The surface of this turn-furrow is curved in the form of the spiral thread of a screw, such as would be generated by a line (u n in the following figure) about 0 or 10 inches long, and either straight or slightly curved, moved uniformly forward iu a direction at right angles to its length, while it revolved uniformly round one of its extremities for or 4 feet, commencing with the horizontal position, and terminating in an angle about 45* beyond the vertical. The curve thus generated will be found to turn over soils of a moderate tenacity very perfectly. If it is very light, the surface may be formed by arca of circles with a considerable diameter,the concave part upwards ' - if it is very tenacious, the convex part of the arches may be upwards. The annexed figures (6, 7, 8, 9) will explain this. The distance of the perpendicular F a from the fin of the share may also be varied, either lengthening or shortening the turn-furrow, as experience may show to be most advantageous.
s n, the Sole; e, the Fin ; n e, the bottom of the Torn-Furrow ; Sc and no being the resolving has traversing the distance e n, mud shown in its 'carious positions by ths tralaJTente lines. • A plough was constructed on this principle by :Messrs. Ilausome, of Ipswich, at the suggestion of the writer of this article (the late Rev. W. 'thorn), and exhibited at the meeting of the Royal Agricultural Society of England, held at Cambridge, July 15, 1840. In soils of a loose mellow nature it answered completely, and did the work more perfectly than any other plough. It united the parallelism of the solo and bottom of the turn-furrow of the Flemish plough with the im proved shape of the turn-furrow. By adopting the variations in the shape of the turn-fun-ow which we have suggested, this plough may be adapted to any soil, and be used with or without wheels.
Ploughs were formerly made of wood having those parts covered with iron where the greatest friction takes place, the share and coulter only being of iron ; but in consequence of the greater facility of casting iron in modern times, it is wholly of this metal. The advantages of Iron are, its dumbilitT, and the smaller friction it occasions when once polished by use. rho inconveniences are, the additional weight of the instrument, and consequent greater friction of the sole, which experiments have proved to be w ter than as i generally A great improvement has been introduced by making the points of the shares of cast-iron, which,by a mode of casting the lower surface on a pinto of metal, makes one surface much harder than the other; and as the softer surface wears more 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 cau be instantly replaced by moving a few screws or bolts. This is a very great isiving of time and expense ; for before this, every time an occident happened to any part of the plough, it took a long time to repair it, and in the meantime the labour was suspended, often at a very critical time of the year. 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 the greatest importance.
Mere the soil is light and crumbling, without stones, es in Norfolk, a single handle or stilt is sufficient ; but where some force is occasion ally required to prevent stones or other obstacles from turning the plough out of its course, two stilts are most convenient, placed at a more obtuse angle with the sole of the plough.
The force required to draw a plough depends not only on the nature of the soil, but also on the shape of the plough, and especially on the position of Its different harts with respect to each other, so that they do not counteract each other.
If a plough were drawn lu the direction of the sole, the obliquity of the turn-furrow would cause it to turn towards one side, and it would require a considerable force to keep it straight. In order to prevent
this, the line of draught is placed at an angle, which varies with that of the turn-furrow and the force required to push the furrow-slice over. To adjust this angle, so as to cause the plough to keep in tho intended line, there is a contrivance at the end of the beam to change the position of the ring by which the plough is drawn to the right or loft of the line of the beam, and another by which it may be raised or lowered, By this device the plough may be drawn from a point on either side of the beam, and higher or lower as may be requirtal. When the plough is found to take too much land, as ploughmen say, that is, tends to increase the width of the slice cut off by the coulter, the bridle is shifted to the left by moving the pin into another hole : when it goes out of the Muddle it is called, that is, diminishes the width of the furrow-slice, the pin is moved a hole or two to the right, until the plough has no tendency to deviate to either ride. If it inclines to rise out of the ground, the ring is shifted in the iron bridle and placed in a hook or notch higher up; if, on the contrary, it dips too deep, the ring is hooked lower. Thus a plough may be made to go straight and at a regular depth, without any more force being applied to the stilts than is required to counteract inequalities in the land, or accidental obstacles, such as stones or roots, which might throw the plough out of the ground. When the soil is of unequal texture, it is useful to have a small wheel connected with the fore part of the beam, so as to prevent its dipping dowewarda, which would require a great pressure on the stilts to keep the point of the share up, and thus increase the friction of the sole on the ground, and consequently the labour of the horses. In other cases, ploughs are provided with two wheels con nected with the beam, one of which runs in the furrow to the right, and the other on the unploughed soil to the left. When the plough has been well adjusted, and the larger wheel runs in the angle of the furrow, it acts as a gauge to regulate the width of the slice as well as its depth : in very uniform soils without stones, the plough, when set in the proper direction, will make a very straight and even furrow parallel to the one in which the wheel runs, without any person holding the stilts; so that all that is required is to turn the plough at the end of each furrow, and set it in to the proper line to form the next. As this admits of very correct adjustment, no unnecessary force is required to draw the plough : and hence this plough appears to be the easiest for the horses; and if the wheels are not very heavy, and the plough is of a good form, it certainly requires less power to move it than many which are without wheels; and it is far superior to the old clumsy wheel-plough, the beam of which rests on a heavy carriage, without being firmly attached to it. This, instead of lessening the draught, increases it by all the pressure of the beam upon the carriage, besides the weight of this last and of the wheels. There are some very irregular and stony soils, where a common swing plough can scarcely be kept steady without the help of wheels, and where it would not be so convenient to have the beam fixed on the wheels. In this case a separate carriage is necessary, that the ploughman may have a fulcrum on which he can raise his plough, or turn it to either side to avoid any considerable stone or other obstacle. Wheels have this advantage: they will enable an inferior ploughman to make better work than lie could possibly do without them ; and that too with less labour to the horses ; because, from his want of skill, the swing-plough would be contieually subject to sudden deviations, requiring him to use his strength to counteract them; and each exertion of the ploughman adds to the labour of the horses.