120 Report on Trials of Plows. 



the said lines being indicated by the figures numbering the several 

 divisions on the line B b. The arc h represents the concavity of 

 the face of the intended mould-board at the second imaginary 

 division. And the point of intersection of the said arc h with 

 the base in the position of the heel of the mould-board and 

 marked c, and the point of its intersection with the division line 

 12 determines the height of the line Ff of the upper edge of 

 the working surface of the mould-board and perpendicularly over 

 the heel of the mould-board. 



" On the said diagram Fig. 6, I draw another line, E e, parallel 

 with the line B b, and at a distance therefrom equal to the breadth 

 of the plow at the heel of the mould-board, and in this case 

 twelve inches. I then draw a straight line, fff^, from the point of 

 intersection of the line A a with the base to the point of intersec- 

 tion of the division line 4 with the arc h, and project it beyond the 

 arc h. But it becomes necessary to determine the height, from 

 the base, at which this line g f^ will intersect the plane of the 

 third division. This I obtain on Fig. 5, which represents the 

 lines on the face of the mould-board when jjrojected on a plane 

 perpendicular to the base. On this figure I draw the three par- 

 allel lines D d, B b^ E e perpendicular to the base, and, as in 

 the other figures, indicating the first, second and third divisions, 

 as also the distance of the pointy of the plow from the second 

 division. I transfer on the line B b oi this Fisr. 5, from diagrrani 

 Fig. 6, the several divisions numbered from one to twelve of the 

 arc h of Fig. 6, and I then draw a straight line from the point g 

 through the division numbered 4 and project it to the line E e, 

 or plane of the third division, and this gives the inclination of 

 the line g f^ to the base, and hence the height of its intersection 

 with the plane of the third division. And this height from the 

 base I transfer to diagram Fig. (3, and draw through it a line M ni 

 parallel with the base until it intersects the line g f^ on this dia- 

 gram Fig. 6, and from this point of intersection I describe thi; 

 arc of a cirle / on a radius equal to the breadth of the plow at 

 the heel of the mould-board, in this case twelve inches; I tiien 

 describe an arc of a circle, k, of a radius of four times the breadth 

 of the plow at the heel of the mould-board, and in this case 

 forty-eight inches, making the said arc pass through the points of 

 intersection of the arc /with the line E e, and the line g f^ with 

 the line Mm. This arc of a circle, k, determines the concavity 

 of the face of the mould-board at the plane of the third division, 



