the land-side, presenting a uniform smooth surface to the firm land, and preventing the crumbled earth from falling within the body of the plough. These last parts cover the body-frame from view; but all the parts described in fig. 2 may be seen in different perspective in this. 664. The plough as seen in fig. 2 is supposed to stand upon a level plane, the heel i and point of the share ƒ touching that plane-these being actually the points on which the plough is supported when in motion, and this plane kk, is called the base line. The dotted line ll above the base-line is the surface-line, which represents the depth of the furrow taken by the plough, and which is seen to intersect the mouldboard and coulter at certain points. 665. Fig. 4 represents the plan of the same plough, in which all the parts described will be easily identified, with the additional advantage of showing that the proper lines of the body on the land-side lie all in one plane as from a to b, which, in working, should be held in the vertical position, or very slightly inclining to the Fig. 5. or cutter e standing to the right, having a breadth of at least two-thirds the breadth of the furrow, the cutting edge of the feather lying nearly as low as the plane of the sole. The neck of the share ƒ is prolonged backward, joining and coinciding with the curve of the mould-board, which curvature is also carried forward on the back of the feather of the share. The character of this plongh is to cut a furrow-slice of 10 inches in breadth, by 7 inches in depth, a rectangle, leaving the sole of the open furrow level and clean. It is for this property, which I consider of paramount importance in ploughing land well and thoroughly, that I give it the preference to all others, inasmuch as others cut the slice more or less of a trapezoidal form, and leave the bottom of the open furrow in an inclined, instead of a level position. The resistance to the draught is generally below the average of ploughs, and this plough is employed for every kind of soil. PLOUGH 666. A necessary accompaniment of every plough is the plough-staff, or plough-spade, as it is called in some places, fig. 5. Its use consists in shovelling off the mould that may happen to adhere to the front of the mouldboard, between d and f, fig. 4; in pushing away any stubble or weeds that may accumulate in the angle formed by the coulter e and beam a, fig. 2; and in striking out the stones that may become fixed between the points of the coulter STAFF. and share. It rests on the plough, when not in use, by its spade being inserted into a staple on the inside of the land-side of the body, and its shank lying on the cross bar, g, fig. 4, of the stilts, with its handle quite convenient to the ploughman. 667. Swing-trees.-Horses are yoked to the plough by means of a set of levers named swing-trees, arranged as to cause the united strength of the horses employed to be exerted in one point, namely, that formed by linking the ring e, fig. 6 of the main lever of the swing-trees bb, to the hook of the bridle of the plough n, fig. 3. By this contrivance the horses draw the plough from one point only. The swingtrees have various other names in different parts of the country. Such as swingletrees, whipple-trees, draught-bars, or simply bars. The swing-trees are used for attaching horses to other implements besides the plough, such as harrows, small ploughs, &c. In the plough yoke a set of swing-trees consist of 3, as represented in fig. 6, where a points out the bridle of the plough, bb the main swing-tree attached immediately to the bridle, cc the furrow or off-side small swing-tree, and d d the land or nigh-side small tree, arranged in the position in which they are employed in working: h is a section of a swing-tree at the centre of attachment, with clasp and eye mounting; the scale of which is double the size of the principal figure in the cut. Swingtrees are for the most part made of wood, oak or ash being most generally used; but the former, if sound English oak, is by much the most durable-though good Scotch ash is the strongest, so long as it remains sound, but it is liable, by long exposure, to a species of decay resembling dry-rot. The small trees are furnished with S hooks, by which they are appended to the ends of the main tree; and end clasps are adapted to receive the hooks of the trace chains, ff, g g, a small part only of which are shown in the figure. oxidation of the iron acting over a large surface, and soon destroying the fabric. Another method has been to form a diamond-shaped truss of solid iron rods, the diamond being very much elongated, with a stretcher between the obtuse angles. A third has been tried, consisting of a straight welded tube of malleable iron, as in fig. 7. In this tube, acting as a strut, a tension rod, also of malleable iron, is applied with a deflection, the extremities of the tension-rod being brought into contact by welding or riveting with the ends of the tubular strut, and eyes formed at the ends and middle, for the attachment of the Fig. 7. 668. Though wood has hitherto been the material chiefly used for swing-trees, there have been some successful trials of malleable iron for the purpose. These have been variously constructed, in some cases entirely of sheet iron turned round into a form somewhat resembling the wooden trees; but in this form, either the iron must be thin, or the bar must be inconveniently heavy; if the former, durability becomes limited, by reason of the TRUSSED IRON SWING-TREE. hooks and chains. A tree thus formed is sufficiently strong for every purpose to which it is applied, while its weight does not exceed 7 lb., and the weight of a wooden tree, with its mounting, frequently weighs 8 lb. The price of a set of common wooden trees, with the iron mounting, is 12s., and of the iron trees 168. 669. This form of swing-trees is adapted for the use of two horses, but ploughing is sometimes performed by three horses, such as in cross-furrowing, or in breaking up stubble in autumn, when the land is clean, or in ploughing old rough lea ground; and sometimes four horses are employed at one time in the plough, when the subsoil or trench plough is used. There are various ways of yoking three horses to the plough, the simplest of which is a pair working in the common trees, fig 6; and for the third horse, a light chain is attached by a shackle to the middle of the main bar b b. To this chain a third horse is yoked, taking his place in front of the other two, in unicorn fashion. This yoke is defective, inasmuch as there are no means of equalising the draught of the third horse. 670. Perhaps the most perfect method. of yoking a 3-horse team, whether abreast or unicorn-fashion, is that by the compensation levers, fig. 8- a statical combination, which is at once correct in its equalisation, scientific in principles, and elegant in arrangement. The apparatus in the figure is represented as applied to the subsoil plough; a being the bridle Fig. 8. means of their shackles at k to the main swing-tree b; and the three small swingtrees c, d, e, are hooked to the compensation lever at h, h and 7. of that plough; b is a main swing-tree, of strength proportioned to the draught of 3 borses; and c d e are three small common trees, one for each horse. The trace-chains are here broken off at f, g, respectively. Between the main swing-tree and the three 671. The judicious farmer will fresmall ones the compensating apparatus is quently see the propriety of lightening placed, consisting of three levers, usually the labour of some individual horse; and constructed of iron. Two of these, hi and this is easily accomplished by the comhi, are levers of the first order, but with pensation apparatus. For this purpose, unequal arms, the fulcrum k being fixed one or more holes are perforated in the at of the entire length from the outward levers h i, on each side of the true fulend of each; the arms of these levers are crum k, to receive the bolt of the small therefore in the proportion of 2 to 1, and shackle k. By shifting the shackle and the entire length of each between the bolt, the relation of the forces h and i are points of attachment is 27 inches. A changed, and that in any proportion that connecting lever l, of equal arms, is jointed may be desired; but it is necessary to to the longer arms ii of the former, by observe that the distance of the additional means of the double short links m, n. holes, on either side of the central hole or The two levers hi, hi, are hooked by fulcrum of equilibrium in the system, should be in the same proportion as the length of the arms in which the holes are perforated. Thus, if the distance between those in the short arm is half an inch, those in the longer arm should be an inch. By such arrangement, every increase to the exertion of the power, whether on the long or the short arm, would be equal. chain of the nigh horse is hooked to the end o of the swing-tree c, fig. 8, and his off-side trace-chain to the end o of the swing-tree d. The middle horse has his nigh-side chain hooked to the end p of the swing-tree c; while his off-side chain goes to the end p of the swing-tree e, and the off-side horse has his nigh-side chain attached to the end g of the middle swing-tree d, and his offside to g of the swing-tree e. This system of yoking is complicated, and though in principle it equalises the forces so long as all the horses keep equally a-head, yet it is in some degree faulty. Whenever the middle horse gets either behind or before his proper station,-or out of that position which keeps all the swing-trees parallel to each other, the outside horses have a larger share of the draught upon one Fig. 9. 672. The same principle of compensation has been applied to various ways of yoking, one of which is a complicated form of that just described. The main swing-tree and the compensation levers are the same, except that they may be a few inches shorter in all the arms, and the middle one of the three small swingtrees also shorter. The yoking is performed in this manner: The nigh trace |