OM THESPEOUGH. 13

~ Another circumftance, wherein the plough departs from the figure of the half- wedge is, the fituation and inclination of the coulter f.

With regard to fituation, the coulter is not placed where the inclination of the mould-board begins. which would render the refemblance more compleat, but ata confiderable diftance before it; fo that the plough acts, for fome time, as a cutting inftrument, before it begins to a&t as a wedge.

Or, the plough may be confidered as a wedge whofe inclination is different at different places, very{mall for a certain length, but very confiderable afterwards.

This fituation of the coulter is a very fimple but ingenious contrivance; for it both di- minifhes the refiftance, and makes the plough move with more feadinefs. It di-

».minithes confiderably the refiftance; becaufe

the earth of the furrow is feparated and broken in fome meafure, before the mould-board reaches it, and in this loofe ftate more readily gives way to the projec-

tion of the board. Had

+ Figure 5. and 6,