AGRICULTURAL ward furrow wheel are adjustable vertically with reference to the frame, for the purpose of controlling the action of the plough. The team is hitched to a clevis at the end of the plough beam, and the machine is guided by a pole secured to an arm on the upper end of the spindle of the forward furrow wheel; and, by means of a connexion between this arm and a controlling arm on the spindle of the rear wheel, the latter is controlled in turninsr by the former. The sulky plough has important advantages over the walking plough from the fact that the weight and downward pull due to its action on the ground are taken by
MACHINERY
167
where the soil is hard and clayey, it is desirable to plough deeper than usual, and for this purpose a subsoiling plough is used, which does not turn a furrow, but digs deeply into the ground and thoroughly stirs it.
Fig. 2.—Disk plough. Where a hillside is to be worked, a swivel plough (Fig. 3) is used. In this machine the mould-board is symmetrical about a line drawn from its point to the middle of its rear end, and is pivoted at its front and
the wheels, and the friction, being thus converted from sliding into rolling friction, is much less, and the draft is correspondingly diminished. It is also easily guided, and the depth of the furrow is readily controlled by the levers, which are assisted in their action by springs, thus greatly lightening the labour. The walking plough also possessed a serious defect on account of the downward pressure on the bottom of the furrow, which not only added to the friction, but had the effect of forming a hard and smooth bottom, which served to turn water, causing it to run along the bed thus formed and wash away the fertile soil. This was remedied to some extent by the sulky plough, as the bottom pressure was taken up by the wheels; but a form of plough intended to overcome this defect is being introduced into extensive use. This plough is built both as a riding and a walking plough, and is shown in Fig. 2. The essential feature is the substitution of a concavo-convex disk, pivoted on the plough beam, for the mould - board and share of the ordinary plough. This disk is carried on an axle inclined to the line of draft, and also to a vertical plane. As the machine is drawn forward the disk turns on its axis and cuts deeply into the ground, and, by reason of its inclination, crowds the earth outwards and thus turns a furrow. A scraper is provided to keep the disk clean and prevent sticking, and a small plough in the rear squares the corner of the furrow. The controlling levers and draft arrangements are similar to those already described in. connexion with the sulky plough. The advantage of tais plough over the ordinary form is in the absence of sliding friction, and in the mellow and porous condition iu which it leaves the bottom of the furrow. Variations in soil and in the character of the surface of farming lands have led to various modifications of the plough to suit it to these different conditions. In cases
Fig. a.—Swivel plough. rear to the landside, so that it can be swung underneath from one side to the other, and thus changed from right to left hand, in order that the furrow may be always turned down hill. Preparation of the Seed-Bed. The ground having been ploughed, it becomes necessary to pulverize it and break up the clods to furnish a good seed-bed, and for this purpose the harrow is used. Harrows.—The oldest and simplest form of harrow consisted of a- frame of wood, having on its under side a number of teeth, which, as the implement was drawn over the ploughed field, combed or raked the surface until it was substantially level. The first step in improving this harrow consisted in building the frame of steel bars and forming them in two or more sections secured to a common draft bar by flexible connexions, thus enabling the harrow to accommodate itself more exactly to the inequalities of the ground, and to secure a more perfect result. A harrow of this type is shown in Fig. 4. In this machine the teeth are secured to bars pivoted at their ends in the side bars of the frame, and provided with crank arms connected to a common link bar, which may be moved horizontally by means of a lever for the purpose of
