to be used in these fuzes after the war. Ultimately the fuze systems became "first class radars" [3]. Technical work focused, inter alia, on security from jamming and thus involved various ways of disguising the signal. The reserve battery power supply was perfected and thermally-activated batteries became the method of choice. A quick perusal of the table of contents of an Army ordnance manual from 1963 shows major emphasis on continuous wave and pulsed Doppler fuzes. Eventually, of course, miniaturization through solid state and integrated circuits became possible. Technical director Horton marveled that the early fuzes using electron tubes were able to survive the stresses of launch.

The Kelly Committee, an ad hoc group, was formed by the NBS Visiting Committee and the National Academy of Sciences at the request of Commerce Secretary Sinclair Weeks after the uproar created by the AD-X2 battery additive controversy. The Committee report of 1953 recommended that the Bureau get back to its congressional charter and separate the bulk of its military work. Cochrane [4] says that 2000 staff were transferred to other agencies, some 1600 of these in three divisions that worked on fuzes. Those three divisions had earlier been placed in the Harry Diamond Ordnance Laboratory within NBS, the unit named in honor of the memory of Harry Diamond, who died at the early age of 48 years in 1948. The Army added the word "Fuze" (and dropped the "Harry") to the title on receipt of the unit-thus, the Diamond Ordnance Fuze Laboratory, or DOFL. The remainder of the affected staff worked on guided missiles at a location in California and were shifted to the Navy. The DOFL remained at the Connecticut and Van Ness site until a new laboratory site could be completed in White Oak/ Adelphi, Maryland. The move was carried out in 1973. This is just one of many examples of significant technical entities created out of the NBS over the years.

The DOFL had a distinguished history in the Army. It continued to work on fuzes although eventually turning over most of the work to various product development and engineering centers, such as Picatinny Arsenal and the Redstone Arsenal. The laboratory at Adelphi developed major research programs in highpower microwaves, electronics, nuclear simulation, radar, sensors, and signal processing-a broad, multiprogram laboratory. In 1992 it became one of the major components of the new Army Research Laboratory and the Adelphi site served as the new entity's headquarters. The central building in the complex carries prominently on its façade the name "Harry Diamond Building."

Inside are portraits of Diamond and Hinman and displays of the early fuze artifacts and documents. In a curious coincidence John Lyons, ninth director of NBS/ NIST, became, in 1993, the first director of the new Army Research Laboratory and made his offices in the Harry Diamond Building. In a sense he felt he had simply moved to one of the Bureau's more significant descendants. He served ARL as its director through 1998, when he retired.

Allen Astin went on to become the fifth director of NBS and served the second longest tour of any director- from 1952 to1969. Diamond died shortly after the war; his close associate, W.S. Hinman, Jr., succeeded Diamond as head of the program and became the first technical director of the DOFL after it moved to the Army. After staying with the DOFL for a few years, Hinman moved on to become the Deputy Assistant Secretary of the Army (Research & Development). Robert Huntoon served as a senior manager at NBS heading atomic and radiation physics. He later became Associate Director of NBS for Physics and, still later, Deputy Director as well. J. Rabinow had a distinguished career as an inventor and innovator, left NBS to form a company which he later sold to Control Data. He returned to NBS and served in various senior capacities and was at work at least part-time until his death in 1999 at the age of 89. Chester Page went on to head the Electricity Division for many years and made many contributions, not least of which were his efforts in developing the concepts that became the international system of units of measurement (SI).

Prepared by John W. Lyons with assistance from E. A. Brown and B. Fonoroff (ret.) of the Army Research Laboratory.

Bibliography

[1] Allen V. Astin (ed.), Radio Proximity Fuzes for Fin-Stabilized Missiles, Vol. 1 of Summary Technical Report of Division 4, NDRC, Vol. 1, National Defense Research Committee, Washington, DC (1946).

[2] N. R. Kellog, I'm Only Mr. Diamond, biographical essay, U.S. Army Laboratory Command, Army Materiel Command, Adelphi, Maryland (1990).

[3] Private conversation in February 2000 with Billy Horton, retired technical director at the Army's Adelphi, Maryland laboratories. [4] Rexmond C. Cochrane, Measures for Progress. A History of the National Bureau of Standards, NBS Miscellaneous Publication 275, U.S. Government Printing Office, Washington, DC (1966) p. 497.

The resistance standard described by James L. Thomas [1] was the result of his extensive effort to develop a new standard by systematically investigating every factor affecting the stability of resistancetime, surface effects, temperature, power, pressure— detectable at the time. The result was a unique standard which was used as part of the National Reference Group of resistors beginning in 1931. Ten of them served solely as the U.S. standard of resistance from 1939 until they were supplanted by the quantized Hall effect (QHE) in 1990. They still serve as working standards at the one ohm level and as a vital check on the QHE standard and the scaling used in the NIST resistance calibration service. The International Bureau of Weights and Measures used this standard to maintain the international unit of resistance, and numerous other national standardizing laboratories around the world used it as their primary standard. This is still largely true for laboratories without QHE standards.

In the period from 1935 to 1980, Thomas's standard provided a basis for evaluating the accuracy of ohm determinations, particularly to compare realizations based on calculable inductors with those based on Thompson-Lampard calculable capacitors. Thomas's standard was commercialized by the Leeds and Northrup Company and Honeywell, and these commercial versions are still used as primary resistance standards by many industrial and commercial standards laboratories, as well as the DOD primary and secondary metrology laboratories. NIST still routinely calibrates about 125 of them annually for domestic users. Thomas's standard remains the most stable resistor of any available, although two more modern designs are nearly a match in predictability.

Much of the research leading to this standard resistor design is described in an earlier paper by Thomas [2]. However, the paper Stability of Double-walled Manganin Resistors [1] is the more popularly known and describes the standard in its final form, after some major modifications in size and connections.

In the 1920s, Thomas had taken up the task of improving the long-term stability of wire-wound resistors, which were used to measure the current in absolute determinations. When a resistor is made by winding wire on a spool, parts of the crystalline structure of the wire are stressed past their elastic limit. Thomas developed wire-wound standard resistors that were annealed at high temperature, which released some of the internal

strains and reduced the rate of change of resistance with time. Heat-treated manganin wire resistors developed by Thomas incorporated hermetically-sealed, doublewalled enclosures, with the resistance element in thermal contact with the inner wall of the container to improve heat dissipation. These 10 Thomas-type standards (see Fig. 1) proved to be quite stable with time [1,2], and quickly came into favor as the primary reference for maintaining the resistance unit at NBS and at many other national metrology institutes.

Work continued on improving the absolute measurements of electrical units and, in 1949, J. L. Thomas, C. L. Peterson, I. L. Cooter, and F. R. Kotter published a new measurement of the absolute ohm [3] using an inductor housed in a non-magnetic environment. Using the Wenner method of measuring a resistance in terms of a mutual inductance and a rate of rotation, their work gave a value of 0.999 994 absolute ohm for the new as-maintained unit of resistance at NBS. The mean value assigned to 10 Thomas-type standard resistors from this experiment was found to have been the same between 1938 and 1948 to within 1 μ/N. As Thomas et al. wrote in the 1949 paper, this was "the first satisfactory method that has been devised for checking the stability of the unit as maintained by a group of wire-wound resistors."

From 1901 to 1990, the U.S. Legal Ohm was maintained at 1 by selected groups of manganin resistance standards. Four different types of resistance standards have been represented in these groups, whose numbers have varied from 5 to 17 resistors. From 1901 to 1909, the group comprised Reichsanstalt-type resistance standards made by the Otto Wolff firm in Berlin. These standards were not hermetically sealed and consequently underwent changes in resistance as a function of atmospheric humidity. In 1907 Rosa at NBS solved the problem by developing a standard whose resistance element is sealed in a can filled with mineral oil [4]. The U.S. representation of the ohm was maintained by 10 Rosa-type 1 resistance standards from 1909 to 1930. Over the years, measurements of differences between the individual Rosa-type resistors indicated that the group mean was probably not constant. In 1930, Thomas reported on the development of his new design for a resistance standard having improved stability [2]. The Thomas resistance standards were more stable immediately following construction than the Rosa-type resistors and two were added to the

primary group in 1930. Eventually, in 1932, the Rosatype resistors in the primary group were replaced by the Thomas resistors. To reduce loading errors, Thomas in 1933 improved the design of his resistor by using manganin wire of larger diameter mounted on a larger diameter cylinder to increase the dissipation surface area, as described in his paper [1]. A select group of the new-design Thomas resistors was used to maintain the U.S. Legal Ohm from 1939 until its re-definition in 1990 based on the quantum Hall effect.

The value of the U.S. representation of the ohm, or "Legal Ohm" maintained at NIST has been adjusted only twice. This occurred first in 1948 when the ohm was reassigned using a conversion factor relating the international reproducible system of units [3] to the precursor of the International System of Units (SI) derived from the fundamental units of length, mass, and time. The second occasion was in 1990 when the ohm became based on the quantum Hall effect. After 1960, ohm determinations were made using calculable capacitors based on the Thompson-Lampard theorem and a sequence of ac and dc bridges. Then came the discovery of the QHE in 1980, which has provided an invariable standard of resistance based on fundamental constants. Consequently, on January 1, 1990 the U.S. Legal Ohm was re-defined in terms of the QHE, with the internationally-accepted value of the quantum Hall resistance (or von Klitzing constant, after the effect's discoverer) based on calculable capacitor experiments and other fundamental constant determinations. At that time, the value of the U.S. Legal Ohm was increased by the fractional amount 1.69 X 10-6 to be consistent with the conventional value of the von Klitzing constant [5].

Shortly after the discovery of the QHE, NBS developed a system based on the QHE to monitor the U.S. Legal Ohm, then maintained by five Thomastype resistance standards, with a relative uncertainty of a few times 10-8 [6]. This system consisted of a constant current source, a potentiometer, and an electronic detector. The current source energized the QHE device and a series-connected reference resistor of nominal value equal to the Quantum Hall Resistance (QHR). With the potentiometer balancing out the nominal voltage across either resistance, the detector measured the small voltage difference between the QHE device and reference resistor. Scaling down to the 1 level was accomplished using specially-constructed Hamon transfer standards.

Since January 1, 1990, the maintenance of the U.S. Legal Ohm has been based officially on the QHE. However, the complexity of the experiment and "oddvalue" resistance of the QHR does not make it practical for the routine support of resistance measurements where comparisons are normally made on standard resistors of nominal decade values. Therefore, banks of 10, 100, and 10 k standard resistors maintain the ohm between QHR measurements.

Today NIST provides a calibration service for standard resistors of nominal decade values from 10 to 1014. To achieve low uncertainties, eight measurement systems have been developed that are optimized for the various resistance levels [7]. Over the years from 1982 to 1997, six of the systems, covering the full 19 decades of resistance, have been automated. The main methods of comparing standard resistors for NIST calibrations

utilize direct current comparator (DCC) bridges and resistance-ratio bridges.

An unknown standard resistor is indirectly compared to a reference bank of the same nominal value using the substitution technique, where the unknown and reference resistors are sequentially substituted in the same position of a bridge circuit. A robotic switching device is shown in Fig. 2. This technique tends to cancel errors caused by ratio non-linearity, leakage currents, and lead and contact resistances. To verify that the values of the reference banks are consistent with the QHR, scaling

measurements are completed periodically proceeding from the 1, 100 or 10 kn banks, whose values are based on recent QHR determinations, to the other reference banks. The up or down scaling is done in steps of 10 or 100 using either a CCC bridge, Hamon transfer standards, or DCC bridge.

Prepared by R. Dziuba, N. B. Belecki, and J. F. MayoWells based on excerpts from the paper The Ampere and Electrical Units [8], authored by members of the Electricity Division.

Bibliography

[1] James L. Thomas, Stability of Double-walled Manganin Resistors, J. Res. Natl. Bur. Stand. 36, 107-110 (1946).

[2] James L. Thomas, A new design of precision resistance standard, Bur. Stand. J. Res. 5, 295-304 (1930).

[3] James L. Thomas, Chester Peterson, Irvin L. Cooter, and F. Ralph Kotter, An absolute measurement of resistance by the Wenner method, J. Res. Natl. Bur. Stand. 43, 291-353 (1949).

[4] Edward B. Rosa, A new form of standard resistance, Bull. Bur. Stand. 5, 413-434 (1909).

[5] Norman B. Belecki, Ronald F. Dziuba, Bruce F. Field, and Barry N. Taylor, Guidelines for Implementing the New Representations of the Volt and Ohm Effective January 1, 1990, NIST Technical

Note 1263, National Institute of Standards and Technology, Gaithersburg, MD (1989).

[6] Marvin E. Cage, Ronald F. Dziuba, and Bruce F. Field, A test of the quantum Hall effect as a resistance standard, IEEE Trans. Instrum. Meas. IM-34, 301-303 (1985).

[7] Ronald F. Dziuba, Paul A. Boynton, Randolph E. Elmquist, Dean G. Jarrett, Theodore M. Moore, and Jack D. Neal, NIST Measurement Service for DC Standard Resistors, NIST Technical Note 1298, National Institute of Standards and Technology, Gaithersburg, MD (1992).

[8] R. E. Elmquist, M. E. Cage, Y-H. Tang, A-M. Jeffery, J. R. Kinard, R. F. Dziuba, N. M. Oldham, and E. R. Williams, The Ampere and Electrical Units, J. Res. Natl. Inst. Stand. Technol., January-February (2001).

The manufacture of robust paper for maps assumed great importance early in World War II. Up to that time, maps used by troops in combat tended to disintegrate rapidly after being subjected to the water, mud, and grime of the battlefield. On the basis of information developed by the NBS Paper Section, the Army Map Service of the Corps of Engineers formulated specifications for paper for the printing of maps. The most critical requirements were very high resistance to tear, high wet tensile strength, high dry tensile strength, high opacity, and superior smoothness. Additionally, the paper needed to be made from commercially available raw materials to meet unprecedented tonnage requirements. The article Experimental Manufacture of Paper for War Maps [1] documents the contributions of NBS to this endeavor.

In the NBS Paper Section, this project was spearheaded by Charles G. Weber and Merle B. Shaw. They attacked the problem by preparing many batches of paper under a variety of experimental conditions on a "Fourdrinier" semi-commercial paper-making machine. This machine, invented by Nicholas Robert in France and named after the Fourdrinier brothers in England who commercialized it in 1804, is basically an endless wire screen belt which runs continuously; a paper pulp suspension flows onto the screen at one end and is removed at the opposite end after most of the water has been removed. The partially dried suspension is transferred onto a felt and transported over drying cylinders. A simple Fourdrinier travels at a speed of less than one mile per hour, but a modern, highly automated machine can travel 30 times as fast.

One of the variables tested by NBS was the relative amount of cutting and fraying, which affect fiber strength. These variables are a function of "beating," a process in which an aqueous suspension of paper pulp is passed continuously between a revolving roll and a bedplate. Knives are installed on the roll and initially separated from the bedplate by about 2.5 mm. Operating the beater with a wide bedplate-to-roll separation frays the fibers, with little cutting, and generates a large surface area. Operation with the roll close to the bedplate produces more cutting and less fraying.

In the early 1940s, it was common practice to permit extensive fraying of fibers as this produced a large surface area for fiber-to-fiber bonding and thus a very strong paper. When a papermaker held the paper up to

the light, his product looked very uniform, and this had become a simple test for paper quality. However, because of extensive fiber-to-fiber bonding, this paper had a high coefficient of hygroscopic expansion, an undesirable property for military maps. Shaw and Weber found that the recently developed melamine resin could be used as a bonding agent to increase wet strength, and that the resin could take the place of beating to increase dry strength. The reduced need for beating diminished the interfiber bonding and consequently the hygroscopic expansivity of the sheet. At first, paper makers objected to the disordered or "wild" appearance when the paper was viewed by transmitted light, as described above. Once it was recognized that the disordered appearance was not a criterion for the quality of map paper, this test was discarded.

With the assistance of NBS ... production (of paper for war maps) exceeding 5000 tons per month was achieved within 6 months. This was a substantial contribution to the war effort.

Ultimately, numerous runs on the Fourdrinier showed that the best paper was obtained by using 100% strong bleached sulfate pulps with the addition of melamineformaldehyde resin to increase wet strength, and titanium dioxide to produce the desired opacity [1]. The large scale of the Fourdrinier in the Paper Section facilitated the transfer of this technology to factory production. With the assistance of NBS, many paper mills were able to meet or exceed the specification prepared by the Army Map Service. Production exceeding 5000 tons per month was achieved within 6 months. This was a substantial contribution to the war effort.

Further studies on paper for defense needs continued after World War II. About 1952 the Naval Research Laboratory and the NBS Paper Section cooperated in the development of the first machine-made paper made from glass fiber, without binder or additives [2]. The paper, which resembles soft blotting paper, was found to have numerous important applications, both in defense