History of the Plow. 



57 



■with a radius of seven inches, describe the arc a t, and concentric 

 to it the arc d u. At an angle of 45 degrees, draw t u a tangent 

 to the arc a t^ and the point of intersection of this tangent with 

 the arc will fix the extreme point, u, of the mould-board at the 

 height of the line of transit, which point will be nineteen inches 

 from the land side plane, b g^ and twelve inches above the plane 

 of the sole or base line, y b. From d lay off divisions of equal 

 parts on the arc, d u, each equal to four and a half inches — the 

 diagonal of a square of three inches — which completes the lines 

 for the fabrication of the pattern. 



The next step in the operation is that of building a blocJc, out 

 of which the pattern is to be shaped. Provide a deal-board of 

 three and a half feet, or thereal)outs, in length, with a breadth of 

 ten inches ; have it dressed of a uniform thickness, and at least 

 one end and edge straight and right angled, as seen at a b c in 



Fig. 52, and a b, fig. 126, Plate 

 IV, forming a basement to the 

 block, a being the right angle, 

 and the continuation of the board 

 being hid from view under the 

 superimposed block. Let the 

 edge, a c, of the ])()ard be marked 

 off in equal divisions of three 

 inches, agreeing exactly with those 

 of the diagram. Fig. 124, mark- 

 ing the divisions with letters or 

 numerals corresponding to the radii of the quadrant. Fig. 12(p, 

 the end, a b, of the l)oard corresponding to the radius, m, of the 

 quadrant, and to the ordinate, 7m, of the diagram. Provide, also, 

 a suit-stock or bevel of the form represented by d e f, the stock, 

 d e, being a straight bar with a head-piece at e fixed at right angles 

 to the stock, and into this blade, a f, is to be jointed in such a 

 manner that when the l)lade and stock are set parallel to each 

 other they shall just receive the thickness of the basement l)oard 

 between them, the length of the blade being equal to the breadth 

 of the slice. Five or more pieces of well seasoned, clean, three- 

 inch Memel or yellow pine deal are now to be prepared, each 

 about thirty inches in length and from six to four inches in breadth. 

 Set the level to the angle, b a m. Fig. 120, and, applying it at the 

 end of the board, as in Fig. 52, it will point out the position in 

 which Ihefii'st block nuisf be placed on llie board in order that it 



J^i^. 62. 



