plough towards the left Hand, the Fin of the Share will rise up, and cut the Furrow diagonally[259], leaving it half unplow’d; beside, the Plough will rise up at the Tail, and go all upon the Point of the Share: To avoid these Inconveniences, the strait Side of the Share must make an Angle on the left Side of the Beam, but so very acute, that the Tail of the Share may only press less against the Side of the Trench than the Point does. This Angle is shewn by the prick’d Lines at the Bottom of _Fig._ 1. where the prick’d Line _e f_ is supposed to be the Axis of the Beam let down to the Surface, and the prick’d Line _g f_ parallel to the left Side of the Share; but this Angle will vary as those Two prick’d Lines are produc’d forwards to the Fore-end of a long and a short Beam, keeping the same Subtense: For Plough-wrights always take this Subtense at the Fore-end of a Beam, whether it be a long Beam or short one; and it is the Subtense _e g_, that determines the Inclination the Point of the Share must have toward the left Hand. Plough-wrights differ much in this Matter; but, by what I can learn by those that make the Ploughs I see perform the best, this Subtense at the Fore-end of an Eight-feet Beam should never be more than one Inch and an half; and by full Experience I find, that whether the Beam be long or short, the Subtense must be the same; for when my Plough-wrights take this Subtense at Eight Feet from the Tail, when they make my Four-coulter Plough, whose Beam is Ten Feet Four Inches long, the Point of the Share will incline too much to the Left, and it will not go well until this Fault be mended, by taking the same Subtense quite at the End of the Beam; which makes the mentioned Angle more acute.