FOR PROMOTING AGRICULTURE 59 



My employments in the war of the Revolution 

 having caused me to take my family to Philadelphia, 

 I remained there after its termination. During four 

 years I lived in the country and paid some attention to 

 husbandry. One day, learning to hold a plough (a 

 good Pennsylvania plough of that period), I observed 

 that the earth, which was moist enough to be adhesive, 

 filled the hollow of the mould-board and assumed a 

 straight line from its fore-end near the point of the 

 share, to its upper projecting hind corner, and that it 

 maintained that same straight line. It then struck me 

 that this straight line should exist in every mould- 

 board and direct its curvature. 



At a subsequent period when in Philadelphia, visit- 

 ing Mr. John B. Bordley, vice president of the Phila- 

 delphia Agricultural Society, he handed me a small 

 model of a mould-board which Mr. Jefferson had left 

 with him. At first glance I saw the straight line before 

 mentioned governing its form, and, asking Mr. 

 Bordley's daughter, then at her needle, for a piece of 

 thread, I stretched it from the lower fore part of the 

 mould-board to its right upper overhanging fore 

 corner. "Here," I said, to Mr. Bordley, "is the prin- 

 ciple on which this mould-board is formed." 



I have given this detail to explain the opinion I now 

 express, that the straight line therein described is 

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

 resistance. Around this line the curvature should be 

 formed. And, by 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 back 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 portion of a spiral screw. 

 Take a large screw augur for an exemplification. No 

 earth can be left on such a mould-board; for every 



