26 Of thé Coulter.

to the dire@ion of the plough’s motion at a medium. The other two, HP and MN, are nearly equidiſtant on each ſide

of NR. Now, although this is the line

which ought to be in the direétion of

the plough’s motion at all times, it can- not be ſo in this conſtruction, except at one particular depth, becauſe, with eve- ry different depth of furrow, the plough makes different degrees of land, on ac- count of the coulter projeéing oblique- Iy to the land fide.

Theſe defects of the common con- ſtruction are ſometimes not obſerved, on account of other defects of the in- ſtrument, and they are thought to be compenſated by the greater quantity of work which the plough /¿ems to per- form, by having the coulter turned ſo

much