1805.] Description of a Mould Board,&c. 7

earth board of the plough Should be formed;) Jet us Suppose the width of the furrow to be nine inches, the deptb Six inch- €s, and the length ofthe beam 1wo feet, then the block, Fig. 1, Should be nine inches wide at its base 6 c, and thirteen Inchezsand a half at its upper part a d; for, if it had above only the breadth a e, equal to that of its base, the ctlod of earth raiSed perpendiceularly would fall back into ihe furrow, by its own elasticity. The experience I have acquired on my estates has demonstrated to me, that in a beigbht of twelve inches, the elevation of the earth board should exceed the perpendi- cular four inches and a half,(which gives an angle of about twenty degrees and a half,) in order that the weight of the clod Should entirely overpower its elasticity.

The block uf wood Should be twelve inches high, because, if the earth board was not in height, twice the depth of tibe furrow, when you plow friable or Sandy lands bey worvid break, and fall over the earth board in irregular Jumps. It Should be three feet in length, of-which one will Serve to form the tail, which fixes the earth board to the handle of ihe plough.

The first operation consists in forming the tail, by Sawing tlie block, fig. 2, across from«a to bon itslett Side, and iwelve inches from its end fg, the incision is continued perpendieu- Jarly the length of 6 c, until within one inch and a half ot its right ide, then taking d: and ea, each equally one inch and 2 half, a cut with the Saw must be made, the length of the line de, parallel to the right Side. The pieces a bed efg will tall out of themselves, leaving the tail cdeh ik ofthethickness of one inch and a half. It is from the fore part abckl/mnof the block, that the earth board Should be made.

By means of a Square rule, trace upon all the faces of the block lines, at the distance of one inch from each other, there wil] be of course twenty-three, then draw the diagonal line km, fig. 3, upon the upper face, and& 0 upon that which is Situated on the right aide, enter the Saw at the point 72, in tlie direction of&, and descending along the line zm /, 111 it marks a rigbt line between& and /, tg. 5. Then enter the Saw at the point o, and preserving the direction ok, descend n along the line o 2, till it meets the central diagonai k /, which had been formed by the first cut; the pyramid kmno(d, fig. 4, wil] fall out of itself, leaving the block in the tor, tig. 5.

Remark, that if in the last Operation in place of Stopping the 5aw at the central diagoval k /, the cut of the block bad been continued in the same plan, the wedge /mnokb, fig. 3, would have been removed, and there woulit have remained another wedge /okbar, which, as I before observed, in Speaking of the principle relative to ihe construction of an earth Board, would be of the most perfect form, if it was in«