24 



Report on Trials of Plows. 



right of the upper part of the heel; slope the face by making it 

 bevel from the diagonal to the right edge which touches the 

 earth: this half will evidently be the properest form for discharg- 

 ing the required functions, namely, to remove and turn over grad- 

 ually the sod, and with the least force possible. If the left of 

 the diagonal be sloped in the same manner, that is to say, if we 

 suppose a straight line, the length of which is equal at least to 

 that of the wedge, applied on the face already sloped, and moving 

 backwards parallel to itself and to the two ends of the wedge, 

 at the same time that its lower end keeps itself always along the 

 lower end of the right face, the result will be a curved surface, 

 the essential character of which is, that it will be a combination 

 of the principle of the wedge, considered according to two direc- 

 tions, which cross each other, and will give what we require, a 

 mould-board presenting the least possible resistance. This mould- 

 board, besides, is attended with the valuable advantage that it 

 can be made by any common workman by a process so exact that 

 its form will not vary the thickness of an hair. One of the great 

 faults of this essential part of the plow is the want of precision, 

 because workmen having no other guide than the eye, scarcely 

 two of them are similar. One may easily conceive and render 

 sensible the manner in which the sod is raised on the mould- 

 board which we have described, by an attentive consideration of 

 the following diagram, Fig. 18. 



-yd 



Fiff. f8. 



Draw on an horizontal plane or parallelogram, ahcfe the 

 lines a b and c e, being each = to twenty-four inches, = the length 

 of the mould-board, and the lines b c^ d e, each = nine inches, = 

 the width of the sole at the heel of the plow, produce the line a e 

 to d, and make e d foui- and u half inches, this being the overhang 



