8^ Description of a Plough-ear^ 



It IS fixed to the plough by morticing the fore part o l 

 (fig. 3 and 10.) into the posterior edge of the sock, which 

 must be made double, like the case of a comb, that it may 

 receive and secure this fore part of the ear. A screw-naiP 

 is then made to pass through the ear ainl the handle of the 

 sock at the place of their contact, and two other screw-nails 

 pass through the tail of the car and the right handle of the 

 plough. The part of the tail which passes t>eyond the han- 

 dle must be cut diagonally, and the work will be finished. 



In describing this operation I have followed the simplest 

 course, that it may be more easily conceived ; but I have 

 been taught by practice, that it requires some useful modi- 

 fications. Thus, instead of beginning to form the block as- 

 represented ahcd (fig. 7'):> where ah is 12 inches in length- 

 and the angle at /' is a right one, I cm off towards the bot- 

 tom, and along the whole length he of the bfock, a wedge 

 Ice, the line I being equal to the thickness of the bar of the 

 sock (which I suppose to be 1^ inch) ; for, as the face of the 

 wing inclines from the bar to the ground, if the block were 

 placed on the sock, withotat taking into the account this 

 inclination, the side ah would lose its perpemlicular direc- 

 tion, and the side ad would cease to be horizontal. Be- 

 sides, instead of leaving at the top of the block a breadth 

 of 13-i- inches from m to n (fig. 8.), I remove from the 

 right side a kind of wedge nk'tcpn of 1-i- inch in thickness; 

 because experience has shown me that the tail, which by 

 these means has become more oblique, as ci instead of kiy 

 fits more conveniently to the side of the handle. The dia- 



in reg^ard to the anterior face of the e;.r. The thicltnc's of the latter bein^ 

 dfterniincd by that of xW part k c d i t h (fig-. 9.), or, what amounts to the 

 same thinij, bv the length of the lines c h; tli, eb, let us first conceive that 

 there has been traced out, proceeding- from the pouit r, the curve cup pa- 

 rallel to k y n, and then, proceeding from the point ji, the curve p 5 parallel' 

 to In. Let us next suppose that the saw cuts the edg-e n I of the face abml 

 in the point ?, situated in the same plane as xt, and ts, which plane has been 

 taVcen for example in rct^ard to the anterior face of the ear. The saw must 

 be directed along the traces Jf and J. 5 in such a manner that its motion shalf 

 stop at the term where its edge on the one hand shall touch the curve ip in 

 the point u situated on the trace .t 7, and on the other shall be situated pa- 

 rallel to the line sxii at v/hich the saw stopped on the other side of the ear. 

 The edge of-the saw will then cut the face nloT in s;ime point i, so situated 

 that the straight line drawn through that point and the point ;i shall be pa- 

 rallel to the straight line which passes through the point s z, y. If you con- 

 tinue in the same manner ontting with tlie saw different points of the edge al, 

 those by which it comes out will form on the face a tor a curve £/.t&; and 

 if through these poin.s and those corresponding to them in the lines cp, p^^ 

 there be drawn straight lines, such as that which passes through the points 

 e,u, and which we have taken as an example, the surface touching these 

 straight lines, and uncovered by means of any sharp instrument, will: form 

 with the remainder ehold/^t of the plane alor, the posterior face of ths ear, 

 such as is rcpresCBted fig. 10.— AVtc of the French Hdilor. 



gonal 



