70 Report on Trials of Plows. 



after its termination. During four years I lived in the country, 

 and paid some attention to husbandry. One day when learning 

 to hold a plow (a good Pennsylvania plow of that day), the soil, 

 rich and moist enough to be adhesive, I observed that the earth 

 filled the holloAv of the mould-board, and assumed a straight lino 

 from its fore end, near the point of the share, to its upper pro- 

 jecting hind corner, and that it mainlained that same straight 

 line. It then struck me that this straight line should exist in 

 every mould-board and direct its curvature. Four or five years 

 afterwards I returned to Philadelphia, having* been again called 

 to public life. And, at a subsequent period, visiting Mr. Bordle}^ 

 the Vice President of the Philadelphia Agricultural Society (of 

 which I was a member, and its secretary at its first formation in 

 1785), he handed me a small model of a mould-board which Mr. 

 Jefferson had left with him. At the first glance I saw the straight 

 line before mentioned governed its form, and asking Mr. Bordley's 

 daughter, then at her needle, for a piece of thread, I stretched it 

 tVinii the left lower fore part of the mould-board to its right 

 upper overhanging fore corner, and found it in a .straight line, 

 touchino; the mould-board in its whole leno-th. 'Here,' said I to 

 Mr. Bordley, ' is the principle on which this mould-board is 

 formed.'" * * * * " I have given this detail to explain the 

 opinion I now express, tJiat the straight line therein described i,s 

 essential to the form of the mould-board of the least resistance. 

 Around this line the curvature is to be formed ; and placing the 

 lower edge or bottom of the mould-board on a level floor, if 

 another straight line be laid transversely^ on the fore end or point 

 of the mould-board, and moved regularly backward on its face 

 in a plane perpendicular to the horizon, it will touch the mould- 

 board in its whole breadth, throughout its whole length, provided 

 the curvature be correct. In a word, the curvature will be a 

 ])ortion of a spiral screw. Take a large screw auger for an exem- 

 j)lification. No earth can be left on such a mould-board ; for 

 every succeeding portion of earth which the plow raises pushes 

 off that which is on the transverse straight line behind it : and 

 the face of the mould-board consists — is made up (mathemat- 

 ically speaking) — of an infinite number of such transverse straight 

 lines. 



" One more observation: The essential straight line indicates the 

 slope of the wedge on which the furrow slice rises until it reaches 

 that ])oint in the line at wliicli the transverse line is perpendicu- 



