Difference between revisions of "Buckingham, Edgar"

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Photograph

Dates

Edgar Buckingham July 8, 1867 (Philadelphia, PA) – April 29, 1940 (Washington DC)

Biography

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. That same year, he began teaching physical chemistry and physics at Bryn Mawr College. 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 mo 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 Elizamous beth 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 the 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. 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.

He is also the originator of the Buckingham π theorem in the field of dimensional analysis.

In 1887, he graduated from Harvard 

with a bachelor’s degree in physics, then worked several years as a graduate assistant in the physics department. During 1902 to 1906 as a soil physicist at the USDA Bureau of Soils (BOS), Edgar Buckingham originated the concepts of matric potential, soil–water retention curves, specific water capacity, and unsaturated hydraulic conductivity (K) as a distinct property of a soil. He applied a formula equivalent to Darcy’s law (though without specific mention of Darcy’s work) to unsaturated flow.He also contrib- uted significant research on quasi-empirical formulas for K as a func- tion of water content, water flow in capillary crevices and in thin films, and scaling. Buckingham’s work on gas flow in soils produced paradigms that are consistent with our current understanding. His work on evaporation elucidated the concept of self-mulching and produced sound and sometimes paradoxical generalizations concerning conditions that favour or retard evaporation. Largely overshadowing those achievements, however, is that he launched a theory, still accepted today, that could predict transient water content as a function of time and space. Recently discovered documents reveal some of the argu- ments Buckingham had with BOS officials, including the text of a two-paragraph conclusion of his famous 1907 report on soil water, and the official letter documenting rejection of that text. 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. Given that Buckingham and his BOS colleagues had been rapidly developing the means of quantifying unsaturated flow, these strained relations probably slowed the advancement of unsaturated flow theory.

Edgar Buckingham tremendously advanced the understanding of water and air in unsaturated soils late during 4 yr at the BOS, which culminated with his fa- paper of 1907 (Buckingham, 1907).He introduced the concept of potential into soil-water flow and used an equation equivalent to Darcy’s law to quantify flow in unsaturated soil. Topics of his investigation included gas flow and aeration, evaporation from soil and consin for the BOS.

Hydrological Achievements

Edgar Buckingham tremendously advanced the understanding of water and air in unsaturated soils, gas flow and aeration, evaporation from soil and the effectiveness of self-mulching (i.e., retardation of evaporation by a thin surficial layer drier than the rest the main subject of of the soil), measurement of water retention curves. relation between water content &theta and matric potential &psi), identification of the retention curve and unsaturated hydraulic conductivity K(&theta) as the two main soil proper- ties for unsaturated flow, and mathematical formulas of the &psi(&theta) and K(&theta) relations (which he proposed and tested to some degree on both experimental and theoretical grounds).

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. To understand the implications of this omission and to be able to evaluate Buck- ingham’s progress on this topic requires some attention

to the evolution since Darcy’s time of what is called
Darcy’s law. Darcy (1856) presented this law as a quantitative relation between the flow rate of water in satu

rated sand and the force that drives that flow. Its essence

was that this flow rate is directly proportional to the

experiments, though, to conclusively generalize on the gradient of what we today might call the hydraulic porelative effect of texture or tightness of packing. The tential (Marshall et al. [1996], p. 79), with the constant second series of experiments explored the drying of soils of proportionality being the hydraulic conductivity of the under arid and humid conditions in four experiments sand. Today, various fields in which fluid flow through that ranged in duration from 17 to 66 d. Figure 3 illus- porous media is important (e.g., soil science, hydrology, trates typical results. In Buckingham’s words, fluid mechanics, and chemical engineering) apply Darcy’s law in a much expanded range of contexts, including

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). The results showed that, especially when capillary flow through the uppermost layer is prevented, soil of various textures can strongly inhibit evaporation. There were not enough

The evaporation from the soil under the arid conditions is much multiphase, gaseous, and unsaturated flow. Its evolution more rapid at first, but after about three days have elapsed the has proceeded in steps, for example Dupuit’s introducrate of loss is less under arid than under humid conditions, so that tion of the differential form in 1863. The term “Darcy’s the total loss under the humid conditions gradually overtakes that law” has come to mean the general statement that the under the arid conditions…. It appears that under very arid condi- flow rate of a fluid in a porous medium is directly protions a soil automatically protects itself from drying by the forma- portional to a force expressible as the gradient of a tion of a natural mulch on the surface. potential. In Buckingham’s time it would not have been In this section, as throughout this report, Buckingham applied so generally, but as a choice of analog it still discusses the flow of water “in a soil which is not very would have been as suitable mathematically as Ohm’s wet” as taking place through thin films on the soil grains, or Fourier’s laws, and was more closely analogous in

that it treats water flow in a natural porous medium. It the one illustrated in Fig. 4, he wrote “…the heaviest is conceivable that Buckingham did not think of his soil, Cecil clay, holds by far the most water, and the capillary potential as an equivalent of the hydraulic head lightest, the Norfolk fine sandy loam, the least.” He used in formulating water flow in saturated porous me- reported surprising results when measurements were dia. Sposito (1986) suggests he simply did not know of done with steady flow rather than equilibrium, finding Darcy’s law. This would explain his neglect of this law soil to be wetter with evaporation rather than drier, that seems to be too closely analogous to ignore. By and the measured results to depend more strongly on the standard of later usage one would say he was pre- electrolytes than the known electrolytic influence on senting and applying Darcy’s law for the case of unsatu- water properties would suggest. Buckingham noted that rated media. In doing so he played a major role in the initial water contents were significantly greater for establishing the generalized version of Darcy’s law in the steady-flow (driven by evaporation) than for the our present science. Consequently, when applied to un- equilibrium experiments. Coupled with his additional saturated flow, this law is sometimes called the Darcy– observation that the duration of these experiments was Buckingham law.

Reference Material

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

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