OW THE, PLOWGH Ff ~~ The plough, then, confidered as a half-

wedge, moves on one of its* edges, with its flat fide towards the firm ground, and its inclined fide towards the ploughed ground. The face of the coulter, which re prefents the tharp angle of the wedge, cuts off the furrow from the unploughed land. The left fide of the plough being flat, and ap- plied to the firm ground, which cannot give way, makes the plough proceed in a ftraight line, and take off a furrow of equal breadth; and the right fide‘being inclined outwards, gradually removes the earth to a convenient diftance, turns, and breaks it.

The left fide of the plough refembles very nearly the flat fide of the half-wedge, becaufe it is almoft wholly in the f fame plane, and has no inclination to the line of direction in which the plough moves, or the

force

* The line AD, fig. IL. reprefents the left fide of the furrow; AB the flat or left fide of the plough applied to the firm ground; BC its inclined, or right fide, applied to the ploughed land.

+ Differentthings are faid to be in the fame plane, when they are fituated in the fame plane furface, whether that furface be real or imaginary.