PLOUGH AND PLOUGHING. 



. previously turned over, so as to bury 

 the grass or weeds wliicli might be 

 rooted there, exposing the roots to 

 the sun and air. The more uniform- 

 ly tills motion is produced, and the 

 more regularly the successive sec- 

 tions follow each other, the less pow- 

 er will be required to turn over the 

 whole slice. The motion of C D 

 round the point D must therefore be 

 uniform. If the turn-furrow is hori- 

 zontal at the point where it joins the 

 share, and of the same width as the 

 furrow-slice, it will slide under the 

 sHce ; and if tlie vertical sections of 

 its upper surface, at eijual distances 

 from the share, are inclined at an- 

 gles regularly increasing with this 

 distance till it arrives at the perpen- 

 dicular, the turn-furrow will, as it 

 advances, turn the slice from a hori- 

 zontal to a perpendicular position ; 

 the section of it will then be Dc ab. 

 The inclination of the section of the 

 turn-furrow must now be to the oth- 

 er side, forming an obtuse angle with 

 the section of the sole, until it has 

 pushed the slice over at the required 

 inclination of Ao°, which theory and 

 experience have shown to be the 

 best adapted to expose the greatest 

 surface to the action of the atmo- 

 sphere, and likewise to form the most 

 regular furrows for the reception of 

 the seed, which the harrow can then 

 most readily bury. 



" The surface of this turn-furrow 

 is curved in the form of the spiral 



A , 



thread of a screw, such as would be 

 generated l)y a line moved uniformly 

 forward in a direction at right angles 

 to its length, while it revolved uni- 

 formly round one of its extremities. 

 This surface is easily constructed 

 mechanically thus : take a rectangu- 

 lar parallelogram, A B C D {Fig. 5), 



Fis.5. 

 A B 



of the width of nine inches, or as 

 wide as the intended furrow, and of 

 a length equal to four times the width. 

 Bisect B C in E, and D C in F ; at 

 F raise a perpendicular F G to the 

 plane of the rectangle, and make it 

 equal to C E. Join E G and produce 

 it to K, making F K equal to F E. 

 Join K D. Draw from every point 

 in C D lines at right angles to C D, 

 meeting the line E K in different 

 points ; these lines will form the re- 

 quired surface. The line K D will 

 be found inclined 45^ to the horizon, 

 at the angle K D H, which is the in- 

 clination at which the furrow-slice is 

 most advantageously laid. To those 

 who are not familiar with solid geom- 

 etry, these lines may be easily ex- 

 hibited, by means of a wire inserted 

 at E, and bent at a right angle at K, 

 B 



E 



XWWWl I /////. 



I) 



'H 



F 



Fig. 6. 



inserting the bent portion into the 

 board A B C D (F(>. 6) at D, so that 

 it shall be inclined 4.5= at D, lying in 

 the direction of E K, in Figs. 5 and 

 6. Care must l)e taken that G F be 

 equal to C E, and perpendicular to 

 the board. 



" It is evident that, as the plough 

 moves on. a particle at E will slide 

 along the line E K. become at G per- 

 pendicular to the bottom of the turn- 



D D D 2 



furrow, which should be parallel to 

 the sole, and at K be at an angle of 

 4.5° with that line. If the slice were 

 a solid substance, this line, E K, 

 would be all that is required to turn 

 it in its proper position ; but as the 

 soil is generally loose, and would 

 crumble to pieces, a support must be 

 given to it by a surface at least as 

 wide as the slice. This surface is 

 generated by drawing lines from dif- 



593 



