Mechanical Conditions of the Plow. 189 



vertically elevated four inches to the point e. At the point g it 

 has been vertically elevated eight inches, and the position of the 

 slice is shown in the parallelogram c g Ji i. When the point d 

 has been i-aised through an entire quadrant, the line cZ c is repre- 

 sented by k c, and the line b chy c m. The vertical line of the 

 mould-board in contact with the line k c is called the zero line, 

 and the point touched by the angle at k is called the zero point. 

 This point is of importance, as from it all measurements of plows 

 are usually made. Up to this time the slice has turned on the 

 centre c, but on its further passage to the positions o p n m and 

 q r m s, the centre of rotation is the point m, until it attains to 

 an angle of 45 degrees, when the slice rests upon the edge of the 

 preceding furrow. If the whole sole of the slice were to be 

 severed by the share, it is clear that it would be very difficult, if 

 not impossible, to lay the slice accurately. The plow would act 

 as a simple wedge, pushing the slice over to the furrow side from 

 the land side; it would not coincide with the twist of the mould- 

 board, and therefore the transverse cracks which it receives, and 

 which is so essential to its pulverization, would not be communi- 

 cated to itj it would frequently leave it in a vertical position, and 

 sometimes, especially on side-hills, the furrow would fall back 

 into its old position. To prevent this, the rear angle of the 

 feather should never be further from the plane of the land side 

 than from one-half to three-quarters of the breadth of the furrow, 

 that is, if the furrow is ten inches wide, the rear angle of the 

 feather should be from five to seven and one-half inches from the 

 plane of the land side, measuring across the sole of the plow by 

 the shortest line between them. The strip thus left unsevered 

 on the furrow side holds the furrow to its place and forms a sort 

 of hinge upon which it turns. 



We have hitherto confined our attention exclusively to furrow 

 slices whose transverse sections are rectangles; but many plow- 

 makers and plowmen insist that a crested furrow, whose trans- 

 verse section is a trapezoid, is better than the rectangular furrow 

 because it forms a deeper seed-bed. This form is produced when 

 the rear angle of the feather lies in a plane from one inch to an 

 inch and a quarter higher than the plane of the point. 



Fig. 98 shows that those who claim a better seed-bed for a 

 trapezoidal furrow are mistaken. A series of triangles, fgf and 

 f g'f", etc., are left undisturbed at the bottom of the furrow, 

 which are eft'ectually cut up by a plow turning a rectangular 



