PLOUGH. The oldest forms of plough of', which we have any description in ancient authors, or which are represented on monu ments or coins, are very simple ; a mere wedge with a crooked handle to guide it, and a short beam by which it was drawn, form the whole instrument. The light Hindoo plough, now in use in many parts of India, seems to differ little from the old model.
The different essential parts of a plough have certain names usually given to them. The Body of a plough is that part to which all the other parts are attached. The bottom of it is called the Sole or Slade, to the fore part of which is affixed the Point or Share; the hind part of the sole is called the keel. The Beam, which advances forward from the body, serves to keep the plough in its proper direction, and to the end of it are attached the oxen or horses, which are employed to draw it. Fixed in the beam in a vertical position, before the point of the share, with its point a little forward, is the `Jointer, which serves to cut a vertical section in the ground ; while the point of the share, expanding into a Fin, separates a slice by the horizontal cut from the subsoil or solid ground under it. The Mould-Board, or TurnEurrow, is placed obliquely behind the fin, to the right or left, in order to push aside and turn over the slice of earth which the coulter and share have cut off: it thus leaves a regular furrow wherever the plough has passed, which furrow is intended to be filled up by the slice cut off from the land by the side of it, when the plough returns. The Stilts, or handles, of which there may be either one or two, as is thought more convenient, direct the plough by keeping it in the line required and at a regular depth in the ground. The single stilt appears to be the most ancient form.
Wheels ottre a modern invention in compd. rison with the other parts. They support the end of the beam, and prevent it from going too deep into the ground or rising out of it while the plough is going on. The greatest improvements introduced into modern ploughs are in the shape of the mould-board or turn-furrow, and the contrivances for regula ting the' line of draught so as to make the plough go at an equal depth, and cut off a regular slice of equal breadth, without any great force being applied by the ploughman who holds the stilts. The mould-board is either fixed on one side, or made so as to be shifted from one side to the other ; in the first case half the furrow-slices lie on one side and half on the other, and there is of neces sity a double furrow where they join. When
it is desirable that the surface should be quite flat, and the furrow-slices all in one direction, the mould-board must be shifted at every turn, and a plough which admits of this is called a Turn-Wrest Plough.
Ploughs were formerly made of wood, having those parts covered with iron where the greatestfriction takes place, the share and coulter only being of iron ; but in consequence of the greater facility of casting iron in mo dern times, most of the parts are nowmade of this metal. The beam and stilts are still usually of wood, but even these are now sometimes made of wrought iron. The advantages of iron are, its durability and tho smaller friction it occasions when once po lished by use. Tho inconveniences are the additional weight of the instrument, and consequent greater friction of the sole. Recent experiments have proved this to be greater than was generally suspected. A great im provement has been introduced by making the points of the shares of cast-iron, which, mode of casting the lower surface on a plate of metal, makes one surface much harder than the other ; and as the softer surface wears mare rapidly, a sharp edge is always preserved. The different parts of a plough are now usually cast so that if any one fails or wears out, it can be instantly replaced, by moving a few screws or bolts. There is another advantage in having the essential parts of cast-iron. If any particular shape has been once discovered to be the best for any part, that shape is preserved without deviation in every plough made on the same pattern, and with respect to the turn-furrow this is of great importance. The stilts of the plough are mostly of wood ; one will suffice for a light soil, but two are required for a heavy soil The shape of a plough must vary with the nature of the soil which it is to earn up. A light soil must be shovelled up ; a mellow one may be turned over with any kind of mould board; a very stiff tenacious soil which adheres to any surface pressed against it, will be more easily turned over by a few points a contact which do not allow of adhesion. hence the point and turn-furrow have been made of all imaginable shapes, and while one man contends for a very concave form, another will admit a nothing which is not vary convex. The lighter the plough is, coa sistently with sufficient strength, the less ,1 draught it requires, all other circumstances remaining the same.