Supposing the Path of the Horse to be a strait Line, and the pricked Line h i (which is at right Angles with the Plank, and equidistant from each Limber) to go exactly over it, without making any Angle on either Side of it; then the Beam must be placed at right Angles with the Plank, to the End that the Share may go parallel to the Horse-path, excepting that very small Inclination that its Point has to the left, shewn by the pricked Lines in [Fig. 1. of Plate 1.] But this Plough seldom follows the Horse in that manner. The said pricked Line h i generally makes Angles with the Horse-path; else when the Beam stood near the left Limber, and the Draw-pin near the right Limber in the Hole 9. (which it must do to keep the Share parallel to the Horse-path) the Weight of the right End of the Plank and its Limber would be too heavy for the right Hand of the Holder to manage; and if the Draw-pin be removed (suppose) to Hole 7. the Parallelism of the Share with the Horse-path will be lost, and the Point of the Share may be inclined too much towards the Left; and when a Furrow is to be plowed on the right Side of the Horse-path, the Beam must be removed nearer to the Middle of the Plank, and the Draw-pin must be placed on the left Side of the Beam, suppose to the Hole 2. This will bring the greatest Part of the Plank to the right Side of the Horse-path; and then the Share, standing at right Angles with the Plank, will make a very large Angle with the Horse-path, and then the Plough will not perform at all. Therefore it being necessary, that the Share always go parallel to the Horse-path, and often as necessary that the Plank go at oblique Angles to the Horse-path; it follows then that the Beam stand at oblique Angles with the Plank, to preserve the Parallelism to the Horse-path; and this cannot be done but by the Holes which are shewn under the pricked Lines which cross the Plank.
The Holes A, B, C, are those to one of which the Beam is screwed up by its Hole G, in [Fig. 2.] These Holes are made as near to the hinder Edge of the Plank, as they can safely be, without Danger of tearing out; which is generally about an Inch distant from the said Edge.
Every one of these Holes are answered by Three others, near the fore Edge of the Plank, as the Hole B has, at the fore Edge of the Plank, the Holes D, E, F, D, E belong to the Hole I of the Beam [Fig. 2.] These Two Holes are made as near together as they can be without breaking into one another. F answers the Hole H in [Fig. 2.] and is made between D and E, as near them as safely it can.
When the Beam is screwed up at B and F, and makes the same Angles with the Plank, as the pricked Line b c doth; then the Draw-pin standing in the Hole 8 or 9, will bring the Plough so much to the Left, that the Share will point too much towards the Right; then remove the fore End of the Beam to the Hole D, and then the Beam will make the same Angle with the Plank as the pricked Line c d, which may bring the Share to be parallel to the Horse-path nearly enough: But if the Draw-pin should be placed in the Hole 1. then the Plank would go so much on the Right of the Horse-path, that the Share would point vastly too much towards the Left, standing in either of these Two Positions: Therefore the foremost Pin must be removed to the Hole E, and then the Beam being at the same Angles with the Plank as the pricked Line f g, it may be parallel to the Horse-path, or so nearly, that by removing the Draw-pin one Hole, it may be made perfectly so.
Note, That tho’ here are but Nine Holes for the Draw-pin; yet we usually make many more in our Planks: And sometimes by changing the Draw-pin either Way into another Hole, tho’ that Hole be but an Inch distant from the former, the Share is brought right without any Inconvenience.
The Holes A and C have each of them their opposite Holes, which (when the Beam is placed into either of the Two) have the same Effect, for keeping the Share parallel to the Horse-path, as the Hole B and its Three opposite Holes have; and if either of the Holes belonging to A, B, or C, should not bring the Beam sufficiently oblique to the Plank, for the Share to be parallel to the Horse-path, when the Draw-pin is in some one particular Hole, then there may be another Hole bored before, on the Right or Left, for the fore Pin to pass thro’ by the Hole H of the Beam [Fig. 2.] which will incline the Beam a little more to the Right or Left, as occasion requires; and if none of all these be sufficient, the Plank may be turned the other Side upwards; and the Beam being fastened there by the hinder Screw into any one of those Holes, which were next to the fore Edge of the Plank before it was reversed, there may be a new Set of Holes to answer the fore Pin, of which that which was an hinder Hole before the Plank was reversed, may be one. These may set the Beam at different Angles from any of the first Holes; so that there may be at one End of the Plank Six Systems of Holes, Three on the one Side, and Three on the other; and if we have a mind to make yet more various Positions of the Plough, we may turn the Plank, End for End, and there make Six different Systems of Holes.
But, instead of turning the Plank, it would be better to have a Fourth Hole in the Beam, standing as near to the hinder Hole as H doth to the fore Hole; to answer which Fourth Hole, there may be Two Holes in the Plank, one at each Side of the hinder Hole of every System at proper Distances, to set the Plough still at more different Angles with the Plank; and these, I believe, will be more convenient for the Purpose than the different Holes in the fore Part of the Plank, it being easier to remove the hinder Screw than the fore Screw; because if the Plank and Limbers are not held up by somebody, whilst the fore Pin is out, their Weight will wrench out the hinder Hole of the Plank by that Screw; but whilst the hinder Screw is out, there is no need of holding up the Plank, because its Weight, bearing upon the Beam, cannot injure the foremost Hole, whilst the Limbers bear upon the Horse. Upon this account, I wonder we had not made the Holes, for changing the Position of the Beam, at the hinder Part of the Plank rather than the fore Part; which convinces me, that new Instruments are seldom perfect in the Beginning.
We can also alter the Standing of the Beam, by cutting away the Wood on one Side of an Hole, and placing a Wedge on the opposite Side of the Pin.
The Holder may make some Alteration in the Going of the Plough by the Handles.
The Reason we never set the Beam on the right Half of the Plank is, that the Plough always turns its Furrow towards the Right-hand; and the strait Side of the Share and the Coulter never go so near to a Row on the Right-hand, by the Breadth of Two Furrows, as it does to a Row on the Left-hand.