humid conditions, with the total loss ending up greater from the humid soil. Buckingham believed this occurred due to the self-mulching behaviour (he referred to it as the soil forming a natural mulch) exhibited by the soil under arid conditions. The third section of Bulletin 38 contains the work on unsaturated flow and capillary action for which Buckingham is famous. He firstly recognized the importance of the potential of the forces arising from interactions between soil and water. He called this the capillary potential, this is now known as the moisture or water potential (matric potential). He combined capillary theory and an energy potential in soil physics theory, and was the first to expound the dependence of soil hydraulic conductivity on capillary potential. This dependence later came to be known as relative permeability in petroleum engineering. He also applied a formula equivalent to Darcy's law to unsaturated flow. Life and achievements 1867 - Born in Philadelphia, Pennsylvania, on July 8 1887 - Graduated from Harvard with a degree in physics 1893 - Received a Ph.D. from the University of Leipzig 1893 - Began teaching physical chemistry and physics at Bryn Mawr College 1897-1899 - Wrote a textbook on thermodynamics 1899 - Left Bryn Mawr and worked at a mining camp in Morenci, Arizona 1901 - Married Elizabeth Holstein in Texas 1901 - Started as an instructor in physics at the University of Wisconsin 1902-1906 - Worked at the USDA Bureau of Soils, where he wrote and published 2 papers on the dynamics of gas and water in soils. 1907 - Began working at the National Bureau of Standards (NBS) 1917, served as President of the Philosophical Society of Washington 1918-1919 - Worked a stint as associate science attaché to the U.S. Embassy in Rome 1923 - First NBS researcher to be given independent status, meaning he was freed of all administrative duties 1937 - Retired from the NBS at the mandatory age of 70, however continued to work there on research problems 1940 - Died in Washington DC on April 29 References The Soil Physics Contributions of Edgar Buckingham by John R. Nimmo and Edward R. Landa 1867 births 1940 deaths American soil scientists American physicists Scientists from Philadelphia Harvard University alumni University of Strasbourg alumni Leipzig University alumni Bryn Mawr College faculty University of Wisconsin–Madison faculty Fellows of the American Physical Society