210 A6RICULTU&AL iESSAYS. 



the sod horizontally from the wing ; to raise it to a proper 

 height for being turned over, and to make, in its progress, the 

 least resistance possible, and consequently to require a less 

 force in the moving power. Were this its only office, the 

 wedge would offer itself as the most eligible form in practice. 

 But the sod is to be turned over also. To do this, the one edge 

 of it is not to be raised at all ; for to raise this would be a waste 

 of labor. The other edge is to be raised till it passes the per- 

 pendicular, that it might fall over of its own weight. And that 

 this may be done so as to give also the least resistance, it must 

 ^e made to rise gradually from the moment the sod is receiv- 

 ed. The mould board then, m this second office, operates as a 

 transverse, or rising wedge, ihe point of which sliding back 

 horizontally on the ground, the other end continues rising till 

 it passes the perpendicular. Or, to vary the point of view, 

 place on the ground a v^edge of the breadth of the plough- 

 share, of its length from the wing backward, and as high at the 

 heel as it is >vide : draw a diagonal on its upper face, from the 

 left angle at the point, to the right upper angle of the heel ; 

 bevil the face from the diagonal to the right bottom edge, 

 which lies on the ground. That half is thea evidently in the 

 best form for performing the two offices of raising and turning 

 the sod gradually, and with the best effect ; and if you will 

 suppose the same bevil continued across the left side of the di- 

 agonal, that is, if you will suppose a straight line, whose length 

 is at least equal to the breadth of the wedge, applied on the 

 face of the first bevil, and moved backwards on it, parallel with 

 itself and with the end of the wedge, the lower end of the hne 

 moving along the right bottom edge, a curved plane will b« 

 generated, whose characteristic will be acombinatien of the 

 principle of the wedge in cross directions^ and will give what 

 we seek, the mould board of least resistance. It offers to tW« 

 great advantage, that it may be made by the coarsest work- 

 man, by a process so exact, that its form shall never be varied 

 ^ single hair's breadth. One fault of all other mould boards is, 

 that being copied by the eye, no two will be alike. In truth, 



