. The Soil Physics Contributions of Edgar Buckingham

years as a graduate assistant in the physics department. He did additional graduate work at the University of During 1902 to 1906 as a soil physicist at the USDA Bureau of Strasbourg and the University of Leipzig, where he studSoils (BOS), Edgar Buckingham originated the concepts of matric ied under chemist Wilhelm Ostwald, who won the Nobel potential, soil–water retention curves, specific water capacity, and Prize in 1909. In 1893, Buckingham received a Ph.D. unsaturated hydraulic conductivity (K ) as a distinct property of a soil. He applied a formula equivalent to Darcy’s law (though without from Leipzig. That same year, he began teaching physispecific mention of Darcy’s work) to unsaturated flow. He also contribcal chemistry and physics at Bryn Mawr College. During uted significant research on quasi-empirical formulas for K as a func1897 until 1899 he wrote a textbook on thermodynamics tion of water content, water flow in capillary crevices and in thin (Buckingham, 1900a). He left Bryn Mawr as an associate films, and scaling. Buckingham’s work on gas flow in soils produced professor in the summer of 1899. paradigms that are consistent with our current understanding. His work After his departure from Bryn Mawr, he spent the on evaporation elucidated the concept of self-mulching and produced next 18 mo vacationing, tutoring prep school students, sound and sometimes paradoxical generalizations concerning condiand working for several months in the copper mining tions that favor or retard evaporation. Largely overshadowing those district of Arizona. Few details on this latter episode achievements, however, is that he launched a theory, still accepted are available. On 13 Sept. 1899 he had a meeting with today, that could predict transient water content as a function of time and space. Recently discovered documents reveal some of the arguHarvard president Charles William Eliot. Within a day, ments Buckingham had with BOS officials, including the text of a he was summoned to New York City to meet with a two-paragraph conclusion of his famous 1907 report on soil water, Mr. Dodge and a Mr. Douglas (probably William Earl and the official letter documenting rejection of that text. Strained Dodge, Jr., and noted metallurgist James Douglas of interpersonal relations motivated the departure of Buckingham and the Phelps Dodge Corp.). Two days later, he was on a other brilliant physicists (N.E. Dorsey, F.H. King, and Lyman Briggs) special train chartered by the American Institute of from the BOS during 1903 to 1906. Given that Buckingham and his Mining Engineers, bound for San Francisco. On 15 Oct. BOS colleagues had been rapidly developing the means of quantifying 1899 he arrived at a mining camp in Morenci, AZ. Paid unsaturated flow, these strained relations probably slowed the ad$100 a week beginning when he left New York, he vancement of unsaturated flow theory. worked an eclectic mix of jobs for the company, including putting up wires for electrical lighting, working as an engine oiler, and analyzing gas samples. He left Morenci E Buckingham tremendously advanced the unlate in February 1900. During his year and a half away derstanding of water and air in unsaturated soils from formal academic life, he was also courting Elizaduring 4 yr at the BOS, which culminated with his fabeth Holstein, whom he had met at Bryn Mawr. They mous paper of 1907 (Buckingham, 1907). He introduced were married in Texas in 1901. He resumed his academic the concept of potential into soil-water flow and used career as an instructor in physics at the University of an equation equivalent to Darcy’s law to quantify flow Wisconsin in 1901. After one academic year he left Wisin unsaturated soil. Topics of his investigation included consin for the BOS. soil gas flow and aeration, evaporation from soil and At the BOS from 1902 to 1906, he investigated the the effectiveness of self-mulching (i.e., retardation of dynamics of gas and water in soils, the main subject of evaporation by a thin surficial layer drier than the rest this paper. He reported this research in two reports of the soil), measurement of water retention curves (the (Buckingham, 1904; Buckingham, 1907). After leaving relation between water content and matric potential the BOS, he went to the National Bureau of Standards ), identification of the retention curve and unsaturated where he remained until retirement in 1937. In 1923, hydraulic conductivity K( ) as the two main soil properhe was the first NBS researcher given the prized “indeties for unsaturated flow, and mathematical formulas of pendent status” (i.e., free of all administrative duties). the ( ) and K( ) relations (which he proposed and His work included research on helium production for tested to some degree on both experimental and theothe military, and technical oversight of NBS support of retical grounds). rocketry studies by Robert Goddard. He served as an Buckingham (Fig. 1) was born in Philadelphia, PA adviser to the U.S. Navy on steam turbine and propeller on 8 July 1867. In 1887, he graduated from Harvard design and lectured on thermodynamics at the Naval with a bachelor’s degree in physics, then worked several Postgraduate School in Annapolis, MD. Buckingham had traveled extensively in Europe during his graduate J.R. Nimmo, U. S. Geological Survey, MS-421, 345 Middlefield Road, school days, and had a life-long love of languages, probaMenlo Park, CA 94025; E.R. Landa, U.S. Geological Survey, MSbly influenced by his father, Lucius Henry Buckingham, 430,12201 Sunrise Valley Drive, Reston, VA 20192. Received 16 Aug. a noted linguist (National Cyclopaedia of American Bi2004. *Corresponding author ([email protected]). ography, 1941c). [His paternal grandfather, Joseph TinPublished in Soil Sci. Soc. Am. J. 69:328–342 (2005). © Soil Science Society of America Abbreviations: BOS, USDA Bureau of Soils; NBS, National Bureau of Standards. 677 S. Segoe Rd., Madison, WI 53711 USA