1 INST

A111D7 E73EbH

NBSIR 76-1125

Interim Report

November 1977

NI8T

PUBLICATIONS

Catalog of Artifacts

on Display in the

NBS Museum

HI. Mason, Editor

QC

100

.U56

no.76-li.

1977

C.3

Special Activities Section

Office of Information Activities

Office of the Associate Director for

Information Programs

U.S. Department of Commerce

National Bureau of Standards

Washington, D.C. 20234

NBsiR 76-1125 Catalog of Artifacts

Interim Report f

November 1977 OH Display ill thc

NBS Museum

HI. Mason, Editor

Special Activities Section

Office of Information Activities

Office of the Associate Director for

Information Programs

National Bureau of Standards

Washington, D.C. 20234

U.S. DEPARTMENT OF COMMERCE, Juanita M. Kreps, Secretary

Dr. Sidney Harman, Under Secretary

Jordan J. Baruch, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director
II
e Index

AREA 1 VAULT

Introduction mm.

Museum Displays Atlas ^»

Working Standards Wfm>.

AREA 2 VAULT National Standards 'mm,

AREA 3 VAULT Historical Standards

AREA Gravitation mm^.

AREA 5 CASE Radioactivity & X-Rays mM^/.

AREA 6 FLAT CASE Radiation, Mechanics, Magnetics

ARE^. 7 FLAT CASE Radio "W^M^.

AREA 8 FLAT CASE Aircraft

AREA 9 FLAT CASE Electricity

AREA 10 FLA.T CASE Standard Reference Materials (SRM's)

AREA 11

Standards Eastern Automatic Computer (SEAC)

AREA 12 Electrical Resistance

AREA 13 DRUM CASE II Pressure ^^^^

AREA 1^ DRUM CASE II Electricity

AREA 15 DRUM CASE II

AREA 16 DRUM CASE I Defense ^^^^

AREA 17 DRUM CASE I Industry ^^^^

AREA 18 DRUM CASE I Science

AREA 19 Ampere

AREA 20. Balance ^^^^

III
IV
eo

3

T3O

V

CATALOG OF ARTIFACTS ON DISPLAY IN THE NBS MUSEUM

This museum is designed to preserve and display apparatus and

other memorabilia illustrative of the past scientific v;ork of NBS

for the information of visitors, for the inspiration of present and

future staff members, and as a part of the historic record of the

evolution of the science of physical measurement.

Most visitor's casual interest will be satisfied by the cards

placed beside the individual items. However, if one really wants

to understand the artifact, this catalog will tell how the

instrument worked, what its technical purpose was, and what part it

played in the long development of scientific achievement at the

National Bureau of Standards. For the scientist or engineer who

wants further details, these may be found in the references

appended, all of which are available in our library. The

arrangement by scientific, industrial or historical categories

makes it easy to choose the groups which are of particular interest

to the visitor.

The Museum's archival repository maintains source materials

for all of the items currently on display as well as for over 400

additional artifacts in its custody.

VII



MUSEUM DISPLAY ATLAS

M indicates assigned Museum Number

R indicates Reference Standard

Museum

Number Page

AREA 1 - VAULT-WORKING STANDARDS

Pyrometry

Lamp, tungsten strip M526

Photometry

Blackbody, platinum, Waidner-Burgess model M197

Lamp, carbon filament M198

Lamp, tungsten filament, vacuum M227

Lamp, tungsten filament, gas-filled M228

Lamp, tungsten filament, vacuum M2 29A

Lamp, tungsten filament, gas-filled M229B

Lamp, fluorescent M23 0

Electrical Resistance

3-4, 5p

6-7, 49-50, 51p

8p

Bp

6, Bp

9p

9p

7, lOp

Resistor, one-ohm double-walled, Thomas R7 11, 12p, 43, 44p,

73

Electromotive Force

Standard cell group, Weston, NBS

Length

Meter, Prototype No. 27

Meter, Prototype No. 21

Gage Blocks

Temperature

Thermocouple, platinum-10 percent

rhodium vs. platinum

Thermometer, platinum resistance

Frequency

Quartz Crystal Resonator

M281

Rl

R2

M569

M522

M523

M571

13, 14p, 15p

17, IBp

17

19, 20p

21, 23p

21, 23p

25, 26p

XI
AREA 2 - VAULT-NATIONAL STANDARDS

Length

Lamp, krypton 86 M543 30, 31p

Mass

Kilogram, Prototype No. 20, replica R5 33, 35p

Kilogram, Prototype No. 4, replica R6 33

Temperature

Triple point cell, water M524 37, 38p

Time and Frequency

Cessium Oven M375 39, 40p, 41p

Electric Current

Resistor, one-ohm double-walled, Thomas R7 11, 12p, 43, 44p,

73

Josephson junction, voltage M550 45, 46p, 47p

Luminous Intensity

Blackbody, platinum, Waidner-Burgess model M197 6, 7, 49-50, 51p

AREA 3 - VAULT-HISTORICAL STANDARDS

Mass

Pound, troy M446 55, 57p

Pound, avoirdupois, "Star" M323 55, 58p

Pound, avoirdupois. Imperial, copy No. 5 M324 55-56, 59p

"Grave" weight M322 61, 63p

Kilogram/ Liter M448 61, 64p

Kilogram, "Committee" M319 62 , 65p

Kilogram, Silberraann M321 62, 66p

Electric Current

Voltameter, silver, Rayleigh M172 67, 69p

Voltameter, silver, Kohlrausch M175 67, 70p

Voltameter, silver, Richards M170 67, 71p

Voltameter, silver, Smith M171 67, 72p

XII
Electrical Resistance

Resistor, one-ohm, P.T.R.

Resistor, one-ohm, B.A.

Resistor, one-ohm, Rosa

Mercury ohm tubes

Electromotive Force

Standard cell, Clark-Fuessner

Standard cell, Carhart-Clark

Standard cell, Weston-Berlin No. 508

Standard cell, Kahle

Frequency

Oscillator, quartz, Marrison

Temperature

Thermometer, mercury-in-glass, Tonnelot

Thermometer, mercury-in-glass, Baudin

M521

Length

Cubit, Egyptian Royal, model

Scale, Troughton

Yard, bronze No. 11

Yard, Low Moor iron No. 57

Meter, "Committee"

Meter, Arago platinum

Luminous Intensity

Candles, standard, with balance

Flame standard, Carcel

Flame standard, Hefner

AREA 4 - GRAVITATION

Gravitation apparatus, mockup, Heyl

Glass balls for gravitation apparatus, Heyl

AREA 5 - FLAT CASE-RADIOACTIVITY AND X-RAYS

Luminous script signs

Ionization chamber, guarded field, Taylor

Radioactivity counter, Seliger/Cavallo

MJ J 4 73 , / 4 , /bp

Ut A A 173o

, 1 A "7 C i-> / 4 , /op

MO D iflZ O /J , /4, / /p

M137 78, 79p

M279 81, 82, 83p

M280 81, 84, 85p

M283 86, 87p

M282 88, 89p

MJ / J 91/

93 , y 4p

93 , y 4p

M444 95, 96p

M316 98, 99p, 10(

M3 17 101

,

102p

M3 18 103 , 104p

M314 105, 106p

M315 107, 108p

xuy

,

xxup 1 1 n r-i M270 109, lllp

M271A,B 109, 112p

Mo 51 TIC 115 , Hop

Ml O lie; X X /p

M272 121, 122p

M337 123 , 124p

M340 127, 128p

XIII
AREA 6 - FLAT CASE-RADIATION, MECHANICS, MAGNETICS

X XiC^ J- ILl^ k^VMl J. CO f X i U> ^ X X^ W ^ 1X !?Q ^ J/

, 1 T n n Strain gage, Tuckerman M34 131, 132p

Strain gage, Whittemore M3 6 135, 136p

Magnegage, Brenner M415 137, 138p

Pp»"rTnf^aTnf^'t"P»T" Ri]t*tows M182 139 1X 4*T OnW A-/ Ma nn fi'f" 1 r* naT'l" i r*! r'liitr'h Rahinow M2X X^ 141 X *x X 1 1X A9H ^ kJn Macfnetic balance Sanford M19 143

A •* ** *-/

AREA 7 - PLAT CASE-RAD10 8^- '

Electric hvcrrometer Dunmore M3 3 147 148p

Radiosonde, Curtiss-Astin M167 149, 150p

Radiosonde, early type M163 149, 150p

Radiosonde, tube type M164 149, 150p

J\ciL4.Xi^oUllvJ.t:f ^ L-i. ci 1 io X o L.\j J. ^j:r^^ Ml 6"^ X i X \J ^ X1 ^ROnu L/ X\,ClLlXU X^l^c:£XVc^X f d X L«.C^X i id U> Xi 1^ LIX X i 1 X i X \j X1 ^"SIX , 1 n M83 153 1 54n

AREA 8 - PLAT CASE-ATRCRAPT

Course indicator, two-reed, type C M86 157, 158p

Course indicator, two-reed, type D MS 7 157, 158p

Runwav localizer M84 159

16 Op

VjXXd^^iU^X L>C^X / X XClliUlXil^ MR1*1 0 -JR X ^ J7 , X1 6nr> O \J \w'\JiUiJXilc^U. XdilUXiX^ XI io L-X LlXUOil l- i'JL X VJ O X 3 7 , 1 6n n

ARPA 9 — FT,AT CASE—ETjECTRTCTTY

J^XXUMC^ XWX XCoXOL^dil^w L.iXwX lUwJlUC ^X V X VJ .J

, 1X 64. U *T A-* n

PXuXw^ 1 ^f^l" po'h'hi \J L-llwX ^TTnill X"i r* vol V w X +"Tn^^^T* ^illw L-CX H<3T"Tn^r'}i

f XXCX iltdV^il M3 1 3 X ^ ^ X1 66d W w A-/ OiiUii^ kJKJ^ 0 fVdXUiiC^X vV^XXX 1 67 X1 68VP O X/n

x\t^o X o L-\^X ^ dU J Lio UdXiXtf ii\«lil XiilXLlL^ L>X Vc? |> A^iic^W MQ7 1X 6QQ 17

, 1 7nn

Xx^oXoC^X 0 KJllx^ ^iiill ULJLiXJXcf WdXX^Ll^ XXiwiUdo M4 9 171 X / X , X1 7/ ^S> X/n

V^^u XwillC^ L.C?X f ^C^X wXX XL/X Xw dV.'Xd Ml 7fi 17X / «J3 , X1 74/ ** X/n

Vjd X V di li^iUc^ L-cx ^ vxxJXdU-xxi^ x MQR 1X 7/ «JR , 1 7fin

\JCX X V dX iiJillt^ L.c^X 0 dUJLloUdJJXc? o^XioXUXVXUy / W tfXiXXt^X MT Q 1X 77/ / , X1 7R/ o n^

Gr5 \J\0*. ^1 v;=5noTnp't'PT V CXX XXn^Xll^^ ^ 0 Ttiovincf XII V 1 Tn^^rfnpt" XllC-X^^ X W 0 Pnhlpn"t"7 \^ \J »J JL 1 1 L» <J M2 19 179

180D

Galvanometer, remotely tuned, Silsbee M95 182, 183p

Ammeter, Kohlrausch M103 185, 186p

Resistor, non-reactive, Curtis M53 187, 189p

Resistor, non-reactive, Wenner M454 187, 190p

Resistor, non-reactive. Moon M52 187, 191p

Resistor, non-reactive. Woven and Card M50 188, 192p

Current balance, Kelvin M89 193 , 194p

XIV
AREA 10 - FLAT CASE - Standard Reference Materials (SRMs)

- Standards Eastern Automatic Computer (SEAC)

Representative SRMs 199, 200p

Representative SEAC Components M538 201-202, 203p

AREA 11 - TIME

Clock, Shortt M516 207, 208p, 209d

Clock, Riefler M515 210, 211p, 212d

AREA 12 - ELECTRICAL RESISTANCE

Mutual inductor, Wenner M41 215, 216p

AREA 13 - DRUM CASE II - PRESSURE

Barometer, U-tube M462 220, 221p

Vacuum pump, two-stage, Stimson M414 223 , 224p

Optical Cell, diamond anvil M325 227 , 228p

Pressure apparatus, tetrahedral anvil M38 231, 232p

AREA 14 - DRUM CASE II OPTICS

Spectrometer, Societe Genevoise

Interferometer, Fabry-Perot, NBS

Wavelength standard, neon

Wavelength standard, mercury-198

Wavelength standard, cadmium

M14 236, 237p

M275 239, 240p

M398 243 , 244p

M274 243 , 244p

M400 243 , 244p

AREA 15 - DRUM CASE II - ELECTRICITY

Capacitor, cylindrical M3 0 248, 250p

Capacitor, parallel plate M47 248, 252p

Electrodynamometer M68 253 , 254p

Wattmeter, heavy-duty. Brooks M366 255, 256p

Potentiometer, deflection. Brooks M24 257 , 258p

XV
AREA 16 - DRUM CASE I - DEFENSE

Sound-ranging system, World War I M480 262 . 263p

Naval ordnance studies, World War I M71,72,77 265, 266p

Proximity fuzes. World War II M4 , 5 ,

6

267, 268p

Carbon monoxide detector tubes. Shepherd,

World War II M193 269, 270p

Buoy circuit assembly, Tinkertoy,

World War II M443 271, 272p

Mine, constant depth, World War II MlOO 273 , 274p

Uranyl nitrate crystals. World War II M82 275, 276p

Graphite, high purity. World War II M81 277, 278p

AREA 17 - DRUM CASE I - INDUSTRY

Saccharimeter , Bates M418 282, 283p

Flexometer, Schiefer M331 285, 286p

Planoflex, Dreby M332 287, 288p

Indenter, pyramidical, Knoop M155 289, 290p, 291cJ

Contractometer , spiral, Brenner M416 293 , 294p

Printing plate, electroformed M441 295, 296p

AREA 18 - DRUM CASE I - SCIENCE

Radiation balance, microcalorimeter

,

Mann M339 300, 301p

Calorimeter, water M509 303, 304p

Proving ring, Whittemore-Petrenko M504 305, 306p

Atomic weight of hydrogen (Palladium used)

,

Noyes M9 309, 310p

Heavy water, Washburn Mil 311, 312p

Omegatron M7 313, 314p

AREA 19 - AMPERE

Coils, Rayleigh current balance M69 315, 317p

TOIEA 20 - BALANCE

Rueprecht balance M291 321, 322p,

XVI
u

-oc

APEA 1 VAULT occ
-2-
WORKING STANDARD OF PYROMETRY

TUNGSTEN STRIP LAMP 1946 M526

Precise temperature measiirements in science and technology are based on the International Practical Temperature Scale of 1968. On

this scale, high temperatures (those above the melting point of

gold, i.e., 1064 °C) are defined in terms of the Planck radiation

law which relates spectral radiance to temperature and wavelength.

The instrument used to realize the scale at the National Bureau of

Standards is a photoelectric pyrometer, calibrated relative to a gold-point blackbody source. Tungsten strip lamps, such as the one shown here , are calibrated with the pyrometer and serve as convenient secondary standards. This lamp is gas filled and has a ribbon filament 0.075 mm thick, 3 mm wide, and 50 ram long. To

increase the reproducibility of observations, the pyrometer is

sighted near the notch. The v-bend in the ribbon allows e^ansion

and contraction without twisting or bending as the temperature is

changed. Rated at 6 volts/30 amperes, the lamp requires about 14

amperes for a brightness temperature of 1000 °C and about 40

amperes for 2300 °C.

The calibration of tungsten strip lamps at NBS was, for many years,

done with a visual optical pyrometer based on the 1923 design of

Fairchild and Hoover. In 1966, the High Temperature Measurement

Section completed development of the photoelectric pyrometer and a horizontal gold-point blackbody, resulting in a significant

improvement in both precision and accuracy. Other national

laboratories have also developed photoelectric pyrometers. The

accuracy with which tiingsten strip lamps are calibrated is

indicated by the results of an international comparison completed

in 1972 . The laboratories participating in this intercomparison

included NBS, the Physikalisch-Technische Bundesanstalt in Germany,

the National Measurements Laboratory in Australia , and the National

Physical Laboratory in England. The maximum difference between the

calibrations of the laboratories was a few tenths of a degree from

1064 °C to 1700 °C and 2 °C at 2200 °C. In general, these diff- erences are less than the sum of the uncertainties assigned to the

calibrations by any two of the laboratories

.

References

Kostkowski, H. J. and Lee, R. D., Theory and Methods of Optical

Pyrometry, Nat. Bur. Stand. (U.S.), Monogr . 41 (1962).

Lee, R. D., The NBS photoelectric pyrometer and its use in

realizing the International Practical Temperature Scale above

1063 °C, Metrologia 2_, No. 4, pp. 150-162 (Oct. 1966) .
Lee, R. D. and Kostkowski , H. J.; Quinn, T. J. and Chandler, P. R.;

Jones, T. P. and Tapping, J.; and Kunz, H., Intercomparison of

the IPTS 68 Above 1064 °C by Four National Laboratories,

Temperature, Its Measurement and Control in Science and

Industry (Instrument Society of America, Pittsburgh, Pa.,

1972), Vol. 4, Part 1, p. 377.

-4-

WORKING STANDARDS OF PHOTOI^ETRY

As early as 1903, NBS adopted seasoned carbon-filament lamps as photometric working standards, having compared them with the Hefner

lam.p (M271) of the Reichsanstalt . Using about 4 watts per candle,

they operate at a filament color temperture of about 210C K, hence

their light is of nearly the same color as that from the WaidnerBurgess standard blackbody.

In 1906, E. P. Kyde carried to Europe nine 50-volt, 64-watt, horseshoe filament lamps (similar to M108) which had been standardized

for intensity in a specific direction defined by lines etched on

the bulb. Another nine taken were 110-volt, 64-watt, oval anchored

filament lamps which had been standardized for mean horizontal

intensity by the method of rotation. These v/ere intercompared with

similar lamps in London, Paris, and Berlin which had been compared

v/ith Harcourt (M65) , Carcel (M270) , and Hefner lamps, respectively.

Upon return to NBS, the mean value of intensity of these lamps was

found to be within 2 or 3 parts per 1000 of the original value.

They were thereupon adopted as the National Reference Standard, and

sim.ilar lamps were sold to users until the tungsten filament v/as

developed. In 1909 an "international candle" was adopted.

By 1914 two-thirds of the incandescent lam.ps submitted to NBS for

certification had the more efficient tungsten filam.ents operating

at a color temperature of about 2360 K, blue in comparison with

carbon- filament stancards . In photometry, this color difference

v/as compensated for by the use of a standard blue-glass screen

placed in the path of the light from the carbon-filament v/orking

standard. Anotiier procedure for coping v;ith the color difference

was the use of flicker photomietry.

Larger lam.ps (200, 450, 750 or 1000 watts) have an efficiency of

about 0.7 watt per candle, and are argon-filled, with tungsten

filaiTients coiled as a closely wound helix (M228) . These lamps

operated at a color temperature of about 285C K. The same blue

filter that compensated fox the color difference betv/een 2100 K and

2360 K was used to compensate for the color difference between 2360

K and 2850 K.

In 1908 C. W. Waidner and G. K. Burgess, both of NBS, had suggested

that a prototype standard of light based on the light emitted from

a blackbody immersed in a bath of freezing platinum would have m.any

advantages over the earlier proposal of Violle v^hich was to use

light from tiie surface of the metal.

-6-
In 1928, K. T. Wensel, V.'. F. Roeser, L. E. Barbrow, ard F. R.

Caldwell at KBS, set up such a standard and compared it v/ith the

national reference standard carbon filament Icimps v;hich had been

assigned values in 19C9 in terms of an agreed "international

candle." They obtained a value of 58.84+0.20 or -0.09 candles per

square centimeter. By international agreement, effective January

1, 1948, a new unit called the "candela" was put into use internationally, having been approved by the General Conference on Weights and Measures (CGPM) . The new standard was defined to have

a luminance of 60 candela per square centimeter.

This model of the Waidner-Burgess standard of light (M197) shows in

cross-section the thoria crucible, metal in the space occupied by

the freezing platinum, and a thoria tube (the blackbody) in the

center thereof.

Luminous intensity and luminous flux of incandescent lamps can now

be referred to tungsten lamps calibrated against the platinum

blackbody. Fluorescent tiibes up to 95 inches in length have been

calibrated against incandescent lamps in large spherical

photometers

.

References

Kyde, En P., Comparison of Units of Luminous Intensity, Bull. Nat.

Bur. Stand. 3_, 65 (1907) .

Middlekauff, G. W. and Skoglund, J. F., Photometry of the GasFilled Lam.p, Bull. Nat. Bur. Stand. 12, 587 (1915-16).

Page, C. H. and Vigoureux, P., Eds., The International System of

Units, Nat. Bur. Stand. (U.S.), Spec. Publ . 530 (1972).

Wensel, E. T., Roeser, W. F., Barbrow, L. E., and Caldv/ell, F. R.

,

The Waidner-Burgess Standard of Light, Nat. B\ir. Stand.

(U.S.), J. Res. 6, 1103, RP325 (1931).
-8
Lxaminous Flux Standard Lamps (1917 to Present) M229A, 229B

-9-
-10-
WORKING STANDARD OF ELECTRICAL RESISTAircE

ONE-OHM RESISTOR, DOUBLE-WALLED 1930 R7

In this type of standard resistor developed by J. L. Thomas a single layer of bifilar manganin wire is wound on a mandrel and

annealed in a vacuiim at red heat. It is then slipped onto a silkinsulated 6-cin brass cylinder with only loose contact between them.

This tube is closed by soldering its flanged ends to an outer 7-cm

tube. The coil is sealed in place with dry air and the leads for

electrical connections are brought out through seals.

Previous to 1910 the U.S. reference standard of electrical

resistance was maintained by resistors of the Reichsanstalt type

(M293) obtained from Germany. From 1910 to 1930 the standard was a group of 10 one-ohm coils of a design of E. B. Rosa (M28) . Between

1930 and 1939 these were gradually replaced by the double-walled

type. The maximum net change of the latter group, with respect to

the mean of the ten, measured at yearly intervals from 1939 to

1969, has been only one part per million.

References

Thomas, J, L. , A new design of precision resistance standard, Nat.

Bur. Stand. (U.S.), J. Res. 5_, 295 (Aug. 1930).

Thomas, J. L. , Stability of double-walled manganin resistors, Nat.

Bur. Stand. (U.S.), J. Res. 36_, 107 (Jan. 1946).

Wells, T. E., Precision Measurement and Calibration, Vol. 3,

Electricity-Low Frequency, Nat. Bur. Stand. (U.S.), Spec.

Publ. 300, p. 139-111 (Dec. 1968).

-11-
One-Ohm Resistor, Double-Walled (1930) R7
WORKING STANDARD OF ELECTROMOTIVE FORCE

WESTON STANDARD CELL 1905 M281

From 1893 to 1972 the international standard of electromotive force

(emf) has been based on an electrochemical "standard" cell. In

1910 scientists from England, France, and Germany met at NBS to

construct a large group of Weston standard cells and assign a voltage to them. Using a number of silver coulometers to fix the

ampere, and a nijmber of resistors to fix the ohm, they adopted the

value 1.0183 volts at 20 °C, using the Ohm's law relation

volt=ampere x ohm.

The Weston cell has a positive electrode consisting of a paste of

mercury and mercurous sulfate HgaSOit, the negative electrode being

an amalgam containing about 10 percent cadmium, with a saturated

solution containing cadmium sulfate CdSOi* 'S/SHaO crystals as an electrolyte. The H-form of container used at NBS is made of sodalime glass with a coefficient of linear expansion approximately

that of the platinum lead-wires. The vertical limbs about 15 mm in

diameter have constrictions near the base to lock in part of the

crystals

Between 1910 and 1972 the U.S. legal volt was maintained by a group

of Weston saturated cells which were held at a constant temperature

in an oil bath. The mean electromotive force was assumed to remain

constant. As new and stable cells were made they were introduced

into the reference group, which grew to 44 cells. In 1969,

reflecting improved realization of the ohm and the ampere, the

international standard for the Weston cell was fixed at 1.018 328 6

volts. Siibsequent check of the U.S. Standard cell group against

the Josephson junction (M550) has shown that the group emf has

actually been drifting down slightly, but by less than 3 parts in

10,000,000 per year.

References

Hamer, W. J., Standard Cells: Their Construction, Maintenance, and

Characteristics, Nat. Bur. Stand. (U.S.), Monogr. 84 (1965).

Eicke, W. G. and Cameron, J. M. , Designs for Surveillance of the

Volt Maintained by a Small Group of Saturated Standard Cells,

Nat. Bur. Stand. (U.S.), Tech. Note 430 (Oct. 1967).

Nat. Bur. Stand. (U.S.), Tech. News Bull. 54_, 43 (Feb. 1970).

Field, B. F., Finnegan, T. F., and Toots, J., Volt maintenance at

NBS via 2e/h: A new definition of the NBS volt, Metro logia 9_, 155 (1973)

-13-

I

-15-

WORKING STANDARDS OF LENGTH

After the Treaty of the Meter had been signed in 187 5, the International Bureau of Weights and Measures (BIPM) at Sevres made 31

prototype line standards of platinum - 10 percent iridium alloy.

These have a modified X-section named for Henri Tresca who devised

it. Small elliptical areas on the upper surface of the central rib

at each end of the bars are highly polished, and three lines

nominally 0.5 mm apart are ruled on these surfaces, the distance

between the middle lines of each group defining the standard

length. One bar, having the length of the Metre des Archives, was selected as the International Meter. Intercomparisons between it

and the 31 National Prototypes yielded a "probable error" of ±0.04

micrometer, and the uncertainty at temperatures between 20 and 25

°C was estimated by BIPM to lie between ±0.1 jim and ±0.2 ym.

METER No. 27 1889 Rl

National Prototype No. 27 was sent to the United States by Delegate

B. A. Gould, and received by President Harrison on January 2, 1890.

It was certified to have a length of

1 m-1.6 ym + 8.657 ym»T + 0.001 ym*T^ ± 0.2 ym

with T in degrees centigrade. Recertification at 0 °C gave the

values 1 m-1.48 ym in 1922, 1 m-1.47 ym in 1933, and 1 m-1.45 ym in

1957. When the Mendenhall Order in the Report for 1893 (Coast and

Geodetic Survey) declared the meter to be a fundamental standard.

No. 27 became the U.S. reference standard for all length

measurements. It remained the primary prototype in 1960, secondary

only to the basic value in terms of the wavelength of krypton 86.

METER No. 21 1890 R2

National Prototype No. 21 is of the same material and design as No.

27. It was received from BIPM later in 1890, certified as

1 m + 2.5 ym + 8.665 ym*T + 0.00100 ym»T^ ± 0.2 ym

References

Tittmann, 0. H., National Prototypes of the Standard Metre and

Kilogramme, Appendix No. 18 - Report for 1890, U.S. Coast and

Geodetic Survey.

Judson, L. v.. Weights and Measures of the United States, Nat.

Stand. (U.S.), Misc. Publ. 247 (1963).

GAGE BLOCKS

M569

In machine shops, these lengths of short workpieces are measured by

comparing them with a stack of these accurately ground and polished

end standards. Over 100,000 length combinations are obtainable

from a set of 81 blocks. An 88-piece set in inch units yields

combinations in increments 0.000025 inch. The modern abundance of

precision low cost mechanisms could not have been achieved without

production methods utilizing interchangeable parts, and this, in

turn, could not have been achieved without modern precision gaging

methods using gage blocks.

NBS master gage blocks are calibrated in the interferometer using

either Hg^^® or a heli^lm-neon-iodine stabilizer. An average of

4,000 master gage blocks are sent to NBS by industry and government

each year for calibration or recalibration. During the era of the

space race, as many as 100,000 master blocks were received for

measurement assurance.

References

Beers, J. S., A Gage Block Measurement Process Using Single

Wavelength Interferometry , Nat. Bur. Stand. (U.S.), Monogr.

152 (1975) .

Pontius, P. E., Measurement Assurance Program—A Case Study:

Length Measurements. Part 1. Long Gage Blocks (5 in to 20

in), Nat. Bur. Stand. (U.S.), Monogr. 149 (1975).

One Ten-Millionth of an Inch, A talk by Dr. I. C. Gardner before

the American Ordnance Association (1955)

.

-19-
Gage Blocks (Representative) M569

-20-
WORKING STANDARDS OF TEMPERATURE

The International Practical Temperature Scale of 1968 (IPTS-68) is

based on values assigned to eleven temperatures that can be

reproduced by equilibria between phases of pure substances

(defining fixed points) . "Standard" thermometric instruments which

meet rather stringent requirements are calibrated at these

temperatures. Interpolation between the fixed point temperature is

provided by specified formulas that relate the indications of the

standard thermometric instruments and the values of temperatures cf

the IPTS-68.

THERMOCOUPLE, PIATINlTM-iO PERCENT RHODIUM vs. PLATINUM M522

This is the standard instrument for the IPTS-68 in the range 903.89

K (630.74 °C) to 1337.58 K (1064.43 °C) . Such instruit'.ents are calibrated at these temperatures and at an intermediate value,

1235.08 K (961.93 °C) . This thermocouple is assembled in a sintered alumina insulating tube having two 1.2 mm bores.

PLATINUM RESISTANCE THERMOIffiTER M523

This is one form of standard IPTS-68 thermometric instrument used

from 90.18 K (-182.97 °C) to 903.89 K °630.74 °C) , with a "capsule"

type for the range from 13.81 to 90.18 K. Nine defining fixed

points provide calibration in the platinum resistance thermometer

range, one being the triple point of water at 273.16 K.

The standard platinum resistance thermometer (SPRT) design shown

consists of a four-terminal resistance coil, approximately 3 cm

long and 0.5 cm diameter, on a mica form. The resistance coil and

its four leads are hermetically sealed in the borosilicate glass

tube (about 7.5 mm o.d. and 50 cm long); the four gold leads em.erge

at the top through metal-to-glass seals and connect to copper

wires. Usually dry air at about one-third of atmospheric pressure

is sealed into these thermometers. The instrument is usually

measured with a Mueller thermometer bridge. Type G-2 or G-3.

(The upper limit of the borosilicate glass is about 500 °C. For

application up to 630.74 °C, a fused silica or Vycor sheath is used

and the thermometer leads are usually platinum)
References

The International Practical Temperature Scale of 1968, Metrologia

5_, 35 (1969) .

Evans, J. P. and Wood, S. D., An intercomparison of high

temperature platinum resistance thermometers and standard

thermocouples, Metrologia 7_, No. 3, 108-130 (July 1971) .

Riddle, J. L., Furukawa, G. T., and Plumb, H. H., Platinum

Resistance Thermometry, Nat. Bur. Stand. (U.S.), Monogr. 126

(Apr. 1973)

-22-
-23-

WORKING STANDARD OF FREQUENCY

QUARTZ CRYSTAL RESONATOR . M571

Designed to vibrate millions of times per second at a very stable

frequency, quartz crystal resonators are the heart of many modern

timepieces. These vibrations function as a "pendulum" for quartz

controlled wrist watches and atomic clocks, although a swinging

pendulum could never keep pace nor be as accurate as the crystal '

s

stabilized vibrations. A precise 5 MHz, 5th overtone frequency is

derived from this working crystal. The physical shape and

thickness of a crystal determines its frequency, while its

frequency amplitude is determined by the amount of voltage applied

to the two flat metallic surfaces coated on the crystal. The

crystal is housed in an evacuated glass enclosure. Metal

enclosures, backfilled with a protective gas, are also used.

References

Hellwig, K., Frequency Standards and Clocks, A Tutorial Introduction, Nat. Bur. Stand. (U.S.), Tech. Note 615 (Rev. Mar.

1974) .
Quartz Crystal Resonator M571

-26-
AREA 2 -

en

73

e

VAULT -

cO

z

-27-

FOUR SI UNITS

The International Committee on Weights and Measures, of which the

United States has been a member^ since 1878, currently recognizes

seven base units in Le Systeme International d'Unites (SI). These

are the meter of length, the kilogram of mass, the second of time,

the ampere of electric current, the kelvin of thermodynamic

temperature, the candela of luminous intensity, and the mole of

chemical substance. Four of them—the meter, the kilogram, the

second, and the kelvin—are used to define units of measxirement for

all other physical quantities, whether mechanical, electrical,

chemical , optical , thermal , or radio

Shown here are the national standard of mass (Prototype Kilogram

No. 20, under bell jars at right) and representative parts of the

equipment used to realize the units for the other three primary

quantities. These are (left to right) the krypton-86 lamp for

length, the cesium becim oven for time, and the triple-point cell

for temperature.

Elsewhere in the museum are displays relating to the ampere , the

candela, and the mole; and to many of the derived and supplementary

SI units.

References

Page, C. H. and Vigoureux, P., Eds., The International System of

Units, Nat. Bur. Stand. (U.S.), Spec. Publ. 330 (Jan. 1971).

-29-
NATIONAL STANDARD OF LENGTH

KRYPTON-86 LAMP 1960 M543

As early as 1829 Babinet proposed defining the meter in terms of

the wavelength of light. In 1892 Michelson used his interferometer

with cadmium red light, and Barrell has summarized the more precise

measurements made in this way between 1892 and 1940. W. F. Meggers

at NBS in 1947 developed a source (M274) using the isotope mercury198, which gives a brilliant green light at room temperature.

However, the General Conference on Weights and Measures (CGPM)

agreed in 1960 to use a krypton isotope source (M543) operated at

64 K. This is now the U.S. primary standard, replacing the

prototype meter bar.

The monochromatic light from this lamp is divided into two beams,

each being directed to a mirror from which it is reflected back.

The two beams are then recombined. If the distance traveled by the

two beams before they are recombined is the same, the waves of

light from each will be in phase and will reinforce each other. If one mirror is then displaced along the beam by a quarter

wavelength, the waves will interfere destructively. Further motion

by a quarter wavelength will again put the two waves in phase. At

an observation point in the path, alternate light and dark bands

will appear, and the number of times the bands change is a measure

of the mirror displacement. The changes may be counted by a photocell, and by the definition adopted by CGPM there are 1 650

763.73 vacuiam wavelengths of krypton-86 in one meter.

References

Michelson, A. A. and Morley, E. W. , On the feasibility of establishing a light wave as the ultimate standard of length. Am.

J. Sci. 3£, 181 (1889)

Cook, H. D. and Marzetta, L. A., An automatic fringe counting

interferometer, Nat. Bur. Stand. (U.S.), J. Res. 65C (Eng.

and Instr.), No. 2 (Apr. -June 1961).

Page, C. H. and Vigoureux, P., Eds., The International System of

Units (SI), Nat. Bur. Stand. (U.S.), Spec. Publ . 330, p. 26,

35 (Apr. 1972)

-30-
Krypton-ae Lamp (1960) M543

-31-

NATIONAL STANDARD OF MASS

After the Treaty of the Meter had been signed in 1875, the

International Bureau of Weights and Measures (BIPM) at Sevres (near

Paris) procured 43 prototype kilograms of 90 percent platinum - 10

percent iridium alloy in the form of right circular cylinders of

equal diameter and height (approximately 39 mm) with slightly

rounded edges.

The volxametric coefficient of expansion of the alloy and the

displacement volumes of each of the weights were determined by

hydrostatic weighing. One of the group, having essentially the

same mass as the Kilogramme des Archives, was selected as the

International Prototype Kilogram, and is now maintained at BIPM.

The others were either sent to the various member countries as Prototype Kilograms (of which the United States has two) or retained at BIPM for future use.

PROTOTYPE KILOGRAM K^° 1889 R5

B. A. Gould, U.S. Delegate to the International Conference of

Weights and Measures, himself supervised the packing of Prototype

Kilogram K^° on October 27, 1889 for its transport to this country

in care of George Davidson of the Coast and Geodetic Survey. On

January 2, 1890, President Harrison broke the seals on the case and

gave the standard to T. C. Mendenhall, Superintendent of Weights

and Measures. Its mass relative to the International Prototype

Kilogram was reported as 0.999 999 961 kg. The reported

displacement volume at a temperature of 0 °C was 46.402 cm^. Since

it was the first of the two prototype kilograms to be received, K^°

is sometimes called the national standard of mass. Of the seven

base units in Le Systeme International, the kilogram is the only

one currently defined by an artifact.

PROTOTYPE KILOGRAM K** 1890 R6

Prototype Kilogram k'* was received by the U.S. Coast and Geodetic

Survey directly from the International Bureau of Weights and

Measures. Its mass relative to the International Prototype

Kilogram is 0.999 999 925 kg and its displacement volume at 0 °C is

46.418 cm^.

Since both Prototype Kilograms are in frequent use in the NBS Mass

Laboratory, the weights on display are replicas to illustrate the

approximate size of the platinum-iridium alloy kilograms . See P

E. Pontius, Mass and Mass Values, NBS Monogr. 133 (1974).

-33-
References

Tittman, 0. H. , National Prototypes of the Standard Metre and

Kilogramme, Appendix No. 18 - Report for 1890, U.S. Coast and

Geodetic Survey.

-34-
Prototype Kilograia K (1889) R5

This is a replica. Original in custody of

llass Standards Laboratory.

-35-

INTERNATIONAL STANDARD OF TEMPERATURE

The temperature of the triple point of water (the state of

equilibrium between the solid, liquid, and vapor phases) is the

single defining fixed point common to the Thermodynamic Temperature

Scale and the International Practical Temperature Scale of 1953.

It is assigned the value of 273.16 K on both scales.

The triple-point cell (M524) is prepared by cooling the inside of

the thermometer well so that water freezes outward from the well

and forms a continuous mantle around the well. Usually a mantle of

about 4 to 10 mm is frozen. Crushed "dry ice" may be placed

directly in the well or a "cold finger" with a^uitable heatconducting fluid may be inserted in the well to freeze the mantle.

After freezing the mantle, a very pure ice-and-water interface

surrounding the thermometer well is formed by melting a thin layer

of ice immediately next to the well. This technique, referred to as an "inner melt," gives a highly reproducible temperature. (The

inner-melt temperatures of cells from different sources agree

within 0.0002 K.)

It is essential that this inner melt should surround the

thermometer well completely. To form the inner melt, the

thermometer well is filled with chilled water after a suitable

mantle is frozen; then, a glass tube at room temperature is

inserted in the well for a period long enough to melt the ice

mantle free. When this occurs, the mantle will move free of the

well when the cell is given a sudden rotation around its axis.

References

Stimson, H. F., Precision Resistance Thermometry and Fixed Points,

pages 133-135 in Precision Measurement and Calibration,

Selected NBS Papers on Temperature, J. F. Swindells, Ed., Nat.

Bur. Stand. (U.S.), Spec. Publ . 300-2 (Aug. 1968).

-37-

NATIONAL STANDARD OF FREQUENCY AND TIME

CESIUM OVEN 1956 M375

In 1967 the International Committee of Weights and Measures

declared that the physical measurement of time would be based on a particular transition between energy levels in the atoms of cesium

13 3. This oven was part of the laboratory frequency standard NBSII about 1956. In it metallic cesium is heated electrically in a vacuum to about 150 °C. The vaporized atoms effuse through the

narrow slit in the front and enter an atomic beam spectrometer

about 2 meters long. The beam traverses a steady magnetic field

H^^, an oscillating field E-^, a uniform "C" field with a collimator

slit, a second oscillating field H2 , and a second steady field Hg.

These fields act on the magnetic dipole m.oments of the atoms to

effect the desired transition at its natural frequency of 9 192 531

770 Hz (cycles per second) , and to establish atomic trajectories

which converge toward a detector. The resulting detected beam

current goes through a maximum when the frequency of the

oscillating fields is swept through the resonance of the cesium

transition. A servosystem uses deviations from the maximum to keep

the frequency on the cesium resonance.

To provide an atomic time standard, cycles of the frequency as given by NBS-II were counted to give atomic seconds, and these were used to calibrate the seconds of a set of five independent quartz

crystal oscillators (similar to M375) each operating continuously

as a clock. These oscillator clocks were used to infer the atomic

time which NBS-II would have kept had it been running continuously.

The time scale so generated was called NBS-A.

References

Beehler, R. E., Mockler , R. C, and Richardson, J. M. , Cesium Beam

Atomic Time and Frequency Standards, Metrologia 1_, No. 3, 114-

131 (July 1965) ; offprinted as pages 95-112 in Precision

Measurement and Calibration, Frequency and Time, Nat. Bur.

Stand. (U.S.), Spec. Publ . 300-5 (June 1972).

Hellwig, H. , Frequency Standards and Clocks: A Tutorial

Introduction, Nat. Bur. Stand. (U.S.), Tech. Note 616 (Rev.

Mar. 1974)

.

-39-
-40-
-41-

NATIONAL STANDARD OF ELECTRICAL RESISTANCE

The International Committee on Weights and Measures (CIPM) voted in

1945 to adopt a system of "absolute" electrical quantities based

only on mass, length, and time. The U.S. Congress made this legal

in 1949. The British National Physical Laboratory (NPL) derived

the absolute ohm by two different methods, the Lorenz rotating

inductor and the Campbell mutual inductor. It was derived at NBS

in 1938 by H. L. Curtis and associates, using a large selfinductor, and verified in 1949 by J. L. Thomas and associates using

the Wenner modification of a Campbell inductor (M41) . The

experiment involved the construction of an inductor whose value

could be computed from its dimensions and the assigned value of

space permeability.

In 1955 the Thompson-Lampard theorem in electrostatics made

feasible the construction of a calculable capacitor whose

configuration is such that only a single length determination is

critical. One can compare resistance with a capacitive reactance,

knowing the frequency and the peirmittivity of space. R. D.

Cutkosky used this device in 1961, 1957, and again in 1974 to check

the value of the NBS unit as maintained by a bank of 1-ohm

resistors. The most recent result shows it to be 0.999 999 18 ohms

± 0.05 ppm.

References

Glazebrook, R. T., Standards of measurement: Their history and

development, Proc. Phys. Soc . 43_, Part 4, No. 2 39 (July 1,

1931)

.

Silsbee, F. B., Establishment and Maintenance of the Electric

Units, Nat. Bur. Stand. (U.S.), Circ. 475 (June 30, 1949).

Cooter, I. L., et al,. Electrical Standards and Measurements, page

9-1 in Precision Measurement and Calibration, Nat. Bur. Stand.

(U.S.), Spec. Publ, 300-3 (Dec. 1958).

Cutkosky, R. D., New NBS measurements of the absolute farad and

ohm, IEEE Trans. Inst. & Meas . IM23, No. 4, 305 (Dec. 1974).

-43-
One-Ohm Resistor, Double-Walled (1930) R7

-44-
NATIONAL STANDARD OF VOLTAGE

JOSEPHSON JUNCTION 1971 M550

Microelectronic circuit modules like the one displayed have been

used since July 1, 1972 as a stable reference for the NBS bank of

electrochemical standard cells. The device consists of two

superconductor layers separated by a 1 nanometer oxide film. VJhen

the module is irradiated at microwave frequencies and cooled to

about 1 K in a liquid nitrogen/liquid helium cryostat, electron

tunneling across the oxide gives rise to what is known as the ac Josephson effect.

The microwave frequency is related to the voltage applied across

the superconductors by the fundamental constant 2 e/h, where e is

the electron charge and h is Planck's constant. For use in

maintaining the U.S. legal volt, NBS has adopted the value 483.593

420 terahertz per NBS volt of 1959. Comparisons with the volt

standards maintained by National Laboratories in Britain,

Australia, and Germany have shown agreement with the NBS volt to

within 1 or 2 parts in 10^.

References

Field, B. F. , Finnegan, T. F., and Toots, J., Volt maintenance at

NBS via 2 e/h: A new definition of the NBS volt, Metrologia

155 (1973)

Finnegan, T. F. , Denenstein, A., Langenberg, D. N. , Phys. Rev. B

4, 1487 (1971) .

Parker, W. H. , Langenberg, D. N. , Denenstein, A., Taylor, B. N.

,

Phys. Rev. 177, 639 (1969).

Taylor, B. N. , Parker, W. H., Langenberg, D. N. , Denenstein, A.,

Metrologia 3_, 89 (1967) .

-45-
Josephson Junction (1971)

-46-
0 5 10mm

I I I

Josephson-device geometry (1971) M550

The cross-hatched region indicates the oxidized film

which is partially covered by the second film to produce four junctions.

-47-

INTERNATIONAL STANDARD OF LIGHT

PLATINUM BLACKBODY 1930 Ml 9

The French physicist Violle in 1881 proposed as a primary standard

of luminance the light emitted by 1 sq cm of surface of melted

platinum at the temperature of its solidification, about 2045 K.

However, studies by Waidner and Burgess of NBS showed that a variation of one degree caused a variation of over 0.5 percent in

the intensity of the light. They suggested the use of a blackbody

(one which completely absorbs all radiation incident upon it) with

the important feature that it be totally immersed in a bath of

freezing platinum.

When Wensel and his coworkers undertook to realize the WaidnerBurgess concept, they used as the blackbody a few grams of fused

thoria placed at the bottom of a sight tube and viewed through a 1.5 mm opening. Molten platinum of exceptionally high purity

(simulated by lead in the cut-away model M197 on display) was contained in a thoria crucible, and uniformity of temperature was achieved by the violent stirring which resulted from heating in a high frequency induction furnace. In terms of the "international

candle," maintained at NBS since 1909 by a group of carbon-filament

lamps (M198) , the luminance was found to be 58.84 + 0.20 or -0.09

c/cm^

By 1933 the Comite International des Poids et Mesures had appointed

a photometry committee and accepted both the blackbody concept and

the freezing platinum reference.

The national laboratories of France, Great Britain and the United

States agreed in 1937 that a standard platinum blackbody represented 58.9 international candles per square centimeter, and in

1946 CIPM adopted the figure of 60 c/cm^ . The name "candela" was adopted for the unit of luminous intensity in 1948.

Besides serving as the basis for the photometric system of units,

the platinum blackbody standard will make it possible to determine

(by the use of Planck's equation and the spectral luminous

efficiency values of the Commission Internationale de I'Eclairage)

the "mechanical equivalent of light" which will be useful when the

blackbody standard is eventually superseded by a radiometric method

for defining the unit of light.

-49-
References

Violle , J., Sur 1' e talon absolu de lumiere, Ann. Chem. et Phys.

(6) 3_, 373-407 (1884) .

Waidner, C. W. and Burgess, G. K. , The Radiation from and the

Melting Points of Palladium and Platinum, Bull. Nat. Bur.

Stand. 3_, 163-208 (1907).

Waidner, C. W. and Burgess, G. K. , Note on the Primary Standard of

Light, Electrical World LII, No. 12, 625-628 (1908).

Wensel, H. T. , Roeser, W. F., Barbrow, L. E. , and Caldwell, F. R.

,

The Waidner-Burgess Standard of Light, Nat. Bur. Stand.

(U.S.), J. Res. 6_, 1105-1117 (1931).

Announcement of Changes in Electrical and Photometric Units, Nat.

Bur. Stand. (U.S.), Circ . 459 (May 1947).

/

-50-




HISTORICAL CUSTOMARY STANDARDS OF I4ASS

TROY POUND 1827 M446

The troy ounce (named for Troyes in France) has been used for the

sale of gold, silver and precious stones from 1527 to the present.

The troy pound is subdivided into 12 ounces, each of which in turn

is subdivided into 480 grains for a total of 5760 grains. To

standardize weights of U.S. coinage in 1827, plenipotentiary Albert

Gallatin procured for the Philadelphia Mint a troy pound reported

to be an "exact copy" of the British standard, the Imperial Troy

Pound of 1758. It was a two-piece unplated brass weight, engraved

"Pound Troy, 1824, Bate, London." The troy pound on display (M446)

is a later copy which proved to be unstable and so was rejected.

"STAR" AVOIRDUPOIS POUND ' 7,^' 1830 M323

Both the British and the U.S. avoirdupois pounds widely used in

commerce, are subdivided into 15 ounces each of which is further

subdivided into 4S0 grains for a total of 7,000 grains. Each

country derived the avoirdupois pound from the troy pound through

the ratio 7,000/5760, The cylindrical brass weight displayed

(M323) is marked on the top surface of the knob with a star.

Although positive identification cannot be made, it appears not

unreasonable to assume that this standard is the actual weight

"made by Mr. Hassler from the troy pound in the United States Mint,

and marked with a star (commonly designated as the star pound) , " as referred to by A. D. Bache , Superintendent of Weights and Measures,

in his report of December 30, 1855, to the Secretary of the

Treasury

.

IMPERIAL AVOIRDUPOIS POUND, 1855 M324

Copy No. 5

A gold-plated brass standard of mass, cylindrical in form, with a circumferential groove instead of a knob to facilitate its

handling. In 1834 the Imperial Troy Pound of 1758 was destroyed by

fire. Using two platinum troy pounds which had been carefully

compared with the lost standard. Prof. W. K. Miller of the British

Standards Commission constructed a new platinum troy pound and from

that a new platiniim imperial avoirdupois pound. As a part of this

work, gilded bronze copies were distributed to English-speaking

nations, and copy No. 5 (M324) was received here in 1856 as a gift

from Great Britain to the United States. It was reported that

Hassler's "star" pound agreed with this copy within 0.001 grain, or

1 part in 7 X lo^ —a truly remarkable achievement.

-55-
Comparisons between the two platinum weights and the Kilogram of

the Archives have provided the basis for the currently accepted

relation

1 avoirdupois pound = 0,453 592 37 kilogram.

References

Chisholm, H. W. , On the Science of Weighing and Measuring,

(Macmillan, London, 1877) .

Judson, L. V. , Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (1963).

-56-
Troy Pound (1827) M446

-57-
-58-


HISTORICAL METRIC STANDARDS OF MASS

1 GRAVE 1793 M322

A cylindrical knob weight, one of six made in 1793 by the French

Temporary Commission on Weights and Measures as representing the

unit of weight of a proposed system of weights and measures. Originally called the "grave," in 1795 the unit was renamed the

"kilogram. " This weight is from a set of weights brought to the

United States in 1793, and it appears that the set came into the

possession of one Andrew Ellicott, at one time an assistant to

Major Pierre Charles L' Enfant who planned the city of Washington.

The subsequent history of this set of weights is somewhat obscure,

but it seems probable that the set remained in private hands,

probably within the Ellicott family until 1952, when what remained

of the set was donated to the National Bureau of Standards by its

owner at that time, Dr. A. Ellicott Douglass of the University of

Arizona.

References

Judson, L. v., Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (1963).

KILOGRAM/LITER 1791 M448

A hollow gold-plated brass sphere having a mass of approximately 1 kg and a volume of approximately one cubic decimetre. It was thus

a physical object having the properties of a kilogram of pure water

free from air. This was the first concept for the definition of

the metric unit of mass, and the original experiments to achieve

this "kilogramme provisionaire" were reported to the Academy of

Paris in 1791. The idea had to be abandoned because the precision

of weighing, with due regard for the buoyancy of the air, was much

better than that with which the water kilogram could be reproduced.

The sphere on display was constructed by Louis A. Fischer of NBS

about 1905 to replace one believed to have been made about 1844 by

Joseph Saxton of the U.S. Coast Survey. Records in the National

Archives indicate that the Saxton sphere was found to leak air.

References

Letter, Lloyd B. Macurdy, November 15, 1973.

-61-
COMMITTEE KILOGRAM 1799 M319

A brass standard of mass of cylindrical form with a knob. This

standard is one of a group of similar standards made in France in

1799 by the Committee that made the Kilogram of the Archives,

whence its designation in the United States as the "Committee

Kilogram." This standard was presented by Tralles, the Swiss member

of the Committee, to his friend F. R. Hassler in 1805. Hassler, in

turn, sold it to a member of the American Philosophical Society in

Philadelphia, who deposited it with the Society. Later, the

standard was obtained from the Society by Hassler, who made use of

it in connection with his standards work for the U.S. Coast and

Geodetic Survey.

SILBERMANN KILOGRAM 1852 M321

A gold-plated brass standard of mass of cylindrical form with a knob. This standard was presented to the United States by France

in 1852. It was used in the Office of Standard Weights and

Measures of the U.S. Coast and Geodetic Survey, particularly in

connection with the adjustment and verification of the early metric

standards supplied to the States.

References

Judson, L. v., Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (1963).

-62-
1 Grave (1793) M322

-63-
Kilogram/Liter (1791) M448

-64-
Committee Kilogram

-65-

(1799) M319
Silberman Kilogram (1852) M321

-66-
HISTORICAL STANDARDS OF ELECTRIC CURRENT

The silver voltameter, better called a coulometer, was chosen as the official primary standard for the measurement of current by the

International Electrical Congress at Chicago in 1893. When a silver anode is suspended in a platin\am container of electrolyte,

the passage of current deposits crystals of pure silver on the

platinum cathode. The principle was used by Poggendorff in 1847.

In a systematic study of the device made by Lord Rayleigh in 1884,

the anode was wrapped in filter paper to catch the particles of

silver slime which might contaminate the deposit (M172) . Another

form used by F. and W. Kohlrausch and described in 1886 had no

septiom, but a small glass dish was hung below the anode (M175) . Richards and Heimrod in 1899 substituted a porous cup of porcelain

for the filter paper (M170) . In 1906, F. E. Smith devised a "nev/

form" (M171) in which the disc-shaped anode rests in a shallov/

glass cup. A movable glass ring, with its lower edge ground to fit

the cup, is supported above the cup during the experiment. Its

lower edge is below the electrolyte surface, to prevent any

floating slime from reaching the outer vessel. At the end of the

experiment the ring is lowered onto the cup, and the cup and ring

assembly containing the anode and anode slime is removed before the

platinum cathode is emptied and weighed.

The London Conference of 1908 adopted specifications for the

mercury ohm and the Weston Normal cell, and defined the

international ampere as "the unvarying electric current which, when

passed through a solution of nitrate of silver in water

deposits silver at the rate of 0.00111800 of a gramme per second."

At the National Physical Laboratory, F. E. Smith made careful

determinations of the electrochemical equivalent of silver using

several forms of voltameter, and at the Reichsanstalt , W. Jaeger

used the porous cup form and another without septum. At NBS , E. B.

Rosa and associates began intensive work in 1908 which showed that

the filter paper was a source of serious disturbance in the

character and weight of the deposit.

Meanwhile, arrangements had been made for Smith, Jaeger, and L. Laporte of the Laboratoire Centrale d 'Electricite to meet at NBS as

a Special Technical Committee, with Rosa as chairman. They began

work in April 1910, using pure electrolytes, and three voltameters

- the new form of Smith (M171) , a 100 cc size of Richards (M170)

and a 300 cc size of Richards. The relative masses of the deposits were respectively l.OOOOOo, and 0,999977, and l.OOOOOg. Further

experiments by Smith and Vinal , and by Rosa, Vinal and McDaniel

showed agreement within 4 parts in 100,000. A complete

specification for materials and procedures was later prepared by

the U.S. team.

\ -67-
The classic experiment of Rosa, Dorsey, and Miller in 1910 provided

a relation between an international ampere determined by coulometer

and an absolute ampere determined by the forces in a current

balance such as M69. In 1948 the international ampere was defined

as 0.99985 absolute ampere.

References

Rosa, E. B. and Vinal , G. W. , The Silver Voltameter - Part I, Bull.

Nat. Bur. Stand. 9_, 151 (1913); Summary of Experiments, Sci.

Pap. Nat. Bur. Stand. No. 285 (1916).

Rosa, E. B., Vinal, G. W. , and McDaniel, A. S., The Silver

Voltameter - Part II, Bull. Nat. Bur. Stand. 9_' 209; Part III,

493; Part IV ibid 10, 475 (1914).

Glazebrook, R. T. , Dictionary of Physics 2_, p. 247, Macmillan,

London (1922)

.

Report to the International Committee on Electrical Units and

Standards, U.S. Government Printing Office, Washington, D.C.

(Jan. 1, 1912).

Richards, T. W. and Heimrod, G., On the accuracy of the improved

silver voltameter, Proc . Am. Acad. Sci. 37, 415 (1902).

-68-
Coulometer, Rs.yleigh (England) (18S4) M172

-69-
Coulometer, Kohlrausch (Germany) (1910) M175

-70-

Coulometer, Smith (England) (1910) M171

-72-
HISTORICAL STANDARDS OF ELECTRICAL RESISTANCE

In 1851 the British Association for the Advancement of Science

appointed a committee for improving the construction of practical

standards of electrical measurements. To specify resistance, they

constructed in 1863 and 1864 wire-wound resistors known as the E.

A. ohm; M51 is of this design. These resistors were manufactured

and used over the next couple of decades. However, because of the

instability of the resistors they were replaced as primary

standards by the "international ohm" defined in the 1880 's as the

resistance of a specified column of mercury at a specified

temperature. This unit was legalized in the United States in 1894.

The precise specification adopted by the London Conference of 1908

called for a mass of 14.4521 g at 0 °C, a length of 106.300 cm and a uniform cross section of about 1 mm^ . In the late 1880 's the

German Physikalisch-Technische Reichsanstalt (PTR) designed a resistor which is known as the PTR type (M334) . These were the

first resistors to use manganin wire and were designed so that the

coil of insulated wire would be in direct contact with the oil of

the bath in which it was placed.

In this country, a group of wire resistors of the PTR pattern, made

in Berlin and certified by the PTR, formed the national reference

standard up to 1907. E. B. Rosa and H. D. Babcock at NBS had noted

that these changed value seasonally, and traced the trouble to the

effect of atmospheric huraidity. In the design which Rosa then

developed (M28) the coil was sealed in a container of very pure dry

oil. Between 1911 and 1913, F. A. Wolff and associates at NBS

constructed four mercury ohm tubes (M137) to the international

specification, and used them to verify five Rosa coils. A group of

resistors of the Rosa type was used to maintain the unit of

resistance in the USA until they were replaced in the 1930 's by a type of resistor designed by J. L. Thomas of NBS. In the Thomastype resistor (R7, M42) a bifilar manganin coil is formed and

heated to red heat in a vacuum before being sealed in dry air

between two tubular shells soldered together at their ends. The

coil of wire is only loosely in contact with the inner shell.

Since 1930 a group of the Thomas 1-ohm resistors has constituted

the U.S. reference standard, being intercompared periodically with

other national laboratories.

References

Glazebrook, R. T. , Standards of measurement: Their history and

development, Proc . Phys . Soc. 43, Part 4, No. 2 39 (July 1,

1931)

Silsbee, F. B., Establishment and Maintenance of the Electrical

Units, Nat. Bur. Stand. (U.S.), Circ. 475 (June 30, 1949).

-73-
B. A. OHM 1887 M44

This standard resistor, made by Elliott Bros., London, was presented in 1887 by the (British) Institution of Electrical Engineers

as a Fahie Premium to A. E. Kennelly (then an associate member) as an award for his paper on "Certain Phenomena Connected with the

Imperfect Earth in Telegraph Circuits." It was calibrated at the

Cavendish Laboratory as Test No. 193 on March 13, 1896, and

certified by R. T. Glazebrook as R = 1.00028 legal ohms at 16.9 °C

with the statement "1 legal ohm = 1.0112 BA units." It was apparently given to NBS by Professor Kennelly about 1930. When

measured at 25 °C by C. Peterson in 1962, in terms of the ohm as then maintained by NBS, its value was fo;ind to be 0.999 950 ohms.

ONE-OHM RESISTOR, PTR 1898 M334

This type of the International Ohm, developed by the PhysikalischTechnische Reichsanstalt (PTR) , was the first to use manganin wire

and was so designed that the insulated coil would be directly in

contact with the oil of the bath in which it was placed. Serial

1403, made by 0. Wolff of Berlin, was presumably purchased by the

Coast Survey and turned over to NBS in 1901. Originally a 2-

terminal standard, definite potential terminals seem to have been

added later. It was retested at PTR in about 1906 and "carried the

ohm" from Potsdam to Washington to establish the U.S. reference

standard in 1907. The NBS design of E. B. Rosa (M28) subsequently

replaced it.

ROSA OHM 1907 M28

In this type of standard resistor, the coil of manganin wire is

wound on a cylinder 30 mm in diameter, then shellacked, dried, and

annealed as specified by the PTR. The outer case 40 mm in diameter

was filled with pure dry oil, and the hard-rubber top screwed on after the threads had been shellacked. This type was used for

primary reference standards of 1 ohm and above from 1908 to 1930.

However, the sealing was difficult to maintain, and for use at the

highest precision, was replaced in 1930 by the Thomas double-walled

type at the 1-ohm level.

References

Rosa, E. B., A New Form of Standard Resistance, Bull. Nat. Bur.

Stand. 5, 413 (1908-09)

.

-74-
B.A. OhiP (1887) M44

-75-
One-Olun Resistor, PTR (1898) M334

-76-
Rosa Ohm (1907) M28

-77-
MERCURY OHM TUBES 1911 M137

The prototype mercurial standard resistor by which the International Ohm (the official unit of electrical resistance from 1908

to 1948) is defined, consists of a column of mercury of specified

length, mass and temperature. One of these glass tubes, fitted

with axial current leads, served to contain the mercury, and could

be immersed in an ice bath. A small theoretical correction was applied for the effective resistance in the bulbs at either end

which carry the potential leads.

Tubes of this group were used in 1911 and 1912 in independent measurements to verify the values assigned in 1910 to the NBS Rosa

ohms, which at that time were the national reference standards of

resistance, on the basis of the international intercomparisons then

made at NBS by the International Committee on Electrical Units and

Standards

.

References

Report to the International Committee on Electrical Units and

Standards, Nat. Bur. Stand., U.S. Government Printing Office

(Jan. 1, 1912)

.

Wolff, F. A., Shoemaker, M. P., and Briggs, C. A., Construction of

Primary Mercurial Resistance Standards, Bull. Nat. Bur.

Stand. 12, 375 (1915-16).

-78-
UDOMs

HISTORICAL STANDARDS OF ELECTROMOTIVE FORCE

In 1893 the International Electrical Congress chose as a practical

standard for electromotive force (emf) an electrochemical cell

devised by L. Clark (M280, M279) which was assigned a value of

1.434 volts at 15 °C. This value was derived from the Ohm's law

relation, volt = ampere x ohm, the latter units having been already

realized. It was legalized in the United States on July 12, 1894.

However, between then and 1905 the Weston saturated cadmium sulfate

cell (M281) was found to have many advantages. To reach agreement

on its precise emf, scientists from England, France, and Germany

met at NBS in 1910, with E. B. Rosa of NBS as chairman. As a result of their experiments with a number of resistors, silver

coulometers, and Weston standard cells, they adopted 1.0183 as the

emf of a Weston Normal Cell at 20 °C, in terms of an international

volt. New determinations of the ampere and the ohm led to a value

expressed in absolute volts and then adopted in 1948. This value

became 1.018 3 28 5 volts by international agreement in 1959.

References

Glazebrook, R. T., Standards of measurement: Their history and

development, Proc . Phys. Soc. 43_, Part 4, No. 2 39 (London,

July 1931)

.

Hamer, W. J., Standard Cells: Their Construction, Maintenance, and

Characteristics, Nat. Bur. Stand. (U.S.), Monogr. 84 (1965).

Field, B. F., Finnegan, T. F., and Toots, J., Volt maintenance at

NBS via 2 e/h: a new definition of the NBS volt, Metrologia 9_, 155-166 (1973) .
CLARK STANDARD CELL 1896 M279

This Clark standard cell, of the Fuessner type with zinc and

mercury-mercurous sulfate electrodes, was manufactured by Hartmann

and Braun, Frankfort A/M Gennany. It had been certified by the PTR

in 1896, presumably for the Office of Weights and Measures, and was taken over by NBS in 1901. The cell is enclosed in a brass case which is filled with a white powder, presumably to absorb liquid in case of leakage and to improve thermal stability. The U.S.

national standard of emf was originally maintained by a group of

Clark cells from 1906 to 1910.

References

Clark, L., On a standard voltaic battery, Phil. Trans. Roy. Soc.

164, p. 1 (1874)

.

-82-
Clark Standard Cell (1896) M279

-83-
CARHART-CLARK STANDARD CELL 1889 M280

This standard cell. No. 88, is of the Carhart-Clark (unsaturated)

type with zinc and mercury-mercurous sulfate electrodes one above

the other in a single tube. It was manufactured by Queen & Company

of Philadelphia.

References

Clark, L., Proc. Roy. Soc . 20, 444 (London, 1872).

Carhart, H. S., Phil. Mag. 28_, 420 (1889).
Carhart-Clark Standard Cell (1889) M28C

-85-
WESTON STANDARD CELL 1901 M283

This unsaturated cadmium sulfate standard cell, No. 508, was manufactured by the European Weston Electric Instrument Company,

GmbH Berlin. It was probably purchased by the Office of Weights

and Measures and transferred to NBS when it was established in

1901.

References

The Weston Standard Cell, The Electrician 30, 742 (London, 1893).

-86-
Weston Standard Cell (1901) M283

-87-
KAHLE STANDARD CELL 1910 M282

This saturated cadmiiom sulfate standard cell, No. 386, was one of a group made at NBS in 1910 for experimental purposes. The inverted

Y shape of the container had been suggested by Wright and Thompson,

and the use of the ground stopper by Kahle.

References

Wright, C. R. A. and Thompson, C, Phil. Mag. V 16, 28 (1883).

Kahle, K. , Instructions for preparing Clark standard cells. The

Electrician 31, 265 (London, 1893) .

-88-


HISTORICAL STANDARD OF FREQUENCY

QUARTZ OSCILLATOR M373

Harrison Type

Within the cylindrical casing is a toroidal plate of quartz, which

will resonate at 100,000 Hz (cycles per second) when it is pointsupported on a horizontal plug through its center and excited by an external vacuum-tiobe oscillatory circuit in series. The quartz

must be carefully selected, and there must be careful control of

ambient temperature, pressure, and humidity. The continuous

oscillation of any one of three such units (v/ith a fourth as check)

" can be fed to a frequency dividing circuit and used to drive a synchronous motor which in turn is geared to a clock.

This piezoelectric system formed part of the national standard ref- erence group from 1929 until 1950. It was possible to obtain

accurate time intervals of any length desired, from about one microsecond up to several hours.

References

Marrison, W. A., A high precision standard of frequency, Proc . IRE

17 ^ , 1103-1122 (1929)

Hall, E. L. , Eaton, V. E., and Lapham, E. G., The National Primary

Standard of Frequency, Nat. Bur. Stand. (U.S.), J. Res. 14 , 85, RP759 (Feb. 1935) .

Hellwig, H. , Frequency Standards and Clocks: A Tutorial

Introduction, Nat. Bur. Stand. (U.S.), Tech. Note 616 (Rev.

Mar. 1974)

Lyons, H. , The Atomic Clock, Nat. Bur. Stand. (U.S.), Tech. News

Bull. 33, 17 (Feb. 1949) describes microwave signal controlled

by ammonia absorption frequency driving quartz oscillator.

-91-

HISTORICAL TEMPERATURE STANDARDS

The mercurial thermometer No. 4332 (M521) made by Tonnelot of Paris

in 1884 was one of six assigned to the United States in 1889 as temperature standards for the range 0 to 100 °C, to accompany the

Prototype Meters Nos . 21 and 2 7 and Prototype Kilograms Nos. 4 and

20. Baudin of Paris constructed the other three shown (M520a,

520b, 520c) between 1900 and 1907. All of these were made of leadfree hard glass, carefully annealed. They v;ere exhaustively

studied by C. E. Guillaume of BIPM, and certificates in the

National Archives attest their errors of graduation, external and

internal pressure coefficients, calibration corrections, and

"supercorrections" to the "mean verre dur" scale. The graduations

are in 0.1 °C intervals, and could be read with a small telescope

to 0.001 or 0.002 °C.

Sixteen of these thermometers served as national reference

standards for three decades. Eventually they were intercompared

with several thermometers of the platinum resistance type (M523)

In 1927 the CIPM adopted an International Temperature Scale defined

in terms of the standard form of resistance thermometer. This

scale was modified in 1948, clarified in 1960, and replaced in 1958

by the present International Practical Temperature Scale (IPTS-68)

References

Waidner, C. W. and Dickinson, H. C, On the Standard Scale of

Temperature in the Interval 0 to 100 °C, Bull. Nat. Bur.

Stand. 3, 663 (1907)

Bussey, J., Liquid-in-glass thermometers, p. 228-255 in book.

Temperature, Its Measurement and Control in Science and

Industry, Reinhold Publ. Corp, (1941)

CIPM, The International Practical Temperature Scale of 1968,

Metrologia 5_, 35 (1969) .

-93-
-94-
HISTORICAL STAI^DARDS OF LENGTH

EGYPTIAN ROYAL CUBIT M444

Five thousand years ago, the Egyptians laid the foundation for all

that is embraced by modern linear dimensional control. They

produced the first master standard of linear measurement, the

cubit, meaning "forearm." This standard was equivalent to the

length of the forearm of the Pharaoh Amenhetep I (c. 1550 BC) . It was about 52.5 cm (20.53 in) long, and was known as the Royal

Cubit. As shown in this replica, the standard was subdivided by

scribed lines which divided the cubit into two spans, six palms,

and 24 digits (five finger breadths). The digits, in turn, were divided into halves, thirds, quarters and down to sixteen parts.

The Royal Cubit Master was made of black granite and placed in the

custody of the royal architect. "Working" cubits made of wood were duplicated from the Royal Cubit and used by artisans in building

the Great Pyramid, tombs and temple.

References

Berriman, A. E., Historical Metrology, Greenwood Press (1969).

-95-
u

CQo

inin

OSOH

r-l

on

4J•Hu

•r-i 4J04

-96-
U.S. YARD STANDARDS

In this country at the time of the American Revolution, the British

imperial yard was a commonly used standard, although there was no official prototype fixing its length. President Washington called

attention to the need for "uniformity in weights and measures" in

his first annual message to Congress in 1790, and John Quincy Adams

submitted an elaborate report in 1821 which reviewed the standards

in England and France

.

References

Fischer, L. A., History of the Standard Weights and Measures of the

United States, Nat. Bur. Stand. (U.S.), Misc. Publ . 64 (1905,

1925) .

Judson, L. v.. Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (Oct. 1963).

-97-
TROUGHTON SCALE 1814 M316

A - graduated line-standard of length, cornmonly designated as an 82-

inch bar, made by Troughton of London in 1813 and procured in 1814

for the United States by F. R. Hassler. The bar, 1/2 in by 2 1/2

in in cross section, is made of brass with an inlaid silver strip

on which 1/lOth-in graduations are engraved. The interval between

the 27th and 63d in graduations was selected by the Treasury in

1832 to define the equivalence of the United States Standard Yard

to the Imperial Standard Yard of 1760. The Troughton Scale

retained its position as the primary reference yard standard of the

United States until about 1857.

References

Fischer, L. A., History of the Standard Weights and Measures of the

United States, Nat. Bur. Stand. (U.S.), Misc. Publ . 64 (1905,

1925) .

Judson, L. v.. Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (Oct. 1963).

-98-
nu

'X3m

J)

C/2

0)c

CO

CH

<0uco

4J

CP ^ 3O fT3 U

u:o

0) •H>

-Uc

0) u

-99-
rH

(TJ o

O

0)

•rH o >

tn <U 'Mm

no CP u (tf H W Cu

-100-
BRONZE YARD NO. 11 1856 M317

A bronze line-standard of length, 1 in by 1 in in cross section,

having an overall length of 38 in. Near each end of the bar is a cylindrical well with an inserted gold plug, the upper surface of

the plug being 1/2 in below the top surface of the bar. The 1-yard

defining lines are engraved on the gold plugs. This bar is of the

same material and form as the Imperial Yard which was constructed

as the British standard in 1855, to replace the one destroyed by a Parliament fire in 1834. It was presented to the United States by

Great Britain in 1855. Being more convenient than the Troughton

scale, this bronze bar was used as the standard yard of the United

States from about 1857 to 1893. It was twice taken to England for

recomparison with the Imperial Yard, once in 1876 and again in

1888.

References

Fischer, L. A., History of the Standard Weights and Measures of the

United States, Nat. Bur. Stand. (U.S.), Misc. Publ. 64 (1905,

1925)

Judson, L. v.. Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (Oct. 1963).

-101-
-102-
LOW MOOR IRON YARD NO. 57 1856 M31S

An iron line-standard of length, similar in design and construction

to Bronze Yard No. 11. It was presented to the United States by

Great Britain in 1856 and was in use in the United States as a standard until 1893, although regarded as secondary in importance

to Bronze Yard No. 11.

References

Fischer, L. A. , History of the Standard Weights and Measures of the

United States, Nat. Bur. Stand. (U.S.), Misc. Publ. 64 (1905,

1925).

Judson, L. v.. Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (Oct. 1963).

-103-
33
METER BARS

"COMMITTEE METER" 1799 M314

An iron end-standard of length, 9 millimeters by 29 millimeters in cross section, designed to be one forty -millionth part of the

length of the earth's meridian. It is one of a group of similar

bars made by a Committee of the French Academy of Sciences that

made the Meter of the Archives, whence its designation in the

United States as the "Committee Meter." This particular bar was presented by Tralles, the Swiss member of the Committee, to his

friend F. R. Hassler. Hassler, in turn, sold it to a member of the

American Philosophical Society in Philadelphia, who deposited it

with the Society. Later the bar was obtained from the Society by

Hassler for the use of the U.S. Coast and Geodetic Survey, where it was used as the standard for scientific work in the United States

from 1807 to 1893.

References

Judson, L. v.. Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (Oct. 1963).

The Bureau of Standards: Its History, Activities and Organization,

G. A. Weber, Johns Hopkins Press (1925) .

-105-
-106-
ARAGO PLATINUM METER 1821 M315

A platinum line-standard of length, 5 millimeters by 25 millimeters

in cross section. The bar was procured from France by Albert

Gallatin, Minister of the United States to France. It derived its

designation from the name of the eminent French physicist who

certified the length of its graduated interval. It appears that

this bar has received essentially no use as a standard in the

United States.

References

Fischer, L. A., History of the Standard Weights and Measures of the

United States, Nat. Bur. Stand. (U.S.), Misc. Publ. 64 (1905,

1925) .

Judson, L. v.. Weights and Measures Standards of the United States,

Nat. Bur. Stand. (U.S.), Misc. Publ. 247 (Oct. 1963).

-107-
ou

4J

c: U
HISTORICAL STANDARDS OF LUMINOUS INTENSITY

STANDARD CANDLES 1889 M269

The London Metropolis Gas Act of 1860 specified two sperm candles

of six to the pound, each burning 120 ± 6 grains an hour, for use

in flame photometry. This specification was confirmed by the Gas

Referees in 1889, but was changed to the Harcourt lamp in 1898.

FLAME STANDARD, CARCEL 1906 M270

Lamps of this type, designed by B. G. Carcel in 1800 to burn colza

(rapeseed) oil, were used as prototype standards of luminous

intensity at the Laboratoire Central d 'Electricite in Paris in

1905. A clockwork pump supplied oil to the v;ick. Earlier

comparisons with Violle's proposed standard (based on the luminous

intensity of 1 square centimeter of a platinum surface at its

melting point) led to assigning a value of "9.6 bougies decimales"

to such a lamp when burning at the rate of 42 grams per hour. The

"bougie decimale" had been defined as 1/20 of a "Violle" and had

about the same value as the British Parliamentary "candle."

FLAME STANDARD, HEFNER-ALTENECK 1893 M271

The legal standard of candle-power adopted in 1893 by the

Physikalisch-Technische Reichsanstalt of Germany is the lamp

devised in 1884 by F. von Hefner-Alteneck. A thin German-silver

tube exactly 25 mm high, 8 mm internal diameter, and 0.15 mm thick

holds a wick of untwisted cotton; the fuel is amyl acetate. The

candle-power of the reddish flame depends appreciably on its

height, and somewhat on humidity and barometric pressure. In 1909

and again in 1921, its value was agreed to be exactly nine-tenths

of the international candle.

References

Stine, W. M. , Photometrical Measurements (Macmillan, N.Y., 1900).

Palaz, A. (transl. G. W. and M. R. Patterson), A Treatise on Industrial Photometry (Van Nostrand, N.Y., 1894).

Walsh, J. W. T., Photometry (Constable, London, 1926, 1965).

Rosa, E. B. and Crittenden, E. C, Flame Standards in Photometry,

Bull. Nat. Bur. Stand. 10, 557 (1914); Sci. Paper 222.

-109-
-110-
I

i

Flame Standard, Carcel (1906) M270

-111-

i

i
-112-
iiiiiiIiiIIIIIIi

GRAVITATION APPARATUS 1942 M561, M12

2 The factor G in the Newtonian formula F = G x Mm/d is the

universal constant of gravitation v/hich enters into the

calculations of geologists, astronomers, and planetologists . It was measured in 1798 in a classic experiment by Henry Cavendish,

and again by Carl Braun in 1897, using a torsion pendulum

apparatus. The experiment was repeated at NBS by Paul Heyl in 1930

and by Heyl and Chrzanowski in 1942, in an effort to improve the

then accepted value

The mockup displayed here shows the 1942 arrangement. Small

platinum balls of 87-grams mass were hung from either end of a 20- cm aluminum tube, which was suspended symmetrically by a 0.025 mm

filament of annealed tungsten one meter long, forming a torsion

pendulum. Cylindrical steel masses weighing about 55 kilograms

were mounted symmetrically on a ring rotatable in azimuth so that

they could be positioned either "near" to or "far" from the small masses. In the evacuated housing the swing of the pendulum,

initially about 4 degrees, could be sustained for nearly 20 hours.

With the "near" configuration the average period was 2200 seconds;

with the "far" configuration 2920 seconds. These data, together

with precise measurements of the spatial geometry, permitted

computation of G as 6.673 ± 0.003 x 10"^^ m^*s"^»kg" . (The four

glass balls (M12) in the case to the left were used in the 1930

experiment .

)

In 1974 the value recommended by the International Council of

Scientific Unions is 6.6720 x lO"'^^ to an uncertainty within 41

parts per million. Of the five major G projects currently going on around the world, two are at NBS, and use improved torsion

pendulums. Deslattes, Luther, and Towler at NBS Gaithersburg are working with apparatus devised by Jesse Beams of the University of

Virginia. Koldewyn and Faller at Boulder (University of Colorado)

are comparing pendulum periods subject to the gravitational pull of

the Rocky Mountains, both with and without the effect of nearby

large masses of bronze.

References

Heyl, P. R. , A redetermination of the constant of gravitation, Nat.

Bur. Stand. (U.S.), J. Res. 5_, 1243 (1930).

Heyl, P. R. and Chrzanowski, P., A new determination of the

constant of gravitation, Nat. Bur. Stand. (U.S.), J. Res. 29 , 1 (1942)

Specifications of the Physical World, Dimensions/NBS 58, 3 (Jan.

1974)

How Big is G, Dimensions/NBS 58 , 176 (Aug. 1974)

-115-
I

Gravitation Apparatus (Mockup) (1942) M561

-116-
IEIIIIII1IIii1i

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CN 0V •H

rH > s o (0 n

Ci CP

rH o iw c 0

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w

QQ (5 2 iH CO <H (4-1 c

(0 0 0 a o

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dJcn r)

-117-

iIIiiII1iii

LUMINOUS SCRIPT SIGNS 1904 M272

Sir William Ramsay of London had just been awarded a Nobel prize

for the identification of the rare atmospheric gases--argon

helium, neon, krypton, and xenon. He sent samples to ITBS , v/hich was planning a novel exhibit in the Palace of Electricity at the

Louisiana Purchase Exposition in St. Louis. Electric discharge

tubes containing gas at low pressure (Plucker tubes) had been used

by P . G. Nutting for the study of gaseous spectra. His design with

2 cm plate electrodes, which provided a much steadier and brighter

light, was used in these signs blown by E. 0. Sperling.

About 1930, the neon tube was commercialized and a whole nev/ industry was thus founded.

References

Travers , M. W. , The Discovery of the Rare Gases (Edward Arnold & Co. , London, 1928)

Cochrane, R, C, Measures for Progress, Nat. Bur. Stand. (U.S.),

Misc. Publ. 275, 83 (1966).

V -121-

IONIZATION CHAMBER, GUARDED FIELD 1928 M337

This lead-lined ionization chamber, for measuring x-radiation in

roentgens, was designed by L. S. Taylor to provide a small lightweight secondary standard which could be used for international

intercomparisons of x-ray standards. The NBS primary standard at

that time had a parallel-plate system and grounded lead shielding

box which was large, and consequently heavy and cumbersome. This

new free-air chamber design retained the parallel-collection highvoltage plate system but introduced the use of guard wires

connected to a potential divider. These provided a uniform

gradient in the electric field from the collector-guard plates to

the high voltage plate, as a result of which the length of the

guard plates and the size of the shielding box could be reduced.

The eight vertical guard wires are about 12 -mm apart except in the

middle where they are 18 -mm apart to provide clearance for the x- ray beam. The chamber was mounted on a swivel base and track to

permit alinement with the x-ray beam. The beam diameter in the

chamber is defined by an 8-mm-diameter lead diaphragm which is

moianted in the lead-lined brass t\abe. The brass tube was fitted

with a solenoid-operated lead shutter to fix the x-ray exposure

interval

.

Such a guarded-field ionization chamber was used in 1931 for the

first direct intercomparison of free-air primary standards of the

United States, England, and Germany. The comparisons showed the

agreement between the standards of the three nations to be within

0.5 percent. Similar chamber designs are still in use.

References

Taylor, L. S. and Singer, G., An improved form of standard ionization chamber, Nat. Bur. Stand. (U.S.), J. Res. 5_, 507 (1930).

Taylor, L. S., International comparison of x-ray standards, Nat.

Bur. Stand. (U.S.), J. Res. 8, 9 (1932).

-123-
-124-
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RADIOACTIVITY COUNTER 1951 M340

This pillbox design of 47T proportional flow counter was designed

and tested by H. H. Seliger and L. M. Cavallo, following a suggestion from C. J. Borkowski of Oak Ridge National Laboratory. It

consists of two 27T counters mounted face to face, and separated by

a thin stainless steel diaphragm with peripheral holes for the

passage of the counter gas (methane) . The tubes in the upper half

are inlets for the gas, which is withdrawn from the bottom.

The pillbox counter made possible the high-efficiency counting of

beta particles from radioactive materials with activities as low as

10 nuclear transitions per second. It was rugged, easily

decontaminated, and proved to be stable over long periods of time.

It has been used for calibrating sources of ^^C, ^^Na, ^ '^Na , ^^S,

60 90 90 198 Co, Sr+ Y, and Au. A thin deposit of source material was mounted on a Formvar-polystyrene film cemented over a 2-cm hole in

the central diaphragm. Operation was in the region of limited

proportionality where the gas gain and the electronic gain are

't 3 about 10 and 5 x lo , respectively.

After some years of use, the pillbox design was superseded by a cylindrical and then by a spherical form of 4iT proportional flow

counter.

References

Seliger, H. H. and Cavallo, L. M. , Absolute standardization of

radioisotopes by 47T counting, Nat. Bur. Stand. (U.S.), J. Res.

47_, 41 (July 1951) .

-127-
-128-
THERT^OPILES 1923 M202

From 1908 to 1940, W. W. Coblentz studied the instiniments and

methods of radiometry, devising various forms of thermopiles and

applying them to the measurement of total radiation from the stars,

the planets, and various materials. The 10- junction linear

thermopile displayed is his #133, constructed in 1923. It is made

of 0.08 mm bismuth wire and 0.031 mm tin foil. The target has a continuous surface and a definite area of 10 mm^ which permits

calibration for measurements in absolute units. Its front is

coated with lampblack, better to absorb the external radiation; the rear is bright, better to reflect radiation from within the

enclosure. To facilitate the joining of these fine wires, Coblentz

in 1913 introduced the idea of welding them close together on tiny

rectangles of tin rather than directly to each other.

For measuring stellar radiation received through a telescope,

increased sensitivity and freedom from convection currents were obtained by enclosing the radiometric element in a strong glass

case evacuated to about 0.1 mm mercury. Its lead wires were sealed

into the tubular extension, as were platinum electrodes, to be used

with an induction coil to test the evacuation. When measurements

were to be made at remote observatories, a quartz tube filled with

chips of metallic calcium was sealed to the bent neck, and residual

gases were removed by heating the tube to redness

.

A balanced thermocouple design (viewed from the bright rear) is

numbered 244 and dated June 14, 1932. Exposed to solar radiation,

its overheating was prevented by a water cell of fused quartz 1 cm

thick. To measure the ultraviolet intensity, first one and then

the other of the two 4 mm thermocouple discs was covered by a quartz window, while the opposite disc was covered by one or two

barium-flint glass filters.

Between 1912 and 1940 Coblentz personally made 264 thermocouples

and thermopiles. Some of these were sold to laboratories

throughout the United States and Europe.'

References

Coblentz, W. W. , Instruments and Methods Used in Radiometry-II

,

Bull. Nat. Bur. Stand. 9_, 7 (1913).

Coblentz, W. W. , A Comparison of Stellar Radiometers and Radiometric Measurements on 110 Stars, Bull. Nat. Bur. Stand. 11 , 613 (1915)

.

Coblentz, W. W. and Stair, R. , Measurement of extreme ultraviolet

solar radiation using a filter method, Nat. Bur. Stand.

(U.S.) , J. Res. 6, 951 (1931)

.

-129-
-130-
STRAIN GAGE, TUCKERI'IAN 1923 M34

Because of the sensitivity, the small size, and the light weight of

this optical extensometer system designed by L. B. Tuckerman, it is

well adapted to measuring deformations on short gage lengths, even

on materials such as celluloid sheet or aluminum v/ire. The gage

body on display carries a knife edge at the upper end and would be

held to the specimen by a light spring. At the lower end is a Martens lozenge of stellite about 3/4 in long, carefully machined

and polished to a square section 0.2 in on a diagonal. One

longitudinal edge of the lozenge bears against the gage body, while

the diametrically opposite edge bears against the specimen.

An essential element in the optical system is a Tuckerman autocollimator (not on display) which originates a collimated light

beam. Inside the gage body is fixed a roof prism which doubly

reflects the beam and projects it through a 45° prism onto a polished side of the lozenge and back into the collimator eyepiece.

As the strained specimen extends or contracts, the lozenge tilts

about its contact with the gage body, and the reflected beam

strikes a reticule with a scale graduated to read strain directly

in inches per inch on a 2-in gage length. Adjustment of the roof

prism position is made by the knurled knob on the gage body.

With this system, strain can be measured with sensitivity of one millionth of an inch per inch, and within an accuracy of about 3 millionths. Collimator and body are available commercially. The

instrument is still used for precise measurement of Young's modulus

and Poisson's ratio, and as a reliable standard for evaluating the

more convenient bonded-vrire strain gages which provide electrical

readout

.

References

Tuckerman, L. B., U.S. Pat. 1,736,582.

Tuckerman, L. B., Optical strain gages and extensometers , Proc.

Ajner. Soc. Testing Mat. 23_, 602 (1923) .

Wilson, B. L. , Characteristics of the Tuckerman strain gage, Proc.

Amer. Soc. Testing Mat. 4£, 1017 (1944).
-132-
-133-
I
STRAIN GAGE, WHITTEMORE 1926 M36

This hand-held device for measuring the elongation of a 10-in gage

length in large structural members such as bridge trusses was designed for use under adverse conditions in the field. Its

conical gage points, which fit into pairs of small drilled holes,

remain perpendicular to the surface of the structure, an advantage

not afforded by earlier strain gages. The gage points are carried

by a pair of Invar channels coupled by flexure plates which permit

small parallel displacements. Their relative motion is measured by

a ten-thousandth inch dial indicator.

The design has been made commercially, and is still commonly used

when structural strains must be measured at intervals over long

periods of time.

References

Whittemore, H. L., The Whittemore strain gage. Instruments I_, 299

(1928) .

-135-
t o IIIII
MAGNEGAGE 1937 M415

This device was developed by Abner Brenner for making rapid non- destructive measurements of electroplated nickel coatings on nonmagnetic base metals. It measures the force (about 10"^ newton)

required to detach one pole of a small permanent magnet from the

nickel surface. That force was found to be proportional to the

thickness of the coating, to within about 10 percent, for a range

of 0.0001 to 0.0025 in (0.0025 to 0.063 mm). The magnet hangs

vertically from a horizontal torque arm. A specimen to be tested

is placed on the stand, and the platfonni lowered until the magnet

just touches it. Rotation of the arm carrying the outer end of the

spiral spring provides a force opposing the magnetic attraction.

The bent lever under the torque arm provides for sensitive detachment when the forces balance.

Calibration is accomplished by noting the detachment force required

for coatings of known thickness. Although different conditions of

electrodeposition were found to affect this force, consistent

results were obtained by annealing to 400 °C. The instr\ament has

been used for measuring thicknesses from 0.0001 to 0.080 in (0.0025

to 2 mm) of nickel coatings on steel, and nonmagnetic coatings on

steel. It has been produced as a commercial tester for many years.

References

Brenner, A., Magnetic method for measuring the thickness of

nonmagnetic coatings on iron and steel, Nat. Bur. Stand.

(U.S.), J. Res. 20, 357, RP1081 (1938).

-137-
-138-
PERMEAMETER 1909 M182

This instriainent for determining the normal magnetic induction curve and the hysteresis loop for a straight round specimen was designed

by C. W. Burrows of NES, utilizing the idea of a distributed and

adjustable magnetomotive force. Its magnetic circuit consists of

two approximately identical bars 250 mm long, their ends being

clamped by brass screws in two connecting yokes of high

perTTieability . Yoke ends are hemispherical to minimize flux leakage

into air. The main magnetizing solenoids consist of 10 layers of

No. 18 copper wire woiind with 7.958 turns per centimeter, to make H = 10 I. They extend over the entire length of the two bars between

the yokes. A compensating coil with four windings in series is

added at the four ends

.

The main test coil is wound closely over the middle quarter of the

bar chosen as test specimen. On each side of this, midway between

it and the yokes, are wound the two halves of a second search coil.

A third coil, similar to the first, is wound over the auxiliary

bar

.

This permeameter was accepted by ASTM for use with magnetizing

forces up to 300 oersteds. It was used to measure the properties

of standard bars for calibrating other instr\iments. However, the

adjustment procedure is tedious, and the device gives dependable

results only when the specimens are known to be magnetically

uniform.

References

Burrows, C. W. , The Determination of the Magnetic Induction in

Straight Bars, Bull. Nat. Bur. Stand. 6_, 31 (1909).

Harris, F. K. , Electrical Measurements, p. 372 (John Wiley & Sons,

N.Y. , 1952)

.

-139-

MAGNETIC PARTICLE CLUTCH 1947 M2

This is the first laboratory model of the variable-torque clutch

(or brake) invented by Jacob Rabinow of NBS . The shaft at the

bottom carries a shallow chamber 5 mm thick and 120 mm in diameter,

made of nickel steel. The shaft at the top carries at its lower

end a nickel steel disc 3 mm thick and 90 mm in diameter, which

turns freely inside the shallow chamber.

A toroidal electromagnet just inside the chamber circumference is

wired to slip-rings mounted atop the chamber.

The chamber is completely filled with a mixture of 8 Um soft-iron

dust particles and light lubricating oil. This offers negligible

resistance to relative rotation of disc and chamber. However, as current is supplied to the electromagnet, magnetic flux is set up

between the disc and the chamber by way of the particles. As the

flux is increased, increasing torque can be transmitted from one shaft to the other.

Because of the simple design, precise torque control, smooth

operation, and long life, similar devices have found v;ide application, ranging from automobile clutches to pilotless aircraft. More

than 300 patents now cite the original NBS patent.

References

Rabinow, J., Magnetic fluid torque and force transmitting device,

U.S. Patent 2,575,360.

-141-
I

-142-
MAGNETIC BALANCE 1932 Ml 9

Stainless (austenitic) steels are extensively used for their

resistance to corrosion. In them, the iron exists originally in

the nonmagnetic gamma phase. The iron may revert to the

paramagnetic form, which is less corrosion resistant in fabrication

processes such as welding, or in severe service conditions. Thus

magnetic permeability measurements provide a convenient index of

corrosion resistance.

This portable device was developed by R. L. Sanford of ITBS at the

suggestion of P. E. McKinney of the Bethlehem Steel Co. Set on the

surface of a structure, it is used to measure the force required to

pull one end of a permanent bar magnet away from the surface. A

graduated dial indicates the angle through which one end of the

helical spring must be turned to accomplish this. The relation

between dial readings and magnetic permeability is approximately

linear from 1.0 to 2.5.

References

Sanford, R. L., A magnetic balance for the inspection of austenitic

steel, Nat. Bur. Stand. (U.S.), J. Res. 10, 321, RP532 (1933).

-143-

AREA 7 - FT.AT CASE

ELECTRIC HYGROMETER 1938 M33

Early radiosondes used a hair hygrometer for measuring humidity in

the upper atmosphere, but the material was too slow to respond to

changes with rapid ascent, and would not function at all above

about 8000 metres altitude. F. W. Dunmore ' s work at NBS was aimed

at developing a sensing device which would use electrical

resistance. His humidity-sensing resistor consists of a short

aluminum tube with 0.01-in wall, coated with polystyrene resin and

wound with 20 turns of a pair of bare palladium wires. A thin film

of partially hydrolyzed polyvinyl acetate and lithium chloride salt

absorbs moisture from the air and provides a variable resistance

between the wires.

For radiosondes, a three-element unit having 1-, 2- and 3-percent

lithium chloride solution was used. With five elements, the range

from 10 to 95 percent relative humidity can be covered. Stability

has been shown to be within ±3 percent over a period of several

months, with a temperature range from +30 °C to -40 °C.

References

Dunmore, F. W. , An electric hygrometer and its application to radio

meteorography , Nat. Bur. Stand. (U.S.), J. Res. 23_, 701 (Dec.

1939) .

-147-
Electric hygrometer (1938) M33

-148-
RADIOSONDES 1935 M163, 164, 165, 167

Practical systems for the study of upper-air phenomena by small

radio-equipped sounding balloons were first exam.ined at NBS for the

Weather Bureau. A design using the Olland principle and a 5 -meter

transmitter was proposed in 1935 and later improved by using a light-weight constant-speed dc motor to drive a rotating contact.

In each revolution contact was made successively with three doublepronged arms whose angular positions were altered proportionally to

temperature, humidity, and pressure by appropriate sensing

elements. M167 is an experimental model of such a radio

meteorograph recovered after flight.

Beginning in 1936, another design was developed for the NavyDepartment. This used an ultrahigh transmission frequency (65 MHz,

later 403 MHz) and a voltage-controlled negative transductance

circuit in which the modulation frequency (20 to 200 Hz) was inversely proportional to the grid-circuit resistance. A

barometric diaphragm capsule responding to pressure at ascension

rates of 200 to 300 meters per minute drove a contactor across a switching element consisting of 80 metallic strips separated by

insulating strips. A reference resistor, switched in at every

fifth contact, served as an index mark on this pressure scale.

Resistance changes corresponding to temperature were provided by a capillary electrolytic thermometer, while humidity was measured by

changes in resistance of a film of lithi\am chloride (M33) .

M163 is an early production model made by Julien P. Friez and Sons

about 1937. M164 is an improved type with pulsed carrier at 403

MHz, in use from 1942 to 1962. M165 is a transistorized version

using the 403 MHz carrier, used from 1959 on.

In 1975 radiosondes are sent up twice a day from 96 stations of the

National Weather Service. In addition to the 403 MHz design, newer

types include hypsometers and automatic wind-direction sensing at

1680 MHz.

References

Curtiss, L. F. and Astin, A. V., J. Aeron. Sci. 3_, 35 (1935).

Diamond, H. , Hinman, W. S., and Dunmore , F. W. , A method for the

investigation of upper-air phenomena and its application to

radio meteorography , Nat. Bur. Stand. (U.S.), J. Res. 20_, 369

(Mar. 1938)

Curtiss, L. F., Astin, A. V., Stockman, L. L. , and Brown, B. W. , An

improved radio meteorograph on the Olland principle, Nat. Bur.

Stand. (U.S.), J. Res. 22, 97 (Jan. 1939).

Diamond, H. , Hinman, W. S., Dunmore, F. W, , and Lapham, E. G. , An

improved radiosonde and its performance, Nat. Bur. Stand.

(U.S.), J. Res. 25, 327 (Sept. 1940).

-149-
-150-
FIRST AC RADIO RECEIVER 1922 M166

In the early years of radio broadcasting, radio receivers were powered exclusively by batteries. P. D. Lowell and F. W. Dunmore

demonstrated at NBS that the inconvenience of batteries could be

avoided by using household 110-volt alternating current (ac)

instead. Their several circuit modifications of a typical battery

receiver (U.S. Pat. 1,455,141) permitted the use of ac house

current with small sacrifice in quality of performance. The

national transition to ac powered receivers required other

inventions and several additional years of development in the radio

art, but the example of the Lowe 11 -Dunmore receiver accelerated the

transition. Their receiver used three stages of vacuum-tube radiofrequency amplification, a crystal detector, two audiofrequency

stages, and a telephone-receiver loudspeaker.

The instrument on display was built in 1923 by the Radio Instrument

Co.

References

Lowell, P. D. , An electron tube amplifier using 60-cycle

alternating current to supply power for the filaments and

plates, Nat. Bur- Stand. (U.S.), Sci. Papers 18, 345, RP450

(1922-23)

.

-151-
-152-
1912 M83

Before World War 1, "radio" consisted almost solely of wireless

telegraphy. The typical spark transraitter emitted a rapid sequence

of radicfrequer.cy iirpulses rather than a continuous wave. The

sharper -he irapulses, the broader the range of frequencies occupied

by the errdssion, and the greater the potential interference v/ith

Owher v.-ireless conrrrMini cation in the same frequency range. To

mininiize interference , the Department of Commerce enforced regulations liriiting the permissible sharpness (the decrement) of the

crans-j.tted intpulse. F. A. Kcls-er, working at !\ES for Comm.erce ' s Bureau of Navigation, developed this instrument, which fiimished

the transmitter operator with a convenient and reliable means for

meas'oring z'r.e emission wavelength (75 to 300C m.eters) and for

monitoring those transmitter adjustments vrhich fixed the decrement

of the imp-jlse.

References

Kolster, J. , direct-reading instrument for measuring the

logarithjaic decrement and wavelength of electromagnetic waves,

^'at. Bur. Stand. (U.S.), Sci. Paper 235 (Aug. 1914).

-153-
-154-
AREA 8 - FLAT CASE

COURSE INDICATORS, TWO-REED 1928 M86,87

These devices were developed to give an aircraft pilot at a glance

a visible indication of whether he was on course as he approached

an airfield and if not, which way to turn. A pair of metal reeds were mounted in the center of a coil connected to the airplane

radio receiving set. One was tuned to vibrate at 65 hertz and one

at 86.7 hertz, and each carried a tiny white vane at its free end.

The reeds were excited by a radio beacon developed by NBS and

installed on the airfield in College Park, Maryland. Two antennas

at right angles sent out waves modulated at 65 and 86.7 hertz

respectively, producing in space four channels along which these

signals were of equal intensity. When the pilot approached the

beacon along one of these channels the vibrating reeds appeared as white lines of equal length. If he flew to the right or left, the

right or left line became longer than the other one, indicating

that he was off course.

As he flew away from the beacon, the reed housing had to be turned

upside down to give the correct indication. In the type C

instrument (M86) this was accomplished by a knob and clamp

arrangement for TO and FROM. In the type D instrument (M87) the

housing was pulled out and plugged in again upside down.

References

Dunmore, F. W. , Design of tuned reed course indicators for aircraft

radiobeacon, Nat. Bur. Stand. (U.S.), J. Res. 751 (Nov.

1928) .

Dellinger, J. H., Diamond, H. , and Dunmore, F..W., Development of

the visual type airway radiobeacon system, Nat. Bur. Stand.

(U.S.), J. Res. 4, 425 (Mar. 1930).

-157-
-158-
INSTRUMENT LANDING DEVICES 1930 M84,85,106

In 1928 a few radio range beacons had been established for pointto-point flying, but there was urgent need for facilities to permit

landings under conditions of poor visibility. The solution

developed by an NBS team working for the Aeronautics Division of

the Department of Commerce provided for the first time a satisfactory indication of glide path. On the runway, a horizontally

polarized radio beam at 100 megahertz was directed at a small angle

above the horizontal. On board the plane the signal current in the

receiving set was rectified and passed through a dc microammeter

.

This instrument, called a fog landing glidometer (MBS) was turned

on its side so that the pointer was horizontal at mid-scale. The

pilot flew the plane on a path, approximately parabolic, which kept

the received signal at constant intensity as he came in to a landing.

For lateral guidance, a runway localizing beacon was provided. It

had 200-watt power and doiible modulation at 60 and 500 hertz. The

two-reed indicator (M87) was replaced by a microammeter of zero- center type, driven by a Dunmore reed converter (M105) and dubbed a runway localizer (M84) . Off-course position to right or left was indicated by right or left deflection of the pointer.

In using the final NBS design of a combination instrument (M106)

the pilot sought to keep the two pointers crossed within a small

circle centered on the dial. Another microammeter, with dial

marked from 1 to 5 miles, was operated from the automatic volume

control on the signal from the range beacon, and showed him the

approximate distance to the point of touchdown.

Many experimental landings were made successfully during 1933 with

use of the beacons and indicators of the NBS system, both at

College Park, Maryland and at Newark, New Jersey.

References

Diamond, H. and Dunmore, F. W. , A radiobeacon and receiving system

for blind landing of aircraft, Nat. Bur. Stand. (U.S.), J.

Res. 5_, 897 (Oct. 1930) .

Dunmore, F. W. , A course indicator of pointer type for the visual

radio range beacon system, Nat. Bur. Stand. (U.S.), J. Res. 7_, 147 (July 1931)

.

Diamond, H., Performance tests of radio system of landing aids,

Nat. Bur. Stand. (U.S.), J. Res. 11, 463 (Oct. 1933).

-159-
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BRIDGE FOR RESISTANCE

THERMOMETRY

1910 M290

By use of resistance thermometers in favorable circumstances, temperature measurements can be made with an uncertainty of less than

0.001 kelvin; in the measiirement of small temperature changes, as in calorimetry, uncertainties of 0.0001 kelvin or less can be

achieved. The first Wheatstone bridge used for resistance

thermometry at NBS (No. 1648) was designed by Waidner and Wolff in

1901. Experience dictated improvements, and the design of M290 in

1910 by E. F. Mueller required that (a) the coils be hermetically

sealed, (b) connecting switches and links as well as coils be

immersed in the thermostated oil bath, (c) the operating mechanism

be rigidly alined (substituting marble for hard rubber) , (d) the

variable resistance arm consisting of six decades (with mercury-cup

contacts for links in the first three, and shunted Waidner-Wolf

f

elements for the last three) , (e) the construction permit readings

to be made with an imprecision within 2 or 3 percent of one step in

the last decade.

This instrument, known in the Thermometry Laboratory as the "Marble

Top" was constructed by the Leeds and Northrup Co. and delivered in

1912. It was used by Dickinson in combustion calorimetry, in

studies of the thermal properties of ammonia, and in many other

applications until it was retired in the 1930 's.

References

Waidner, C. W. , Dickinson, H. C, Mueller, E. F., and Harper, D.

R. , A Wheatstone Bridge for Resistance Thermometry, Bull. Nat.

Bur. Stand. 11, 571 (1915).

-163-
-164-
ELECTROTHERMIC VOLTMETER 1947 M313

This instrioment was the first of a series of ac-dc transfer standards developed by F. L. Hermach, which greatly improved the

accuracy of ac measurements at audio frequencies. The

thermoconverter element (in the small black box at one end)

consists of a straight-wire heater mounted in a ceramic bead with a thermocouple which responds to its temperature rise. The element

is housed in an evacuated glass envelope, and is connected in

series with a commercially available shielded resistor of 5 decades. The output emf of the thermocouple (5 millivolts for a 20

milliampere heater current) is measured by an elementary form of

deflection potentiometer. It is the same to within less than 0.01

percent with the same level of either dc or ac voltage applied to

it. It can thus be used with dc standards to measure ac voltages

or currents, at frequencies between 25 and 20,000 Hz.

Model A was constructed in 1947, used steadily until 1953, and then

intermittently until 1960, when it was superseded by newer models.

References

Hermach, F. L. , A precision electrothermic voltmeter. Trans. AIEE

67, No. 2, 1224 (1948)

.

Hermach, F. L., Thermal converters as ac-dc transfer standards,

Nat. Bur. Stand. (U.S.), J. Res. 48, 121 (1952).

-165-
-166-
SHUNT BOX, WAIDNER-WOLFF 1902 M393

Each of the four independent circuits in this shunt box consists of

a Waidner-Wolff 10-step adjustable element.

The Waidner-Wolff resistance element was devised at NBS by C. W.

Waidner and F. A. Wolff in 1902. It consists of a small fixed

resistance shunted by a much larger resistance that is variable in

ten unequal steps so chosen that the resultant parallel combination

is varied in ten equal steps; for the highest step the shunt

resistance may be infinite. This arrangement eliminates the effect

of switch-contact resistances from the decade, and permits

construction of decades whose steps may be as small as 1 micro-ohm

or as large as 0.1 ohm. A second advantage of the arrangement is

the suppression of parasitic thermal emfs in the circuit.

The instrument was purchased from 0. Wolff of Berlin in 1903. It seems probable that in an early application its four circuits were

shunted around four graded resistors in one ratio arm of a bridge

circuit.

Waidner, C. W. and Dickinson, H. C, Apparatus for platiniim resistance thermometry, Phys. Rev. 19_, 51 (1904).

Mueller, E. F. and Wenner, F., The Waidner-Wolff and other adjustable electrical resistance elements, Nat. Bur. Stand. (U.S.),

J. Res. 15, 477, RP842 (1935).

-167-
-168-
RESISTOR, ADJUSTABLE

NONINDUCTIVE

1909 M97

This noninductive shunt, with a range of 0.025 to 0.11 ohms, was designed by P. G. Agnew for the secondary circuit of a current

transformer under test for ratio and phase angle. Projecting from

the two binding posts at the left is a manganin strip folded over

thin mica, one of several with fixed values of 0.025, 0.035, 0.045,

etc., ohm. Two curved manganin strips separated by thin mica

provide adjustable resistance between the two movable arms

(potential terminals) . The inner one, connected by taps to the 10

numbered studs, gives steps of 0.001 ohm. The outer one,

projecting half a millimeter above the other, has a tctal

resistance of 0.001 ohm and by estimating to tenths of its 10

divisions, 0.00001 ohm can be read. Current terminals are located

at the right, with connection through a straight copper strip. At

60 hertz the phase angle of the shunt is less than one minute.

After its use in the classic study of 1909, the instrument served

for calibration testing of current transformers until 1915, when

superseded by resistor M96 having wider strips.

References

Agnew, P. G. and Fitch, T. T. , The Determination of the Constants

of Instrument Transformers, Bull. Nat. Bur. Stand. 6_, 281

(1909-10)

.

Agnew, P. G. , A Study of the Current Transformer with Particular

Reference to Iron Loss, Bull. Nat. Bur. Stand. 7, 428 (1911).

-169-
-170-
ONE-OHM RESISTOR,

DOUBLE WALLED

1930 M42

In this type of standard resistor developed by J. L. Thomas a single layer of bifilar manganin wire is wound on a mandrel and

annealed in a vacuum at red heat. It is then slipped onto a silkinsulated 6-cm brass cylinder with only loose contact between them.

This tube is closed by soldering its flanged ends to an outer 7-cm

tube. The coil is sealed in place with dry air and the leads for

electrical connections are brought out through seals.

Previous to 1910 the U.S. reference standard of electrical resistance was maintained by resistors of the Reichsanstalt type (M293)

obtained from Germany. From 1910 to 1930 the standard was a group

of 10 one-ohm coils of a design of E. B. Rosa (M28) . Between 1930

and 1939 these were gradually replaced by the double-walled type.

The maximum net change of the latter group, with respect to the mean of the ten, measured at yearly intervals from 1939 to 1969,

has been only one part per million.

References

Thomas, J. L., A new design of precision resistance standard, Nat.

Bur. Stand. (U.S.), J. Res. 5_, 295 (Aug. 1930).

Thomas, J. L., Stability of double-walled manganin resistors, Nat.

Bur. Stand. (U.S.), J. Res. 36.' (Jan. 1946).

Wells, T. E., Precision Measurement and Calibration, Vol. 3,

Electricity-Low Frequency, Nat. Bur. Stand. (U.S.), Spec.

Publ. 300, 139-111 (Dec. 1968).

-171-
-172-
COULOMETER, PERCHLORIC ACID 1957 M176

The classic method for determination of the faraday in-voives the

electrolytic deposition of silver on platinum from an aqueous

solution of silver nitrate, but it is subject to uncertainty

because of possible foreign occlusions in the deposit. The

apparatus shown here electrolytically oxidizes a silver anode

(shown at the right) in an aqueous perchloric acid solution. The

platinum cathode is at the left, and the intermediate beakers and

siphons serve to collect any mechanically detached silver

particles. In the test tube at the right was placed a reference

silver anode for checking the electrolytic potential at the

dissolving anode.

Currents of 0.1, 0.2, 0.3, and 0.5 amperes (typically 0,20363887 A) were used in 31 runs under various conditions for durations of 3 hours or more, known to within 1 ppm. The number pf ampere-seconds

needed to dissolve a given weight of silver was found to be

1.117972 mg coulomb"^ with an overall uncertainty of 19 ppm. With

107.9028 ± 0.0013 for the atomic weight of silver as measured with

the mass spectrometer, the faraday was determined to be 95,516.5 ± 2.4 coulombs g-equivalent~ ^ (physical scale).

References

Craig, D. N. , Hoffman, J. I., Law, C. A., and Hainer, W. J.,

Dtermination of the value of the faraday with a silverperchloric acid coulometer, Nat. Bur. Stand. (U.S.), J. Res.

64A, 381 (1960)

.

Shields, W. R. , Craig, D. N., and Dibeler, V. H., J. Am. Chem. Soc.

(Sept. 1960) .

-173-
-174-
GALVANOMETER, VIBRATING REED 1919 M98

In ac measurements where null methods are employed, maximum sensitivity of the detector is obtainable by tuning the moving element

so that its natural period is the same as that of the electrical

circuit. In this instrument designed by P . G. Agnew and improved

by J. H. Pirn and R. D. Wyckoff, the moving element is a fine steel

wire polarized by being mounted on one pole of a permanent magnet.

A small electromagnet, energized from the circuit in which current

is to be detected, carries pole pieces in the shape of truncated

pyramids which stand on either side of the free tip of the wire

reed. Resonance frequency of the reed, largely dependent on the

length and stiffness of the wire, is adjustable through a small

range by shifting the position of the electromagnet poles with

respect to the tip of the wire.

Resonant vibration of 5 micrometres is easily observable through

the microscope, and a current of 0.05 microampere or an emf of 3 microvolts can be detected. Galvanometers of this type were used

in all precise calibration of standard voltage transformers at NBS

from 1919 until about 1945, when electronic methods were adopted.

References

Wenner, F., A Theoretical and Experimental Study of the Vibration

Galvanometer, Bull. Nat. Bur. Stand. 6_, 347 (1909-10) .

Agnew, P. G., A new form of vibration galvanometer, Nat. Bur.

Stand. (U.S.), Sci. Papers 16, 37 (1920).

-175-
I

-176-
GALVANOMETER, ADJUSTABLE

SENSITIVITY

1910 M39

This taut-suspension galvanometer has its center of gravity displaced behind the axis of rotation determined by the suspension

strips, introducing an element of gravity control into the central

moment of the moving system. Thus tilting the instrument altered

the gravity component of the moment and changed the effective

stiffness of the suspensions and hence the sensitivity, period, and

external critical damping resistance of the galvanometer. With a sensitivity of 22 mm/yv on a scale 150 cm distant, its period is 10 sec and its cdrx is 80 ohms.

This galvanometer was designed about 1910 by Frank Wenner, who

treated the coil with copper chloride to minimize the magnetic dust

inclusions that give rise to zero instability.

Galvanometers of this type, used for a number of years in the

resistance laboratory at the old NBS site, are very susceptible to

mechanical disturbances; these disturbances, transmitted to the

galvanometer wall mount from increasingly heavy neighborhood

traffic, finally led to their abandonment.

References

Wenner, F. , General Design of Critically Damped Galvanometers,

Bull. Nat. Bur. Stand. 13, 211 (1916-17).

-177-
Galvanometer, Adjustable Sensitivity (1910) M39

-178-
GALVANOMETER, MOVING MAGNET 1907 M219

This miniature instrument is one of several constructed by W. W.

Coblentz for his work on radiometry. There are two sets of two

flat-faced 20-ohm current coils each wound on a special mandrel

with 0.07, 0.127, and 0.199-min pure copper wire. Each has an external diameter of 32 mm and the internal diameter of 2 mm. The

needle system, suspended on a quartz fiber from the top of the 8-mm

tube, consists of two sets of 6 tungsten steel magnets, 1.2 x 0.2 x 0.1 mm, arranged astatically. The sensitivity achieved was 2.5 x 10"^^ ampere for a full period of 36 seconds. The coils are completely covered with chamois to exclude air currents, but the

deflection of a mirror mounted on the glass staff between the

magnet sets can be viewed through the small window on the right.

The set of three soft iron shields shown at the rear (upside down) were used to reduce the effect of external magnetic fields.

There was a considerable demand for these instriiments ; from 1920 to

1940 they were manufactured by Leeds and Northrup Co. to Coblentz

specifications

.

References

Coblentz, W. W. , Instruments and Methods Used in Radiometry, Bull.

Nat. Bur. Stand. 4, 391 (1907-8); 9, 7 (1931).

-179-
Galvanometer, Moving Magnet (1907) M219

-180-
Schematic drawing of Galvanometer, Moving Magnet (1907) M21S

-181-
GALVANOMETER, REMOTELY TUNED 1933 M95

This form of vibration galvanometer (D'Arsonval type) was invented

by F. B. Silsbee. The moving coil, suspended between shaped

polepieces of the large permanent magnet, consists of 10 turns of

wire stretched taut between suspensions of copper strip. A rough

adjustment of the natural frequency is obtained by adjusting the

distance between the clamps which hold the suspensions. A fine

adjustment of tuning to resonance with the circuit under study can

be accomplished by an observer while he watches the oscillation

amplitude of the mirror. The lower end of the lower suspension

carries a small soft iron plunger which hangs partly inside a solenoid. Adjustment of the direct current flowing in this

solenoid changes the tension and thus the natural frequency.

At resonance the sensitivity is about 0.3 mm per microvolt at a scale distance of one meter. The iron case (set at one side) gives

protection from air currents and stray magnetic fields. The

instrument was used as an ac detector in the precise calibrations

of ratio and phase angle of standard current transformers for 25

hertz, until superseded by an electronic detector about 1935.

References

Silsbee, F. B. , et al.. Equipment for testing current transformers,

Nat. Bur. Stand. (U.S.), J. Res. 11_, 114 (1933).

Wenner, F., Characteristics of vibration galvanometers, Proc. AIEE

31, 1073 (1912)

.

-182-
Galvanometer, Remotely Tuned (1933) M95

-183-

AMMETER, KOHLRAUSCH 1885 M103

An early form of this simple dc instrument, which Friedrich Kohlrausch called a spring galvanometer, was described in 1884. A

magnetized rod (or a soft iron tube) is suspended by a weak spring,

with part of its length extending into a current-carrying coil. As

the current is increased, the core is pulled further into the coil,

and its position is indicated on a scale marked in amperes. The

accuracy claimed was about 10 percent.

The model shown was imported about 1900 by Queen & Co. of

Philadelphia, and was later presented to H. B. Brooks of NBS by S.

Krasnow of the Georator Co.

References

Kohlrausch, F., Uber ein Federgalvanometer fur technische Zwecke,

Elektrotechn. Zeitschr. 5, 13-20 (1884); Uber einen einfachen

absoluten Strommesser fiir schwache electrische Strome, Ann.

Physik, Series 3, Vol. 27, 403-409 (1886).

-185-
Ammeter, Kohlrausch (1885) M103

-186-
NONREACTIVE RESISTORS

Several NBS staff members were pioneers in developing special windings in which the turns were frequently reversed in direction to

minimize inductance or capacitance in resistors used on alternating

current. Later, manufacturers developed looms for weaving such

resistors

.

CURTIS WINDING 1912 M53

These two resistors, each of 1000 ohms, are wound with 0.05 mm manganin wire on a slitted porcelain cylinder so that successive

turns lead the current around the form in opposite directions.

Thus the inductance is reduced to +30 microhenrys, while the

difference of potential between adjacent turns, and hence the

effective capacitance, is much smaller than in the more usual

bifilar winding.

References

Curtis, H. L. and Grover, F. W. , Resistance Coils for Alternating

Current Work, Bull. Nat. Bur. Stand. 8, 495 (1912).

WENNER WINDING 1930 M454

This construction by which the inductance can be kept very low was suggested by Frank Wenner. A small flexible core of insulating

material about 1 mm diameter is mounted parallel and close to the

main rigid ceramic core. After a few turns of resistance wire have

been wound around the main core, one turn is looped around the

small core. This starts the winding on the main core in the

reverse direction.

The resistor can be made much more quickly than the Curtis type

(M53) , but puts more strain in the wire at the small loops.

MOON WINDING 1935 M52

This resistor is a modification of the Curtis type, in that the

direction of winding is reversed at every 12th turn, the wire passing through holes in the grooved insulating form. It is one of a group constructed by Charles Moon to serve as arms in the MaxwellWien ac bridge used in his absolute determination of the ohm. The

residual inductance is about 60 microhenrys for a 1000-ohm coil.

-187-
References

Curtis, H. L., Moon, C, and Sparks, C. M. , An absolute determination of the ohm, Nat. Bur. Stand. (U.S.), J. Res. 16_, 28

(1936)

.

WOVEN AND CARD TYPES 1940 M50

In a machine-woven "fabric" tape by the Leeds and Northrup Co. the

resistance wire forms the filling, the warp thread being textile.

A 10,000-ohm and a 1000-ohm resistor are supported mechanically by

being wrapped around insulating cylinders.

The other 1000-ohm coil is of wire wound on a thin flat insulating

card.

References

Curtis, H. L. and Grover, F. W. , Resistance Coils for Alternating

Current Work, Bull. Nat. Bur. Stand. 8, 495 (1912).

-188-
Nonreactive Resistor, Curtis VJinding (1912) M53

-189-
Nonreactive Resistor, VJenner Winding (1930) M454

-190-
Nonreactive Resistor, Moon Winding (1935) M52

-191-
-192-
CURRENT BALANCE, KELVIN 1902 M89

This is a secondary standard for use in calibrating ac ammeters up

to 5 00 amperes. It was designed by Lord Kelvin and purchased by

NBS in 1902 from Kelvin & White, Glasgow. As described by F . A.

Laws, "Thfere are four fixed and two movable coils, the latter being

carried at the ends of a balance arm which turns about a horizontal

axis. Each movable coil is situated between two fixed coils and

all six coils are connected in series. In place of a knife edge,

the beam is suspended by a large number of filaments of copper

wire, forming a sort of stranded ribbon, which provides a ready means for making the electrical connection to the movable coils.

Absence of friction, large radiating surface, and cooling by con- duction to the frame are the advantages attained by this means."

A uniformly graduated scale, with its zero at the left end, is

attached to the suspended coil system, and carries a shelf on which

weights can be placed in the V-shaped trough attached to the righthand end. When current flows through the six coils the total

moment due to the weights can be balanced against the force exerted

on the movable coils, which is proportional to the square of the

current

.

References

Laws, F. A., Electrical Measurements, 1st edition, p. 92 (McGraw

Hill, 1917)

.

-193-

Current Balance, Kelvin (19C2) M89

-195-

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-197-

STANDARD REFERENCE MATERIALS

Standard Reference Materials (SRM's) are well-characterized ma- terials disseminated by NBS to be used to calibrate and evaluate

measuring instruments, methods, and systems or to produce

scientific data that can be referred readily to a common base. The

materials are certified for chemical composition or for a particular physical or chemical property. They are used on-site in

science and industry to calibrate instruments and methods used in

production and quality control of raw materials, chemicals, metals,

ceramics, fuels, and radioactive nuclides in manufacturing

processes and in research. Almost 1000 SRM's are available for

sale today. One important application is the development of

clinical standards. Several billion laboratory tests are performed

each year to assist physicians in making diagnoses. NBS has

developed more than 20 SRM's for use by clinical chemists to help

assure the accuracy of these tests. Another important class of

SRM's apply to environmental standards. More than 40 SRM's are now

available which provide a common set of accurate standards on which

manufacturers and federal, state, and local agencies can base their

measurements of potentially harmful air and water pollutants. Over

30,000 SRM's are sold annually.

The SRM effort, initiated in 1906, made the United States the first

country with a program of this kind. The first SRM's were transferred to NBS in 1905 by the American Foundrymen '

s

Association. They were a series of irons of certified chemical

composition. Several of the original SRM's may be traced through

numerous renewals to SRM's in existence today. The SRM number

uniquely identifies a particular material and renewals are identified by the letter suffix. Thus 5L represents the 12th

renewal of SRM5, Cast Iron C, first issued as Iron C of the

American Foundrymen 's Association.

References

Catalog of NBS Standard Reference Materials, Nat. Bur. Stand.

(U.S.), Spec. Publ. 260 (June 1975).

NBS Annual Report 1906, p. 14; Annual Report 1907, p. 13. The

methods of analyses and range of samples were described in NBS

C14 (1909) , NBS C25 (1910) , NBS C26 (1910) and their

successive editions.

-199-
-200-
COMPUTER DEVELOPMENT

SEAC (Standards Eastern Automatic Computer)

The design and construction of SEAC was perhaps the major contribution of NBS to the development of computer machinery. Design of

this large scale electronic digital computer started in 1948 and

construction was completed in May 1950. For the initial two years

of its operation, it was the most powerful computer installation

readily available to the Government and thus was scheduled for

round-the-clock for a full seven day week.

Some of the problems handled by SEAC in its early years were

:

Solution of partial differential equations by the Monte Carlo

method, generation of optimum sampling plans for the Bureau of

Census, problems in crystal structure, relative abundance of the

elements, wave functions of atoms, lens design, synchrotron design,

electric circuit design, transient stresses in aircraft structures,

social security accounting procedures, and classified problems for

the AEC.

SEAC was a serial computer operating completely in the binary

system at a one megacycle rate. It included many innovative ideas,

such as the use of 16000 germanium diodes to carry out all logic

functions and ac coupling using pulse transformers for highly

variable duty factor service. Vacuiim tubes were used for power

amplification only, rather than as grating devices. The original

high speed memory on SEAC was 512 words of 45 binary bits each,

which later expanded to 1024 words. The original SEAC is now in

the custody of the Smithsonian Institution.

REPRESENTATIVE SEAC COMPONENTS M538

CRYSTAL CLUSTER AND CURRENT

SEAC was probably the first large scale computer to make extensive

use of diode grating. This is the method by which the logic

functions of the machine were carried out. The display shows the

construction technique. There were perhaps 20 or so versions of

this type of cluster.

MERCURY DELAY LINE

Early form of mercury delay line used for memory in SEAC development. Heavy aluminum extruded form was used to retain heat.

-201-
ACOUSTIC MEMORY AMPLIFIERS AND GATING CIRCUITS FOR SEAC

This device amplified the small signals coming out of the mercury

delay lines. It also permitted the "writing" of new information in

the lines. Each line was capable of storing 384 binary bits.

References

Computer Development (SEAC and DYSEAC) at the National Bureau of

Standards, Nat. Bur. Stand. (U.S.), Circ. 551 (Jan. 25, 1955).

-202-
-203-

AREA 11 E

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-205-

CLOCK, SHORTT 1921 M516

The mechanical clock designed by W. H. Shortt of the Edinburgh Observatory has two pendulums with one-second periods. The master

pendulum swings essentially free in the evacuated chamber on the

left. Every 3 0 seconds, at the instant when the pendulum has

reached the left extreme of its swing and begun the return to its

position, a small lever descends under the action of gravity and

gives the pendulum a gentle impulse. Thus there is negligible

interference with the uniformity of its oscillation.

The lever is tripped by a circuit closed by a slave pendulum in the

cabinet below the clock faces. It oscillates at a rate a little

slower than the free pendulum, but is periodically speeded up to

within ±0.003 seconds of the master by the action of a "hit-andmiss" synchronizer. The synchronizer consists of a very light

spring which is attached to the rod of the slave pendulum and which

is flexed by striking an electrom>agnet-positioned stop.

This clock was purchased in 1929 from the Synchronome Co. of

London. Having a precision within about 1 ms per day, it quickly

supplanted the Riefler Clock (M515) in astronomical observatories,

but was in turn replaced within a few years by quartz crystal

oscillators similar to M373.

References

Rawlings, A. L,, figure 44, p. 123 in Science of Clocks and

Watches, 2d edition (Pitman Sons, 1948).

Hope-Jones, F., Chapter XVII in Electrical Timekeeping, 2d edition

(N.A.G. Press, 1949)

.

-207-

2 s

-H ^7 C

-209-
CLOCK, RIEFLER 1891 M515

In a mechanical clock, the essential action in maintaining a uniform time interval is the regular oscillation of a pendulum of

fixed length. For greatest precision, this oscillation must be

free from the drag of the escapement and gear train which is used

to drive the hands of the clock.

Dr. Siegmund Riefler of Munich devised a means by which regular

impulses are imparted to the pendulum by means of the short leaf

spring by which it is suspended. This spring is flexed each second

when its upper end is rocked through a small angle by the motion of

the escapement wheel. The escapement arbor is driven by the torque

exerted by a small weight (hidden behind the clock face in M515)

which falls a distance of about one centimeter every 30 seconds.

At the bottom of its fall it closes a circuit which actuates a battery-energized electromagnet (visible at the right) which lifts

it up again.

This clock was purchased from Clemens Riefler in 1904 and served

for precise time interval measurement (to within about 10 ms per

day) through ' NBS until 1929, when it was replaced by the Shortt

Clock (M516) . Its pendulum mass, carried by a long rod of nickel

steel nearly insensitive to temperature changes, swings in a partially evacuated chamber.

References

Haswell, J. E., Horology, p. 30 (Chapman & Hall, 1928).

-210"
Clock, Riefler (1891) M515

-211-
PENDULUMS

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-212-
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MUTUAL INDUCTOR, WENNER 1938 M41

This computable standard mutual inductor was the principal element

in the absolute measurement of resistance by the Wenner method.

That operation, together with measurements by a second method at

NBS, and another method at the National Physical Laboratory in

England, was the basis on which the International Committee on Weights and Measures assigned the value: 1 mean international ohm

(1947) = 1.000484 absolute ohms (1948).

The primary is wound on a porcelain cylinder 41 cm in diameter and

83 cm in length, lapped with grooves of 2 mm pitch by the

techniques of C. Moon. The two gaps in the winding are Dr.

Wenner 's improvement of A. Campbell's design. They provide a larger volume in the central plane in which the magnetic field is

very small and in which the positioning of the secondary coil, of

218 turns in 24 layers, is not so critical to the measurement. The

mutual inductance at 2 3 °C was 10.897220 millihenrys.

The other elements in the Wenner method include an electronically

synchronized reversal of the primary current and of the associated

switching operations, using a flat-topped waveform.

References

Thomas, J. L., Peterson, C, Cooter, I. L., and Kotter, F. R. , An

absolute measurement of resistance by the Wenner method, Nat.

Bur. Stand. (U.S.), J. Res. 43, 291, RP2029 (1949).

-215-
Mutual Inductor, VJemier (1938) M41

-216-
3

AREA 13 - DRUM CASE II Su

-217-

Driim Case II

Segment A

PRESSURE

The need for more accurate pressure measurements has been constant

throughout NBS history. From the first working standard, obtained

in 1904 for calibrating aneroid barometers, to present requirements

for high pressure standards in the 100 , 000-atmosphere range or the

extremely low pressure measurements needed in space research, the

advance of science and technology in this country has been aided by

the Bureau's ability to meet these needs.

-219-
U-TUBE BAROMETER 1941 M462

This design was developed as a laboratory standard to calibrate

portable mercury barometers and aneroid barometers. Vacuum was maintained in the right-hand leg of the 20 mm bore U-tiibe by the

diffusion pump at the rear. Cold traps (chilled by liquid air

dewars) kept oil vapor away from the mercury. The McLeod gage on the right was used to measure the vacuum. The left-hand leg of the

U-tube was connected to the test instrument through a glass wool

filter, and the test pressure was maintained constant by a novel

pneumatic barostat while the observations were being made.

Protection against overpressure was provided by the 5 mm mercury

column and cistern on the left. Both legs of the U-tube were striped with copper paint to reduce the contamination of the

mercury, apparently caused by the contact potential difference

between mercury and glass

.

The difference in mercury levels in the two legs was read by telescopes equipped with vernier reticules, and mounted so as to view

alternately the menisci and the adjoining graduated scale. Mercury

surfaces were illuminated from behind by flashlight bulbs in

carriages movable by a small electric motor. In the basement

laboratory where the barometer was mounted on a cork-and-concrete

foundation, the temperature was held to 25 ± 0.1 °C. The precision

of pressure measurement was within ±0.02 mm mercury, with

systematic errors estimated at about the same value.

The instrument was used during the war years (1941-45) to calibrate

hundreds of barometers for the U.S. Air Force. In later years it was used mainly to calibrate barometers of the U.S. Weather Bureau

and the International Meteorological Society, and for aneroids of

the Federation Aeronautique Internationale. Pressure altitude

recording instruments for the USAF 1957 stratosphere flight to a record 100,000 ft were checked against this mercury barometer. By

1960 several manufacturers were producing portable instruments

which they calibrated with primary standards of mass, length, time,

and temperature, to show accuracies approximately equal to those of

this instrument similarly calibrated. Consequently it was retired

about 1963. The NBS standard is now the low pressure manometer

used for ultra-precise work in gas thermometry.

References

Brombacher, W. G. , Johnson, D. P., and Cross, J. L. , Mercury

Barometers and Manometers, Nat. Bur. Stand. (U.S.), Monogr. 8

(May 1960)

.

Nat. Bur. Stand. (U.S.), Tech. News Bull. 55, 73 (Mar. 1971).

-220-
1

U-Tube Barometer (1941) M462

-221-

VACUUM PUMP, TWO-STAGE 1917 M414

The single-stage mercury vapor pump developed by Langmuir in 1916 was not only simple, but provided a higher vacuum and a larger

exhaustion rate than piimps previously existing. At NBS , H. F.

Stimson modified the design by using two stages to permit the use of a simple water aspirator as a fore-pump.

A stream of mercury vapor generated in the jacketed glass boiler at

the rear is fed to both stages at a temperature of about 290 °C.

Both stages are water- jacketed to cool the mercury, which is

returned to the boiler as a liquid. In the first stage on the

right is a diverging nozzle 4 cm long in the top of the Pyrex glass

envelope. The nozzle produces a high velocity jet of mercury vapor

which entrains gas from the vessel to be evacuated, and sweeps it,

at increased pressure, to the second stage.

At the second stage , a short nozzle produces a further pressure in- crease of the entrained gas . From the bottom, of the second stage

the gas flows to a fore-pump from a connection on the left. Its

absolute pressure (about 2 cm Hg) is indicated by a small mercury

manometer, on the bottom left.

References

Stimson, H. P., A two-stage mercury vapor pump, J. Wash. Acad.

Sci. VII, No. 15, 477 (1917).

-223-
Vacuiam Pijinp, Two-Stage (1917) M414

-224-
Vacuum Pump, Tv/o-Stage (1917) M414

Schematic drawing

-225-

DIAMOND ANVIL OPTICAL CELL 1958 M325

In order to study the effects of very high pressure on molecular

interactions, finely powdered material is squeezed to a film

between the flat surfaces of two gem-cut diamonds. The facets

2 2 which form the anvil have an area of about 0.1 mm (0.0002 in ) and

the diamonds are of Type II which is transparent to infrared

radiation between 1750 cm" and 300 cm"''. Each diamond is mounted

in a close-fitting recess in a piston of 1 cm diameter and having

an axial hole which permits passage of the radiation beam. The

anvil faces can be adjusted to parallelism by means of a set of

tiny leveling screws.

The entire assembly is sufficiently compact to be held on the stage

of a microscope or placed in an infrared spectrometer or an x-ray

diffractometer . Anvil pressures up to 20 gigapascals (200

kilobars) can be developed, the force being applied to the anvil

facets through the mounting pistons by compression of the helical

spring acting through the 2:1 lever system.

References

Weir, C. E., et al.. Infrared studies in the l-to-15 micron region

to 30,000 atmospheres, Nat. Bur. Stand. (U.S.), J. Res. 63A,

55 (1959)

.

Weir^ C. E-, et al. , High-Pressure Optical Cell, U.S. Patent

3,079,505 (Feb. 26, 1963).

Piermarini, G. J. and Weir, C. E., A diamond cell for x-ray

diffraction studies at high pressures, Nat. Bur. Stand.

(U.S.), J. Res. 66A, 325 (1962).

-227-
-228-


TETRAHEDRAL ANVIL

PRESSURE APPARATUS

1959 M38

In order to study the properties of bulk material at pressures on

the order of 10 gigapascals (100,000 atmospheres) this wedge-type

tetrahedral anvil device was developed at NBS as a modification of

the multiple hydraulic rams used by H. T. Hall in 1958. The

specimen is inserted in a drilled hole in a 1.5-cm regular

tetrahedron of pyrophyllite , a soft mineral which serves as gasketing material. Strips of silver foil at either end of the

test specimen provide electrical connections for measurement of the

polymorphic transition pressures evidenced by resistance change.

The three lower faces of the tetrahedron are supported by three

tungsten carbide anvils, shown here with the top anvil and its

supporting block removed and inverted. The three lower anvils and

their supporting blocks are held in a conical carrier, of 18-1/2

degrees half-angle. Sheets of Teflon separate the carrier from its

retaining ring, and the lower anvils are wedged toward one another

when a force (up to 50 ton) is applied to the top anvil and

holder.

References

Lloyd, E. C, et al.. Compact multi-anvil wedge-type high pressure

apparatus, Nat. Bur. Stand. (U.S.), J. Res. 63C , No. 1, 59

(1959) .

-231-
9

00

in

-P

(0u

a<

m

u

(U

Of

(a -p

Eh

-232-
AREA 14 - DRUM CASE II

Drum Case II

Segment B

OPTICS

Since its establishment, NBS has pioneered in optics research and

measurement. The Bureau's establishment of standards and its

development of measurement methods and instrumentation has

contributed materially to the tremendous scientific advances in

such fields as spectroscopy, polarimetry, refractometry , glass

technology, microscopy, photometry, colorimetry and interferometry

.

-235-
SPECTROMETER, SOCIETf GENEVOISE 1912

To lessen independence on foreign suppliers of optical glass, NBS

undertook study of its manufacture in 1914. Good quality prisms

and lenses require precise measurement of refractive index, and

this spectrometer was probably the best instrument commercially

available at the time. A light source is set up on the left, in

front of the adjustable width slit attached to the collimator tube,

which directed a beam of parallel rays onto the specimen set on the

central table. The long telescope on the right is mounted on a rotatable frame so that it can be alined with the emergent beam.

The frame carries five short micrometer microscopes, which look

through tiny windows at the graduations on a stationary circle 308

mm in diameter (not visible) . By taking measurements of the angle

between collimator and telescope at several positions around the

circle, accuracy of less than one second is obtainable.

This instrxament was used during World War II to supply data to

firms making optical glass, and during World War II to examine all

optical glass produced at NBS, as well as to study the effect of

various annealing procedures. In the 1930 's it served for a classic study of the refractive index of distilled water, and in

the 1950 's for similar measurements on other substances needed as standards for the calibration of spectrometers. Since 1952 smaller

and more convenient devices have become available.

References

Cochrane, R. C, Measures for Progress, Nat. Bur. Stand. (U.S.),

Misc. Publ. 275, 186 (1966).

Tool, A. Q. , Tilton, L. W. , and Saunders, J. B., Changes caused in

the refractivity and density of glass by annealing, Nat. Bur.

Stand. (U.S.), J. Res. 38, 519, RP1793 (1947).

Tilton, L. W. and Taylor, J. K. , Refractive index and dispersion of

distilled water for visible radiation, Nat. Bur. Stand.

(U.S.), J. Res. 20, 419, RP1085 (1938).

Stephens, R. E. and Malitson, I. H., Index of refraction of

magnesium oxide, Nat. Bur. Stand. (U.S.), J. Res. 49_, 249,

RP2360 (1952)

.

-236-
-237-

INTERFEROMETER, F^ABRY-FEROT 1907 M275

This is one of the first instruments built in the MBS shops, and

waF designed by Director Stratton. The heavy steel bed carries a precision screw of 0.5 mm pitch which adjusts the position of a steel carriage carrying a circular frame. In the frame was mounted

a fully silvered glass mirror adjusted to an angle of about 14 min

with the optical axis. The brass block at the left held a second

partially silvered mirror which split the reflected beam. The worm

and wheel on the end, readable to 0.01 mm, drove the precision

screw, and the incremental difference of carriage positions, giving

rise to interference patterns, was read from a scale and microscope

not shown.

Work by I. G. Priest determined the bright yellow neon line as Axa=5852 . 4862 international angstroms referenced to the cadmium red

standard, with an average probable error in 6 determinations of

about one part in 9,000,000.

References

Priest, I. G. , A modified method for the determination of relative

wave-lengths, Bull. Nat. Bur. Stand. 6, 573 (1909-10).

-239-

-241-

WAVELENGTH STANDARDS 1889-1960 M398, M400, M274

Many chemical elements of the solar system can be identified by the

bright lines observed at specific wavelengths in the spectra cre- ated by diffracting the light they radiate. As early as 1889, A.

A. Michelson and E. W. Morley suggested the feasibility of

establishing such a wavelength as the ultimate standard to replace

the meter bar. In 1894 Michelson carried out the comparison with

the standard meter, using the red, green, and blue lines of

cadmium. Lamp M400, made by F. 0. Westfall about 1947, also uses

cadmium.

In 1889 Fabry and Perot used a parallel-plate interferometer in

further development of an international system of wavelength

normals. Their method was modified in 1910 by I. G, Priest at NBS,

who introduced reflection fringes and subsequently measured 10

wavelengths in the neon spectrum, using lamp M398.

In 1942, W. F. Meggers of NBS developed an electrodeless lamp using

the isotope mercury-198 suggested earlier by Prof. Louis Alvarez.

Subsequent models, like lamp M274, were made with this isotope as produced by neutron bombardment of gold. The 5461-angstrom line is

very brilliant, and when the lamp is excited by 200 megahertz, its

life is indefinitely long.

The red line of cadmium was the wavelength standard adopted by the

International Astronomical Union in 1938, and the orange-red line

of krypton-86 was adopted as a length standard by the International

Comraittee on Weights and Measures in 1960. However, the simplicity

of operation of the mercury-198 lamp for laboratory length

measurements causes it to be used more frequently than any other

source

.

References

Baly, E. C. C, Spectroscopy (Longmans, London, 1905).

Priest, I. G., Wavelengths of Neon, Bull. Nat. Bur. Stand. 8, 539

(1912) . ~

Meggers, W. F. and Westfall, F. 0., Lamps and wavelengths of

mercury 198, Nat. Bur. Stand. (U.S.), J. Res. 44, 447 (1950).

-243-
-244-
AREA 15 - DRUM CASE II 'i:

UJ

Drum Case II

Segment C

ELECTRICITY

Charged with the duty to establish, maintain, and disseminate the

electrical standards of measure, NBS has held a position of

research leadership throughout its history in the development of

standards, methods of measurement, and instrumentation. These

developments serve all of science and technology within the

framework of a national measuring system that applies equally to

the electricity meters in 80 million homes and to the complex

guidance and control systems of space vehicles.

-247-
COMPUTABLE CAPACITORS 1904 M30, M47

The ratio of the electrostatic to the electromagnetic units of

electricity is important to electrical theory, and its square root

is also the speed of light. E. B. Rosa had measured the ratio at

Johns Hopkins in 1889, using a spherical capacitor. By 1904, he

felt that superior facilities at NBS warranted a redetermination,

using a cylindrical and a parallel plate capacitor as well as the

spherical one which was borrowed from the university.

The cylindrical capacitor (M30) consists of four silver-plated

brass sections 12, 20, 20 and 12 cm long, the lowest and uppermost

sections serving as guards for the study of end effects. Each

section consists of an outer cylinder of 7.241 cm radius and an inner cylinder of 6.257 cm radius. (In the display the upper 20 cm outer cylinder has been removed and set to one side.) At the top of

the upper guard section is a knurled knob attached to a screw of

0.5 mm pitch, by which the axial clearance between inner cylinder

and its guard can be adjusted over a 10 mm range.

In the parallel plate capacitor (M47) the insulated collector plate

is not visible. Below the supporting top plate 6 mm thick and 30 cm in diameter may be seen a silver-plated guard ring which

surrounds the collector plate. Electrical screening of the latter

is completed by the top plate and by a short cylinder fastened to

the guard ring and reaching nearly to the top plate. The lower

capacitor plate of 20 cm diameter is supported on 3 leveling screw?

carried by a threaded rod of 1.5 cm diameter which moves axially

between rigid posts, and has it its lower end a screw of 0.5 mm

pitch. Adjustment of the dielectric space between capacitor plates

is made over a range 1 to 30 mm with the micrometer dial below, and

may be read by a micrometer microscope rigidly attached to the

base

.

Measurement of the capacitance of a condenser in electrostatic

units depends on the dielectric (in this case air) and the dimensions of the dielectric space, with due regard for fringe effects.

Two methods were used by Rosa and Dorsey to measure the capacitance

in electromagnetic units. The first, recommended by Maxwell,

consists of replacing one of the resistances in a Wheatstone bridge

by a condenser and a suitable commutator for rapidly and regularly

charging and discharging the condenser. By adjustment of the

frequency of the charging, and of the resistances of the net, a balance of the galvanometer can be obtained. In the second method,

the charging or the discharging current is passed through one coil

of a differential galvanometer, while through the other coil is

passed a steady current. The latter is shunted off from part of a high resistance circuit which permanently connects the terminals of

the battery employed to charge the condenser.

-248-
In this classic work extending over a period of two years, numerous possible sources of error were examined and corrections were made

for them. The mean value found for square root of the ratio for an air capacitor was 2.9963 x 10^° with an uncertainty of not more

than 1 in 10,000.

References

Rosa, E. B. and Dorsey, N. E., A New Determination of the Ratio of

the Electromagnetic to the Electrostatic Unit of Electricity,

Bull. Nat. Bur. Stand. 3, 433, 541 (1907).

-249-
Cylindrical Capacitor (19C4) M30

-250-
-251-
Parallel Plate Capacitor (19C4) M47

-252-
ELECTRODYNAMOMETER COIL 1905 M68

This movable coil consists of 8 3 turns of bare copper ribbon spaced

0.6 mm apart on a porcelain cylinder, giving an average effective

diameter of 75.5854 mm. Constructed at NBS, it was one of two used

by Guthe for the first precise absolute measurement here of

electric current by the electrodynamometer method. It was suspended with its axis horizontal at the exact center of the

opening of a much larger cylindrical coil, and at right angles to

the axis of the latter. While the upper end of its torsional

suspension is being twisted through 90° , an increasing current is

passed through the coils until the opposing torques are balanced at

the original right-angle position.

References

Guthe, K. E., A New Determination of the Electromotive Force of

Weston and Clark Standard Cells by an Absolute ElectroDynamometer, Bull, Nat. Bur. Stand. 3, 33 (1906).

-253-
Electrodynamometer Coil (1905) M68

-254-
WATTMETER, HEAVY-DUTY 1903 1^366

This taut-suspension astatic electrodynamometer was designed by H. B. Brooks over one weekend to meet an emergency request for a 50-

ampere wattmeter. It served until 1925 as a standard ac-dc

transfer instrument for calibrating wattmeters used on alternating

current of power frequencies. Thereafter it was little used

because the development of current transformers made feasible the use of 5-ampere instruments.

Connections of the two sets of fixed and moving coils were made so as to eliminate the effect of any uniform stray magnetic field.

The coarse wire of the fixed coils, which may be either in series

or in parallel, carried line current, while the moving coils of

fine wire (in series with a large noninductive resistance) were connected in parallel with the voltage circuit of the wattmeter

under test. Deflections were read by an optical lever reflecting

from the small mirror attached to the suspension.

References

Harris, F. K. , Electrical Measurements, Chapter 10, pp. 412-15

(John Wiley, N.Y,, 1952),

-255-
-256-
POTENTIOMETER, DEFLECTION 1906 M24

Designed by H. B. Brooks and built by the NBS shops, this instrument combines the potentiometer principle with that of the indicating instrument. By the use of compensation for most of the

unknown quantity, only the uncompensated residuum needs to be read

on an indicating instrument which has a resolution no better than

0.1 scale division. The overall resolution is thus improved by two

orders of magnitude. Further, since complete balance is not

required, as with a null potentiometer, the instrument can follow

accurately any variation of the unknown within the range of the

indicator.

The device is self-contained except for a standard cell for ref- erence and a storage cell. The main potentiometer dial covers the

range from 95 to 125 volts in 15 steps of 2 volts, and a residual

unbalance can be read to within 0.02 volt from the deflection of

the nearly aperiodic galvanometer needle.

This instrxament was used extensively for voltage measurements in

the photometric laboratory over a period of thirty years, the

original Weston model A being replaced by a Weston model 440

galvanometer, and later by an L & N model 8. Improved models are widely used today in instrument manufacturing plants and

standardizing laboratories

.

References

Brooks, H. B., A New Potentiometer for the Measurement of Electromotive Force and Current, Bull. Nat. Bur. Stand. 2_, 225

(1906)

.

-257-
-258-
(A AREA 16 - DRUM CASE I §

Q

-259-

Drum Case I Segment A

DEFENSE

NBS research and development for defense goes back to World War I when several hundred projects, important to the national effort, were successfully carried out. Drawing on the Bureau's broad

competence in the physical sciences, the subject matter included a wide variety of aeronautical, chemical, electrical, magnetic,

metallurgical, radio, photographic, and acoustic problems. During

World War II the Bureau again devoted its staff and facilities to

military problems in the physical sciences. Three of the principal

projects were the atomic bomb, proximity fuzes, and guided

missiles. Many of the techniques, methods, materials and products

developed for defense later proved important in peacetime

application

.

-261-
SOUND-RANGING SYSTEM M480

A technical achievement late in World War I in which NBS was instrumental was the improvement in many components of a soundranging system for locating enemy artillery. The system involves

installing microphones at three known stations to receive the sound

pulse produced by the firing of a gun. An oscillograph at a central point recorded the instant of arrival of the soxind pulses

at each station. Intervals of time between pulses indicated the

differences in distances from the gun to the stations. After

correcting for such variable factors as temperature and wind

velocity, enemy artillery could be pinpointed with such accuracy

that a writer observed, "Camouflage was powerless .. .Actual sight of

the gun could not add to the precision."

An improved oscillograph indicated the times at which the sound

pulses from a gun's firing were received. It was rugged and

reliable under combat conditions and gave clearer records than

earlier British and French models. This oscillograph tape made on NBS equipment in France between Bois de Dapoitoux and la Grande

Souche records the firing of a German 77-mm gun.

Dr. Ernest E. Weibel , a member of the NBS team that made important

developments in the sound-ranging system, accompanied the equipment

overseas and was killed while testing it in actual combat near

Ypres

.

References

War Work of the Bureau of Standards, Nat. Bur, Stand. (U.S.), Misc.

Publ. 46, 265 (1921)

.

-262-
-263-

NAVAL ORDNANCE STUDIES

During World War I and for some years after, an NBS team under H.

L. Curtis developed both apparatus and methods for measuring such

characteristics of large naval guns as muzzle velocity, time of

firing and ejection, motion of projectile in the bore, and motions

of the gun in recoil. Studies were conducted in experimental

firings with 14-in guns on U.S. battleships.

References

Nat. Bur. Stand., Ballistic Experiments on Battleships, 1917-21.

(Unpublished reports UF820.U5)

POWDER PRESSURE GAGE M77

This pressure gage was capable of measuring pressures up to 50,000

pounds per square inch. Fitted inside the breech block of a 14-in

gun, it contained a multiply tapped resistor with spring-controlled

contactor. When the gun was fired, pressure exerted on the

contractor drove it past a number of the taps. A single, insulated

wire extended outside to permit measurement of the change in

resistance

.

EXPANSOMETER M71

Used in studying the progress of a projectile along the bore of a 14-in naval gun, a series of expansometers were clamped along the

barrel of a gun by slender steel straps encircling the barrel. As

the projectile passed inside, the barrel bulged and separated the

contact points, thus breaking the electric circuit of each

expansometer in turn causing sequenced timing signals on an oscillograph.

MUZZLE FINGER M72

This notched, hardened steel finger was one of a pair mounted at

the muzzle of a 14-in gun. It extended into a rifling groove while

a longer one reached to the gxin axis. The long finger was broken

by the tip of the projectile, and the short finger later by the

rifling band as the projectile left the gun. From these signals

and the length of the shell, the projectile's velocity and time of

ejection were computed.

-265-
-266-
WORL-D WAR II

PROXIMITY FUZES M4 , M5 , M6

A major technical development during World War II was the variable

time (VT) or proximity fuze which causes a shell, bomb, or rocket

to explode when merely in effective proximity to its target, rather

than on impact. Three kinds of fuzes for nonrotating projectiles

were developed at NBS while the Johns Hopkins Applied Physics Lab

developed a fuze for rifled artillery shells. The Photoelectric

fuze T-4 (M4) , for use on the M-8 antiaircraft rocket, is equipped

with a photoelectric cell and lens and is triggered by changes in

light intensity when an object passes between the lens and the sky.

Work on this fuze was discontinued as the radio fuzes showed more promise. The T-89 (M5) first used in early 1945 is a tiny radio

sending and receiving station mounted in the nose of an aircraft

bomb or rocket. When its continuously emitted waves reach a target, they are reflected back to the receiver. At a predetermined distance, the reflected waves reach a certain

intensity, and an electronic switch detonates the fuze. The T-171

(M6) developed around 1944 triggers trench mortar shells at a predetermined height above their target. It was similar to the T89, but was modified to withstand the shock of being fired from the

mortar

.

References

Summary Technical Reports, Nat. Def. Res. Comm. Div. 4, Vols. 1 and

3, U.S. Office Sci. Res. & Dev. (1946).

Hinman, W. S. and Brunetti , C, Radio proximity fuse design, Nat.

Bur. Stand. (U.S.), J. Res. 37, 1, RP1723 (1946).

-267-
-268-
CARBON MONOXIDE DETECTOR TUBES M193

Developed by M. Shepherd at NHS to detect small amounts of carbon

monoxide in airplane cockpits, these tubes contain a silica gel of

palladium sulfate and ammonium molybdate which changes color if

carbon monoxide is present. More sensitive and reliable than

previous detection devices, over a half million of these tubes were made at NBS during World War II.

References

Shepherd, M. , Rapid determination of small amounts of carbon

monoxide. Anal. Chem. 19, 77-81 (1947).

-269-
-270-
BUOY CIRCUIT ASSEMBLY

(TINKERTOY)

1953 M443

This device is the electrical circuit assembly of one type of Sonar

Buoy used in antisubmarine warfare. It is contained in a buoy,

several of which can be dropped from an aircraft in a known pattern

in an area where enemy submarines are suspected. A microphone

suspended below the buoy picks up any underwater noise and feeds

its electrical signal to the input to this circuit. The signal is

amplified and used to modulate the carrier of an HF transmitting

circuit, energized by external dry cells, and feeding an antenna

extending several feet above the buoy. By tuning successively to

the various buoys in the pattern, the aircraft can recognize and

estimate the location and direction of motion of a submerged

submarine

.

This circuit assembly is an early example of the type of modular

construction developed by the NBS "Tinkertoy" Section under the

sponsorship of the Navy Department during and after World War II,

and under the initial leadership of Mr. Robert Henry. This section

had developed automatic machinery for manufacturing the individual

ceramic wafers, imprinting an appropriate electrical component or circuit on each, and assembling them by riser wires in larger

modules. Mass production of complex circuitry with a minimum of

labor was thus made possible, and it served as a stimulus to many

private companies to follow similar procedures.

After the circuits had been "translated" by NBS from the older Navy

forms to this modular type, about 3,000 sample circuits were produced on contract by Sanders Associates for evaluation studies

by the Navy's AN/SSQ-2 Sonabuoy.

References

PROJECT TINKERTOY: Modular design of electronics and mechanized

production of electronics, Nat. Bur. Stand. (U.S.), Tech.

News Bull. 37, No. 11, 161 (Nov. 1953).

-271-
-272-
CONSTANT DEPTH MINE MlOO

Invented at NBS by Charles Moon and R. L. Driscoll during World War

II, this apparatus was attached to a free-floating mine to keep it

at a nearly constant, predetermined depth. When it deviated from

that depth, a pressure-sensitive device started a small propeller

which returned the mine to the set depth and readjusted the

buoyancy of the system by changing the volume of an extensible

chamber. In 1944 and 1945 more than 250 such mines were dropped

from aircraft into the Chindwin and Yangtze Rivers to interfere

with Japanese shipping.

References

U.S. Patent No. 3012502

Duncan, R. C. , America's Use of Sea Mines, U.S. Naval Ord. Lab., p.

144 (1962)

.

NBS War Research: The National Bureau of Standards in World War II,

p. 60 (1946)

.

-273-
-274-
URANYL NITRATE CRYSTALS M82

Crystals of uranyl nitrate used in an ether extraction method for

purifying uranium oxide were developed by J. I. Hoffman and J.

Scherrer of NBS in 1941. This process permitted commercial

production of uranium to a degree of purity seldom achieved even on

a laboratory scale. It was an important breakthrough in the atomic

weapons program.

References

Smyth, H. D. , Atomic Energy for Military Purposes, p. 93 (Princeton

Univ. Press, 1945) .

-275-
Uranyl Nitrite Crystals (1941) M82

-276-
GRAPHITE BLOCK M81

High purity graphite similar to the material tested in quantity at

NBS in the early 1940 's to insure almost complete absence of

neutron-absorbing impurities. The graphite used in the early

nuclear reactors was found to contain boron, which prevented a chain reaction. C. J. Rodden and other NBS men patiently studied

the various steps in the manufacture of graphite and discovered and

eliminated the source of the boron.

References

Smyth, H. D. , Atomic Energy for Military Purposes, p. 94 (Princeton

Univ. Press, 1945)

.

-277-
Graphite Block (vn^li) M81

-278-
AREA 17 - BRUM CASE I

Drum Case I Segment B

INDUSTRY

NBS has contributed substantially through its testing activities to

the advance of commerce and industry. At the request of various

industries, Government agencies, and other organizations, the

Bureau invented and developed apparatus and methods for testing a wide variety of materials and equipment. Such testing not only

directly benefited science and industry but resulted in better

products for the consumer.

-281-
SACCHARIMETER, BATES 1907 M418

The duty levied on sugar imports by the U.S. Customs Service is

based on the readings taken on an instrument of this type, graduated to the International Sugar Scale. On that scale, 100 °S

refers to the optical rotation of a beam of polarized light

measured on passing through a 200-mm tube filled with a solution

prepared with 26.00 g of pure sucrose dissolved in water to a volume of 100 ml at 20 °C.

In a saccharimeter , the observer's field of view is divided, half

showing the optical rotation of the sugar solution, and half showing the opposite rotation effected by a compensating pair of quartz

wedges. The observer seeks to obtain a photometric match between

the two fields. The planes of polarization in the two fields

differ by the so-called halfshade angle. In the conventional

instrument, the half shade angle is fixed at 6 to 8 degrees, a compromise intended to provide adequate illumination of the fields

when testing a dark molasses, and satisfactory precision when a clear solution is being tested. In this model, designed by F. J.

Bates at NBS and constructed by Fric of Prague, a halfshade angle

from 2.5 to 15 degrees can be selected by the knurled ring just

below the eyepiece, thus providing an adjustable sensitivity. A

modified gear train resets the zero position of the analyzing

prism. The knurled knobs marked C and N adjust the quartz wedges

used to match the fields. A concentrated-filament incandescent

lamp, fitted with a potassium dichromate filter which eliminates

the blue end of the spectrum where the quartz compensation is less

effective, provides an improved white-light source.

References

Bates, F. J., A Quartz Compensated Polariscope with Adjustable

Sensibility, Bull. Nat. Bur. Stand. £, 461 (1908); 5, 193

(1908)

.

Bates, F. J., et al., Polarimetry, Saccharimetry , and the Sugars,

Nat. Bur. Stand. (U.S.), Circ . 440, 810 pages (1942).

-282-
-283-
I

I

I

I

p

p

p

m

m
FLEXOMETER 1930 M331

In the device developed by H. F. Schiefer the stiffness of a fabric

is related to the energy required to fold a pair of rectangular

specimens. Similarly, the elastic energy recovered upon unfolding

is a measure of resiliency, an important property of parachute

fabrics. The difference, or hysteresis energy, is related to

wrinkleability

.

The flexometer has been useful for the evaluation of the effects of

different kinds of fiber, yarn, and fabric constructions, and of

finishing treatments. It was especially valuable in studying the

effect of resin finishes on wrinkle resistance, and in developments

leading to wash-and-wear garments

.

References

Schiefer, H. F., The flexometer, an instrument for evaluating the

flexural properties of cloth and similar materials, Nat. Bur.

Stand. (U.S.), J. Res. 10, 647, RP555 (1933).

-285-
Flexometer (1930) M331

-286-
PLANOFLEX 1940 M332

This instrument was developed by E . C. Dreby to provide objective

evaluation of the "hand" or "feel" of fabrics---a characteristic

dependent on the free space between yarns and the flexural stiff- ness of the yarns themselves. The ends of a strip of fabric are clamped under tension, and then one end is moved laterally until

the strip wrinkles. The measurement is related to pliability,

drapability, and appearance, and is useful in fabric design and in

the evaluation of finishing processes on fabrics of similar

construction

.

References

Dreby, E. C, The planoflex, a simple device for evaluating the

pliability of fabrics, Nat. Bur. Stand. (U.S.), J. Res. 27 , 469, RP1434 (1941)

.

-287-

KNOOP INDENTER 1936 M155

U.S. Patent 2,091,995 covers a four-sided pyramidical diamond indenting tool, two of its opposite cutting edges having an included

angle smaller than the other two. This tool makes an elongated

diamond-shaped impression that is long enough to give consistent

measurements of hardness in thin materials such as dental enamel or sheet metal, even when- light loads are used. It is useful for

elastic materials because only minor distortion is produced at the

ends of the elongated indentation, but it can equally well be used

for plastic materials such as waxes, or brittle materials such as glass

.

The mechanism shown (M155) was specifically designed for light

loads; it includes a cam-controlled weighted arm for applying a known load. Three samples of the indenting tool are laid at the

side

.

References

Knoop, F., Peters, C. G. , and Emerson, W. B. , A sensitive

pyramidal -diamond tool for indentation m.easurements , Nat. Bur.

Stand. (U.S.), J. Res. 23_, 39, RP1220 (1939).

Tarasov, L. P. and Thibault, N. W. , Determination of Knoop hardness

numbers independent of load. Trans. Am. Soc. Metals 38.' -^-^^ (1947)

.

-289-
Knoop Indenter (1936) Ml 5

5

-290-
c -291-

SPIRAL CONTRACTOMETER 1947 M416

Excessive internal stress in electroplated coatings may cause peeling, blistering, or cracking of the deposit. This instrument

developed by Abner Brenner measured internal stress as it develops

in the plating process, and has been widely used both for research

and for production control in the plating industry. It permits

study of such variables as composition of the bath and grain size

of the deposit.

The coating is applied to one surface of a copper or stainless

steel helical strip 0.25 to 0.75 mm thick. As deposition occurs,

the helix coils or uncoils slightly, and the rotation is magnified

by 10:1 gearing. After stripping, the helix may be used again and

again.

References

U.S. Patent 2,568,713.

Brenner, A. and Senderoff, S., A spiral contractometer for measuring stress in electrodeposits , Nat. Bur. Stand. (U.S.), J.

Res. 42, 89, RP1953 (1949).

-293-
-294-
ELECTROFORMED PRINTING PLATE 1930 M441

Early in the century NBS cooperated with the Bureau of Engraving

and Printing in developing improved intaglio plates for printing

currency. In 1930, C. T. Thomas and W. Blum worked out a process

of electrodepositing nickel, iron, and chromium to provide wear resistance, with a thick steel backing to limit distortion. In

1966, the method was modified to adapt the plates for use in rotary

presses

.

References

Thomas, C. T. and Blum, W. , The production of electrolytic iron

printing plates, Trans. Am. Electrochem. Soc. 57_, 59 (1930) .

-295-
«

Electroformed Printing Plate U930) M441

-296-
c

c

u AREA 18 - DRUM CASE I J

-297-

Drum Case I Segment C

SCIENCE

NBS research in diverse areas of physics, mathematics, chemistry,

metallurgy and engineering has had one single unifying theme

:

precise measurement of natural phenomena. The resultant knowledge,

instruments, measurement techniques, and reference data have

contributed significantly to the advance and growth of science.

-299-
MI CROCALORIMETER

(RADIATION BALANCE)

1952 M339

In this twin microcalorimeter using Peltier-effect cooling to

balance the rate of energy emission of small radioactive sources,

precise comparison can be made between samples held in the two

small cylindrical copper (or gold) "cups." As designed by W. B.

Mann to utilize a principle suggested by H. L. Callendar in 1911,

two constantan-chromel wires soldered to the lower end of each cup

form the Peltier junction, while similar pairs of wires forro a thermocouple for measuring the cup temperature.

« The calorimeter is used in the vertical position, with the larger

aluminum (or copper) block uppei^ost. Each cup is supported on the

upper end of a six-junction chromel-constantan thermopile by means

of an equatorial annular ring, and this entire assembly is mounted

on an insulating plate supported in the copper disk mount. The

lower junctions of each thermopile dip into silicone vacuum-pump

oil contained in the cavities of the lower block.

The Peltier junctions, with coefficient P, are connected in opposition so that one cup is heated and the other cooled when a current C flows in that circuit. With a radioactive source in one

cup (or one in each) the current is adjusted until equal

temperatures are achieved in each. The difference in rate of

energy emission is then given by 2 PC watts, to within about 0.3 yw

over a range of 100 yW to 10 mW.

A similar microcalorimeter was used to intercompare the national

radium standards of Britain, Canada, Germany and the United States;

to calibrate the samples used to prepare solution standards of

radium; to deteirmine the activity of hydrogen 3 (tritium) ; sulfur

35, nickel 63, polonium 210; and to measure the energy output of

Plutonium 2 39.

References

Mann, W. B. , A radiation balance for the microcalorimetric

comparison of four national radi-um standards, Nat. Bur.

Stand. (U.S.), J. Res. 53_, 277 (1954).

Mann, W. B., Radiation calorimetry—A review of the work at NBS,

Nuclear Instr. Meth. 112, 273 (1973) .

-300-
Microcalorimeter (Radiation Balance) (1952) M339

-301-

WATER CALORIMETER 1937 M509

This calorimeter was designed and used by Osborne, Stimson, and

Ginnings in 1937 for precise measurement of heat capacity and heat

of vaporization of water from 0 to 100 °C. The nearly spherical

inner shell (cut away to show the construction) holds the water

sample, which siabmerges the rotating stirrer and electric heater.

The space just outside that shell is evacuated to reduce heat loss.

The double-walled outer shell holds a nearly isothermal steam bath,

and an extension of the steam jacket surrounds the reference temperature block (shown through the oval cutout) which holds a platinum resistance thermometer and the reference junctions of the

aiixiliary theirmocouples

.

References

Osborne, N. S., Stimson, H. F., Ginnings, D. C, Measurements of

heat capacity and heat of vaporization of water in the range

0° to 100 °C, Nat. Bur. Stand. (U.S.), J. Res. 23_, 197,

RP1228 (Aug. 1939)

.

-303-
Water Calorimeter (1937) M509

-304-
PROVING RING 1925 M504

The accurate measurement of large compressive and tensile forces

has been made practicable by the Whittemore-Petrenko elastic

proving ring, developed about 1925 to provide calibration of

mechanical testing machines for structural members and machine

parts. When the ring is loaded along a vertical diameter, its

change of shape is measxired by means of a micrometer screw and a thin flexible reed, each of which is attached to the ring at the

neutral axis where the stress is negligible. The reed is set to

vibrating by pushing its free end to one side, and the micrometer

screw is then advanced so that its tip "buzzes" the moving end of

the reed. The deflection of the ring can thus be read with a sensitivity of a few hundredths of a millimeter, and an accuracy

within 0.1 percent.

The unit displayed was designed for compression loads, and made in

the NBS shop. Today this type of proving ring is made by several

commercial firms in sizes from 200 to 1,500,000 pounds force.

References

U.S. Patent 1,648,375 and 1,927,478, H. L. Whittemore and S. N.

Petrenko.

Wilson, B. L. , et al.. Proving Rings for Calibrating Testing

Machines, Nat. Bur. Stand. (U.S.), Circ. C454 (Aug. 1946).

-305-
-306-
u AREA 19

-307-

ATOMIC WEIGHT OF HYDROGEN 1907 M9

When a year-long series of 2 0 experiments on the atomic weight of

hydrogen indicated a value of 1.00819 as compared with the 1.00762

reported by Morley in 1895, W. A. Noyes refined his techniques and

embarkeii on four more series of experiments in which he weighed the

amount of water formed from a weighed amount of hydrogen and/or

oxygen. The latter came from highly purified copper oxide that he

prepared. Noyes used palladium to catalytically purify his

hydrogen and also took advantage of its unique adsorbtive property

for hydrogen. Palladium was saturated with hydrogen at room temperature and weighed, then heated to release hydrogen and

reweighed to give the amount used in the experiment. Weighing was done on the Ruprecht balance (M291) shown elsewhere in the Museum.

The exhibit (M9) shows the actual palladium used - 360 g of 0.05 mm

foil that released 2 g of hydrogen for each experiment. From five

series of experiments Noyes obtained a value of 1.00787 differing

from Morley by 15 parts in 100,000. The presently accepted value

is 1.00797.

References

Noyes, W. A., The atomic weight of hydrogen, J. Am. Chem. Soc. 29 , 1718 (1907)

.

-309-
-310-
HEAVY WATER 1931 Mil

When in 1934 Harold C, Urey was awarded the Willard Gibbs Medal

(and later the Nobel Prize) for his work on the isotopes of

hydrogen, he acknowledged the help of "his young friend. Dr. F. G.

Brickwedde of the Bureau of Standards" who supplied the gas distilled from liquid hydrogen. In 1931 Urey had "calculated the

difference in electrode potentials of H^ and H^ with a view to

separating the isotopes by an electrolytic method, but no separation seemed possible." E. W. Washburn and E. R. Smith (at

NBS) did not calculate but experimented instead, and found that a very appreciable separation did occur in electrolytic processes.

The experiment which started at NBS on December 9, 1931

electrolyzed normal water between platiniom electrodes, condensed

the evolved gases and continued until 98 percent of the original

sample had been decomposed. The residual water in the ampoule

displayed here has a specific gravity of 1.000164.

References

Washburn, E. W. , Smith, E. R. , and Frandsen, M. , The isotopic

fractionation of water, Nat. Bur. Stand. (U.S.), J. Res. 11 , 453, RP601 (1933)

.

Urey, H. C, Significance of hydrogen isotopes, Ind. Eng. Chem. 26 , 803 (1934)

.

-311-
-312-
OMEGATRON 1951 M7

This cyclotron resonance device which accelerates positive hydrogen

ions (protons) was used for a determination of the value of the

faraday, previously determined by electrochemical methods. The

relation is F = Ay_(b^^/b)) where A is isotopic weight and the

gyromagnetic ratio of the proton, LO^ is the cyclotron resonance

frequency, and 00^ is the nuclear resonance frequency.

In operation, the glass envelope is evacuated except for a trace of

hydrogen, and its lower end is placed in a strong magnetic field.

Electrons produced from a tungsten filament are accelerated into

the box-like space surrounded by the stack of rectangular guard

rings, where they create ions by impact. A small r-f voltage

applied between the top and bottom of the space accelerates these

ions in expanding spirals, provided the r-f frequency is the same

as £jO^. The resonant ions are collected at the top of the guardring space, and the current to this collector gives the indication

of resonance.

References

Sommer , H . and Hippie , J . A . , The Faraday and the Omegatron , Nat

.

Bur. Stand. (U.S.), Circ. 524, p. 21 (1953).

-313-
Omegatron (1951) M7

-314"
COILS, RAYLEIGH

CURRENT BALANCE

1906-1942 M69

Weighing a current in apparatus of the Rayleigh type calls for

measuring the force exerted on a moving coil suspended in the

magnetic field supplied by a pair of fixed coils. Two important

parameters are the local acceleration due to gravity, and the ratio

of effective diameters of the moving and fixed coils. In this

display, the aluminiam and plexiglass mounts were used to hold the

coils for measurement of this ratio by adjusting currents to

produce equal magnetic fields at the center.

The coils of round copper wire or (later) flat aluminxjin ribbon are completely enclosed in build-up aluminum forms, 2 cm x 2 cm x 50 cm diameter for a fixed coil, and 1 cm x 1 cm x 25 cm diameter for the

moving coil. For weighing the current, two of the larger coils

were rigidly mounted about 20 cm apart, on a vertical axis. The

moving coil was hung from one pan of a precision balance, which

must be sensitive to the change of only a few grams, occurring when

the current in the coils is reversed.

In the classic experiment of Rosa, Dorsey, and Miller, 1906-1910, a series of nearly 500 measurements determined the absolute ampere to

be slightly larger (4 parts in 100,000) than the international

ampere determined by silver voltameters (M170, M171) . Multilayer

windings were used in both the fixed and the moving coils. A

redetermination in 1934 indicated the need for improved windings,

and in 1939 two new moving coils were made. One was wound as a single-layer helix with 41 turns of copper wire of 0.51 mm

diameter, the other as a flat compact spiral of 45 turns of

aluminum ribbon 0.072 mm thick. The fixed coils were spirals with

125 layers of 0.104 mm aluminum ribbon. The weighted mean of these

experiments gave 1 NBS international ampere = 0.999 86 absolute

ampere. Another apprach in 1940-1942 to the problem of measuring

effective coil diameters used a subdivided helix of 27.516 54 cm axial length which served as the two fixed coils. That work was one of the major contributions from which the International

Committee on Weights and Measures assigned the value effective

January 1, 1948 of 1 NBS international ampere = 0.999 85 absolute

ampere

.

References

Rosa, E. .B., Dorsey, N. E., and Miller, J. M. , A Determination of

the International Ampere in Absolute Measure, Bull. Nat. Bur.

Stand. 8_, 269, S171 (1912) .

Curtis, H. L. , Curtis, R. W. , and Critchfield, C. L., An absolute

determination of the ampere using improved coils, Nat. Bur.

Stand. (U.S.), J. Res. 22, 485, RP1200 (1939).

-315-
Curtis, H. L. , Driscoll, R. L. , and Critchfield, C. L. , An absolute

determination of the ampere using helical and spiral coils,

Nat. Bur. Stand. (U.S.), J. Res. 28, 133, RP1449 (1942).

-316-


f

c

AREA 20 J

-319- (S

RUEPRECHT BALANCE 1901 M291

This precision equal-arm two-pan balance, constructed about 1901 by

A. Rueprecht & Sohn of Vienna, was purchased by NBS in 1945 from

the Case School of Applied Science, and used for calibrating

secondary kilogram standards against National Prototype No. 20. It was retired about 1960, with the advent of good Swiss one-pan

balances with only two knife-edges, and with design improvements in

coxanterweight location and arrestment mechanism which resulted from

lengthy experiments by the NBS Mass Laboratory. Copies of the new

NBS design are being used at the International Bureau in Sevres,

and are being purchased by the national laboratories of Sweden and

Italy.

The 30-cm Rueprecht beam has a truss form, and carries a hardened

steel knife-edge which rests on an agate flat. At the ends of the arms are knife-edges set a few micrometres below the central one,

and parallel to it. On each of these rests crosswise a short knife

(Thiesen compensator) from which hangs down a two-piece link

supporting a weight pan; this construction lessens the effect of

off-center loading. The whole instrument is encased in glass to

lessen the effects of temperature and humidity changes on the

buoyancy of air. All operations can be accomplished from a distance by means of long control rods.

To compare a secondary standard mass with the Prototype Kilogram,

each was placed on one of the cork-covered cut-out platforms at the

base, and the case was closed. Using the control rods, the

operator raised the cork-covered cruciform member, swung it over

above the cut-out weight pans , and lowered the weights onto the

pans. The arrested beam was released, allowed to oscillate, and

its rest position noted. To improve the sensitivity, the operation

was repeated after the weights were lifted off the pans, returned

to the central platforms, and transposed to the opposite pans.

Then, using the small sensitivity weights of 120 to 126 mg selected

from the top of the case, the comparison was repeated to evaluate

the mass which was equivalent to the change in the scale

observation when the major weights being compared were

interchanged. Any difference between the major weights could be

estimated to a fraction of a milligram.

References

Pontius, P. E., Mass and Mass Standards, Nat. Bur. Stand. (U.S.),

Monogr. 133 (1974)

.

Bowman, H. A. and Aimer, H. E., Minimization of the arrestment

error in one-pan, two-knife balance systems, Nat. Bur. Stand.

(U.S.), J. Res. 67C (Eng. and Instr.), No. 3 (July-Sept.

1963)

.

-321-
Rueprecht Balance (1901) M291

-322-
-323-

NBS-114A (REV. 7-73)

1 U.S. DEPT. OF COMM.

' BIBLIOGRAPHIC DATA

SHEET

1. public;ation or report no. NBSIR 76-11252. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

Catalog of Artifacts on Display in the NBS Museum

5. Publication Date November 1977

6. Performing Organization Code

H.L. Mason, Editor

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Taslc/Worlc Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Same as 9

13. Type of Report & Period Covered

Interim

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

Artifacts currently on display may "be replaced or rearranged periodically. The

Catalog will be amended accordingly to keep it current.

16. ABSTRACT (A 200-word or less factual summary of most si^ificant information. If document includes a significant

bibliography or literature survey, mention it here.) Apparatus and other memorabilia illustrative of the scientific and engineering

achievements of NBS are described, with statements of their technical function

and their historic place in the evolution of physical measurement.

f

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

History of science; measurement instoruments ; measurement standards; National Bureau

of Standards; National measurement standards; physical measurement; weights and

measures

.

18. availability it Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

1

' For Official Distribution. Do Not Release to NTIS

UNGL ASSIFIED

1

1 Order From Sup. of Doc, U.S. Government Printing Office Washington. D.C. 20402. SD Cat. No. C13

1

1 X! Order From National Technical Information Service (NTIS)

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20. SECURITY CLASS

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22. Price $11.00

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