Without entering into any comparison of ploughs differently con structed, it is evident that the shape of the plough must vary with the moture of the soil which it is to turn up. A light soil muat be shovelled up ; a mellow one may be turned over with any kind of mould-board ; a very stiff tenacious eoil which adheres to any surface pressed against it, will be more easily turned over by a few points of contact which do not allow of adhesion. Bence 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 of nothing which is not very convex. That plough will no doubt have the least draught which is best suited to the eoil which it has to move. The lighter the plough is, con sistently with sufficient strength, the less draught it requires, all other circumstances remaining the same. Lightness and strength combined are consequently great advantages, and if a very light plough does its work as well as a heavier, there VIII be no doubt that it is preferable. Durability is nothing compared with the saving of one horse in three: it is cheaper to have a new plough every year than to keep an Additional horse all the year. If R wooden plough is found to be more easily moved than an iron one, there can be no doubt which should be preferred.
The Flemish plough is made of wood, and is very light ; the share and coulter only are of iron, besides a thin sheet of iron over the mould board, which is shaped as if it had been rolled obliquely over a cylinder,a shape well adapted to sandy soils. In ploughing land which is more or (less mellow and crumbling, the great object is to bring to the surface that portion which has lain buried, and has not served to nourish the preceding crop, and to bury that which has produced vegetation, and in which the roots of various weeds have established themselves. When manure is to be covered with a certain depth of earth, a more complete subversion is required, in order that no part of it may remain uncovered. When the land is in a compact state, from the roots which pervade it, and it is only ploughed once to prepare it for receiving the seed, much greater nicety is required to lay the slices at a certain angle so as to leave regular lines or depressions in which the seed may fall and be readily covered by the harrows which follow. In this ease the angle of '45° is found to be the most convenient at which the furrow-slices may be laid against one another. The field will then have the appearance of being laid in small ridges as in the annexed figure, all towards the same side if ploughed with a turn-wrest plough, or towards a middle line if a plough with a fixed turn-furrow has been used. To produce this regularity, the:end of the turn-furrow is made to press on the slice turned over. And if the mould-board be
convex, as it is in most Scotch ploughs, and in those made by Hornsby of Grantham, this pressure is applied just at the right place to close the junction of the several slices.
When the seed is to be dibbled on the sward, which is reversed by a single ploughing, it is necessary that the sod should be completely turned over and laid flat. To do this, and at the same time to bury all the grass, requires the furrows to be very equal and parallel ; so that when a roller has gone over the land, it is perfectly flat, without any interstices between the slices which are turned over. It requires a good ploughman to do this perfectly.
When clover-lea or old grass is ploughed up, it is difficult to bury all the grass which grows on the edge of the slice ; and if it remains exposed, it will grow and increase to the detriment of the corn. To prevent this, a wing is sometimes added to the side of the coulter, a few inches from the point, or an additional skim-coulter is made to precede the ordinary coulter of the plough. It cuts a small horizontal slice off the surface before the sod is turned over, and this falls into the bottom of the furrow and is buried there. The coulter with such a wing is called a skim-coulter, because it, as it were, skims the aurface. This instrument may require an additional horse to be put to the plough in tenacious soils, but this cannot be avoided. There is no doubt that no more horses should be put to a plough than can do the work ; but whatever be the number required, the work must be done well. There is no saving in doing the work imperfectly. The dis cussions about the number of horses which should draw a plough might easily be settled, if the nature of the soil were sufficiently taken into consideration. The shape of the plough may make some difference, but the tenacity of the soil makes a much greater.
Very little attention was formerly paid to the straightness of the furrows. natural to follow the shape of the boundary of the field, which was seldom straight ; and this practice increased gradually till no straight furrow was to be seen ; and there was a prejudice, if not a superstition, in favour of crooked ridges. Those who defended them with the least vehemence, asserted that if crooked furrows were not better than the straight, the difference was unimportant ; but no curves can be laid so perfectly parallel as two straight lines. Every deviation from parallelism causes a defect in the contact of the slices, and a lees of force by the obliquity of the draught. A superficial observer would not 'perceive this, but minute examination proves it. Hence equal and straight furrows are a sign of good ploughing.