32 Repobt on Trials of Plows. 



shown me that the tail which, by these means, has become more 

 oblique, as c z, instead of d i, fits more conveniently to the side 

 of the handle; the diagonal of the upper face is consequently 

 removed back from a to c, and we have m c, instead of m d, us 

 above. These modifications may be easily comprehended by 

 /hose acquainted with the general principle." 



This method, devised by Mr. Jefferson, removing, as it does, 

 the formation of the plow out of the domain of empiricism, and 

 enabling workmen in diflerent sections of the country, without 

 communicating with each other, to form their mould-boards pre- 

 cisely alike, was one of the most valuable contributions towards 

 the perfecting of plows that has ever been made by any one man, 

 and will always entitle him to a conspicuous place among the 

 benefactors of agriculture. 



But the credit that we award to him must be confined to the 

 service which he rendered in demonstrating that plows could be 

 made by rule, and to the actual discovery of one of the many 

 rules that are applicable to the formation of the mould-board. 



A very slight examination of Mr. Jefierson's method will show 

 its very great defects. For instance, the overhang of the wing to 

 the right, e d, Fig. 19, is only four and one-half inches. This 

 would only be sufiicient to turn the furrow slice, when it was 

 turned down hill, or, on some soils, it would answer on a level, 

 but, on other soils, it would be quite insufiicient to invert the slice, 

 while it would be sure to tumble back into its original position 

 when the furrow was turned up the hill. Modern practice shows 

 that no plow can be safely relied on to invert the furrow where 

 Ihe overhang is less than forty-five degrees. 



To make this angle, the line e d, Fig. 18, must be made twelve 

 inches instead of four and a half inches. Then, to complete the 

 plow, according to Mr. Jefferson's rule, the perpendiculary would 

 be advanced six inches towards c, and the line gr h would be 

 carried forward, so that it would stand within five and a quarter 

 inches of the point c. It will be very obvious that such a 

 degree of bluntness would be impracticable without an expendi- 

 ture of power which no farmer could afford to throw away. In 

 other words, the rule is only applicable when we have an imprac- 

 ticable rear wing to the mould-board or an impracticable share. 



The lower edge of the mould-board is quite too long, increasing 

 the friction very unnecessarily. In our best modern plows the 



