History of the Plow. 49 



end to end. The plow which insures this result most certainly is 

 the best plow in their eyes, even though it should require more 

 power to draw it, though it should wear out faster, and though it 

 were far more costly than another. 



The English plowmen would not subscribe to our chapter on 

 " The Objects to be Accomplished by Plowing." The plow is not 

 the implement to pulverize, in their view, but the harrow. Pul- 

 verizing properties would be objectionable to them, as it would 

 interfere with a sharply defined crest. Since the vertical lines of 

 the plow are those which determine the shape of the crest, it is 

 not Avonderful that their formation should have monopolized the 

 ingenuity of the English plow wrights. 



Turning our attention to the sections of the various plows given 

 in Plates III and IV, we shall see plainly enough that all the 

 plows there given have been constructed with reference to this 

 object. On inspecting Fig. 112 we see that the lines of the plow 

 in front, c c, b b and a a, are concave above the line of transit, 

 while those in the rear , 1 1 and 2 2, are concave beloiv that line. 

 The lines in contact with the slice are all of them straight, or 

 nearly so, agreeing in this respect with the plan of Mr. Jefferson, 

 It differs from his in this, that as the generating line of this plow 

 as Small finally made it, is a catenary curve, Mr. Jefferson's gene- 

 ratines line is a straight line. This will be understood l)y a recur- 

 rence to Fig. 18, which represents Mr. Jefferson's method of 

 forming the twist of his mould-board. 



If we now take in elevation. Fig. 49, what is shown in plan in 

 Fig. 18, by erecting a post, d d', twelve inches high at the point 

 d. and stretching a cord tightly from d ' to b, we shall have Mr. 

 4 



