6 Description of a Mould Board,&c.(July,

Should continue rising till it has passed the perpendicular, in order that the clod of earth may turn over by its own gravity, and to obtain Such effect with the least possible resistance, the inclination of the earth board Should gradually increase from the moment it receives the clod.

In this Second function, the earth board operates as a wedge placed sloping or rising, the point of which collects the earth in an horizontal line, whilst the other end continues to raise it til] it has passed the perpendicular; or to consider it under another point of view, let us place on the ground a wedge, whose breadth is equal to that of the Share of the plough, and whose length is equal to that of the hare from its wing to its end, and the height of the heel equal to the thickness of the Share. Carry a diagonal line over the upper Surface from the left angle of the point, to the right angle of the upper part of the steel, Slope ihe face in levelling or slanting it from the diagonal to the right edge which touches the eatth; this half will be found evidently of the form best adapted to perform the two functions required, namely, to raise up and turn over the clod gradually, and with the least posSible force. If we Slope in like manner the leſt Side of the diagonal, namely, if we Suppose a right line, the length of which shall be at least equal to the length of the wedge applied upon» the face already Sloped, and moving itself behind on that Surface parallel to itself and to the two ends of the wedge, at the Same time that its lower end will remain always the length of the inferior line of the right face, ihere will result a curved Surface, whose es- Sential character will] be a combination of the principle of the wedge, conszidered according to two directions which cross It, and will give what we require, an earth board of a plough of- fering the least possible resistance.

This mould board, presents moreover-this great advantage, that it can be executed by a workman of small abilities, in a manner 80 exact, that its form will never vary an hair's breadgth.

One of the great defects of this part 50 essential to ploughs, is the little precision which is bitherto generally found in them, because the workman being only guided by his eye, Scarcely two will be made alike.

It will certainly be more easy to execute with precision, the mould board in question, when the method oft doing it has been once seen in practice, rather than by describing it 10 lan- guage, or representing it in figures. 1 will, however, attempt to giwe Such a description.| 4

"Che breadth and depth of the-proposed furrow being given, as well as the length of tbe beam ofthe plough, trom its juneuon with the wing to its hinder part,(for hese data deter-

wine the dimensioas of the block oi wood, from whence the

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