Mechanical Conditions of the Plow. 185 



CHAPTER IX 



OF THE MECHANICAL CONDITIONS OF THE PLOW. 



In order to fulfill the indications described in the preceding 

 pages, it is necessary to form the plow so that, in sandy land, or 

 in light crumbly loams, the furrow shall be completely inverted, 

 so that the surface of the soil shall be laid upon the bottom, and 

 that which was upon the bottom shall be turned upon the top. 



In stiffer soils it is necessary to lap the furrows, so that the 

 upper surface shall form an angle of 45 degrees with the base, 

 when the lower edge of the last plowed slice will lap over one- 

 third of the preceding slice. 



As will be seen on Fig. 94, where the lines a c and c?y are nine 

 inches long, and the lines a g and d h are six inches long, and the 

 lines a h and d e are each three inches long, or one-third of the 

 length of the lines a c and d e, which represent the breadth of 

 the furrow. When the furrow slices are laid in this position, the 

 line 6 c is always equal to the line c e, and the line eftofi. 



It may be shown by the following reasoning which we borrow 

 from Mr. Stephcus, that this position insures the exposure of the 

 greatest possible surface of earth to the atmosphere. It also 

 elevates the maximum cubical mass of earth, and makes the 

 deepest seed-bed when the angles are drawn off by the action of 

 the harrow. 



Let a b, Fig. 95, represent the breadth of a ten-inch furrow 

 slice, and describe the semicircle, a c b, upon it as a diameter. 

 From this well known property of the circle, that the angle in a 

 semicircle is a right angle, every triangle formed upon the 

 diameter as a base, will be right angled; and the only isosceles 

 triangle that can l)e formed within it will be that Avhich has, c d 



