ceed to this part, it will be necessary to demonstrate how the extreme width of the mould-board, at top, is found.

In Fig. 1, (Plate IX.) Let A B C D represent a section of the block; and A EF D, a section of the horizontal position of the furrow, nine inches broad by six deep; D G H I will then represent the ascending position of the furrow in equilibrium, where the line D H is perpendicular to the horizon, and passing through a, the centre of gravity, divides the furrow into two equal portions.

In this position there is no farther pressure upon the perpendicular inclined plane; but by the least pressure of the horizontal inclined plane, the furrow will fall of itself upon the end D K, and rest in the perpendicular position D K L M, or upon its edge..

From this position it is removed by the horizontal inclined plane pressing upon it at M, which causes it to turn upon the point or corner K, until it arrives at K N OP, the descending position in equilibrium; where the line KO is perpendicular to the horizon, and passing through a, the centre of gravity, divides the furrow into two equal parts: when it has passed this position, it will fall of itself.

Hence it is evident that the extreme width at a height only equal to the breadth of the furrow, cannot be less than the aggregate of the breadth and depth of the furrow taken together, viz. 9 + 6 = 15 inches, even upon sward land, and which gives this general rule.

DM: ML:: DT: TC + BT = BC.

As 9 6 :: 12: 8

+917.

inches for the width at top, in a height of 12 inches.

But

But as a sward furrow is shifted about one inch to the right hand in its rise and twist, on account of its diagonal position and parallelism to the mould-board, it will therefore appear in the position a, b, c, d, when it leaves the mould-board: and in order that the gravity of the furrow may, in all cases, get the better of its elasticity, the width at top should be rather increased than diminished. Hence it is evident that the extreme width at top, in a height of 12 inches, cannot be less than 17; for the line DL C cuts the line B C, exactly 17 inches from the land side B, leaving the furrow in the position a, b, c, d, to fall into its proper place 1, 2, 3, c.

From the foregoing daigram it is palpably evident that the extreme width of a mould-board at top is entirely regulated by its height, and the depth of the furrow. The following table shews at one view all the proportions necessary in plough-making.

Length

Column 1st. Shews the length of the wooden part of the plough-sole.

2d. Shews the solid part of the plough-share.

3d. Shews the width of the furrows.

4th. Shews the depth, or projection, at a height equal to the breadth of the furrow.

5th. Shews the height of the mould-boards.

6th. Shews the projection at the top of the mouldboards.

7th. Shews the breadth of the furrows, which must be added to the projection at the top, and gives the extreme width of the mould-boards from the land side of the plough, in column 8.

9th. Shews the radius of the circles which form the curves of the breast.

10th. Shews the radius of the circles which form the curves on the outside of the mould-boards at top.

11th. Shews the distance between the toe of the plough, and where the perpendicular of the breast must be erected.

But as the furrows are not only shifted one inch to the right hand, but the plough is also obliged to be biassed a little to the left; the width therefore at top should rather be increased than diminished.

These preliminaries being settled, I shall proceed to describe the method of constructing a mould-board of the least resistance, which should be a continuation of the wing of the share, beginning at its hinder edge, and in the same plane.

AB

ABCDQRS, is a perspective view of the end, top, and left side of the block of wood from which the mould-board is to be made; in which the height A B is 12 inches, the width at top B C is 17, the width at bottom A D is nine, and the length BQ is 27 +3=30 inches.

Divide the length of the block into 30 equal parts; then, by a carpenter's square, trace upon all the sides of the block, lines an inch distant from one another, as represented by the occult lines.

Fig. 2, is a perspective view of the end, top, and right side of the block; on the top of which draw the diagonal line C E; and on the right side, draw the diagonal line C H.

Then take a fine-toothed saw and make it enter at E, directing it toward C, and inclining it along the corner line E G, until it makes a right line between C and G (as in Fig. 4.); then make the saw enter at H, and keep the direction H C, inclining it along the base line G H, until it encounters the central diagonal C G (Fig. 4), which had been formed by the first cut; the pyramid C EFGH (Fig. 3.) will then fall off, and leave the block in the form of (Fig. .), which clearly exhibits the two inclined planes, and the central diagonal line CG, formed by the division of the perpendicular height and the horizontal width; upon which, and the right side base line D H, the curve, which a combination of those inclined planes ought to make, is formed by straight lines from the bottom edge of the right side of the block across the central diagonal to the breast and upper edge of the mould-board.

Attention must be used, not to confound the lines. drawn on all the sides of the block, since they are now

separated