122 



MECIIaXICS. 



expended for cutting off the side and bottom of the furrow- 

 slice, in firm soils, to exceed all the rest of the force re- 

 quired to draw the plow. The point or share should 

 therefore be kept sharp, and form as acute an angle as 

 practicable, as shown in Fig. 123. Some plows which other- 



Fig. 123. 



Fig. m. 



Fig. 125. 



wise work well are hard to draw because the edge, being 

 made too thick or obtuse, raises the earth abruptly. 

 Fig. 124. 



Where stones or other obstructions exist in the soil, it is 

 important that the line of the cutting edge form an acute 

 angle with the land-side, or, Fig. 120. Fig. 127. 



in other words, that it form a 

 sharp wedge, (Fig. 125.) It 

 will then crowd these obstruc- 

 tions aside, and pass them 

 with greater ease than when formed more 

 obtuse, as shown in Fig. 126, for the same 

 reason that a sharp boat moves more freely 

 through the water than one which is blunt 

 or obtuse. The gardener or ditcher proves 



this advantage when he thrusts a sharp- 

 pointed shovel. Fig. 127, more easily through 

 stony or gravelly soil, than one with a square 

 edge. (Fig. 128.) 



But when the soil is free from stones, or 

 obstructions, or is filled with small roots 

 which the plow should cut off, as in the 

 Western prairies, the sharpness of the edge 

 is more important than its form ; and hence 

 the reason that the use of the rasp or file becomes iieces- 



