80 Description of a Plough-ear. 



go oil ascending u^itil it has pas^od the perpendicular, ia 

 order that the sod may be inverted by its own weight ; and 

 to obtain this etiect wiih the least possible resistance, the 

 inclination or the ear must increase gradually from the mo- 

 ment that it has received tlie sod. 



In this second function the ear acts then like a wedge 

 situated in an oblique direction or ascending, the point of 

 which recedes horizontally on the earth, while the other 

 end continues to rise till it passes the perpendicular. Or, 

 toconsidv-T it under another point of view, let us place on 

 the '1-round a wedge, the breadth of which is equal to that of 

 the sock of tlie plough, and which m length is equal to the 

 sock from the wing to the posterior extremity, and the 

 height of the heel is equal to the thickness of the sock; 

 draw a diagonal on the upper surface from the left angle of 

 the point to ihe angle on the right of the upper part of the 

 heel ; slope the face by making it bevel from the diagonal 

 to the right edge which touches the earth : this half will 

 evidently be the properest form for discharging the required 

 functions, namely, to remove and turn over gradually the 

 sod, and with the least force possible. If the left of the 

 diaii;onal be sloped in the same manner, that is to say, if 

 we suppose a straight line, the length of which is equal at 

 least to that of the wedge, applied oii the face already sloped, 

 and moving backw arus on that face, parallel to itself, and 

 to the two ends of the wedge, at the same time that its 

 lower end keeps itsdf always along the lower end of the 

 rieht face, the result will be a curved surface, the essential 

 character of which is, that it will be a combination of the 

 principle of the wedge, considered according to two di- 

 rections, which cross "each other, and will give \yhat we 

 require, a plough -ear presenting the least possible re- 

 sistance. 



This ear, besides, is attended with the valuable advantage 

 that It can be made by any common workrnan by a process 

 so exact that its form will not vary the thickness of a hair. 

 One of the great faults of this essential part of the plough is 

 the want of precision, because, workmen having no other 

 guide than the eye, scarcely two of them are similar.. 



It is easier, ii'.deed, to construct with precision the 

 plough-ear in question when one has seen the method which 

 furntshes the means once put in practice, than to describe 

 the method by the aid of language, or to represent it by 

 ficrures. I shall, however, try to give a description of it. 



-Let the proposed breadth and depth of the furrow, as well 

 as the length of the licad of the plough, from its junction 



with 



