Besides the improved Rotherham plough, now in ge neral use, and worked by two horses, another imple ment, constructed upon the same principles, but of smaller dimensions, and considerably lighter, is used For cleaning beans, potatoes, and turnips. This plough, :See Fig. 10. Plate V.) wrought by one horse, does the business completely. It is of advantage to put a piece of plate iron betwixt the coulter and sheath or head, hat the loose earth may not fall through upon the young plants. A horse hoe, called a scraper, is also used to clean drilled crops on light soils, and is very efficacious when annual weeds are to be destroyed ; hut when quick en or other root weeds are in the ground, a deeper fur row is required, and in that case the light Rotherham plough becomes necessary.
Mr Jefferson, president of the United States of Ame rica, who has cultivated the study of agriculture with considerable success, has given the following descrip tion of a plough-ear, which we shall lay before our rea ders in his own words.
The body or a plough ought not only to he the con tinuation of the wing of the sock, beginning at its poste: viol' edge, but it must also be in the same plane. Its first function is to receive horizontally from the sock the earth, to raise it to the height proper for being turned over ; to present in its passage the 1,yrs• noNsible resistance', and consequently to require only the 11711712 of moeing power. Were its confined to this, the wedge would present, no doubt, the prop( rest form for practice ;* but the object is also to turn over the sod of earth. One of the edges of the ear ought then to have no elevation, to avoid an useless wasting of force ; the other edge ought, on the contrary, to go on ascending until it has passed the perpendicular, in or der that the sod may be inverted by its own weight ; and to obtain this effect with the least possible resistance, the inclination of the ear must increase gradually from the moment that it has received the sod.
In this second function the car 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 perpendicu lar. Or, to consider it under another point of view, let us place on the ground a wedge, the breadth of which is equal to that of the sock of the plough, and which in length is equal to the sock from the wing to the poste rior extremity, and the height of the heel is equal to the thickness of the sock : draw a diagonal on the upper sur face from the left angle of the point to the 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 es idently 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 diagonal
be sloped in the same manner, that is to say, if we sup pose a straight line, the length of which is equal at least to that of the wedge, applied on the face already sloped, and moving backwards on that fare, parallel to itself, and to the two ends of the wedge, at the same time that its lower end keeps itself always along the lower end of the right face, the result will be a curved surface, the essen tial character of which is, that it will be a combination of the principle of the wedge, considered according to two directions, which cross each other, and will give what we require, a plough-car presenting the least pos sible resistance.
This ear, besides, is attended with the valuable advan tage, that it can be made by any common workman 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 arc similar.
It is easier, indeed, to construct with precision the plough-ear in question, when one has seen the method which furnishes the means once put in practice, than to describe the method by the aid of language, or to repre sent it by figures. I shall, however, try to give a scription of it.
Let the proposed breadth and depth of the furrow, as well as the length of the head of the plough, from its junction with the 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 breadth of the furrow to be 9 inches, the depth 6, and the length of the head two feet ; the block then (Plate VI. Fig. I.) must be 9 inches in breadth at its base b c, and 13,1- inches at its summit a d ; for, if had at the top only the breadth a c equal to that of the base, the sod, raised in a perpendicular direction, would. by ice own elasticity, fall back into the furrow. The ex perience which 1 have acquired in my own land, has pt oved to Ole, that in a height of 12 inches the elevation of the ear ought to go beyond the perpentlicuiar inches, which gives an angle of about 20r, in order that the weight of the sod may in all uses overcome its elas ticity. The block must be 12 inches in height ; because if the height of the ear were not equal to tw ice the depth of the furrow, when friable and sandy earth is tilled, it would pass the car, 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.