The ploughs in use in different countries in Europe underwent little change for many centuries; it is only lately that any attempt has been made to vary the old forms.
The Roman plough, such as is described by Virgil in the a Georgics' (i. 174), is still used in many parts of France, under the name of A raire Ronsain. It consists of a beam (tam), a body (Lewis), a share (ronter), and a handle or stilt (atira). The office of the turn-furrow is per formed by two pieces of wood about six inches long projecting ob liquely upwards, and very properly called teeth (dentalia) E r (Fig. 1). The sole of the plough a n has two pieces of wood cc and n is fixed to it on each side, forming an acute angle with it, in which the teeth are inserted. This exactly answers the description of Virgil, " Duplici aptantur dentalia dorao " (the teeth are fitted to the double back).
These teeth help to push aside the earth to the right and left, and the instrument resembles what is called a moulding plough, which is used in throwing the soil aside against young plants growing in rows, as turnips, potatoes, &c. A chain or pole connected with the end of the beam was hooked to the middle of the yoke on the neck of the oxen, and thus the plough went on making parallel furrows, so near to each other that the preceding was partially filled with the earth which the dentalia pushed aside. The point wa.s in the shape of the bead of a lance. This plough might suffice in light mellow soils, which had been long in cultivation, and had more the texture of garden mould than of stubborn clay.
The small double mould-board plough, common in other parts of France, is evidently taken from this. The teeth not being sufficiently strong, a slanting board was substituted on each side, and wheels were added, to diminish the labour of the ploughman The stilt remained the same at the place where it is attached to the plough, but higher up it was divided into two, like a fork, for the convenience of holding it with both hands. This plough acts exactly like the other, but it is stronger and better adapted for heavier land. Neither of them goes much deeper than four or five inches, leaving shallow parallel ridges, in which the seed falls, and is buried by light wooden harrows, which are drawn over the land after sowing. This is an imperfect tillage,
the bottoms of the furrows being only partially stirred. The broad flat share, and the single mould-board which turns the earth com pletely over, after lifting it up, is a far more effectual instrument, and has been adopted wherever agriculture has made any improvement. This plough snore nearly imitated the digging with a spade; and the more perfect the imitations, the better is the work.
The mould-board of a modern plough 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 necessity a double furrow where they join. 'When it is desirable that the surface should be quite flat, and the furrow-slices all in one direc tion, the mould-board must be shifted at every turn, amid a plough which admits of this is called a turn-wrest plough.
It is evident that the mould-board of a turn-wrest plough must be so constructed as to act with either side uppermost; it can therefore have only a very slight convexity to push over the slice cut off by the coulter and share; and a considerable force is lost by the obliquity of the action in doing so. The share of this plough is pointed like a lance, or present., a flat edge like a broad chisel, according as the soil is light or heavy. The point of the coulter is placed in line with that side of the point which is nearest to the unploughed land, and this is done by means of a piece of wood a an (Fig. 2), which presses it against one side or the other of the mortice in which it is placed in the beam CD, by changing the position of the pieces w 13 to the other side of the projec tion E on the beam, and pressing the head of the coulter r to the other side. The mould-board has a hook at the fore part, which goes into a staple in the side of the fore part of the body of the plough towards the preceding furrow : a piece of wood on the inside of the mould-board keeps it at the proper angle with the line of the sole.