which were previously inaccessible to standard radionavigation methods, thereby closing some big "black holes" in global air traffic control. Furthermore, radar provides the means to control the movement in the vicinity of most major airports today. Summary reports about this phase of NBS Research appear in [5] and [6]. Francis W. Dunmore and Harry Diamond were both born and raised in the vicinity of Boston. Dunmore got his degree in physics from Penn State in 1915, while the younger Diamond graduated from M. I. T. with a degree in electrical engineering in 1922. He worked for General Electric and B.F. Sturtevant Companies in Boston, taught electrical engineering and picked up another degree from Lehigh University. Diamond came to the Bureau of Standards' radio laboratory in 1927, not long after it was handed the responsibility for the research and development work of the Commerce Department's newly organized Bureau of Air Commerce. Diamond would soon become the chief of the Aeronautics Branch there. Prior to World War II, Diamond, Dunmore, and Wilbur Hinman developed methods for remote weather measurements with the first practical "meteorological radiosonde." In 1939 they had developed the "remote weather station," a ground-based radiosonde for automatic telemetering in remote and inhospitable locations. During World War II Diamond was transferred into the newly established Ordnance Division where he materially contributed to the development of the radio proximity fuse. In 1940, he received the Washington Academy of Sciences Engineering Award for his work, and the IRE honored him with its Fellow Award in 1943 for his efforts in radiometeorology. The successor organization, IEEE, has renamed that award in honor of Harry Diamond. The NBS organization chart listed him as Chief of the

Ordnance Development Division in 1945. Diamond was personally presented with Navy and War Department Certificates for Outstanding Service in 1945 [7]. His untimely death in 1948 was a profound loss for the National Bureau of Standards, which had relied heavily on Diamond's visions and plans for the post-war development of civilian technology. To honor him, NBS named the newly constructed electronics laboratory the Harry Diamond Laboratories. That organization was turned over to the U.S. Army in 1952 and continues to operate under that name to this day.

Prepared by Hans J. Oser.

Bibliography

[1] J. H. Dellinger, H. Diamond, and F. W. Dunmore, Development of the Visual Type Airway Radio-Beacon System, Bur. Stand. J. Res. 4, 425-459 (1930).

[2] F. H. Engel and F.W. Dunmore, A Directive Type of Radio Beacon and Its Application to Navigation, Sci. Pap. Bur. Stand. 19, 281-295 (1923).

[3] Robert Robinson, Diamond-Dunmore, Federal Science Progress 1 (3), 16-20 (1947).

[4] Rexmond C. Cochrane, Measures for Progress: A History of the National Bureau of Standards, NBS Miscellaneous Publication 275, National Bureau of Standards, U.S. Government Printing Office, Washington, DC (1966) pp. 294 ff.

[5] NBS Research in Navigation, Tech. News Bull. Natl. Bur. Stand. 34 (6), 80-85 (1950). (Summary of a talk by Edward U. Condon before the Eastern Regional Meeting of the Institute of Navigation, February 10, 1950.)

[6] Frank G. Kear, Instrument Landing at the National Bureau of Standards, IRE Trans. Aeronaut. Navig. Electron. ANE-6, 61-67 (1959).

[7] Nelson R. Kellog. I'm Only Mr. Diamond, A Biographical Essay, Public Affairs Office (History), U.S. Army Laboratory Command, November 1990.

Before the publication of this definitive paper on the discovery of deuterium [1,2], the existence of a heavy isotope of hydrogen had been suspected even though Aston [3] in 1927, from mass spectrometric evidence, had discounted the presence of the heavier isotope at a hydrogen abundance ratio 'H/2H < 5000. (The modern best estimate of that ratio is 5433.78 in unaltered terrestrial hydrogen.) Harold Urey, however, continued to suspect the existence of the heavier isotope, based upon evidence from the sequence of properties of known nuclides and from faint satellite peaks in the Balmer series of the atomic hydrogen spectrum in the visible region. Birge and Menzel [4] had gone further by estimating the abundance ratio 'H/2H at about 4500 from the difference in the atomic weight of hydrogen measured by chemical versus mass spectrometric

means.

Still, the world of science was unwilling to acknowledge the existence of a hydrogen isotope without direct experimental proof. Thus Urey solicited the collaboration of a physicist he had known well at Johns Hopkins University, Ferdinand Brickwedde, who had moved to the National Bureau of Standards after completing his graduate work and had begun to assemble an unexcelled center for thermodynamic measurements, especially at low temperature.

This was a time when isotopes, because of their identical configuration of extra-nuclear electrons, were believed to be chemically inseparable. Prout's old hypothesis of atomic weights being whole-number multiples of that of hydrogen now applied more satisfactorily to isotopes than to elements, but-apart from the effects from some radioactive processes applicable exclusively to elements of high atomic number—all atomic weights were still regarded as constants of

nature.

Urey, Brickwedde, and their colleagues evidently did not share that contemporary viewpoint. These scientists had knowledge of the differences in nuclear spins, as well as magnetic and quadrupole moments, between isotopes of the same element. They had mastered quantum physics and thermodynamics, so surely they expected differences in physical and chemical properties and hence would have anticipated some differences in reaction dynamics and equilibria. They probably estimated the chemical differences among isotopes to be small, perhaps too small to be measured by contemporary experiments. Any successful separation, therefore,

was likely to be achievable largely by virtue of the difference in masses of isotopes of the same element. A suspected isotope of hydrogen had a mass two or three times that of the predominant 'H. The search for a hypothetical hydrogen isotope caused great excitement and led to a high-stakes competition among laboratories. None exceeded Urey and his coworkers in understanding and determination to find proof for the existence of an isotope of hydrogen by a clear-cut measurement. Actually, Urey and George Murphy had found, but not yet published, spectrographic evidence for the lines of 2H obtained from samples of commercial tank hydrogen. These lines, however, were seen only after long photographic exposures. The suspicion persisted that these extra lines could have arisen from irregularities in the ruling of their grating or from molecular hydrogen. Urey and Brickwedde recognized that the proportional mass difference of a possible hydrogen isotope 2H or 3H was most likely to show in molecular hydrogen (H2). A fractional distillation near the hydrogen triple point (about 14 K) gave the best chance of achieving a high concentration of the hypothesized 2H. Despite the considerable experimental difficulties, Brickwedde at NBS undertook the attempt to separate partially the hypothetical isotope by fractional distillation of liquid hydrogen [1,2].

Murphy much later [5] recalled the fear of being beaten in the race for priority in a proof for the existence of 2H at a time when Brickwedde reported a manufacturing delay in the large NBS hydrogen liquifier. The delay, however, appears to have been well used. The authors attempted a quantitative calculation of the enrichment to be expected. By making use of the equality of free energy of gas and solid in equilibrium and the Debye theory of the solid state, they calculated, with minor additional assumptions, the ratio of the vapor pressures p('H2)/p('H'H) at the triple point as 2.688.

For the actual experiment Brickwedde started with 400 ft of hydrogen gas which was liquefied after precooling with liquid air boiling at reduced pressure. Liquid hydrogen was then fed into a 1.6 L evaporation flask. Evaporation took place until about 1/3 of the hydrogen remained, which was then fed into sample tubes and transported to Columbia University for atomic spectroscopic comparison with normal hydrogen by Murphy [1,2]. Assuming the above-quoted abundance ratio to be 4500 [3], the mole fraction left in the still should by their calculation have increased by a

factor of 4000. (It would have been higher, if 3H were involved.) Although the concentration factor of 4000 was never achieved, the 'H concentration was so greatly enhanced that its existence could be demonstrated from the spectroscopic measurements without any remaining doubt. A Letter to the Editor [1] narrowly achieved the desired priority and alerted the scientific community to the upcoming full paper [2], which was recognized as much for the low-temperature advances the first of a series of similarly significant low-temperature measurements related to superconductivity at NBS [6]-as for the scientific significance of a separable stable hydrogen isotope. This full paper [2] earned Urey the 1934 Nobel Prize for Chemistry.

Although he refrained from stealing the limelight and the priority from the Urey, Brickwedde, and Murphy classic experiment, Edward Washburn of NBS, in association with Urey [7], published in 1931 a demonstration of the existence of 2H based upon a simpler and subsequently much more important method of enrichment. Washburn and Urey argued that chemically unbonded 2H✶ might have a lower mobility and/or higher cathodic potential in electrolysis. In fact, such concentration was demonstrated in a number of samples, including those from residual solutions from commercial electrolytic cells that had operated continuously for two to three years. These samples were examined spectroscopically by Murphy at Columbia, and the quantification of the enrichment was also carried out at NBS using water density measurements. The high accuracy of these measurements stands as a great tribute to NBS. This work is recorded in many papers authored or co-authored by E. R. Smith. In a very elegant experiment, for example [8], the authors compared the densities of four kinds of samples: natural water, water prepared by combining hypothetically enriched hydrogen with normal oxygen, water prepared by combining natural hydrogen with enriched oxygen, and water prepared by combining hypothetically enriched hydrogen with enriched oxygen. Thus they were able to show not only that the 2H enrichment is real, but that the enrichment of the higher isotopes of oxygen is also measurable. Washburn showed great ingenuity in searching out waters that were enriched or denuded in 2H. In one experiment he and his son compared water from sap taken from the top of a tree with water from the roots. The results showed conclusively that 2H existed and that isotopic compositions, and also atomic weights, could no longer be regarded as invariable.

The 2H isotope, as early as in 1934 [9], was named by Urey as deuterium (symbol D) with a nucleus called deuteron (symbol d). As is common to many significant discoveries in science, this event was widely anticipated but, in contrast with most other discoveries, its

applications followed swiftly. Within a year, an NBS group had used isotopic composition in an electrolytic process control. A Cambridge group under Rutherford [10] had prepared deuterated compounds such as D3PO4, bombarded them with deuterons, and correctly identified the reaction: D+D = T+H (T is the symbol for the new radioactive isotope of hydrogen of mass 3, called tritium). The nuclear reaction type (d,n) was also identified, in which the neutron that is produced carries off the excess energy in the deuteron (the excess energy over that of a neutron separated from the nucleus of 'H). Within a decade of the discovery of D, the thermodynamic properties of the hydrogen isotopic species had been measured (see, for example, Fig. 1) and definitive values published by NBS [11]. Furthermore, the application to a fledgling nuclear industry was realized, and the cosmological significance began to be appreciated.

The literature resulting from the discovery of deuterium grew very fast. As early as 1935, Urey with Gordon Teal [12], who much later became Director of the NBS Institute for Materials Research, wrote a comprehensive review of the methods of separation of deuterium, its properties in gas, liquid, and solid phases, the chemical kinetics of deuterated compounds, analytical applications for deuterium, the nuclear spin and

moments, and the atomic and molecular spectra. The discovery of deuterium had started a whirlwind of change in science.

The above description may give the false impression of a straightforward, orderly path to the discovery of deuterium. To correct that illusion, the reader might enjoy reading Brickwedde's memoirs [13] written after all the dust had settled and after Urey, Murphy, and Washburn had died. In that article Brickwedde first pays great tribute to Urey "who proposed, planned, and directed the investigation. Appropriately, the Nobel Prize for finding the heavy isotope of hydrogen went to Urey." Brickwedde then points out that the work stumbled on by a succession of errors, some detrimental, some accidentally fortunate to furthering progress. One such error was made on authoritative, but false, advice that electrolysis could not alter significantly the hypothetical isotopic composition of hydrogen, so that the first sample of hydrogen used by Brickwedde for fractional distillation by the above described tour de force was already denuded in deuterium! At that juncture, Washburn at NBS was again the hero who suggested the preparation of the hydrogen sample was faulty.

After receiving the degree of AB (chemistry) and PhD (physics and mathematics) from Johns Hopkins University, Ferdinand Graft Brickwedde started at NBS in 1925 as postdoctoral Mansell Research Associate. In 1926 he became Chief of the Low Temperature Laboratory. In 1946 the Heat and Power Division was restructured and Brickwedde was appointed its Chief in recognition of his leadership potential. At the same time Brickwedde organized and led the Thermodynamics Section, one of the component parts of the new Division. Besides his key contributions to the discovery of deuterium, his research covered a diversity of topics including measurement of thermodynamic properties, the liquefaction of gases, the superfluidity of liquid helium II, the absolute temperature scale, applications of refrigeration, solar energy, rheology, octane rating, and the properties of deuterium compounds. Simultaneously with his appointment at NBS, Brickwedde served as a part-time physics professor at the University of Maryland, where he gave graduate courses in statistical mechanics, relativity, electrodynamics, and quantum mechanics. He organized the University of Maryland Extension Program in physics at NBS. This program was important in that it gave opportunities for NBS staff to keep abreast of current developments in specialized fields, to acquire knowledge in new fields, and to satisfy interests to teach while at a non-academic establishment. It also enabled many young staff members at NBS and

other Federal agencies to satisfy their course requirements towards advanced degrees by attending classes at NBS after working hours. He also was consultant to Los Alamos Scientific Laboratory, the University of California Lawrence Livermore Laboratory, and a commission member of the International Institute of Refrigeration and the International Union of Pure and Applied Physics. Brickwedde won the Hillebrand Prize of the Chemical Society of Washington and was Associate Editor of The Physical Review. As NBS expanded in the early 1950s, he helped recruit young PhDs for the new programs. He and his wife, Langhorne Howard Brickwedde, an NBS electrochemist, were gracious hosts to many of the new arrivals. In 1956 Brickwedde, when only 53 years old, left NBS to accept the post of Dean of Physics and Chemistry at Pennsylvania State University and, in 1978, the Evan Pugh Research Professorship there. He died in 1989 at the age of 86. Prepared by Walter J. Hamer and H. Steffen Peiser. Bibliography

[1] H. C. Urey, F. G. Brickwedde, and G. M. Murphy, A Hydrogen Isotope of Mass 2, Phys. Rev. 39, 164-165 (1932).

[2] H. C. Urey, F. G. Brickwedde, and G. M. Murphy, Phys. Rev. 40, 1-15 (1932).

[3] F.W. Aston, Bakerian Lecture- A new mass-spectrograph and the whole number rule, Proc. R. Soc. London A115, 487-514 (1927).

[4] R. T. Birge and D. H. Menzel, The relative abundance of the oxygen isotopes and the basis of the atomic weight system, Phys. Rev. 37, 1669-1671 (1931).

[5] G. M. Murphy, The Discovery of Deuterium, in Isotopic and Cosmic Chemistry, H. Craig, S. L. Miller, and G. W. Wasserburg (eds.), North-Holland Publishing Company, Amsterdam (1964).

[6] F. G. Brickwedde, R. P. Hudson, and E. Ambler, Cryogenics, Annu. Rev. Phys. Chem. 6, 25-44 (1955).

[7] E. W. Washburn and H. C. Urey, Concentration of the H2 Isotope of Hydrogen by the Fractional Electrolysis of Water; Proc. Natl. Acad. Sci. U.S.A. 18, 496-498 (1932).

[8] E. W. Washburn, E. R. Smith, and F. A. Smith, Fractionation of the isotopes of hydrogen and of oxygen in a commercial electrolyzer, J. Res. Natl. Bur. Stand. 13, 599-608 (1934).

[9] Harold Clayton Urey, in Nobel Lectures, Chemistry 1922-1941, Elsevier Publishing Company, Amsterdam (1966) pp. 331-356. [10] M. L. E. Oliphant, B. B. Kinsey, and Lord Rutherford, The transmutation of lithium by protons and by ions of the heavy isotope of hydrogen, Proc. R. Soc. London A141, 722-733 (1933).

[11] H. W. Woolley, R. B. Scott, and F. G. Brickwedde, Compilation of thermal properties of hydrogen in its various isotopic and ortho-para modifications, J. Res. Natl. Bur. Stand. 41, 379-475 (1948).

[12] H. C. Urey and G. K. Teal, The hydrogen isotope of atomic weight two, Rev. Mod. Phys. 7, 34-94 (1935).

[13] F. G. Brickwedde, Harold Urey and the Discovery of Deuterium, Phys. Today 35 (9), 34-39 (1982).

Shortly after arriving at NBS in 1929 as an employee in the Electrical Division, Galen B. Schubauer enrolled in a graduate study program at Johns Hopkins University in Baltimore, as did about two dozen of his newly hired colleagues. These studies required a commute to Baltimore several times per week. The difficult trip was made more efficient by cramming six to eight students into a 1930s sedan, which made the trip much more arduous. During his graduate studies, Schubauer's interest began to focus on aerodynamics, and on boundary layer phenomena in particular. Consequently, he transferred to the Aerodynamics Section of NBS, then headed by Hugh L. Dryden, where he began an illustrious career of research on this topic.

His 1935 paper, Air Flow in a Separating Boundary Layer [1], provided great insight into separation (or stall) of a laminar boundary layer developing over an airfoil with the cross-section of an elliptic cylinder. The purpose of the work was to test an approximate solution to the applicable flow equations advanced by K. Pohlhausen. Schubauer's experimental results showed that Pohlhausen's solution produced good agreement in the forward portion of the surface, but it began to fail near the separation point on the surface and could therefore not be used to predict the location of the separation point. The next paper, The Effect of Turbulence on the Drag of Flat Plates [2], concerned the effects of free-stream turbulence on four objects: a flat plate, a thin circular disk, a vane anemometer, and a Pitot static tube. The results indicated that there is no appreciable effect of turbulence on the vane anemometer and the Pitot static tube, but there is a small effect on the drag of a flat plate and on the pressure difference between the front and rear of a disk. Furthermore, the effect of turbulence was found to be independent of the air speed or Reynolds Number.

The hot-wire anemometer had emerged as the fundamental instrument for measuring boundary layer turbulence as well as boundary layer velocity distributions. This instrument was known to be sensitive to other parameters which could cause errors in the turbulence and velocity measurements if proper corrections were not made. Water vapor (humidity) in the air stream was recognized to be such a possible extraneous parameter. In his next paper [3], Schubauer quantified this effect by verifying recent results published by W. Paeschke which

showed that the effect was to increase the hot-wire heat loss at higher humidities, giving a fractional change of about 2% for an increase in relative humidity from 25% to 70%. It was concluded that the phenomenon could be explained by the effect of humidity on the thermal conductivity of air.

During the next decade, Schubauer continued to focus his attention on the stability of the laminar boundary layer. He was particularly interested in an instability theory which had been under development over a 40-year period and which was published in the mid-1930s by two German investigators, W. Tollmien and H. Schlichting, who were working independently. This theory postulated that a small disturbance introduced into a laminar boundary layer would lead to transition of the laminar layer to a turbulent boundary layer, depending primarily upon the frequency of the disturbance and the longitudinal (in the flow direction) Reynolds Number. For certain values of the governing parameters the disturbance would be amplified and transition would occur, but for other parameter values the disturbance would be attenuated (or damped) and would not cause transition. The regions where disturbances are amplified or damped are separated by a curve of "neutral stability" as shown in Fig. 1. This curve is sometimes referred to as a "TollmienSchlichting noodle curve" because of its peculiar shape.

Working during the mid-1930s on his own time and with available equipment, Schubauer began to investigate the T-S theory experimentally. His jury-rigged experimental setup was substantially less than ideal, but he was able to acquire enough data to convince himself that the T-S theory was basically valid. However, Dryden argued that the relatively crude experimental setup employed by Schubauer could not possibly allow measurement of the T-S phenomenon. There were too many extraneous sources of disturbances in the flow, and the signal-to-noise ratio of the available hot-wire instrumentation was insufficient. Substantial improvement of the experimental equipment would be required to provide necessary control of all the parameters and make high quality measurements. Because of higher priorities, Dryden would neither allow any of the Aerodynamic Section's current financial resources to be used for this work nor assist in soliciting additional funds for the research.