NATIONAL BUREAU OF STANDARDS REPORT

7523

STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS

PROGRESS REPORT No. 15

January 1 - March 31, 1962

Contract No. DO (33-616) 61-02

Task No. 73603

AERONAUTICAL SYSTEMS DIVISION

AIR FORCE SYSTEMS COMMAND

UNITED STATES AIR FORCE

WRIGHT-PATTERSON AIR FORCE BASE, OHIO

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March 3, 1901, as amended by Congress in Public Law 619, 1950. These include the development and maintenance of the national standards of measurement and the provision of means and methods for making measurements consistent

with these standards; the determination of physical constants and properties of materials; the development of methods and instruments for testing materials, devices, and structures; advisory services to government agencies on scientific and technical problems; invention and development of devices to serve special needs of the Government; and the development of standard practices, codes, and specifications. The work includes basic

and applied research, development, engineering, instrumentation, testing, evaluation, calibration services,

and various consultation and information services. Research projects are also performed for other government

agencies when the work relates to and supplements the basic program of the Bureau or when the Bureau’s

unique competence is required. The scope of activities is suggested by the listing of divisions and sections on the inside of the back cover.

Publications

The results of the Bureau’s research are published either in the Bureau’s own series of publications or

in the journals of professional and scientific societies. The Bureau itself publishes three periodicals avail- able from the Government Printing Office: The Journal of Research, published in four separate sections,

presents complete scientific and technical papers; the Technical News Bulletin presents summary and pre- liminary reports on work in progress; and Basic Radio Propagation Predictions provides data for determining

the best frequencies to use for radio communications throughout the world. There are also five series of nonperiodical publications: Monographs, Applied Mathematics Series, Handbooks, Miscellaneous Publications,

and Technical Notes. A complete listing of the Bureau’s publications can be found in National Bureau of Standards Circular

460, Publications of the National Bureau of Standards, 1901 to June 1947 ($1.25), and the Supplement to National Bureau of Standards Circular 460, July 1947 to June 1957 ($1.50), and Miscellaneous Publication 240,

July 1957 to June 1960 (Includes Titles of Papers Published in Outside Journals 1950 to 1959) ($2.25); avail- able from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.
NATIONAL BUREAU OF STANDARDS REPORT

ms PROJECT nbs report

1009-11-10491 7523

STANDARDIZATION OF THERMAL EMITTANCE MEASUREMENTS

PROGRESS REPORT No. 15 , January 1 • March 31, 1962

Contract No. DO 33(616) 61-02

Task No. 73603

The two phases of: this project are conducted under the supervision of

the following persons, who have approved this project.

Horace M. Joseph

Electronic Englne^xj/

flU **’ ~r-- Datd'rrocessing Systems Division

_ William N. Harrison - Coordinator

^Chief, Metallic Building Materials Section, Buildings Research Division

NATIONAL BUREAU OF S

intended for use within the to additional evaluation and

listing of this Report, elthei the Office of the Director, F however, by the Governmen

to reproduce additional cop

t©

AERONAUTICAL SYSTEMS DIVISION

All FORCE SYSTEMS COMMAND

UNITED STATES AIR FORCE

WRIGHT-PATTERSON AIR FORCE BASE, OHIO

IMPORTANT NOTICE

progress accounting documents Approved for public release by the jrmally published it Is subjected

Director of the National Institute of ’’ f

! eproduction ' °! open-literature

ssion is obtained In writing from Standards and Technology (NIST) such permission Is not needed, on October 9, 2015. 1 prepared if that agency wishes

<NBS>

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NOTICES

When Government drawings, specifications, or other data are used for

any purpose other than in connection with a definitely related Government

procurement operation, the United States Government thereby incurs no responsibility nor any obligation whatsoever; and the fact that the

Government may have formulated, furnished, or in any way supplied the

said drawings, specifications, or other data, is not to be regarded by

implication or otherwise as in any manner licensing the holder or any

other person or corporation, or conveying any rights or permission to manufacture, use, or sell any patented invention that may in any way be re- lated thereto.

This document may not be reproduced or published in any form in whole

or in part without prior approval of the Government. Since this is a progress report, the information herein is tentative and subject to changes,

corrections, and modifications.

I

SUMMARY

The work of preparing and calibrating working standards of normal

spectral emittance is proceeding, with no serious hindrance.

The data-processing equipment was delivered and installed. Several

minor malfunctions were discovered, and some of them have been corrected.

The task of correcting the remaining deficiencies is continuing, and proposed modifications offer promise of providing the means whereby the equipment will meet the design specifications.

II. INSTRUMENTATION

A. Normal Spectral Emittance Equipment

Two new photomultiplier detectors for use in the short wavelength

portion of the spectrum were received during the quarter. These are identified by the manufacturer as types 9528B and 9529B. These tubes have been

reported to have adequate sensitivity over the spectral range of Q.3 to 1.0\

microns. The voltage divider and amplifier modifications required to use the

2529B tube were designed and constructed.

An indium antimonide detector was procured. This detector is reported

by the manufacturer to have a usable spectral range of 0.6 to 7.6 microns.

Preliminary tests have indicated that this detector does not have sufficient

sensitivity for use with the equipment at hand.

The necessary changes in the amplifier circuits were made, and the

data-recording and processing attachment was connected to the spectralemittance equipment.

III. CALIBRATION OF WORKING STANDARDS

A. Oxidized Inconel Specimens

Inconel specimens were prepared for use as working standards of normal

spectral emittance. The specimens were machined from 0.053 inch Inconel

sheet, and were cleaned with acetone to remove any oil or grease from the

machining operation. They were then marked for identification, and sandblasted with 60-mesh fused alumina grit at an air pressure of approximately

70 psi. They were cleaned ultrasonically in acetone, passivated for one minute in 10% nitric acid at 316°K (110°F), rinsed in distilled water, and

then acetone. They were placed in a cold furnace, which was brought to

1340°K and held for 24 hours; the temperature was then reduced to 1100°K

and held for 24 hours, after which the specimens were allowed to cool in

the furnace.

1

About half of the measurements required in calibrating the Inconel

specimens were completed during the quarter.

B. Oxidized Kanthal Specimens

The search for a suitable material from which to prepare working standards

of intermediate spectral emittance, and the treatment and testing of specimens

to determine their stability, has been described in several previous reports.

During this report period, Kanthal that had been polished and then oxidized

was rejected as unsuitable for this purpose. It was found that the oxide layer

chipped from such specimens after heating in air for periods of 600 hours or more, and that the interference peaks mentioned in previous reports shifted to

longer wavelengths with continued heating of the specimens in air.

On the other hand, the spectral emittance curves of Kanthal that had been

sandblasted prior to oxidation did not exhibit the interference peaks found

with the pre-polished specimens, and the oxide did not chip from the sandblasted specimens that were heated for up to 800 hours at 1300 K. Specimens

that had been oxidized for periods of 400, 600 and 800 hours, respectively,

showed differences in emittance of less than ± 0.03, and no consistent trend

of spectral emittance with time between 400 and 800 hours of heating in air was observed. In view of these facts, sandblasted Kanthal that had been oxidized for 400 hours at 1300°K was selected for use as the working standard of

intermediate emittance. Specimens of the various sizes and shapes required

were prepared, by the same procedure as that outlined above for Inconel.

IV. DATA- PROCESSING EQUIPMENT

The data-processing attachment was delivered on February 12, and was installed by a representative of the manufacturer. Fig. 1 is a photograph of

the installed equipment.

A. Principles of Operation

The data-processing equipment was designed to perform the following functions: (1) to produce a corrected graphical record of the normal spectral

emittance of a specimen as a function of wavelength, (2) to record in digital

form on punched paper tape the corrected spectral emittance values, for possible use in a separate electronic digital computer, and (3) to accumulate the

digitalized emittances at wavelengths which have been preselected to yield

specific information as described further in this report.

The direct input to the data-processing attachment, in the form of electrical potential, is proportional to the apparent emittance of the specimen;

that is, the emittance that would be recorded by the spectrometer without benefit of the data-processing attachment. This signal is corrected for systematic

instrumental deviations on the basis of previous calibration tests. The re- sulting record tends to be systematically correct, with only random instrumenta

tion and digitalization errors remaining.

The spectrometer generates two d.c. potentials, one, I proportional

to the flux reaching the detector by way of the comparison (blackbody) beam,

and the other, I

s , proportional to the flux reaching the detector by way of

the specimen beam. The apparent emittance is the ratio of the latter potential to the former. When the instrument is operated with the Function

Selector Switch in the "bypass" position (see figure 2), thus bypassing the

data-processing attachment, the ratio is measured by applying the I c potential to the slidewire of a potentiometer recorder, and balancing the I

s potential against the potential of the potentiometer arm. The I

g potential

is recorded on the chart as a decimal fraction of the I c potential, representing the apparent (uncorrected) emittance as a function of wavelength. ,

However, the optical paths of the two beams in the spectrometer are not

quite identical, and somewhat different fractions of the flux in the two

beams are measured. This condition is compensated by the data-processing

attachment, as described below.

The position of the recording potentiometer arm is digitalized by an en- coder which is actuated by the arm shaft. The encoder comprises two axially

centered discs, one stationary and one shaft-mounted. Each disc is made of

transparent material, to which curved, but nearly radial, opaque stripes of a black coating have been applied. A source supplies -light which is alternately

passed and blocked as the movable disc rotates. This light is sensed by

photoelectric cells, so placed that one cell receives light first when the

movable disc is rotated in the clockwise or "upward" direction, and the other

cell receives light first when the direction of rotation is reversed. A

directional flip-flop is operated by the pulse from the cell first detecting

light. A pulse is produced for each increment of rotation corresponding to

0.1 scale division on the chart, or 0.001 in emittance. The pulses are counted in a reversible counter that is gated so that it increases in count

when actuated by pulses received in the forward direction of the flip-flop,

and decreases in count when actuated by pulses received in the opposite

direction. The drum dial position, which determines the position of the

Littrow mirror and hence the wavelength of the radiant flux being measured, is

also digitalized in the same manner and the resulting pulses are counted.

This dial is driven by a synchronous motor. Since the magnetic tape in the

tape recorder is likewise driven by a synchronous motor, the two speeds also are

synchronous. The tape is a 16-mm wide, four-channel type, perforated along

one side and driven by a sprocketed capstan to prevent slippage.

One source of error in the apparent emittance values is deviations in the

#9 10Q7o line", which result from differences in loss of effective flux along

the two optical paths. A second source is deviations in the "zero line", due

to stray radiation in the monochromator, which produces a spurious X signal

when there is in fact no flux in the specimen beam.

— 3 —
‘
To correct the deviations in the 100% line, the reference blackbody furnace is substituted for the specimen, and its apparent spectral emittance is

recorded with the equipment connected as indicated by the block diagram,

figure 3. The data-processing equipment records the pulses from the potentiometer shaft encoder on two channels of the magnetic tape, the pulses in the

"upward" direction on one channel, and those in the "downward" direction on the other. Only the change in position of the potentiometer, not the position

itself, is recorded. For this reason it is necessary to note and record the

reading on the potentiometer at the start of the 1007»-line calibration.

The same procedure is used to record the zero-line deviations on another

pair of magnetic tape channels, except that the specimen beam is blocked near

the specimen furnace. The initial value must also be noted and recorded, as

in the case of the "1007» line."

When a specimen is under test, each digitalized value of apparent emittance is corrected automatically for deviations in the 1007. line and the zero

line, respectively. The correction for the former is made by feeding the I potential to the 1007,-line potentiometer, connected as indicated in figure 4.

The arm of this potentiometer is driven by a ratchet motor, actuated by two

monostable multivibrator circuits, one for each direction of rotation. During the determination, the previously recorded magnetic calibration tape is

played back synchronously with the wavelength drive , the pulses from the upward channel driving the arm of the potentiometer upward, by increments of

0.17o, and the pulses from the downward channel driving it downward an equal

amount. The 1007»-line potentiometer has the same overall resistance as the

recorder potentiometer (4680). Before the spectrometer is started, the 10070-

line potentiometer is set to the value that was recorded at the start of the

1007o-line calibration. The 1007o-line potentiometer, as controlled by the

magnetic tape during playback, modifies the Ic signal to a value representing

the Ir signal at the same wavelength that was recorded during thfe 1007o-line

calibration. This modified potential is applied, through an isolating unitygain amplifier, to the high-voltage end of the slide wire of the recorder

potentiometer. Thus the ratio measured by this potentiometer is I s /lr, a value which has been corrected for the "1007o-line error."

The zero-line correction is made through a similar zero-line potentiometer, connected as shown in figure 5, and driven by a similar ratchet motor

and multivibrator circuits, actuated by pulses from the zero-line channels on

the magnetic tape. The zero-line potentiometer also is set at the value that was recorded at the start of the zero- line calibration before starting the

spectrometer. The zero- line potentiometer, as controlled by the magnetic tape

during playback, produces a signal representing the I 0 signal at the same wavelength that was recorded during the zero- line calibration. This signal is

applied, through a similar isolating unity-gain amplifier, to the low-voltage

end of the slidewire of the recorder potentiometer, maintaining it above

ground potential. The net effect of this adjustment is to subtract this zero- line potential from both the corrected Ic (=Ir ) potential and the I 8 input

potential, thus compensating for the zero-line error.

The potentials from the 100%-line and zero-line potentiometers are applied to the recorder potentiometer through isolating unity-gain amplifiers

to prevent reduction in potential due to load. A block diagram of the equipment during a specimen run is shown in figure 6.

Figure 7 is a photograph of a portion of a recorder chart, showing the

recorded "1007c line", "specimen line" and "zero line." In manually computing

the emittance of a specimen at any wavelength from such a chart, the height of

a "specimen line" above the "zero line", designated AE S on the chart, is divided by the height of the "1007c line" above the "zero line", designated as the distance AEgg on the chart. This computation Is repeated at each wavelength of interest, usually at 100 points in the wavelength range of 1 to 15

microns. The pips in the lines on the chart are wavelength markers, and occur

at each 0.1 revolution of the wavelength drum (hence do not represent equal

wavelength intervals). An extra pip appears at 0.95 revolution of the drum to

Identify the number of revolutions.

B. Mathematical Analysis of Operation

The operation of the data-processing equipment may be analyzed mathematically as follows:

Let I c = comparison blackbody signal

X r = reference blackbody signal

I Q = zero signal (spurious signal received when specimen beam is

blocked)

I s = specimen signal

Wg = radiant flux from blackbody entering the optical system to produce I c or I . (The flux from the reference and the comparison

blackbody furnaces is equal since they are at the same temperature.)

Ws = radiant flux from specimen entering the optical system to produce I . © Note: All of the signals, I c , X r, I Q and X s , appear as potentials in the

output of the spectrometer amplifier, before entry into the potentiometer re- corder or data-processing attachment.

a = proportionality factor between flux entering specimen beam of

spectrometer and signal produced- Wg = a I r, Ws = a I

g

.

Note: All of the above terms are functions of wavelength, X., and all are referred to at a specific value of X., but for simplicity, the subscript X. is

omitted in the mathematical treatment that follows.

- 5 -

Let us first consider what is needed, in terms of signals, to give the

true emittance of the specimen. The zero signal, I Q, is measured only in the

specimen beam of the spectrometer and is assumed to have the same spectral

distribution for the reference blackbody and for the specimen at the same temperature. Also, the reference blackbody and the specimen are interchanged

for measurement in the specimen beam. Therefore, for

specimen beam,

each wavelength of the

ii 2s3 a (Ir

- I 0 ) (1)

and W

s = * ds - i 0> (2)

Since the spectral emittance, E, is defined as

E = Vm

b

(3)

the desired equation, in terms of signals, becomes

E =

(I, - Io)

(Ir

- Io)

(4)

The factor a cancels out, and need not be considered further.

However, the spectrometer is used as a double-beam instrument, which

measures the ratio of the signal from the specimen beam to that in the com- parison blackbody beam, and we must work with these instrumental ly obtained

ratios to obtain the desired corrected emittance values.

First, assume that I = 0. Then, from equation (4),

E = I

s /Ir (5)

The output of the spectrometer is the position of the recording potentiometer arm, which represents the ratio of the signals from the respective

beams in terms of the fraction, f, of the total range of the arm. This

fraction, f, may also be recorded on a strip chart as a decimal fraction.

During calibration, see figure 3, the two signals are I c in the comparison beam and I r in the specimen beam. Consequently,

f* = ^

(6)

I C

This ratio, f', is recorded as the "100% line" on the magnetic tape, and may

also be recorded on the chart, during the 100% calibration. During the testing

of a specimen, in which the automatic data-processing attachment functions to

make automatic corrections, the playback from the magnetic tape controls the

position of the arm on the 100%-line potentiometer in the attachment to the

fraction, f', of its range, while the potential applied to its slidewire is

the signal I c

„ Hence the output of the 100%-line potentiometer is

( 7 ) c which is applied to the recording potentiometer slidewire by the amplifier.

The signal input is I , and for this condition

s f" =1/1 (8)

s r the corrected spectral emittance, for 1=0. o The situation is more complex when I > 0^ as it usually is. In figure

5, the potential from the 1007o-line potentiometer, which was shown in equation

(7) to be equal to I is applied to the top end of the recording potentiometer

slidewire. The potential from the zero-line potentiometer is applied to the

bottom end of the slidewire. This potential is equal to I Q , as is shown by

the following treatment.

During zero-line calibration, the position, f

1 * * , of the arm on the re- cording potentiometer is

f" = I /I (9) 0 c During playback, the position of the arm on the zero-line potentiometer is

controlled by the signals from the magnetic tape to the fraction, f ,M

, of

its range, while the potential applied to its slidewire is a constant voltage,

K, representing I c

. It should be noted that the slit servomechanism of the

specrometer automatically opens and closes the slits of the monochromator to

keep I c constant during a test.

The potential drop across the recording potentiometer slidewire is thus

X r

- I0 . The potention, X s , is balanced against the arm potential:

I 0 + f ,,89(l r

- I 0 ) = I

s (10)

1 - I consequently f

1 ’ 1 ’ = — — (11)

I - I r o

the spectral emittance corrected for both absorption and stray radiation,

see equation (4).

Since equation (11) involves signals from a blackbody furnace and a specimen at the same temperature and at the same source position (the effect

of the signal I from the comparison blackbody haying been cancelled out in

derivation of tfie expression) the proportionality factor, a, is in both

numerator and denominator, hence cancels out, as was shown in equation (4).

- 7 -

The emittance, or appears as a shaft position of the recording

arm and pen which is encoded as before. The results are counted in the re- versible counter. The positions of the counter are punched in Friden Programmatic Single Case Code on paper tape at preset intervals of drum rotation.

The counter numbers are also accumulated , in the electronic accumulator, at

other preset intervals. The results shown by the recording pen counter, the

digitalized drum dial counter, or the accumulator can be selected for display

as decimal digits. These digits are punched in a word group whose first four

characters are the drum dial division numbers. The latter three are the pen

position digits. The most significant digits are first. The eighth character

is always a "Carriage Return."

The preset wavelengths for punching and addition are selected separately.

These intervals for punching are each

1/2 drum dial division,

1 drum dial division,

2 drum dial divisions

5 drum dial divisions,

or 10 drum dial divisions, as desired.

The increments between successive wavelengths at which spectral emittance

values are to be accumulated are pre-recorded on punched paper tape. The tape

is read into the data-processing equipment during a determination by the tape

reader. The method of coding the tape is explained below.

The theory of the selected ordinate method of computing total emittance,

or absorptance for radiation having any known spectral distribution of flux, was explained in WADC Technical Report 59-510. In brief, the total flux

from the source (blackbody at the temperature of the specimen for total emittance) is divided into N equal parts, and the wavelengths bracketing the intervals between \ = o and \ = 00 within which the respective 1/N fractions of

the flux lie, are established. The N wavelengths at which the normal spectral

emittances are to be accumulated are the median wavelengths of the N intervals

The total normal emittance is then 1/N times the sum of the normal spectral

emittances at the N wavelengths.

C. Preparing Punched Paper Tape

Punched paper tape is required to trigger the accumulator to sum the

readings of corrected emittance for the purpose of using the selected ordinate

method of computing total emittance (or absorptance). It is first necessary t determine the wavelengths at which the accumulation is to be performed, and

then to record these values on punched paper tape in the proper manner. The

method of selecting the wavelengths was outlined briefly above.

After the proper wavelengths have been selected, they are processed as follows:

1. Convert the selected wavelengths, into wavelength drum positions,

by means of a calibration curve, to the nearest 0.2 dimension on the scale

(1/500 of a revolution of the wavelength drum)

2. Compute the increments between successive wavelength drum positions,

in units of scale divisions and fractions.

3. Multiply the increments by 5, to get them into integral numbers of

1/5 scale divisions.

Note : The first increment is that between the starting position of the

wavelength drum and the position corresponding to the first preselected wavelength.

4. Convert the integral decimal numbers obtained in 3 to three-digit,

hexa-decimal numbers; i.e., base 16 numbers. The digits in this system are

0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, F. The number 108 xq then becomes

06Ci6> or 3118io becomes C2Ei£.

5. Form the F complement of these numbers, i. e., subtract the number from

FFF . Thus 108^o = 06Ci£ becomes F93i£, and 3118^q = C2E^ becomes 3D1^.

(An alternative procedure is to subtract the original 'number in decimal form

from 4095, and convert the difference to hexa-decimal numbers. Thus for 108 ^q

4095 10 - 10810 = 3987

10 = F93

lf

.

and for 3118^0

4095io " 311810 = 977 10 = 3D1 16 .)

6. Prepare a 9-channel punched paper tape in word groups of 4 characters

each. The first character of the word is a Carriage Return and the following

one is the least significant digit of the hexadecimal number, followed by the

middle digit, followed by the most significant digit. For the two examples, one would type for 108.^

C 39F

R

and for 3118^

R

1M •

For use, the punched paper tape is inserted into the paper tape reader,

and the wavelength drum is set to the starting position. The accumulator se- lector switch is set to the tape reader position, and the tape reader is turned

on. As the spectrometer traverses the spectrum, the tape reader will trigger

the accumulator circuit each time the wavelength drum has advanced an amount

equal to the recorded increment. The paper tape reader automatically advances

the tape one position after each accumulation.

9

D. Current Status

The electronic data-processing equipment was installed during the week

following delivery by a representative of the manufacturer. The functions of

counting the pulses from the recording pptentiometer shaft encoder, and from

the accumulator, were each checked and found to operate properly. The calibration tape punch produced the correct numbers. The separate controls for

accumulation and punching by fixed increments and by reading from a prepunched tape were checked, and the events occurred at the expected times.

However, the magnetic tape reel held only about 300 feet of tape and the

tape drive ran so fast that calibration runs were limited to about 8 minutes,

compared to approximately 32 minutes required for a complete traverse from 1 to 15 microns. Although the tape was not long enough to be operationally

useful, it could be used in checking the operation of the equipment. Larger

reels and a 1200- foot tape were procured for use with the equipment, which

permits calibration runs of approximately 32 minutes.

A number of check tests of the equipment were made, and several tapes

were punched. One tape was plotted on a digital- type plotter. Intermittent

troubles soon appeared, which indicated that reliable results could not be

obtained. For instance, the drum dial counter and accumulator did not advance

the more significant digits as they should, and the recording potentiometer

counter jumped counts abruptly. It was not possible to set the (analog) isolating amplifier input voltage to the proper value when the counters operated

properly. Later the punch did not operate.

The manufacturer was informed of these developments, and sent a representative to remedy the difficulties. The tape drive motor was replaced with

one operating at half the speed of the original, which increased the time

available for calibration runs to about 64 minutes. Diode gates were added

to prevent counts from occurring during sign reversal. Some additional

grounding was added, but the difficulty of setting the initial voltage of

the d.c. isolating amplifiers and their rapid drift after adjustment, and

the troubles due to the effect of variable contact resistance in the switches

within the signal path have not yet been corrected. The remaining difficulties appear to be comparatively minor in nature, but they prevent obtaining

usefully accurate results with the new attachment, prior to their elimination.

The manufacturer is aware of these troubles, and has agreed to correct them

in the near future.

10

V. MATHEMATICAL EQUATIONS

In furthering the approach mentioned in the preceding report, namely the

assumption that more than one "family" of free electrons governs the emissive

properties of platinum within the wavelength range covered by experiments

reported herein, additional numerical experiments were carried out during the

report period. These experiments indicated that a better fit of the spectral

emittance curves could be obtained from the equation (see WADC Tech. Rept.

59-510, Part III, equations 2, 3 and 4) than when only one family of free

electrons was considered. An attempt to find the best values of the parameters

describing the two free-electron families was begun. Numerical experiments

dealing with bound- electron families were continued.

11 USC0MM-N13S-DC


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U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A. V. Astin, Director THE NATIONAL BUREAU OF STANDARDS

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., and

Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering in the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover. WASHINGTON, D. C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements

Dielectrics. High Voltage.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.

Mass and Scale. Volumetry and Densimetry.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pine Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research. Crystal Chemistry.

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls. Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standards and Research. Dental Research.

Metallurgy. Engineering Metallurgy. Microscopy and Diffraction. Metal Reactions. Metal Physics. Electrolysis

and Metal Deposition.

Inorganic Solids. Engineering Ceramics. Glass. Solid State Chemistry. Crystal Growth. Physical Properties.

Crystallography.

Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materials. Codes and Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Bunding Materials. Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Operations Research. Data Stocessing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

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Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation. Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Molecular Kinetics. Mass Spectrometry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering Laboratory. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical Services. CENTRAL RADIO PROPAGATION LABORATORY

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical Soundings Research.

Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Modulation Research. Antenna Research. Navigation Systems.

Upper Atmosphere and Sftace Physics. Upper Atmosphere and Plasma Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

RADIO STANDARDS LABORATORY

Radio Physics. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency and Time-Interval

Standards. Millimeter-Wave Research.

Circuit Standards. High Frequency Electrical Standards. Microwave Circuit Standards. Electronic Calibration Center.