Jefferson's Plow Moldboard of Least 
Resistance
Jefferson had an abiding interest in improving the technology of farming. One of his more important contributions to agriculture was the "mouldboard of least resistance" for a plow.
While serving as minister to France, Jefferson had the opportunity
to observe European plow designs. Their deficiencies inspired
him to set down in a memorandum (1788) his plans for an improved
moldboard, the wooden part of 
the
plow that lifts up and turns over the sod cut by the iron share
and colter. He wished to make that lifting and turning action
as efficient as possible, so that the plow could be pulled through
the soil with the least expenditure of force. He brought his love
of mathematics to his design, which he declared was "mathematically
demonstrated to be perfect."
By 1794, Jefferson had put his plans into action at Monticello. He had a plow fitted with a wooden moldboard of his design and reported to Sir John Sinclair (23 March 1798) that "an experience of five years has enabled me to say, it answers in practice to what it promises in theory." In addition to offering the least resistance as it was pulled through the soil, Jefferson's moldboard had a further advantage: "It may be made by the coarsest workman, by a process so exact, that its form shall never be varied by a single hair's breadth." Ease of duplication was thus another measure of the usefulness of his design.
In 1814 Jefferson began to have his moldboards cast in iron. He informed Charles Willson Peale (21 March 1815) that the plow with his iron moldboard was "so light that the two small horses or mules draw it with less labor than I have ever before seen necessary. It does beautiful work and is approved by everyone."
Just how widely Jefferson's moldboard was adopted by others is unclear. He never sought to patent it, and in fact sent numerous models to friends at home and abroad, where his design met with general approval. Jefferson's moldboard was featured in James Mease's Domestic Encyclopedia (Philadelphia, 1803), and the French Society of Agriculture awarded Jefferson its gold medal and membership as a foreign associate.
A full-scale model of a plow with Jefferson's moldboard is on
display at the Monticello Visitors Center near Monticello. For
further reading, see Edwin M. Betts, ed., Thomas Jefferson's
Farm Book (pp. 47-64) and Betts, ed., Thomas Jefferson's
Garden Book (pp. 649-654). Publishing
information is available.
--Russell L. Martin and Lucia C. Stanton, Monticello Research Department, October 1988
Pictured: A model of Jefferson's moldboard plow, photo by Skip Johns