Edgar Buckingham July 8, 1867 (Philadelphia, PA) – April 29, 1940 (Washington DC)
Edgar Buckingham was born in Philadelphia, PA on 8 July 1867. He graduated from Harvard with a bachelor's degree in physics in 1887. He did additional graduate work at the University of Strasbourg and the University of Leipzig, where he studied under chemist Wilhelm Ostwald. Buckingham received a PhD from Leipzig in 1893. He had a life-long love of languages, probably influenced by his father, Lucius Henry Buckingham,who was a noted linguist. Returning from Europe, he began teaching physical chemistry and physics at Bryn Mawr College in 1893. During 1897 until 1899 he wrote a textbook on thermodynamics (Buckingham, 1900a). He left Bryn Mawr as an associate professor in the summer of 1899.
After his departure from Bryn Mawr, he spent the next 18 months vacationing, tutoring prep school students, and working for several months in the copper mining district of Arizona. Few details on this latter episode are available. On 13 Sept. 1899 he had a meeting with Harvard president Charles William Eliot. Within a day, he was summoned to New York City to meet with a Mr. Dodge and a Mr. Douglas (probably William Earl Dodge, Jr., and noted metallurgist James Douglas of the Phelps Dodge Corp.). Two days later, he was on a special train chartered by the American Institute of Mining Engineers, bound for San Francisco. On 15 Oct. 1899 he arrived at a mining camp in Morenci, AZ. Paid $100 a week beginning when he left New York, he 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 in February 1900.
During his year and a half away from formal academic life, he was also courting Elizabeth Holstein, whom he had met at Bryn Mawr. They were married in Texas in 1901.He resumed his academic career as an instructor in physics at the University of Wisconsin in 1901. After one academic year he left Wisconsin for a position as a soil physicist at the US Bureau of Soils (BOS). At the BOS from 1902 to 1906, he investigated the dynamics of gas and water in soils. He reported this research in two reports (Buckingham, 1904; Buckingham, 1907). After leaving the BOS, he went to the National Bureau of Standards where he remained until retirement in 1937. In 1923, he was the first NBS researcher given the prized “independent status” (i.e., free of all administrative duties).
Buckingham's first work on soil physics is on soil aeration, particularly the loss of carbon dioxide from the soil and its subsequent replacement by oxygen. From his experiments he found that the rate of gas diffusion in soil was not dependent significantly on the soil structure, compactness or water content of the soil. He explained in a footnote that these experiments, like the others in his report, were performed by J.O. Belz and J.R. McLane (Buckingham, 1907, p. 9). Using an empirical formula based on his data, Buckingham was able to give the diffusion coefficient as a function of air content. This relation is still commonly cited in many modern textbooks and used in modern research. The outcomes of his research on gas transport were to conclude that the exchange of gases in soil aeration takes place by diffusion and is sensibly independent of the variations of the outside barometric pressure.
Buckingham then worked on soil water, research for which he is now renowned. Buckingham’s work on soil water is published in Bulletin 38 USDA Bureau of Soils: Studies on the movement of soil moisture, which was released in 1907. This document contained three sections, the first of which looked at evaporation of water from below a layer of soil. He found that soils of various textures could strongly inhibit evaporation, particularly where capillary flow through the uppermost layers was prevented. The second section of Bulletin 38 looked at the drying of soils under arid and humid conditions. Buckingham found evaporative losses were initially higher from the arid soil, then after three days the evaporation under arid conditions became less than under 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 potentialmatric 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.
Though Buckingham repeatedly mentions the analogy of his developments to what was known of electric current and heat flux, nowhere in Bulletin 38 does he mention Darcy or Darcy’s law. Darcy (1856) presented this law as a quantitative relation between the flow rate of water in saturated sand and the force that drives that flow. Its essence was that this flow rate is directly proportional to the gradient of what we today might call the hydraulic potential, with the constant of proportionality being the hydraulic conductivity of the soil. In Buckingham's time it would not have been applied so widely as today and Sposito (WRR 1986) suggests that Buckingham simply did not know of Darcy's work, even though his work is effectively a generalisation of Darcy's Law to unsaturated flow, making use of the differential form introduced by Dupuit in 1863. The resulting representation is consequently now sometimes called the Darcy-Buckingham equations, or Darcy-Buckingham-Richards equation following the later formulation by L. A. Richards in 1931.
Buckingham attempted to measure soil water retention curves and developed a hanging column method of measuring the capillary potential. He explained the differences in soil water retention between different soil samples in terms of the distribution of pore sizes. In particular, he found that his heaviest soil, Cecil clay, holds the most water at a given potential. He also reported surprising results under steady flow rather than equilibrium conditions, with soil being wetter when evaporation was allowed than without, and a greater dependence on the electrolytic influence than expected, and the observation that it took a very long time to achieve a steady flux. Buckingham also carried out some of the first work on trying to relate pore structures to hydraulic conductivity of the soil.
Buckingham's work was not without controversy at the time. The paper of Nimmo and Landa (2005) relates how Buckingham's supervisor at the end of his period at the BOS, Frank Kenneth Cameron (1869-1958) suggested after Buckingham had left BOS but while Bulletin 38 was still being prepared for publication, that there were some contradictions in the work with the fundamental laws of thermodynamics. Strained interpersonal relations motivated the departure of Buckingham and other brilliant physicists (N.E. Dorsey, F.H. King, and Lyman Briggs) from the BOS during 1903 to 1906. After his resignation from the BOS and return to the University of Wisconsin, F H King published an extensive criticism of the conclusions of Buckingham's Bulletin 25 in Science in 1905.
Edgar Buckingham was also the originator of the Buckingham π theorem in the field of dimensional analysis. This was later the basis for work on similarity theory for scaling soil water characteristics in soil physics (Miller, E E and Miller, R D, 1956, Physical theory for capillary flow phenomena. J. Appl. Phys. 27:324–332).
Source: Edgar Buckingham Wikipedia page
Source: John R. Nimmo and Edward R. Landa, 2005, The Soil Physics Contributions of Edgar Buckingham, Soil Sci. Soc. Am. J. 69:328–342
Buckingham, E. 1900. An outline of the theory of thermodynamics. Macmillan, New York.
Buckingham, E. 1904. Contributions to our knowledge of the aeration of soils, Bulletin 25. USDA Bureau of Soils, Washington, DC.
Buckingham, E. 1907. Studies on the movement of soil moisture. Bulletin 38. USDA Bureau of Soils, Washington, DC.
Buckingham, E. 1914. On physically similar systems; Illustrations of the use of dimensional equation. Phys. Rev. 4:345.
Buckingham, E. 1921. On plastic flow through capillary tubes. Proc. Am. Soc. Testing Mat. 21:1154–1161.