Line of Draught of Plows. 167 



CHAPTER VIII. 



ON THE LINE OF DRAUGHT OF PLOWS. 



Ill using a double mould-board plow it is very obvious that the 

 line of draught will be in the direction of the middle line of such 

 plow; that is, the resistance of the earth to the action of the 

 mould-board on the right side of the beam tending to throw the 

 heel of the plow to the left hand, will be exactly counterbalanced 

 by the resistance of the earth on the left mould-board, tending 

 to throw the heel to the right hand. These two faces being equal 

 and contrary will therefore neutralize each other, and the plow 

 will move steadily forward in the direct line of the draught. 



This is not the case when the left side is cut off, as in our ordi- 

 nary plows, and the whole of the work is done by the share and 

 mould-board of the right side. Here the plow is acted on by a 

 lever whose length is the breadth of the plow, the eifect of which 

 is to throw the heel of the plow against the land side, and there- 

 fore to throw the point away from land, thus constantly narrowing 

 the breadth of the furrow. lu order to obviate this tendency of 

 the plow to run out, the English and Scotch plowmakers make 

 their beams oblique to the plane of the land side, so that the for- 

 ward extremity of the axis of the beam falls from an inch and a 

 quarter to two inches to the right of the plane of the land side 

 produced to that point. Although this obliquity of the beam 

 eflectually resists the tendency of the plow to run out, yet it 

 introduces an element of unsteadiness into the motion of the plow 

 which keeps the eye of the plowman continually upon the watch, 

 and his hand continually in motion to rectify the aberration. 



Messrs. Prouty & Mears devised a much better plan for accom- 

 plishing this object, which has been since adopted by the greater 

 number of our American plowmakers. 



They considered that there was a plane passing lengthwise 

 through the plow, which was so situated that the forces on each 

 side of it would balance each other. Since the greatest amount 

 of the force required to move the plow is employed in severing 

 the furrow slice from the solid land, it follows that the plane will 

 lie much nearer to the land side than to the furrow side of the 

 plow. They accordingly found, from carefully repeated experi- 



