10 Dezcription of a Mould Board,&c.[July,

It is fixed to the plough by joining the fore part o 2, fig. 5 and 10, in the back part of the share wbich Should be made double like the case of a comb to receive and guard the fore part of the earth-board. A Screw Should then be passed through the earth-board and end of the Share at their place of contaet, then iwo other Screws Should cross the tail of the earth-board and the right handle of the plough. The part of the tail which extends beyond the handle must be cut dia- gonally, and the work will be finiShed.

In describing this operation, 1 have followed the easiest mode to make it understood, but practice has taught me that Some advantageous modifications may yetbe made. For in« Stance, in place oft beginning by forming the block as repre» Sented a ö cd, fig. 7; where a 6 is of twelve inches, and 43 right angle at 6, 1 cut off near the bottom, and from the whole length 5 c nf the block, a wedge 65 ec e, the line 6 e be- ing equal to'the thickness of the bar of the ghare,(which I Syppose to be an inch a half thick) for the face of the wing inelining from the bar to the ground, if ove comes to place the block upoy the Share without caleulating this inclination, the Side a 5 would lose its perpendicularity, and the side a d would cease to be horizontal. Moreover, instead of leaving the top of the block thirteen inches and a half wide from m to 2, fig. 8, Lake away from the right Side a kind of wedge 72 Eicpn of oneinch and a halt thick, experience having proved to me, thar the tail becomes, hy this means, more obligue as c 7, in place of k 2, and adapts itself more advan- tageously to the Side of tbe handle. The diagonal of the up- per face finds itself consequently drawn back from& to c, and we have m c in place ot 7z k as above. These modifications will be easy to adopt by any person who comprehends its yeneral principle.:

In the different trials to which the earth-boards of plough have been Submitted to determine the quantum which the

with regard to the front of the earth board. We will direct the ſaw along the

races D F and D s, in ſuch a manner that its movement stops at the time, when its edge on one ſide, ſhall touch the curve c, p, at the point u, ütvated an the track x z, and on the other ſMall be ſituated. parallel to the line 5 Zy; upon which the ſaw 1s(topped at the otber ſide of the earth board. The edge of the ſaw will then cut the face a| or,in ſome point E, ſo ſituated that:he direction conducted by this point and by the point u will be pa- rall:! to the direction which paſſes by the points s z y. If we continue in the ſame manner cutting with the ſaw different paints on the edge al, thoſe by which it will come out will form upon the face a lor curve EMH, and if we continue by theſe points and by thoſe which correſpond with them vpon the lines c p H. The right lines ſuch 25 thoſe which paſs by the

oint E u, and that we have taken for example, the tangent ſurface to theſe right lines, and laid open by means of a ſharp inſtrument, it will form wiih the remainder eh o IHM E oftheplana 1 or:he hinder part of the earth board ſuch as is repreſented at fig. 10,