JOURNAL OF RESEARCH of the National Bureau of Standards-C. Engineering and Instrumentation Vol. 66C, No.3, July- September 1962 Method of Measuring of Metals in the * Arthur G . Maki and Earle K. Plyler

(April 20, 1962)

A method of measuring normal spectral emissivities in the infrared region from 1 to 13 J1. is described. It consists of comparing the rate of emission of from a blackbody with that from the specimen. The two observed are made equal by adjusting the temperatures. An equation is derived for use in calculating the for the observed temperatures. The main sources of error arise in the measure­ ment of the temperature of the specimen and the temperature of the blackbody. As an example of the method, the normal spectral emissivity of gold has been measured in the range from 4 to 13 J1. at temperatures from 550 to 1,000 OK. The emissivity was found to range from 0.014 at 4 J1. and 550 OK to 0.0256 at 9 J1. and 1,000 OK A table is included which li sts the values of emissivity from 4 to 13 J1. and from 550 to 1,000 OK at intervals of 50 OK.

1. Introduction 2 . Experimental Procedure The normal spectral emissivity of many metals The experimental arrangement consisted of an such as gold, platinum and aluminum is very low infrared spectrorarliometer with a sodium chloride in the infrared region from 4 to 13}./,. Some meas­ prism and thermocouple for m easuring the rate of urements have been carried out fl,t high temperatures emission of energy in the region from 1 to 13 }./,. in the visible spectrum [1-4]/ but in A double pass optical system was employed so that the infrared spectrum to 13 }./, have not been under­ the stray rfl,diation would be greatly reduced. The taken. The emissivity of metals in the infrared may spectroradiometer was calibraLed for wfl,velength be calculated from the reflectivity, R, using the settings with the absorption bands of polystrycne, Kirchhoff relationship CO2 and H 20. Rather large spectral slit widths were used in this work varyi ng from 0.18 }./, at 2 }./, to €= 1- R. 0.1 }./, at 10}./,. However, since neither the blackbody curve nor the emitted-energy curve of the specimen has a very large second derivative with respect to For this calculation measurements made , the emissivity values which were deter­ at room temperature are availfl,ble from several mined were nearly independent of the slit width sources, but in most cases the reflectance measure­ used. A blackbody and the specimen to be measured ments are only good to about ± 1 percent thus giv­ were placed on a platform which could be moved ing rise to uncertainties of ± 5 to ± 50 percent for so that the specimen or the blackbody radiated on the calculated emissivities of most metals. A note­ the entrance slit of the spectrometer. This general worthy exception to this is the recent very accurate type of arrangement has been used in previous work reflectance meaSUl'ements made by Bennett and and a more detailed description of the procedure can ; Koehler [5] on aluminum. In addition Harris and be found elsewhere [8]. Fowler [6] and Lameris [7] have made some very An essentially different method of comparing the good measurements on gold. from the blackbody and the specimen has While this paper is primarily concerned with the been devised. This method consists of adjusting the development of a method for measuring the spectral radiance of both sources (at the same wavelength) emissivity of metals, some results are reported on to be nearly equal. The effect of nonlinearity of the the normal spectral emissivity of gold in the infrared detector amplifier response is minimized by this spectrum from 4 to 13}./,. A method of measuring procedure. Since the measurements were to be the spectral emissivity of metals will be described made on metals of low emittfl,nce, this required that in the next section. the blackbody be at a lower temperature than the specimen. In order to reduce the elTor of ambient change to a minimmn, alLernate readings were 'This work was supported through a contract with Redstone Arscnal. made on the blackbody and specimen during a small 1 Figures in brackets indicate the literature references at the end of this paper. time intervfl,l. 283 The emissivity calculations were based upon the Combining terms we obtain, following equations. If we define N b(A, tb) - Nb (A, tT) Nb(l' b) = rate of emission of radiant energy by a (10) blackbody radiator at temperature tb Nb(A , t s) - Nb (A, t T)' within the wavelength interval A± dA per unit of time, area, and , The values of Nb (A, t) in eq 10 can be evaluated Ns(Ats) = rate of emission of radiant energy by the from tables of blackbody radiation or calculated specimen at temperature ts within the from the relation. wavelength interval A± d).. per unit of time, area, and solid angle, N(A, t) Es(At s) = emissivity of the specimen at temperature t. for the wavelength interval A± d).., where tT = room temperature, ts=specimen temperature, O2=1.4380 cm °I\:' The constant 0 1 cancels out. tb= blackbody temperature, tm=monochromator and detector temperature, 3 . Discussion of Possible Errors R b(Atb) = reading of instrument set to view black­ body at temperature tb, Since the emissivity of a metal is a quantity R.(At.) = reading of instnUl1ent set to view speci­ intrinsic to the substance one may consider sources 1" men at temperature ts; of error as divided into two categories: (1) deviation then, of the sample from the ideal, and (2) experimental (1) errors. and The first type of error may generally be attributed to impurities in the metal sample and/or nonideal R . ().., ts)=k2{[N.().., ts)-N b( ).. , tm)] surface effects peculiar to the specimen. It is believed that the purity of our specimen was not a ' +[l - E.(A, t s)] N b().. , t,)}. (2) source of error. The gold ribbon which has been measured by this method was part of a sample which Here kl and k2 are proportionality constants and had been tested by spectral analysis and found of kl = k2 in this method. high purity. The specimen surface was mirror smooth. It has been shown [9] that small surface Also, irregularities can cause rather large changes in the emittance characteristics. However, at the longer N.(A, ts)+ [I - Es().., t s)]Nb ().., t T ) of infrared radiation the emissivity is N s(A, t.) - N ().. , tm)+ [I-Es(A, t s)] N ().., tT) much less sensitive to small surface irregularities b b than at the shorter wavelengths of visible radiation. N b().. , tb) - Nb ().. , t m) The smooth appearance of the surface when viewed by visible was taken as an indication that the [N ().., tb)-N ().., tm)]+N ().., t ). (3) b b b m surface is practically optically smooth in the infrared By substitution, region and that the errors due to surface roughness are negligible. Because of the inertness of gold no surface oxide coa ting is possible. To remove any other possible surface layers the specimen was washed with dis­ -[I - Es(A, ts)]Nb(A, tT)' (4) tilled water and acetone and then heated to 800 oK Let for several hours before use. After this initial treat­ R s(A, ts) ment the samples were maintained at temperatures 1· (5) above 100 °C until the measurements were com­ R b ().., tb) pleted. As a consequ ence it is felt that the state of Then the surface of the specimen was nearly ideal. There N s().., ts)= Nb(A, tb)-[I - Es(A, ts)] Nb(A, tT)' (6) is of course some question as to the crystal structure of the optically in1portant region of the metal ncar By definition, the surface, but the manner in which this changes N s(A, t s) the emittance of m etals has not yet been established. E,(A, ts) (7) Nb(A, ts) Since the radiation observed was within 5 deg of From eq (6), normal to the specimen, polarization effects are negligible and were disregarded. N b( A, tb)- [I - Es(A, ts) ]Nb(A, tT) (8) Errors due to incorrect emissivity values assigned Nb(A, ts) to the specim en are more directly related to the or actual experimental measurements. In the emis­ sivity measurements the errors may be divided into ES(A, ts)Nb(A, t ,)=Nb (A, tb) three categories: (a) errors in wavelength measure­ - N b(A,tT) + E.(A,t.)Nb(A,tr ). (9) ment, (b) errors in energy , and (c) 284 enol'S in temperature measurements. The magni­ made of fine wires but even then there is some con­ tude of these errors will be discussed separately duction of heat from the specimen. When the speci­ belo"\' . men can be heated to high temperatures the tempera­ Wavelength Errors. With modern ins Lnmlenta- tUTe gradients can be evn,luated with an optical > tion and standard techniques of calibration it is a pyrometer. At lower temperatures the radiation relatively simple matter to calibrate infrared spec­ fro111 different areas of the specimen can be fo cused trometers to within 0.02 J1. over the entire range used on the slit of the spectrometer and temperature in this work. Inasmuch as both the blackbody gradients of the specimen can be detected and curve and the emissivity curve of the specimens are evaluated. In the applicaLion of this method to smooth curves with no sharp extremes or discon­ measurements on gold it wa fo und that the varia­ tinuities, eITors in wavelength hould be entirely tion of temperature was never greater than 5 deg K negligible in this work. The rather large spec­ over the area used. The error introduced in the trometer slit used at the shorter wavelengths, em.issivity by a 5 de~ error in temperature for a however, may introduce a nonneO'ligible error. The specimen at 800 OK has been calculated and the exact value of this error is difficult to determine and results are shown in figure 1. It will be no Liced that is in fact different for each wavelength and tempera­ the error is between 1 and 2 percent from 6 to 14 J1. , ture. It is estimated to amount to no more than but at shorter wavelengths the error increases 1 percent. rapidly reaching a value of 6 percent at 2 1-'. When Errors in Energy lvleasurements. The measure- the specimen is at temperatures above 800 OK, the 1 m en t of the energy given off by the specimen was uncertainty in the emissivity will be smaller than accomplished by comparison with a blackbody as tho e shown in figure 1 and the error will be grea ter described in the section on experimental procedure. for temperatures less than 800 OK. In making these measurements the temperatures A large source of uncertainty is introduced by were so arranged tha t the energy reaching the de­ errors in the temperature of the blackbody. This tector from the blackbody was nearly equal to that temperature should be measured to ± 1 0 K . When from the specimen. In this way instrumental errors the gold specimen is at a temperature of 800 OK, the due to amplifier or detector nonlinearity were blackbody is at 351 OK for equal energies being re­ practically eliminated. Almost all values reported corded at 10 J1.. In the above example a change of are the average of several determinations with 1 OK will produce an error of about 4 percent in the slightly different blackbody temperatures. emissivity. With an uncertainty of 5 OK in the The inlportant source of error in energy measure­ temperature measurement of the blackbody the ment is due to the signal to noise ratio. For measure­ elTors become much greater as shown for different ments at higher temperatures and at wavelengths wavelengths in figure 2. It should be noted that near the blackbody radiation maximum the signal large errors will be made in the determination of to noise ratio is of course very favorable and uncer­ emis ivities by this method unless the temperature tainties are quite negligible. For lower temperatures of Lhe blackbody is measured with an accuracy of and especially for measurements near the long or the order of 1 0 K . short wavelength extremes of this work the signal to noi e ratio becomes sufficiently small that rather large uncertainties arc introduced into the results. Because of the low energy levels involved in these measurements, especially at long wavelengths, stray radiation might be expected to cause appreciable errors. Use of a polyethylene-black filter to elimi­ nate any short wave stray radiation proved, how­ ever, that stray radiation is quite negligible even at the longest wavelengths measured. Errors in Temperature lvleasurement. In the de­ termination of the emissivity by the method of equal = = radiance, the most in1portant measurement is the =cu temperature. Four temperatures must be measured or contTolled j the temperature of the detector, the temperature of the room, the temperature of the specinHm, and the temperature of the blackbody. The temperature of the room and of the detector can be measured to better than 1 deg K and the errors introduced by these measurements are small com­ pared to the uncertainties in measurement of the temperature of the specimen and the blackbody. The temperature of the specimen is usually meas­ 1 ~ ____L- ____~ ____~~ ____~ ____~ ______~ ured by an attached thermocouple and when the 2 8 10 12 14 material is a metal with the form of a thin ribbon, WAVEL EN GTH, f-L

the thel'mocouple may be welded on the back sur­ FIGU RE 1. Error in emissivity measurement at 800 0 K resulting face of the specimen. The thermocouple should be from an e1'r01' in specimen temperature measurement of 5 oK . 285 20 ,------,------,------,------,------,--;---, temperatures are shown in figure 3. Experimental points which are the average of several deteI'mina­ 18 tions have been superimposed on the curves to shmy how closely the experimental values agree with the 16 smoothed curves. Data were obtained at 50 oK ",,14 temperature intervals so that much more data were used in making these curves than is shown in the figure. The small inCI'ease in the emissivity curve at 9 p, 10 is curiously unexpected, but appears consistently. This abnormality may be due to some unlmown, consistent errol' in the data, but all attempts to

6 ~ _____L ______~ ____~ ____~ ______~ ____~ eliminate it failed. Lameris [7] shows a similar rise 2 8 10 12 14 in his data at about 10 p, (he made no observations WAVELENGTH, p. between 7 and 10 p, ). There seems to be no other measurement of the FIGURE 2. En'or in emissivity measurement at 1,000 oJ( Tes1dt ­ ing fl'om an error in the blackbody temperature of 5 °Ie rmissivity or reflectivity of gold in the temperature range reported in this paper. Consequemly, the 4. Results only independent observations with which our results can be compared are the I'oom tempeI'ature The normal spectral emissivity of gold has been measurements for which reflectivity values are given measured over the spectral range from 4 to 13 p,. in references 5 and 6. By extrapolation of the Table 1 lists the values of emissivity determined by emissivity versus temperatme curves it is possible to this work. In order to make this table, smooth use the data of this work to obtain approximate curves of emissivity versus temperature at constant emissivity values at lower temperatures. The wavelength and emissivity versus wavelength at extrapolated values are tabulated in table 2. These constant temperature were drawn through the ob­ values are, of course, considerably less accurate than served experimental values. The table entries were those given in table 1 since the extrapolation is not then read from these curves. The I'esults for three very reliable.

TABLE 1. Normal spectral emissivity of gold

~ ~ Temp. 550 600 650 700 750 800 850 900 950 1000 ~ . ~o K -----~------4.0 ______. __ 0.014 0.0147 0.0158 0. 0169 0. 0181 0.0193 0.0206 0.0219 0.0232 0.02413 4.5 ______. 0142 .0151 .0163 . 0174 .0184 .0196 .0208 .0221 . 0234 . 0248 5.0 ______.0145 . 0155 .0165 .0176 .0187 .0198 .0210 .0223 . 0236 . 0249 5.5 ______.0145 .0155 . 0165 .0176 .0187 .0198 . 0210 .0223 .0236 .0249 6.u ______.0142 .0152 .0162 .0173 .0183 .0195 . 0208 .0221 .0235 .0249 6.5 ______.0150 .0160 .0170 .0181 .0193 .0206 .0220 .0234 .0249 7.0 ______.015 .0162 .0172 .0183 .0194 .0207 .0220 .0234 .0248 7.5 ______.016 .0169 .0178 . 0187 .0198 .0209 .0221 .0234 .0246 8. 0______.018 . 019 . 0197 .0206 . 0215 .0225 .0235 .0244 8.5______.019 .020 .021 . 0218 . 0225 .0233 . 0240 .0247 9.0 ______. 022 . 0228 . 0235 .0242 .0249 .0256 9.5 ______. 023 .0234 . 0241 .0248 .0255 10.0 ______. 022 .023 .0238 .0245 .0252 11.0______. 023 . 023 .024 . 024 12.0 ______. 023 . 024 13.0______.023

0.030 I ~ TABLE 2. Approximate emissivity of gold obtained by 1000 'K extrapolation f1'om higher temperatw'e values ;:: 0.025 5' ~OK 200 300 400 500 8i ~~ ------~ 800 'K 4 ______0.0073 0.0000 0.0108 0.0127 5 ______. 0083 .0099 .0117 .0135 6 ______.0082 .0098 .0115 .0133 0.015 I~ __ ...l..-___"______l ____ _'_ __ ...J.... ______l. __ .l_._ ...I..._~ 4 8 9 10 12 13 7 ______.0085 .0100 .0117 .0134 WAVEL EN GTH ,p. 8 ______. 0108 . 0123 .0138 .0154 FIGURE 3. Normal spectral emissivity of gold from 4 to 13 JL at 7'00,800, and 1,000 oJ(. Dashed line is theoretical emiSSivity at 800 OK calculated from Drude equations.] 286 5 . Discussion Cn,lculations based on the Hagen-Rubens equation give rise to values of the emissivity which are about It is of considerable interest to compare the 100 percent greater than the experimental values. observed emissivity values of metals to those pre- As Schulz [12] has shown, the cause of this dis­ > dieted by the classical free-electron model proposed crepancy i evident from an analysis of the assump­ by Drude [10]. Roberts has recently shown [11 ] tions made in the derivation of the Hagen-Rubens that Drude's original consideration of several classes equation. Calculation of the value of l' indicates of electrons in some cases give 1'i e to calculated that v is of the arne order of magnitude and in results more compatible with expe)'iment ; however, fact i slightly larger than 'Y. This means that this idea has not been used in this experiment. n~lc. MeasUl'ements of n andlc by Schulz for the According to the Drude model Lhe refractive index near infrared confirms the fact n~ le at a wave­ > (n) and the absorption coefficient (Ie ) may be repre­ lengLh of 1 J.L . Calculations using Druclo's equations 'lented by the two equations indicate that n doe not approach the value of lc except for rather large wavelengths (about 100 J.L ).

2 As a consequence it is not surprising that the Hagen­ 2 1. 2-1 2 Ne 1 n - e - - 27rm* 1/+ 1' 2 Rubens equation does not always yield correct values of the emissivity in the ordinary infrared and reglOn. On the other hand, if the Drude equations are used to calculate the emissivity, better agreement where with the measured values is obtained. The results of such a calculation for 800 OK are shown in figUl'e 3. These calculations assumed one free electron per atom and that the effective electron mass (m *) is N number of free elect)'ons per unit volume, equal to the usual electron rest JWl,SS. e= electronic chargc, m *= effective mass of electron, v Ireq uency, and The authors express their gratitude to William p= d-c electrical resistivi ty. F . Roeser for his helpful suggestions concerning A simplification suggested by Hagen and Rubens these measurements. Appreciation is also expressed is often used as a means oI making emissivity cal­ to Robert Thibault who performed the very tangible culations. This simplification rests upon the assump­ service of transforming most of the raw data into tion that v 4;:.1' and consequently is valid in the long values of emissivity. , wavelength (low ) region. This assump­ tion leads to the result that 6. References

[1) J . C. DeVos, Phy iea 20, 690 (1954). n = lc= (:v) 1/2. [2) R. D. Larrabee, J. Opt. Soc. Am. 49, 619 (1959). [3) D. T. F. Marple, J. Opt. Soc. Am. 46, 490 ( l956). [4] D. J. Price, hoc. Phys. Soc. (London) 59, 118 (1947). Substituting this in the equation for emissivity, [5) H. E. Bennett and \V . F. Koehler, J . Opt. Soc. Am. 50, 1 (1960). 2 [6) Louis Harris and Peter FOlder, J . Opt. Soc. Am. 51, 164 lc + (1- n)2 (1961) . lc2+ (1 + n)2' [7) P. F . Lameris [R. B. Dingle, Physica 19, 348 (1953»). [8) A. G. Maki, R. Stair, and R. G. Johnston, J. Research 64C (Eng. and lnstr.), 99 (1960). yields the result [9) H . E . Bennett and J . O. Porteus, J . Opt. Soc. Am. 51, 123 (1961). f= 2(pV) I/2_ 2(pv) + ... [10) P . Drude, Ann. Physik 14, 936 (1904). [11) S. Roberts, Phys. Rev. 118, 1509 (1960). With appropriate changes of units this becomes the [12) L. G. Schulz, J . Opt. Soc. Am. 44, 540 (1954). i more familiar Hagen-Rubens equation ,

f= 0.3 65 (f) 1/2-0.0464 ~,

where p = resistivity in ohm centimeters and (Paper 66C3- 104) A = wavelength in centimeters.

287 JOURNA L OF RESEARCH of the National Bureau of Standards-C. Engineering and Instrumentation Vol. 66C, No. 3, July-September 1962 Publications of the National Bureau of Standards *

Selected Abstracts work, usi ng ~o ly bd e num radiation, t o pressures of approxi­ mately 60 kllobars. Previously reported t ransit ions have been observed in silver iodide, potassium iodide bismuth Glass filters for checking perfor mance of sllectrollho tometer­ a nd thallium. The high p ressure forms and lattice p aram ~ integrator systems of co lor measure ment, H . J . K eegan, eters were found to be: AgI-f.c.c. (NaCI type), ao= 6.0 67A; J . C. Schleter, and D . B. Judd, J . Research NBS GGA KI-s.c. (CsCI type), ao = 4. 0!l 3A; TI-Lc.c. (NaCI type), (Phys. and Chem.) No.3, 203 (May- J une 1962) 70 cents. ao = 4.77SA; Bi structure not determined. T hese dataconfirm previous ,repor ts o.n t he high pres ure forms of AgI and IeI. A s~t of fi ve specially selected colored-glass fil ters to id entify van ables of m alfunctIO n of photoelectric recording spectro­ D ata on Tl a nd 131 are apparently reported for the first t ime. equipped with t ristimulus integrators have been The hi ~ h pressure m odifi cations were sLudied at t he following standardized on a n umber of spectrophotometers cor rected approx imate p res.s ures which arc not indicative of t he point foy all . kno:vn errors (wavelength, zero, 100 percent, sli t­ w!lere t~e transItIO n occur : AgI-3.3 kilobars, K I-20 kil obars, WId th, l nertla, back reflectance, and stray-energy). T o t hese Bl-~S kllobars, a nd T I-60 kilobars. The pres ure limit to standardized spectrophotometri c data defini te a mounts of wInch t he Ull1t can be used successfully has not been ascer­ these errors were deli berately introd uced and converted to tained. It is beli eved to be m uch higher than t he pressu res values and chromaticity coordinates of the reported . . The .present instrument is capable of prod ucing p owde ~' dIffractIOn patterns of materi als of relatively high ~nternat l onal Commission of Illumination system of color­ Imetry for Sources A, 13, and C. Similar reduct.ions show the scattenng power, giving data to 20 =35°. High baekground effects of sl it widths of 1, 5, 10, and 15 mjlJ i;nicrons on com­ on t he X-ray powder patterns is believed to ari se from puLed results both by t he selected-o rdinate method of 10 30 scattering by t he diamonds. T hi s background may obscure and 10 0 ordinates, and by the wpjgh ted-ordinate method of weak .di ffraction rings. T hi s effect may be reduced by 1, 5, 10, and 15 milli micron intervals. Duplicate sets of sereel1l ng, m onochromatization, a nd other improvements in t hese glasses have been evalu ated by visual comparison with experimental tech nique. thIS set of master sLan da rds, and are available as part of t he Standard Materials P rogram of the National Bureau of Light source for produc:ng self-reversed s pectral lines, Stand ards. By comparing the certified values of luminous J . Sugar, J . Research N B S GGA (Phys. and Chem.) No. 4- and chromaticity coordinates fo r a set of these (.htly-Aug. 1962) 70 cents. glasses with the values obtained on a particular inte"rator­ A new light so urce has been developed whi ch prod uces numer­ spectrophotometer combination, the type anri ext~nt of ous self-reversed lines in boLh t he first and second specLra of i nstrurnental errors may be evaluated . ra re-eart h elemenLs. It co nsists of a pulsed arc discharge wl th a peak current of 75 a mperes and an on-ti me of one milli­ Calibration of small gratin g spectrometers from 166 to 600 second per cycle. Re o ll a nce lin es are nearl y completel~ ' cm- I , L. R . Blaine, E. K. Ply ler, and W . S. Benedict, J . Re­ absorbed, a nd can be distin guis hed by this character. From search NBS 6GA (Phys. and Chem.) No.3, 223 (NJay-hme s pectrograms obtained with Lhi s light SOUTce. th e grou nd states 1.962) 70 cenls. of T b I a nd U IT were determin ed, and those reported for Yb I , Yb iI, Tm T, Tm If, a nd U I were confi rmed. I n order to provide standards for t he calibration of smal! g r at ~ ng spectrometers over the region from 166 to 600 cm- I , Thermal co nductivi ty of gases. I. The coax:ial cylinder cell , t raclllgs of t he spectr um of atmospheric water vapor are L . A. Guildner, J ReseaTch NBS GGA (Phys. and Chem.) presented. The lines are identifi ed and tabnlated. \Vavl'­ No. 4- (J u/!J-l l. ug. 1962) 70 cenls. numbers obtained from energy levels derived from the best available high-resolution spectra are given, together with an By combining appropriate geometric configuration and indication of their relative reliability. The best li nes are mathematical analysis wit h improved measuring techniques, believed accurate to ± 0.03 cm- I . t he cell constant of a coaxial cylinder thermal conducLivitv cell was determined within 0.1 percent. . A n analysis of t he rate of heat transfer in such a cell showed a P urification by automatic gas chromatography, M . Tenen­ way to treat t he data so t hat t he error con tribu Lio n of experi ­ baum and F. L. H oward, J . Research N B S GGA (Phys. and mental deviations from idealized condit ions is kept small . Chem.) No.3, 255 (May-J une 1.962) 70 ceflts. The principal considerations are: 1. That heat t ransport by convection is sig nifi cantly large A completely auton1 atic apparatus has been developed for t.he . preparat.ive-scale purification of c Otnpound ~ by gas­ in a dense gas. This transport was analy zed mathem atically liq UI d chromatography. A clock timer periodicall y activat es from basic principles . The agreement of experimental resu l. ts a PUml? t hat injects a ~amp l e into t he column. The recording with t he analysis indicated t hat t he expression s are valid a nd potentiOmeter on wIn ch t he chromatograph is traced has a t hat t he convective heat transport could be accounted for switch mou nted at t he upper m argin. Collection of t he puri­ with little more error t han was involved in t he precision of fi ed m ain component occ urs when t he recorder pen goes to the hl' at. transfer meaRurements. t he end of t he scale and t rips t he switch. The sensitivity of 2. That t he heat transfer in a vaeuum correspon ds to the t he detector bridge circuit is adjusted so t hat only the t race heat transfer by radiation and solid contacts in t he presence caused by t he m ajor component will activate t he collection of a gas. The uncertainty was that associated with t he process. accuracy of determining t he vacuum values. T olu ene, ethylbenze ne, a nd m esitylene were purified with 3. That other effects were small enough to be computed t he apparatus. Best results were obtained with toluene. a nd corrected for without increasing t he uncertainty of t he I n olle p ass through t he apparatus, 92 perce nt of t he impurities values of the t hermal co nductivity. were removed from t he t oluene a nd t he purifi ed product was collected at a rate of 25 ml of liquid per day. Thermal conductivity of gases. II. Thermal co nductivity of carbon diox:ide near the critical poin t, L. A. Guildner, J. R esem'ch N BS GGA (Phys. and Chem.) No. (hdy-Atbg. A diamo~d cell.f~r X-ray dift'raction studies at high pressures, 4- G. J . Plerman lll a nd C. E. Weir, J . Research NBS GGA 1962) 70 cents. (Phys. and Chem.) N o. 4- (J uly-Aug. 1962) 70 cenls. The t hermal conductivity of CO2 has been measured in 11 coaxial cylinder cell as a function of pressure over a range of A high pressure X-ray powder camera has been constr ucted. te mperatures from 3.66 to 75 .26 °C. P articular attenLion T he instrument has bee n found t o be useful for routing X-ra? was given to t he measurements from 1 to 9 deg C rt bove the 289 critical temperature at pressures closely spaced to include t he propagation over an irregular ground surface (phenomenon critical density. of albedo). The thermal conductivity of CO2(0), near t he critical point is very large compared to one atmosphere values around Currents induced on the surface o[ a conducting circular room temperature. At 1 deg C a bove the critical point t he cylinder by a slo t, G. I-I asserjian and A. I shimaru, J. R eseal·ch t hermal conductivity reaches a maximum at t he critical den­ N BS 66D (Radio Prop. ) No.3, SS5 (IVray-June 1962) 70 cents. sity. T his maximum is greater than t he maxima at higher This paper is a partial study of currents induced on circular, temper atures. At 75.26 °c, 44 deg C above t he crit ical conducting cylinders by narrow radiating slots. First, a brief temperature, lit tle unusual increase at t he critical density and general formulation of the r adiation fi elds of slots on was observed. cylinders is made. Then , t he problem of an infi nite axial The rate of heat transport by convection in t he critical region slot is examined t horoughly for all cylinder sizes. An ex­ is a lso very large. This problem was studied carefully in pansion for t he fields, very close to the slot, on large radius order t hat t he temperature differences u sed were restricted cylinders, is also obtained. Sample computations are made, to the region of laminar flow, and t hat appropriate extra­ for various ranges of cylinder radius, and the order of t he polation procedures were used to find t he rate of heat transfer errors is discussed . by t hermal con duction alone. The problem of a circumferential slot, of constant excitation, Also, at densities and temperatures away from the critical is also consider ed. An asymp totic expansion obtained for region, new t hermal conductivity values were obtained. t his case yields t he surface current distribution fo r values of axial distances t h at are small er t han t he square of t he cir­ Derivation of the r elaxation spectrum r epresen tation of the cumference of t h e cyli nder. m echanical response function, R. S. Marvin, J . Resemch N B S Since one of t h e objectives of this study is to determine GSA. (Phys. and Chem.) No.4 (J uly- Aug. 1962) 70 cents. mutual co upling between two slots on a cylinder, the last Relaxation spectr a have been used in both t he prcsentation section presents a formulation of the equivalent network in and interpretation of measurements of the mechanical prop­ terms of the surface and feed line currents. erties of rubberlike polymers. The interaction b etween an obliquely incident plane electro­ H indsigh t technique in machine tra nslation of n atural lan­ magnetic wave and a n electron beam in the presence of a guages, 1. Rhodes and F. L . Alt, J . R esearch N BS 66B s tatic m agnetic field of arbitrary stren gth, K . I-I. B. Wil­ (Math. and Math. Phys.) No.2, 47 (A pr.- J une 1962) 75 cents. h clmsson, J . Research NBS 66D (Rad1·o Prop.) No. ';,439 In the proposed system for autom atic syntactic analysis of (J uly- Aug. 1962) 70 cents. Russian sentences developed at the National B ureau of The purpose of the paper is to study th eoretically t he inter­ Standards, t he computer splits each Russian word into stem action between an obliquely incident plane electromagnetic a nd ending and combines the information obtained from these wave and an electr on b eam . We assume that a static mag­ two clements into a morphological description of the word, netic fi eld of arbitrary strength is present in the axial direc­ frequently containing several alternatives. The decision tion. among such alternatives is normall y made on the basis of M achine computations made for the case of a cylindrical " predictions" arising from preceding words of t he same electron plasma sh ow that resonances occur in t he back­ clau se. There are, however, cases in which no prediction scattering cross section as a function of the angle of incidence is available to account for a word, e .g., whcn thc object of of the plane wave. The dependence of the resonance angles a v erb occurs before the verb itself. I n such a case, instead on the plasma frequency for fixed gyro frequency suggests of t he usual prediction of t hc object, wc need "hindsight". a possibility to ut ilize t he results of the investigation for Also, It may happen t hat morc than one of t he morphological diagnostics of a cylindrical plasma. a.lternatives of a word agrees wit h predictions; or t hat a smgle morphological alternative agrees w ith several predic­ T he impedance of a ci rcular loop in an in fi nite co nducting tions; or t hat only one of t hem agrees, yet there is a suspicion m edium, M. B. Kraichman, J . Research NBS 66D (Radio that the agreement is spurious; or t hat no agr eement at all Prop. ) No. ,;, 499 (July-Aug. 1962) 70 cents. is found . It t urns out t hat t he alternating u se of predi ctio n Expr essions are derived for the resistance and reactance of a a nd hindsight techniques overcomes most of these tr oubles. circular loop of thinly insulated wire which carries a uniform current and is immersed in a conducting medium. The Graphs for determining the power of Studen t's t-test, M. C. result for the resistance is compared with that known for a Croal·kin, J . Research N BS 66B (Math. and Math. Phys.) circular loop in a spherical insulating cavity. No.2, 59 (A pr .- J une 1962) 75 cents. This presents char ts for determini ng t he operating Calibration procedures fo r direct-current r esistance a ppara­ characten stlcs of Student's t-test. For a fixed level of sig­ tus, P. P . B. Brooks, NBS Mono. 39 (Mar. 1962) 40 cents nificance a, the charts give constant contours of t he power The equipment and procedures used at NBS for the precise {3 depict ing t he number of obser vations plotted against a measurement of d-c r esistance are explained in detail. The function of t he differen ce in means. Both t he one-sa mple specifi c application of t hese procedures to the calibr ation of and t he two-sample (equal sample sizes) cases are t reated bridges and potentiometers is explained. It is expected t hat for all combinations of this paper will be of considerable help to the many company and governmental standardizing labor atories now being a = .01 , .02, .05, .10, .20 and established. {3 = .10, .50, .90, .95, .99 excep t (a,{3) = (. 10, .10), (.10, .20). T hermocouple m aterials, F . R. Caldwell, NBS Mono . 40 (Mar. 1962) 30 cents. The graphs were constructed for two-sided tests but within Thermocouple m aterials are considered that are used pri­ the given accuracy are equall y appli cable to one-sided tests. marily as immersion temperature sensors in the range from ° °C up. I ncluded are the eonvent.ional thermocouples that On the role of the process of r e fl ection in r adio wave propa­ have survived since t he beginnings of the ar t of t hermoelectric gation, F. du Castel, P . Misme, A. Spizziehino, and J . Voge, temperatur e measurement, newer noble m etal ther mocouples, J . Research NBS 66D (Radio Prop.) No.3, 273 (May-J une and thermocouples of refr actory metals for use in the extreme 1962) 70 cents. r ange for immersed sensors. Thermocouples for thermo­ Nature offers numerous examples of irregular stratification of electric generators are not considered, nor are the types com­ t he medium for t he propagation of radio waves. A study of monly used chiefl y in radiation receivers such as those con­ t he process of reflection in such a medium distinguishes be­ taining antimony, bismuth, and their alloys. Because of the tween specular reflection and diffuse refl ection . The phe­ wide use and increasing popularity of ceramic-packed thermo­ nomenon of t rans-horizon tropospheric propagation offers an couples in metal sheaths, they are included. example of t he application of such a process, necessary for Limitations of t he thermocouple wires are given as to range, t he interpretation of experimental results. Other examples stability, environment including atm osphere, magnitude of are t hose of ionospheric propagation (spomdic-E layer) and t hermoelectric emf, and accuracy of commercially available


------materials of standard and extra quality. I n addition, prop­ fading, which have appeared in t he literature through 1960. erties of the separate elements that are per tinent to t he selec­ The primary emphasis is on a n oblique incidence propagation, tion or use of thermocouples have been compiled. Among although many a rticles pertaining to fading at vertical and these are: chemical behavior, mechanical p roperties, specific near vertical incidence (incorporating winds experiments) are heat, density, thermal conductivity, thermal coefficient of also included . No effort was made to include the fading and expansion, emissivity, electrical resistivity, and magnetic and scintillation studies in t he literature of radio astronomy a nd catalytic properties. satellite propagation, where they pertain to determining t he In the case of t.he ceramic-packed thermocouples the foll ow­ characteristics of the ionosphere, and not to MY and HF ing properties are presented: temperature range of thc sheath, communication. mcchanical properties of the sheath, kinds of packed ins ula­ Information is avail able on t he origin of fading, t he approxi­ tion, resistance between t hermocouple wires and between m ate dependence of fading rate on distance and frequency, wires and sheath, minimum bending radius of the packed a nd t he a mplit ude distributions fo r particular transmi ssion stock, gas-tightness of the packed insulation, and types of paths. This info rmation is, however, not sufficient either for measuring junctions available, i.c., groundcd, ungrounded, a realistic estimate of the performance of communication bare, t otally enclosed, stagnation mounting, etc. systems or for signal design co nsistent with the medium Not all of the above information is presented for all thermo­ statistics. couples, but all that is readily available in the general litera­ With respect to communication systems at MF and HF, ture catalogs, and by private communication is included. information which is needed for a nalysis a nd design includes Limitations on use of thermocouples normally are given in statistics on the ampli tude di stribution and the fade rate, the text, a nd properties of t he materials generally are pre­ depth, a nd duration. Such in formation should be obtained sented in tables. as a function of p ropagation mode, frequency relative to t he predictable MUF, ti me, season, geographic loeation, and A transistor-magnetic core digital circuit, E. W. Hogue, su nspot cycle. NBS T ech. Note 113 (PB161614) (1961 ) $3.00. A digital amplifier of simple noncritical design incorporating A s tudy of F2-layer e ffects as observed with a Doppler an emi tter-follower and a small magnetic amplifier is de­ technique, K . Davies, J. M. , a nd D. H. Zacharisen, scribed. Timing and some of the operating power are pro­ J . Geophys. Research 67 , 601-609 (Feb. 1962). vided by a 300-kc 2-phase 7-volt sine-wave source. In Changes in the height and shape of the ionosphere p roduce structure and mode of operation, the amplifier is par Licularly variations in frequency, at a receiver, of waves emitted from sui ted for use with two-level diode gati ng to provide the astable sender. WWV- 10, WWV- 15, vVWV-20, and WWVH- AND and OR logical openttions. A NOT-amplifier provides 10 have been recorded, at Boulder, on slow-moving magnetic' negation with amplifi cation. The volt-second transfer char­ tape. By rapid playback the Doppler frequency is converted acteristic of the stage critically determines the stab ilit~' of into an audio frequency and the spectrum analyzed by propagation of bi nary signals. Factors governing the required conventional techniques. shape of this transfer characteri stic are di scussed. Records obtained by this technique are presented to illustrate the phenomena observ d during magnetically quiet and A s urvey of the literature on heat transfer fro m s olid s ur­ disturbed peri ods. Experimental effects assoeiated with faces to cryoge nic fluids, R. J . Richards, 'vV. G. Steward, and sola r flares and magnetic sudden co mmencements are pre­ R . B. J acobs, NBS Tech. Note 122 (PB161623) (1961) $1.25. sented. The frequency dependence of t he frequency varia­ A bibliography of 156 references on heat transfer from soli d t ions is shown to give information concernin g the height surfaces to fluids a nd related phenomena is presented. H eat location of the associated ionospheric effects. transfer data obtained from experimental wo rk on cryogenic fluids are p resented in graphical form. The theoretical and Displacement and strain-e nergy distribution in a longitudi-· empirical formulations appearing in the references arc pre­ nally vibrating cylindrical rod with a viscoelas tic coating, sented. In those cases where suffi cient, information is avail­ P. Hertelendy, J. Appl. Mechanics, No. 61-WA-30 (1962). able to make n umeri cal computations, the formulations a rc A numerical solution by R. M. Davies of the Pochhammer presented graphically to permit comparison with the results frequency equation is used to determine t he displacement and of the experimental work. strain energy di stribution across the cross-section of an infinite elastic circular cylindrical rod for a number of wave-· F unctional and design problems of the NBS RF voltage bridge, lengths of the first, second, a nd third modes of symmetric L . F. Behrent, NBS Tech. Note 123 (PB161624) (1961) $1.00. longitudinal vibration. With these results the effect of a A detailed presentation is given of the practical sol utions to t hin uniform layer of damping material on the surface is the design and operating problems encountered in construct­ investigated. It is shown t hat with proper choice of bar­ ing a Thermistor Bridge similar to that used by the NBS for material and frequency range the attenuation of a progressive R F Voltage Standardization. Measurement and operating wave is virtually independent of the b ulk modulus viscosity techniques, critical structural features, as well as the proper parameter, enabling one to relate the shear viscosity directly use of available components are discussed. to t he rate of signal attenuation. Evaluation of convolution integrals occurring in the theory of Superconducting magnets, R. H. Kropschot and V. Arp, mixed path propagation, J . R. J ohler and C. M . Lilley, NBS Cryogenics 2, No. 1, 1-15 (Sept. 1961) . Tech. Note 132 (PB161633) (1961) $1.00. The feasibility of employing superconducting windings for­ The theory of propagation of electromagnetic waves around :J, use in electromagnets is discussed. The principal problem sphere t reats the smoot h homogeneous case, i.e., the case in is one of finding a material wit h a sufficiently high critical which t he surface impedance of the sphere is uninterrupted by fi eld so that the magnetic field does not quench the super­ an abrupt change in conductivity such as a land/sea boundar y. conductor at t he desired operating condition. For fields up It is known, however, t hat such a theory can be extended to to 20 kilo-oersteds materials such as Niobium and some of t reat inhomogeneous, irregular terrain by formulating certain the superconducting alloys appear practical. For fields convolution integrals which utili ze the smooth homogeneous greater than 20 kilo-oersteds superconducting films having a formulas. The evaluation of t hese integrals can be accom­ t hi ckness less than the penetration depth arc considered. plished with dispatch on a large-scale electronic computer Although t heory and experiment on t hin films are very meager with t he aid of numerical analysis techniques. a distinct possibility exists t hat t hese materials can be used The particular case of a land/sea bounda ry in a s mooth, to produce "air core" solenoids of up to 90 kilo-oersteds. spherical surface is illustrated for a variety of cases by The p ower required (refrigeration only) to operate a magnet evaluating the con volution integrals on a large-scale co mputer. of this type m ay be co nsiderably less than for a co nventional ambient temperature magnet. Historical survey of fading at m edium high radio , R. K. Salaman, NBS 'Tech. Note 133 (PB161634) (1962) 75 Parametric behavior of an ideal two-frequency varactor. cents. G. F. M ontgomery, Proc. IRE 50, No.1, 78-80 (1962). This condensed hi storical survey contain information on The :Ma nley-Rowe equations for a lossless varactor network many of t he ft rticles co ncerned \rith HF a nd MF ionospheric yield little information for t he two-frequency case. With the

291 assumption of a linear signal termination, it is shown t hat and industry have become extremely exacting. Questions of the ratio of signal and pump frequencies must be M(2, where precision and accuracy are now raised on every hand. M is an integer. For M odd, a regenerative network is Among t he statistical problems con nected with t he d evelop­ possibJe at t he signal frequency. For M even, t he network ment of improved physical stand ards are t he estimation of is possibly regenerative or nonregenerative. Other frequency measurement precision ; t he design of experimcnts to provide ratios are not possible; frequency division is not possible information on t he accuracy; and the reconci liation of results except for regenerative division by 2. The effects of strong obtained in t he national laboratories of the countries under­ pumping are predictable if the varactor characteristic is given. taki ng t his work. This paper reviews and illustrates by actnal examples, some of t he ways in which statistical Design of retarding fi eld energy analyzers, J . A. Simpson, methodology can m ake con tributions in t his fi eld. R ev . Sci. I nstr. 22, No. 12, 1283-1293 (Dec. 1961). R etarding fi eld a nalysers of t he plane parall el plate, t he Rapid m ethod for interpolatin g refractive index measure­ spherical condenser, t he F araday cage, and t he fi lter le ns ments, O. N. Stavroudis and L. E. Sutton, J. Opt. Soc. Am. types are examined in some detail. The often neglected lens 51, N o.3, 368-3?'0 (M ar. 1961) . effect of the hole in t he pla ne parallel plate t hrough which This paper d escribes a method for fitting m easured values the beam passes is shown to have significant effect on t he of refractive index versus wavelength to a two-termed energy resolution . The previous a nalysis of the spheri cal Sellmeier dispersion formula, condenser is extended to the hemispheri cal case and the effect of the apert ure in t he inner sphere calculated. It is shown 2_ AJ/.. 2 A2/.. 2 t hat for certain relations betwee n t he sphere sizes a nd t he n - 1 + /.. 2_ /.. ~+ /.. 2_ A ~ position of t he source very high resolu tion may be ob tained. The general restrictions on t he performan ce of imaging re­ by a modified least squares procedure. By clearing fractions tarding fi elds are considered and a design procedure based and introduci ng auxiliar y variables, a linear expression is upon empirical knowledge of immersion lenses is given. ob tained, t he least squares solution of which pr ovides a start­ ing point for a linear improvement rout ine. T he process is Radiation beam mapping with , W . L. very fast and is particularly applicable t o high-speed digital M cLaughlin, Radiology 78, No.1, 119- 120 (Jan. 1962). computers. Wllile t he results do not represent t he ultimate An experimen t was carried out at the National Bu reau of in obtainable accuracy, t hey provide a start ing point for Standards t o examine with photographic fi lm the u niformity obtaining better fi ts using a more complex formula. of X - and -y -ray beams used in the calibration of radiation instruments. By exer cising ce rtain p reca utions in film selec­ A specimen for use in investigating the stress-corros ion t ion, positioning, processing, and photometri c measuremen t, cracking of metals at elevated temperatures, H. L. Logan, it was possible t o determine the distribu tion across 'Materials Research and Standards (ASTM Bull.) 2, No.2, the beams wit h an accuracy of one percent. 98-100 (Feb. 1962). Stress-strain relationships in yarns s ubjected to rapid impact A hollow specimen t hat con tains t he con odent under pres­ loading. Part VIII: Shock waves, limiting breaking velocities, sure and is subjected to known tensile stresses at known temperatures is described. and critical velocities, J . C. Smith, J . M . Blandford, and K . M. T ype 304 stainless steel specimens of this design, exposed to Towne, Textile Resew'ch J. 32, N o. 1, 67- 76 (Jan. 1962). distilled water containing 20,000 ppm of chloride, a nd oxygen, An impact velocity just su ffi cient to cause immediate breakage 0 0 in a fil ament impacted in tension is called a critical velocity. in t he temperature range of 455 to 615 F , generally de­ Theories rcquired for calculatin g critical velocit ies from veloped stress-corrosion cracks under m echanically applied stress-strain data valid under crit ical velocity impact con­ stresses of 25, 000 and 30,000 psi. Stress-corrosion cracking ditions are reviewed a nd extended. Cri tical velocity estimates was more severe at stresses of 30,000 psi t ha n at t he lower are then calcul ated for some textile yarns using stress-strain stress level. T he presence of oxygen was necessar y for the data obtained at impact speeds near 40 m/sec. The velocities development of cracks. obtained ra nge in value from approximately 100 m/sec for The three-dimensional nature of boundary-layer instability, cotton sewing t hread and glass fiber yarn to approximately 300 m/sec for some vinal, rayon t ire cord, acryli c, a nd n ylon P . S. Klebanoff, K. D . Tidstrom, a nd L. M . Sargent, J . Fluid M echanics 12, Pt. 1, 1-34 (1962). yarns. Theo ry is devcloped for estimating cri tical velocity An experimen tal investigation is described in which princip al from the sp ecifi c breaking energy obtai ned by high-velocity emphasis is given to revealing the nature of t he motions in impact tests. It is shown t hat t he estimate in t his case is t he nonlinear range of boundary layer instability and t he high if t he stress-strain curve is p redominantly co ncave onset of t urbulence. The experimental method consisted of downward, low if t he stress-strain curve is predominantly introducing in a two-dimensional boundary layer on a fl at concave upward, and equal to t he cri tical velocity est. im ate if plate at imcompressible speeds t hree-dimensional disturbances the curve is linear. Critical velocities are also estimated fro m under controlled conditions using t he vibrating ribbon tech­ stress-strain dat a obtained at 100 % /min straining rates and nique, and studying their growt h and evolution using hot-wire compared with calculations from high velocity impact data. methods. It is definitely established t hat associated with the Good agreement is found in many cases. nonlinear three-dimensional wave motions t here are longi­ Current-limited rectifi ers, G. F . Montgomer y, Proc. I RE 50, tudinal vortices. Existing t heoretical considerations arc N o.2, 190-193 (Feb. 1962). evaluated , and the results support t he point of view t hat t he Several ac rectifier circuits have t he property, inherent in principal nonlinear mecha nism i nvolves the nonlinear be­ t he rectifi cation process, of limiting t heir out put current to havior of a t hree-dimensional perturbation. It is also demon­ a specified maximum. They are technically simple a nd can strated t hat the breakdown of t he wave motion to t urbulence be used as t he found ation for power supplies t hat remain is a consequenee of a new instabi lity which arises in t he undamaged and absorb little power with a short-circui ted aforementioned three-dimensional wave motion. It is also load . In combination with a d c regulator, such a rectifier shown t hat t he results obtained from the study of controlled provides a co nstant -voltage supply with desirable oveTload disturbances are equally applicable to "natural" transition. characteristics. A modified bridge rectifi er is especially useful. Dynamic behavior of a simple pneumatic pr essure reducer , D . H . T sai and E. C. Cassidy, J . Basic Eng., 253-264 (J une Statistical problems arising in the establishment of physical 1961) . s tandards, W. J. Youden, Proc. Fourth Berkeley Symp. on This paper presents an analysis of t he dynamic behavior of a M ath. S tatistics and Probabnity I I I , 321-335 (1961). simple pneumatic pressure reducer. Both the non-linear and T he establishment and m aintenance of physical stand ards is t he li nearized problems were studied . Some experimental indispensable for scient ifi c research, commerce and industry. results were also obtained on a working reducer model to The fi rst standards were suffi ciently ahead of t he existing check t he validity of t he analysis. The agreement between needs so t hat questions of p recision and accuracy were the non-linear solutions and t he experimental res ults was hardly raised. In recent years t he requirements of research satisfactory. The non-linear and t he linearized solutions 292 were compared in detail so as to bring out the essential and frequency range, can give information about motions in features of the dynamic behavior in both cases. The stability polymers involving orientation of polar segments. Insofar problem was also studied, and a set of stabili ty criteria for as motion of polymers studied by other methods involves the linearized case was formulated in term of the design and motion of polar segments, the results and interpretations operating parameters of the reducer. In t he felY sample should agree with t hose from dielectric relaxation data. cases studied, these criteria gave correct quali tative predic­ tions of the stability of the reducer in both the linearized A statistical comparison of the wearing characteristics of two case and the non-linear case. The flow forces 011 three types of dollar notes, E. B. Randall, Jr., and J. Mandel typical flow-metering valves were also determi ned by experi­ Materials Resew'ch and Standards (AS'l'M Bull.) 2, No.1; mental measurements (Appendix 2). The e res ults were used 17- 25 (Jan. 1962). in the analytical part of the paper. Two types of one-doll a r notes, printed b y two difl'erent methods on two different papers, are in circulation. The E ffect of porosity on Young's modulus of alumina, F. P . wearing properties of these dollar notes have been co mpa red ICnudsen, J . Am. Chern. Soc. 45, No.2, 94-95 (Feb. 1962). by a statistical method based on the concept of su rvival A graphic compilation is presented of available data of the curves. Young's moduli of porous polycry talline alumin a at room Doll ar notes in circulation in the Washington, D.C. a rea were temperature. The apparent dependence of Young's moduli sampled. Data [rom 15 a mplings, or a total of 30,000 notes, (E) or porosity (P ) could be satisfactorily approximated by were obtained after t he notes had been sorted according to the equation type (old or new), fitn ess and age. E (in kilobars)=4102 e- 3 •95P • It is concluded that the median life of the l1ew dollar note is approximately 30 percent longer than t hat of the old type of A new a pproach to the mechanical syntactic analysis of note using the usual Treasury standards for the evaluation Russian, I. 1. Rhodes, M ech. 'I'mnsl. 6, 33- 50 (Nov. 1961). of fitness. The Mechanical Translation scheme used at the National Bureau of Standar'ds has dealt so far only wi th the syntactical No n- additi vity in two-way a nalysis of variance, J . Mandel, aspects of the problem. The report describes how the diffi­ J . A.m. Stat. Assoc. 56, 878- 888 (Dec. 1961). culties encountered in t his portion of the task are being over­ In two-way classification analysis of variance situations there come. Mention is made of the additional difficulties, belong­ often ex isLs a sy tematic type of row column interaction. ing to the fi eld of semantic a nalysis, whi ch have not yet been A model is proposed in which the interaction is of t he type considered by t he N BS translation group. Q hi where Qi is a parameter of the ith row, not necessarily Double probe measure ments of ionization in active nitroge n, associated with t he main efrect for rows, and 'Yi is the main II. P. Broida and 1. T anaka, J. Chem. Phys. 36, No.1, 236- efrect for column j. The a nalysis of data accordin g to this 238 (Jan. 1962). model is given, in cluding estimation and tests of sign ificance. Electron temperatures and ion densities have been measured The model is more general than that involved in Tukey's in nitrogen afterglows in a flow system at short t imes after "one degree of freedom for non-additivity" and includes the the discharge. In pure niLrogen a maximum occurs in the latter as a special case. The relationship between the two ionization density and in the electron temperature at 5 to 10 methods is discussed. Applications of t il(' method to different msec after the discharge. The position of this maximu m types of problems are mentioned and a numerical example is coineides with the visible short-duration nitrogen afterglow included. in which N 2+ emission is prom inent. Small amounts of added impurity decrease this ion density but cause an increase On the impedance of long wire s ll spended over the ground, in the ion density at longe r times, reaching a second maxi­ J. R. Wait, PTOC. IRE 49, No. 10 (Oct. 1961). mum at 80 to 100 msec after the discharge. These results Much has been written over the years on the subject of the show that ions and electrons are being produced co ntinuously impedance of wires lying 011 the ground or suspended above it. in nitrogen afterg lows and that the rate of production is The possibility that a long horizontal wire will be a feasible affected strongly by impurities. radiator of very-low-frequency radio waves has reopened interest in the problem. It is the purpose of this note to Fitting refractive index data by least squares, L. E. Sutton and ouLline a rather simple soluLion for the impedance of an O. N. Stavroudis, J. Opt. Soc. Am. 51, No.8, 901-905 (Aug. infinitely long wire located at a height h over a homogeneous 1961). flat ground. The accessibility of high speed computin g machinery makes practicable the use of a routine for t he least-squares fitting Automatic screeni ng of normal and abnormal electrocardio­ of a t hree-term Sellmeier equation to a et of experimentally grams by means of a digital electronic co mputer, H. V. Pipber­ determined values of index of refraction. The constants of ger, R. J. Arms, and F. IV. Stallmann, PTOf. Soc. Hxperimental a two-term Sell meier equation are evaluated by a m ethod Biology and Medicine 106,130- 132 (1961). described previously. These are then used in a preliminary The spatial ventricular gradient was determined in 256 fitting of another term. The rough fit is then improved by electrocardiograms by means of a digital eleetronic computer. an iterative process which includes an acceleration technique This automatic procedure allowed separation of normal and to speed convergence to the fin al result. In a typical abnormal records with a high degree of precision. 98 percent example the average residual of index is only about 2X 10- 5 of all cases with old myocardial infarctions, which are of for 46 wavelengths from 0.2652 microns to 10.346 microns. prime interest in electrocardiographic diagnosis, were recogn­ Maxwell and modern , D. B. Judd, J. Photo­ ized as abnormal. gmphic Sci. 9, No.6, 341-352 (Nov.-Dec. 1961). The methods used by Maxwell to reduce colour-matching data Electromagnetic bearing, H. Sixsmith, Rev. Sci. Instr. 32, from rotating sector discs (Maxwell discs) so as to represent 1198- 1197 (Nov. 1961) . the chromaticity of the unknown colour on a chromaticity A shaft is supported by means of a laminated rotor which is diagram (Maxwell triangle) form the basis of modern colorim­ magnetically suspended inside a four pole laminated stator. etry. Maxwell's determination of the colour-matching The diameter of the rotor is 1%" and the radial clearance is functions for two observers carried out by these methods is 0.002". The position of the shaft is sensed with the aid of found, when expressed in terms of units instead of the Four quadrant electrodes which surround the shaft with a slit-width units used by Maxwell, to be in essential agree­ small radial clearance. Each electrode provides part of the ment with the 1931 CIE standard observer defining the colour tuning capacity of an R.F. tuned circuit which is tuned to scales currently u sed internationally. one side of its resonance peak with respect to an R.F. gener­ ator. The R.F. signal is detected and amplified to provide Dielectric properties of solid polymers, A. J. Curtis, SP E the control current in the corresponding winding on t he stator. Trans. , 82-85 (Jan. 1962). The bearing was found to run smoothly up to 23000 rpm. Basically, the study of dielectric relaxation, by the measure­ With further development, a reliable and useful bearing should ment of dielectric constant and loss indf)x over a temperature result. 293 Traveling pressure waves associated with geomagnetic Light source for producing self-reversed spectral lines. J. activi ty, P. Chrzanowski, G. Greene, K. T. Lemmon, and Sugar. (See above abstract.) J. M. Young, J . Geophys. R esearch 56, No. 11, 3727-3733 A diamond cell for X-ray diffraction studies at high pressures. (Nov. 1961). G. J. Piermarini and C. E. Weir. (See above abstract.) Traveling atmospheric pressure waves with periods from 20 T hermal conductivity of gases. 1. The coaxial cylinder cell. to 80 seconds and pressure amplitude from about 1 to 8 L. A. Guildner. (See above abstracL) dynes/cm2 have been recorded at a microphone station Thermal conductivity of gases. II. Thermal conductivity of at 'Washington, D.C., during intervals of high geomagnetic carbon dioxide near the critical point.. L. A. Guildner. activity. Trains of these waves can be expected at vVash­ (See above abstract.) ington from a quadrant approximately centered on north Derivation of the relaxation spectrum representation of the whenever t he magnetic index J{ v rises to a value above 5. mechanical response function. R. S. Marvin. (See above Their horizontal phase velocity across the station is usually abstract.) higher than the local speed of sound. During two 'red' Intermediate phases in super conducting niobium-tin alloys. auroras, clearly visible at W'ashington and at lower latitudes, L. L. Wyman, J . R . Cuthill, G. A. Moore, J . J . Park, and the 20- to 80-second-period waves were accompanied by H . Yakowitz. longer period, higher pressure, and much slower t raveling pressure disturbances. Observational data on the wave Journal of Research 66B (Math. and Math. Phys.) No. 2, systems are presented and discussed. (Apr.- June 1962) 75 cents. Use of an operational amplifier with H elmholtz coils for Hindsight technique in machine t ranslation of natural lan­ reducing ac induced magnetic fi elds, L. A. Marzetta, R ev . guages. 1. Rhodes and F. L. jUt. (See above abstract.) Sci. Instr. 32, No. 11, 1192-1195 (Nov. 1961). An extension of Jensen's theorem for the derivative of a A feedback system is described for canceling magnetic fields polynomial and for infrapolynomials. O. Shisha. resulting from alternating currents. The design fe atures of Two matrix eigenvalue inequalities. S. Haber. an operational amplifier are offered. I n addition the nature Graphs for determining the power of Student's t-test. M. of t he phase shift contributed by mutual inductance elements C. Croal·kin. (See above abstract.) in the feedback path is discussed. Magnetic fi elds with a flux density of one milligauss can be reduced by about two Journal of Research 66D (Ra dio Prop.) No.3, (May- June orders of magnitude with the system. 1962) 70 cents. Die lectric properties of polyarnides, A. J . Curtis, J. Chem A theory of radar reflections from a rough moon. D. F. Winter. Phys. 340, No.5, 1849-1850 (May 1961). A l unar t hcory reasserted. K . M. Siegel and T. B. A. Senior. The dielectric relaxation in two polya mides has been studied Statistical distribution of the amplitude and phase of a mul­ over a t emperature range from - 100 0 to 175 0 C and a fre­ tiply scattered field. P . BecklTlann. quency range from 50 cps to 10 Mc/s. T he effects of variolls Amplitude distribution for radio signals reflected by meteor thermal treatments on the relaxation behavior have been t rails, II. A. D . Wheelon. studied. The polyamides were poly(hexamethylene adipam­ High resolution pulse measurements of meteor-burst propaga­ ide) and poly(hexamethylene sebacamide). Four relaxation tion at 41 Mc/s over a 1,295-km path. R. J. Carpenter phenomena have been identified. Mechanical relaxation a nd G. R. Ochs. processes are compared with the di electric phenomena and Ionospheric irregularities and long-distance radio propaga­ possible molecular mechanisms are discussed. tion. H. A. ·Whale. On the role of t he process of reflection in radio wave prop­ Other NBS Publica tions agation. F. du Castel, P. Misme, A. Spizzichino, and J. Voge. (Sec above abstract.) Correlation between hourly median scattered signals and Journal of Research 66A (P hys. a nd Che rn .) No.3 (May­ simple refractivity parameters. A. S. Dennis. J une 1962) 70 cents. Observations of radio wave phase characteristics on a high­ Glass filters for checking performance of spectrophotometcr­ frequency auroral path. J . W. Koch and W. M . Beery. i ntegrator Rystem~ of color measurement. H. J . Keegan, Diurnal and seasonal changes in structure of t he mid-latitude J. C. Schleter, and D . B. Judd. (See above abstract.) quiet ionosphere. J. W . Wright. Calibration of small grating spectrometers from 166 to 600 Schumann resonances of the earth-ionosphere cavity-ex­ cm-I . L. R. Blaine, E. Ie Plyler, and W. S. Benedict. (See tremely low frequcncy reception at I{ingston, R.1. C. a bove abstract.) Polk and F. Fitchen. Franck-Condon factors to high vibrational quantum numbers Propagation of plane electromagnetic waves past a shoreline. II: SiO, MgO, SrO, AlO, VO, NO. R. W. Nicholls. J. Bazer and S. N. Karp. Oxidation of aldoses with bromine. H. S. Isbell . Currents induced on the surface of a conducting circular An analysis of the solid phase behavior of the normal paraffins. cylinder by a slot. G. Hasserjian and A. Ishimaru. (See M. G. Broadhurst. above abstract.) Methylene groups in determination of disulfide and methylene sulfide crosslinks in polycaprolactam fibers. S. D. Bruck. Journal of Research 66D (Radio Prop.) No. 4 (July- Aug. Purification by automatic gas chromatography. M. Tenen­ 1962) 70 cents. baum and F. L. Howard. (See above abstract.) High resolution investigation of some infrared bands of carbon Propagation problems with space radio communications. K. disulfide. D. Agar, E. K. Plyler, and E. D. Tidwell. Rawer. On t he absolute intensity of incoherent scatter echoes from the ionosphere. K. L. Bowles, G. R. Ochs, and J. L. Journal of Research 65A (Phys. and Chern.) No.4 (J uly­ Green. Aug. 1962) 70 cents. On the forward scattering of radio waves in the lower iono­ Dielectric properties of semicrystalline polychlorotrifluoro­ sphere. T . Hagfors. ethylene. A. H. Scott, D. J . Scheiber, A. J. Curtis, J . 1. The representation of diurnal and geographic variations of Lauritzen, Jr., and J . D. Hoffman. ionospheric data by numerical methods. \'1. B. Jones and Thermal degradation of fractionated high and low molecular R. M. Gallet. weight polystyrenes. S. L. Madorsky, D . McIntyre, J. H. The interaction between an obliquely incident plane electro­ O'Mara, and S. Straus. magnetic wave and an electron beam in the presence of a Synthesis of 2-propoxy-5-mcthylbenzoic acid. G. M. Brauer static magnetic field of arbitrary strength. K . H. B. and L. Simon. Wilhelmsson. (See above abstract.) Gamma-ray distribution from oriented cerium-141. J. F. An analysis of VLF mode propagation for a variable iono­ Schooley, D. D. Hoppes, and A. T. Hirshfeld. spheric height. J . R. Wait.

294 A method for the determination of lower iOllosphel'e prop­ On t he average at n~os phe ri c radio refractive index structure erties by means of fi eld measurements on sferics, F, B. over North Amenca, B. R. B ean a nd J . D . Horn Beitr H a rris, Jr" and R , L, T anner. Phys. Atmos. 3<1, 92- 104 (1961). ,. Defocusing of radio r ays by t he t roposphere. R . E. Wil­ Concerning th~ bi~ ex pon e n tia l nature of the tropospheric kerson. radIO refractIve Index, B. R. Bean Beitr. Phys. Atmos Magnetotelluric fi elds in the frcq uency ra nge 0,03 to 7 cycles 34, 8 1- 91 (1961). ' . per kilosecond: Part 1. Power spectra. C. 'Y. Horton Atomic beam.frequ ency standards, R. C. Mockler, Advances I and A. A. J . Hoffman. III ElectrolllcS ,and Electwn Phys, 15,. 1- 71 (1961) . Magnetotelluric fields i n t he frequency r ange 0 ,03 to 7 cycles Memory effects III ll'reverslble t hermodynamics, R. Zwanzig pel' kilosecond: P art II, Geophysical interpretation. C. Phys. R ev. 124, No, 4, 983- 992 (Nov. 15, 1961). ' I W. H orton and A, A. J . Hoffman, A study of t he fluorescence of cellulosic polymers, Ie. F. P li tt The impedance of a ci rcular loop in an infinite condueti ng and S. D. Toner, J . App1. Polymer Sci. 5, No, 17 534- 538 medium. M. B . Kraichman. (See above abstraet.) (1961). ' Formulae for a n a~cu:ate intermedi ary orbit of an a rtiftcial Standard X -ray diffraction powder patterns, H. E. Swanson, satellIte, J. P . Vlllt l, Astronomical J. 66, No. 9 514- 516 M. C. Morris, R. P . Stinchfield, a nd E. H . Evans, NBS (Nov, 1961). ' Mono. 25-Section 1 (March 9, 1962) 40 cents. Drift mobility of an ionic impurity in an electric fi eld, J . R. T heory and methods of optical pyrometry, H . J. Kostkowski Mannll1g, P~ ys. Rev. 125, .N~. 1, .103- 108 (Jan. 1962). and R . D. Lee, NBS Mono. 41 (March 1, 1962) 25 cents. Some observatIons of metal dlstnbutlOn G. Ogburn a nd M A Report of t hc 46th National Conference on Weights and Morris, Plating Mag. 49, No.1, 72-75 (Jan. 1962). . . Measures, 1961 , NBS Misc. Pub1. 239 (J an. 1962) 65 cents. Comments on ~~. Vozoff's paper "Calibration of pulsation Standard materials issued by the National Bureau of Stand­ detector CO Ils, J. R Walt, J . Geophys. R esearch 66 No 10 dards. A descriptive li st with prices, N BS Misc. P ub1. 3603 (Oct. 1961). ' . , 241 (March 12, 1962), Supersedes C 552, 3d edition, 30 Precision .of reverberation chamber measureme nts of sound cents. absorption coefficlCnts, R. V. Waterhouse, Book, P roc. 3d Computer simulation of street t raffic, M. C. Stark, NBS Intern. Congress on AcoustIcs, Stuttgart Germany p 886 T ech. Note 119 (PBJ61620) (1961) $2.25. (Elscvier PubL Co., Amsterdam, The N~the rl ands ' 1959) , . A tabulation of the thermodynamic properties of normal A comment on R yser's "normal a nd integral implies in'cidence" hydrogen from low temperatures to 300 oK and from 1 theorem, K . Goldberg, Am. Math. Monthly 68 No 8 to 100 atmospheres, J . W. Dean, NBS Tech. Note 120 770- 771 (Oct, 1961). ' ., (PB161623) (1961) $1.25. Concerning radiosondes, lag constants, and radio refractive Papers from the symposium on collision phenomena in astro­ Inclex profi les, B. R Bean and E. J , Dutton, J. GeopllYs j:>hysics, geophysics, a nd masers, M. J. Seaton, M, J, R esearch 66 ,3717- 3722 (Nov. 1961). . Dalgal'llo, and C. Peckel', NBS Tech. Note 124 (P £161625) On the interpretation of pwminence spectra IV. The Balmer (1961) $1.00. and p,aschen continua in a quiet prominence, J . T. J effe ri es Provisional thermodynamic functions for para-hydrogen, a nd I' ..Q. o l'l'all , As~rophys: J . 134, No. 3 (Nov. 1961) . H. M. Roder and R D. Goodwin, NBS Tech. Note 130 Ionosphel'l c effects aSSOCIated WIth the solar flare of September (PB161631) (1961) $3.00, 28, 1961, K. Davies, Nature Letter 193 763- 764 (Feb 2-1- Photoionization of atoms and 1I1Olecules, F. L. Mohler, 1962). " , NBS Tech. Note 131 (PB161632) (1962) $1.25, Sferie observations of the severe weather on May 19 1960 Technique for calculating infrared by a regula r C. A. Samson and R. F. Linfield J . Geophys. Hesea;'ch 67 ' band, L. R Mcgill and P. M, Jamniek, J . Opt. Soc. Am. 627- 635 (Feb. 1962).' , 51, No. 11, 1294- 1297 (Nov. 1961). On the mean .temporal variations of electron density at a Polymorphism of AB0 3 type rare earth borates, E. M. Levin, fixed he ight III the F regIOn, A, J . Hirsh and R. W. E:necht, R S. Roth, and J. B. Martin, Am. Mineralogist 46, 1030- J. Geophys. Research 67, No.2, 595- 600 (Feb. 1962). 1055 (Sept. 1961) , Low temperature thermometry, R. p, Hudson, Experimental Sun storms and the earth: The aurora polaris a nd the space Cryophys" pp, 214- 253 (1961). a round t he carLh, B. Chapman, Am. Scientist 49, No.3, PhotolYSiS o~ .acetone-da in the presence of propane-2, 2-d,. 2-19- 284 (SepL. 196J). DecomposItIOn of the n-propyl radical, W. M. J ackson Colorimetric dete rmination of 5, 6-dichloro-2-benzoxazoli­ and J . R . McNesby, J . Am. Chern. Soe. 83 4891- 4896 none in leathers, S. Dahl, J . Am. Leather Chemists Assoc. (1961). ' LVII, No.1 (Jan, 1962). Comparison of United States and Canadian free-air ionization Lower bounds for eigen values of Schrodinger's equation, chamr~e r s , J. I-I. AItken, L. De LaVergne, W. H. Henry, N. W. Bazley and D. W. Fox, Phys, Rev. 124, No, 2, and 1. P. Loftus, Brit. J. Radiol. 35, No. 409, 65- 70 483- 492 (Oct. 1961). (J an. 1962). Formation of polymer crystals with folded chains from Analysis of the absorption spectrum of YbC13·6H,O J C dilute solution, J, 1. Lauritzen, Jr., and J . D. Hoffman, Eisenstein, J. Chem. Phys. 35, No.6 2097- 2ioo ('Dec' J . Chem. Pllys. 31, No.6, 1680- 1681 (Dec. 1959). 1961). ,. This works for us, approval books for a science library, A string language for symbol manipulation based on ALGOL V. S. Barker, Special Libraries 52, No.3, 471- 472 (Oct. 60, J . H . Wegstein and W. W. Youdeu, Commun. ACM 5, 1961). No.1, 54- 61 (Jan. 1962). Chemical reactions at very low temperatures, A. Thomas, Polymorphism. in monob.r0m~acetic acid and the diagram Trans. Faraday Soc. 57, No. 446, Pt. 10, 1679-1685 (Oet. of state of dlchlOl'?acetIC aCId at elevated pressures, A. R. 1961). Glasgow and J . Tlmmermans, Bull. Soc. Chim. Belges 70 Theoretical dielcetric behavior of an ethyl sterate-heneico­ 623- 641 (1961). ' sane mixture, !\II. G. Broadhurst, J . Chem. Phys. 33, No. Ray-tracing formulas for uniaxial crystals, O. N. Stavroudis, 1, 221- 226 (July 1960). J . Opt. Soc .. Am. 52, No: 2,187- 191 (Feb. 1962). 5, 6-diehloro-2-benzoxazolinone as a leather fungieide, S. Doppler studIes of the Ionosphere with vertical incidcnce Dahl and A. M, Kaplan, J. Am. Leather Chemists Assoc. E~. D avies, .Proc. IRE 50, No.1, 94 (Jan. 1962). ' LVI, No. 12, (Dec. 1961). An Il1t~'oductlOn to flame and a review of recent Departure from the Saha equation for ionized helium. II. studIes, M. Margoshes, Book, Physical Techniques in Atmospheric thicknesses too small to satisfy detailed Biological Research, W. L. Nastok, Ed., IV, 215- 260 balance in the resonance lines, R. N. Thomas and J. B. (Academic Press, New York, N.Y., 1962). Zirkel'. Astrophys. J . 134, 740- 746 (Nov. 1961). The ionization constant of p-nitrophcnol from 0 to 600 E lectron diffraction studies on soli d a-nitrogen, E. M. Hor! G. F. Allen, R. A. Robinson, and V. E. Bower, J. Phys: and L, Marton, Acta Cryst. 14, No. 11, P t. 1 (J an. 1961). Chem. 66, 0.1,171-172 (1962). F ra nck-Condon factors and the shape of ionization efficiency Oscillator models in unimolecular reactions, M. L. Vestal curves, M . E. vVacks and M . Krauss, J . Chem, Phys. a nd H. M. Rosenstock, J . Chem. Phys. 35, No.6 2008- 35, No.5, 1902- 1903 (Nov. 1961). 2016 (Dee. 1961) , 295 Some physical properties of monochloro-, dichloro-, and Net heat of combustion and other properties of kerosine and monobromoacetic acids at 1 atmosphere, A. R. Glasgow related fuels, G. T. Armstrong, L. Fano, R. S. Jessup, and J. Timmermans, Bull. Soc. Chim. Belges 70, 599- 622 S. Marantz, T . W. Mears, and J. A. Walker, J. Chern. (1961). Eng. Data 7, No.1, 107- 116 (J an. 1962). Auroral zone geomagnetic micropulsations with periods of On the thermodynamic propertics of fluids, E. H . Brown, 5 to 30 seconds, W. H. Campbell and S. Matsushita, J. Inst. Intern. Du Froid, Intern. Inst. of Refrigeration, Geophys. Research 67, 555- 573 (Feb. 1962). Commission 1, 169- 178 (1960). On the interpretation of prominence spectra. V. The emission Characteristic electron energy loss measurement at low lines in quiescent prominences, J . T. Jefferies and F. Q. temperatures, E. M. Horl and J . A. Suddeth, J. Appl. Orrall, Astrophys. J. 135, 109-121 (Jan. 1962). Phys. 32, No. 12,2521- 2525 (Dec. 196] ). Intramolecular rearrangements: IV. Photolysis of 2-pen­ Compton scattering by K-she11 electrons, J. W. Motz and G. tanone-4, 5, 5-d3, R. P. Borkowski and P . Ausloos, J. Phys. Chern. 65, 2257-2260 (1961). Missoni, Phys. Rev. 124, No.5, 1458- 1468 (Dec. 1961). Electrophoretic mobilities and surface adsorption in the Intramolecular rearrangements. III. Formation of I-meth­ polystyrene latex· aliphatic soap system, C. L. Sieglaff and ylcyclobutanol in t he pbotolysis of 2-pentanone, P. J . Mazur, J. Colloid Sci., V, 17, No.1, 66- 85 (Jan. 1962). Ausloos and R. E. Rebbert, J. Am. Chern. Soc. 83, 4897- An equation of state for calculating the thermodynamic 4899 (1961). properties of helium at low temperatures, R. D. McCamy Re-examination of the polymorphism of dicalcium silicate, and R. B. Stewart (1962 2d Symp. Thermophysical D. K. Smith, A. J. Majumdar, and F. Ordway, J . Am. Properties, Janua ry 24- 26, 1962, Princton University, Ceram. Soc. 44, No.8, 405- 411 (Aug. 1961). Princeton, New J ersey), Progress in International Re­ Fluorine calorimetry, G. T . Armstrong, Books, Experimental search on Thermodynamics and Transport Properties, Am. Thermochemistry II, Chapt. 7, 129- 145 (Interscience Soc. Mech. Engrs., (New York, N.Y.), p. 107 (1962). Pub!., London, England, 1962). A lattice with an unusual frequency spectrum, R. J. Rubin and R. Zwanzig, J. Math. Phys. 2, No.6, 861- 864 (Nov.­ *Publications for which a price is indicated (except for Dec. 1961). Technical Notes) are available only from the SupeTintendent National Bureau of Standards, 'IVashington, D.C. and of Documents, U.S. Government Printing Office, Washington Boulder, Colorado, C. E. Moore, Astron. J. 66, No. 10 25, D .C. (foreign postage, one-fourth additional). T echnical (Dec. 1961). Notes are available only from the Office of Technical Services, The standa rds challenge, A. H. Scott, Insulation 8, No.2, U.S. Department of Commerce, 'Washington 25, D.C. (order 48- 50 (Feb. 1962). by PB number). Reprints from outside journals and the Average decay laws for VLF fields, J. R. Wait, Proc. IRE NBS Journal of Research may often be obtained diTectly from 50, No.1, 53- 56 (Jan. 1962). the allthors. o