Practical Questions in Plows and Plowing. 151 



be better done by a proper twist. If the furrow slice is twisted 

 with a force insufficient to overcome its cohesion it will assume 

 the form (Fig. 75) represented in section at B. The radius, a b, 



J^ig. 76. 



is shorter than a c, hence the arc at h is smaller than that at c; but 

 the lines before flexure were equal in length, therefore while the 

 inner circle, h h i\ forms a complete semicircle the outer line, 

 f G d, falls short of being a semicircle by the distances d e and gff, 

 and the lines d i and / A, which were before parallel with each 

 other, now when bent into the curve form an acute angle. Sup- 

 pose the twist is increased until the force of cohesion is over- 

 come, the section now breaks asunder as at 6 c cZ, &c., the fracture 

 being greatest at the outer circle and growing smaller as it 

 approaches the inner one; the edges^ li and i d are again parallel, 

 and are in fact in the same straight line. We have thus accom- 

 plished by a twist applied at the right point all and more than 

 Tull accomplished by his four coulters. 



We have now, as shown in the furrow slice. Fig, 76, by a proper 

 2^ b adjustment of the enter- 

 ing wedge of the plow, 

 split it into layers on 

 the face, c d, the fissures 

 J'^iff. 70. runninor through to the 



opposite face, and also by a proper arrangement of the twist we 

 have split it on the fjice, a b, through to the bottom. These 

 fissures are seen crossing each other at right angles on the 

 end, a c. 



By a proper adjustment of the wing of the mould-board we 

 may break the slice in still another direction. Suppose the wing 

 of the mould-board were to be turned at right angles to the 

 direction of the ascending slice, as in Fig. 77. Then the ascend- 

 ing slice, e d f c, would be compelled to change its direction 

 from the line e d to the line a b; but to accomplish this the 

 particle of earth at d would move through the arc b d, while 

 the particle at f would only move round the centre. Now it is 

 evident that since each particle in lli<^ dotlcd line y (Z is moving 



