History of the Plow. ^3 



whole, which had no unity of phm, and the discordant parts could 

 not, therefore, be expected to accomplish satisfactory results. 



In view of these great difficulties in the way of making uni- 

 formly good plows, it must be admitted that the discovery of Mr. 

 Jetferson, by Avhich mould-boards could be made by any one with 

 Ihe absolute certainty of having them all exactly alike, was an 

 era in agriculture, and the root of all real progress in the manu- 

 facture of this all-important implement. 



W(; have therefore thought that it would be desirable to give 

 a full description of his method, which we hope will prove intel- 

 ligible to every one who desires to understand it. 



In order to obtain a clear idea of the curve of the mould-board 

 which Mr. Jeft'erson considered to be the best, we give his ideas 

 in his own words, except that we shall take the liberty of chang- 

 ing the antiquated names given by him, for those which are used 

 to designate those parts at the present day: 



" The mould-board of the ])low ought not only to be the con- 

 tinuation of the shield of the share beginning at its posterior 

 edge, but it must also be in the same plane. Its first function is 

 to receive horizontally from the sock the earth, to raise it to the 

 height proper for being turned over; to present, in its passage, the 

 least possible resistance, and consequently to require the minimum of 

 moving power. Were its function confined to this, the wedge would 

 present, no doubt, the properest form for practice; but the object 

 is also to turn over the sod of earth. One of the edges of the 

 mould-board ought then to have no elevation, to avoid an useless 

 wasting of force; the other edge ought, on the contrary, to go on 

 ascending until it has passed the perpendicular, in order that the 

 sod may be inverted by its own weight; and the inclination of 

 the mould-board must increase gradually from the moment that 

 it has received the sod. 



" In this second function the mould-board then acts like a wedge 

 situated in an oblique direction, or ascending, the point of which 

 recedes horizontally on the earth, while the other end continues 

 to rise till it passes the perpendicular. Or, to consider it under 

 another point of view, let us place on the ground a wedge, the 

 breadth of which is equal to that of the share of the plow, and 

 which in length is equal to the share from the wing to the poste- 

 rior extremity, and the height of the heel is equal to the height 

 of the rear of the share above the sole: draw a diagonal on the 

 upper surface from the left angle of the point to the angle on the 



