Farmers of Forty Centuries David Erdman added much new

David Erdman added much new material that came to light after the original publication of the book in 1954

and a full discussion of the vector operator "nabla" proceeds to a treatment of potential theory and Laplace's equation

tiny changes

Opus 46 (1878)

Farmers of Forty Centuries David Erdman added much newFor more than 40,000 years, Asian farmers worked the same fields repeatedly without sapping the land's fertility and without applying artificial fertilizer! How they accomplished this miraculous feat is described by author Franklin Hiram King, a former official of the U. S. Department of Agriculture. King traveled to Asia in the early 1900s to learn how farmers in China, Korea, and Japan were able to achieve successful harvests century after century