877 



PLOUGH. 



PLOUGH. 



678 



tion E on the beam, and pressing the head of the coulter F to the 

 other side. The mould-board has a hook at the fore part, which 



goes into a staple in the side of the fore part of the body of the 

 plough towards the preceding furrow : a piece of wood on the 

 inside of the mould-board keeps it at the proper angle with the liue of 

 the sole. 



The defect of this plough, which is roughly represented below, is in 

 its weight and clumsiness more than in the shape of the mould-board ; 

 for when it is made lighter, it is not so bad a construction as appears 

 at first sight, and it does its work very neatly in heavy loams with a 

 dry subsoil. If, instead of one mould-board, two were used alternately, 

 of a better shape for turning over the furrow-slice, this plough would 

 be much improved ; and this plan is adopted in many other forms of 

 the turn-wrest plough, as in that made by Cousins, of Southmolton. 



The form of the turn-furrow is of material importance, for on this 

 depends not only the perfection of the work, but also the lightness of 

 the draught. When we follow a plough working in a mellow soil 

 which slightly adheres to the plough, we often perceive that, instead 

 of being turned aside, the earth is carried forward, and only falls off 

 when the accumulation of it becomes heavy enough to overcome the 

 adhesion. It does not slide off from the mould-board itself, but 



wwSsso* e/iUS^ 



Raiuorac's Kentish Turn Wrttt Plough. 



"^-^UjO V^-' 5 ^ 



separates from the earth which adheres to the latter; thus showing 

 that the shape in defective, and giving good hints for its improvement. 

 But as the same plough will sometimes turn over the same earth better 

 when it ia either drier or moister, it in very difficult to determine, by 

 experiment only, what may, on the whole, be the best shape. A 

 little reflection and the application of scientific principles may greatly 

 us here. It us not sufficient however to find the curve which 

 will make the plough go through the ground with the least force. The 

 plough must also perform its work perfectly, and if anything is to be 

 sacrificed, it is better to employ more power than to plough the ground 

 badly. After having ascertained the mechanical principles which bear 

 working of the plough, we must observe its action carefully, 

 follow the plough day after day, in different soils and different weather, 

 and thug we may be led to observe all the circumstances which attend 

 its operation, and correct any mistakes which an erroneous theory 

 iiiL-ht have led to. 



Many attempts have been made to ascertain the exact curve which 

 the turn-furrow should have to perform the work well and at the same 

 timer '-he leart resistance. The ililli-Milt.y .,f Hi.- problem 



lies ill determining the data, . |n in. i],l.-i gn which the investigation is 

 founded; and these are so various, that it is not surprising that no 

 very satisfactory conclusion has yet been obt-iiiii-il. \V,- will make an 

 attempt at a solution from a simple examination of the motion to be 

 <-il in tin: portion of earth to be turned, which we will call the 

 furrow-slice. We shall supiwse this separated from the adjacent soil 

 by the vertical cut of the coulter, and at the same time from the subsoil 

 }>y the horizontal cut of the share ; a section of the slice, by a plane at 

 right angles to the line of the ploughing, will be a parallelogram 

 A B D c ( I'i'j. 4), the depth, A c, being the thickness of the slice, and A 11 

 its width. Confining our attention to this section of the slice, the 



AUTg AND SCL DIV. VOL. VL 



object is to move it from ita position A B D c, as cut off by the coulter 

 and share, to that of b'd' c' a', where it is inclined at an angle of \y 



Fig. i. 



to the horizontal lino ; the surface, A B (I/ a,'), being laid on the slice 

 previously turned over, so as to bury the grass or weeds which might 

 be rooted there, exposing the roots to the sun and air. The more 

 uniformly this motion is produced, and the more regularly the successive 

 sections follow each other, the less power will bo required to turn over 

 the whole slice. The motion of c D round the point u must therefore 

 lie uniform. If the turn-furrow is horizontal at the point where it 

 joim the share, and of the same width as the furrow-slice, it will slide 

 under the slice; and if the vertical sections of its upper surface, 

 at equal distances from the share, are inclined at angles regularly 

 increasing with this distance till it arrives at the perpendicular, the 

 turn-furrow will, as it adv;meen, turn the slice from a horizontal to a 

 perpendicular position: the section of it will then be, DC ah. The 

 inclination of the section of the turn-furrow must now be to the other 

 side, forming an obtuse angle with the section of the sole, until it has 

 I the slice over at the required inclination of 45, which theory 

 and experience have shown to be the best adapted to expose the 

 greatest surface to the action of the atmosphere, and likewise to form 



