Description of a Plough-ear. 81 



with ihe wing to its posterior end, be given, for these data 

 will determine the dimensions of the block from which the 

 ear of the plough must be cut. Let us suppose the breadih 

 of the furrow to be 9 inches, the depth 6, and the lenglh 

 of the head two feet : the block then (Plate I. fig. 1.) must 

 be 9 inches in breadth at its base be, and 13-^ inches at its 

 summit ad; for, if it had at the top only the breadth ae 

 equal to that of the base, the sod, raised in a perpendicular 

 direction, would by its own elasticity fall back into the 

 furrow. The experience which I have acquired in my own 

 land, has proved to me that in a height of 12 inches the 

 elevation of the ear ought to go beyond the perpendicular 

 4-i- inches, which gives an angle of about 20^°, in order 

 that the weight of the sod may in all cases overcome its 

 elasticity. The block must be IG inches in height, because, 

 if the height of the ear were not equal to twice the depth of 

 the furrow, when friable and sandy earth is tilled it would 

 pass the ear, rising up like waves. It must be in length 

 3 feet, one of which will serve to form the tail that fixes the 

 ear to the stilt of the plough. 



The first operation consists informing this tail by sawing 

 the block (fig. 2.) across from a to b on its left side, and 

 at the distance of 12 inches from the endy^: then con- 

 tinue the notch perpendicularly along be till within an 

 inch and a half of its right side ; then taking di and e h, 

 each equal 1^ inch, make a mark with the saw along the 

 linede, parallel to the right side. The piece abedefg 

 will fall of itself, and leave the tail cdehik, an inch and a 

 half in thickness. It is of the anterior part abcklmn of 

 the block that the ear must be formed. 



By means of a square trace out on all the faces of the 

 block lines at an inch distance from each other, of which 

 there will necessarily be ?3 : then draw the diagonals k?n 

 (fig. 3.) on the upper face, and ko on that which is situated 

 on the right ; make the saw enter at the point m, directing 

 it towards k, and making it descend along the line m I 

 until it mark out a straight line between k and I (fig. 5.) ; 

 then make the saw enter at the point o, and, preserving the 

 direction ok, make it descend along the line o/ until it 

 meet with the central diagonal kl, which had been formed 

 by the first cut: the pyramid ^7/i no/ (fig. 4.) will fall of 

 itself, and leave the block in the form represented by fig. 5. 



It is here to be observed, that in the last operation, in- 

 stead of stopping the saw at the central diagonal k I, if we 

 had continued to notch the block, keeping on the same 

 plane, the wedge Imnokb (fig. 3.) would have been takea 



Vol. 22. No. 85. June 1805. F away. 



